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2 MATERIALS WITH SUPRAMOLECULAR CHIRALITY: LIQUID CRYSTALS AND POLYMERS FOR CATALYSIS BY KAREN VILLAZOR MARTIN MASSACHUSErS IS OF TECHNOLOGY ' ARCIHIv. MAR B.S., Chemistry, cum laude, 1999 Boston College, Chestnut Hill, MA LIBRARIES Submitted to the Department of Chemistry in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHONOLOGY February, 2005 Massachusetts Institute of Technology, All Rights Reserved. Signature of Author: Certified by: Accepted by: 7) Department of Chemistry October 27, Timothy M. Swager Thesis Supervisor Robert W. Field Chairman, Departmental Committee on Graduate Studies

3 This doctoral thesis has been examined by a Committee of the Department of Chemistry as follows: Professor Timothy F. Jamison: 2' Chairman Professor Daniel S. Kemp: 4- Department of Chemistry '1 Professor Timothy M. Swager: \ -J Thesis Advisor 2

4 With much love and gratitude, I dedicate this thesis to my family and friends, who all came along for the ride. 3

5 MATERIALS WITH SUPRAMOLECULAR CHIRALITY: LIQUID CRYSTALS AND POLYMERS FOR CATALYSIS By KAREN VILLAZOR MARTIN Submitted to the Department of Chemistry, February, 2005 In partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry ABSTRACT Mesomorphic organizations provide a powerful and efficient method for the preorganization of molecules to create synthetic materials with controlled supramolecular architectures. Incorporation of polymerizable groups within a liquid crystalline template can set the stage for the synthesis of anisotropic molecular networks. This dissertation details the synthesis and characterization of chiral liquid crystals and crosslinked polymer networks, with an eye toward applications in asymmetric catalysis. Chapter One gives an introduction to the study of liquid crystals and their phases. Chapters Two and Three describe the incorporation of terminal olefins as polymerizable groups within a columnar liquid crystalline template as an effective method for the synthesis of robust, anisotropic polymeric materials. Upon in situ acyclic diene metathesis (ADMET) polymerization, the original mesophase order is retained. Chapter Two involves the room temperature polymerization of iron(iii) tris(diketonate) liquid crystals, resulting in densely crosslinked materials. The focus of Chapter Three is the polymerization of dioxomolydenum-based liquid crystals, performed at high temperature, and their potential to serve as catalysts for asymmetric epoxidation. In Chapter Four, a different approach towards the synthesis of catalytically active anisotropic materials is taken, incorporating well-established, transition metal catalysts within a liquid crystalline framework. Progress towards the formation of liquid crystal phases containing C 2 - symmetric bis(oxazoline) and pincer ligands is detailed. Finally, Chapter Five describes the immobilization of chiral monodentate oxazoline ligands for use as catalysts in asymmetric cyclopropanation. Preliminary results indicate that the heterogeneous system gives higher enantioselectivities than the analogous homogeneous system. Thesis Supervisor: Timothy M. Swager Title: Professor of Chemistry 4

6 Table of Contents Dedication Abstract Table of Contents Table of Figures Chapter 1: An Introduction to Liquid Crystals The Liquid Crystal Phase Classification of Liquid Crystals Metallomesogens Chirality in Liquid Crystals Characterization of Liquid Crystals Polarized Microscopy Differential Scanning Calorimetry X-Ray Diffraction Outlook on Future Applications References Chapter 2: In Situ Polymerization of Columnar Liquid Crystals using Acyclic Diene Metathesis Polymerization: Iron(III) Diketonate Complexes Introduction Results and Discussion Concluding Remarks Experimental Section R eferences Chapter 3: In Situ Polymerization of Columnar Liquid Crystals using Acyclic Diene Metathesis Polymerization: Dioxomolybdenum Complexes Introduction Results and Discussion Concluding Remarks Experimental Section R eferences

7 Chapter 4: Liquid Crystals containing Catalytic Ligands Introduction Pyridine bis(oxazoline) Ligands Background Results and Discussion Pincer Liquid Crystals Background Results and Discussion Concluding Remarks Experimental Section R eferences Chapter 5: Immobilized Chiral Monodentate Oxazolines: Heterogeneous Catalysis within an Organic Polymer Network Introduction Results and Discussion Concluding Remarks Experimental Section R eferences Appendix 1: 1 H and 13 C NMR Spectra for Chapter Appendix 2: 1 H and 13 C NMR Spectra for Chapter Appendix 3: 1 H and 13 C NMR Spectra for Chapter Appendix 4: 1 H and 13 C NMR Spectra for Chapter Curriculum Vitae Acknowledgements

8 Table of Figures Figures Figure 1.1. Examples of lyotropic liquid crystals Figure 1.2. Micellar aggregates and phases formed by lyotropic liquid crystals Figure 1.3. Examples of calamitic liquid crystals Figure 1.4. Some phases formed by calamitic liquid crystals Figure 1.5. Examples of discotic liquid crystals Figure 1.6. Phases formed by discotic liquid crystals Figure 1.7. Some chiral mesophases formed by calamitic mesogens Figure 1.8. Frustrated chiral phases Figure 1.9. Examples of helical arrangements in columnar phases Figure Low (1) and wide (w) angle maxima for calamities and discotics Figure Periodicities within the hexagonal lattice which give rise to low angle peaks. The lattice constant a corresponds to the distance between neighboring columns, while the distance d corresponds to planes of columns Figure Order (a) and disorder (b) within a column Figure 2.1. Schematic representations of in situ crosslinking of an aligned smectic C* phase and an inverted hexagonal phase Figure 2.2. Acyclic diene metathesis polymerization of terminal olefins Figure 2.3. Grubbs' "first generation" catalyst (a) and "second generation" catalyst (b) for olefin metathesis Figure 2.4. Iron(III) octahedral complexes Figure 2.5. In situ polymerization of columnar hexagonal liquid crystals Figure 2.6. Microphotographs of the columnar hexagonal texture of 6a. Samples were sandwiched between untreated glass slides and viewed through crossed polarizers

9 Figure 2.7. Top: X-ray diffraction profiles of 6a on aluminum plates (a) before polymerization and (b) after polymerization. Bottom: X-ray diffraction profiles of 6b on aluminum plates (a) before polymerization and (b) after polymerization Figure 2.8. Circular dichroism of 6a on aluminum plates (a) before polymerization and (b) after polymerization Figure 2.9. Circular dichroism of mixtures of 6b with chiral dopants, lb or lc Figure Left: X-ray diffraction profiles of 6b with 30% chiral dopant on aluminum plates (a) before polymerization and (b) after polymerization Right: CD spectra of crosslinked films of 6 on aluminum plates with (a) 30% chiral dopant and (b) 0% chiral dopant Figure Guest chromophores for porous networks Figure 3.1. Dioxomolybdenum liquid crystals Figure 3.2. Tapered columnar phase formed by dioxomolydenum complexes Figure 3.3. X-ray diffraction pattern of crosslinked film of 7a Figure 3.4. Phase behavior of mixtures of 7a with 7b(S) as chiral dopant Figure 4.1. C 2 -symmetric pyridine bis(oxazoline) ligand Figure 4.2. Previously studied chiral oxazoline liquid crystals Figure 4.3. Microphotographs of the columnar hexagonal texture of CuDOS(7a). Samples were sandwiched between untreated glass slides and viewed through crossed polarizers Figure 4.4. a-ketone solvents used as additives for CuDOS(7a) Figure 4.5. Microphotographs of the columnar hexagonal texture of CuDOS(7a). Samples were sandwiched between untreated glass slides and viewed through crossed polarizers Figure General structure of pincer ligands Figure 4.7. Bimetallic pincer catalyst (a) and grafted onto silica support (b) where R = phenyl, t-butyl Figure 4.8. Previously studied pincer liquid crystals Figure 5.1. Swelling behavior of polymer films obtained by Route A

10 Schemes Scheme 2.1. ADMET mechanism Scheme 2.2. Synthesis of iron(iii) complexes Scheme 3.1. Peroxomolybdenum-catalyzed olefin epoxidation Scheme 3.2. Synthesis of dioxomolydenum complexes Scheme 3.3. Attempted epoxidation of crotyl alcohol Scheme 4.1. Example of bimetallic catalysis observed in system using pybox ligands...81 Scheme 4.2. Synthesis of pyridine bis(oxazoline) ligand Scheme 4.3. Synthesis of Cu(DOS)(7) Scheme 4.4. Synthesis of Pincer Complexes Scheme 4.5. Addition of 4'-Pentyl-4-biphenyl-carbonitrile to Scheme 5.1. Copper-catalyzed cyclopropanation of styrene with ethyl diazoacetate Scheme 5.2. Immobilization of bis(oxazoline)s Scheme 5.3. Synthesis of chiral oxazoline monomer Scheme 5.4. Preparation of polymeric copper oxazoline catalysts Scheme 5.5. Polymerization of monomer 5 and the potential linkages present in the resulting polymer network Tables Table 2.1. Phase Behavior of 6a and 6b Table 2.2. X-ray Diffraction Data for 6a and 6b Before and After Crosslinking Table 3.1. Phase Behavior of 7a-b Table 3.2. X-ray diffraction data for 7a-b Table 5.1. Results of cyclopropanation reactions

11 Chapter 1 An Introduction to Liquid Crystals

12 1.1 The Liquid Crystal Phase The phases of matter can be characterized by the degree of molecular order present within a given phase. Molecules in the solid phase are highly ordered, possessing both positional order, wherein molecules occupy a specific site in a crystal lattice, and orientational order, wherein the molecular axes are pointed in a specific direction. On the other hand, molecules in the liquid phase possess neither positional nor orientational order, resulting in a highly disordered, fluid phase. A discrete phase exists in which the molecular order is intermediate between a three-dimensionally ordered crystalline state and a disordered liquid state. Such phases are often referred to as mesophases and can be separated into two broad categories: plastic crystals and liquid crystals. Plastic crystals are formed when molecules in a crystal phase lose orientational order while retaining positional order, allowing molecules to freely rotate while remaining in their original position in the crystal lattice. Solid methane is an example of a plastic crystal. When positional order is lost and orientational order is retained, a liquid crystal phase is formed. Molecules in a liquid crystal phase possess the orientational order of a crystal phase, as the molecular axes tend to point along a preferred direction (called the director n), but also freely diffuse throughout the sample, retaining the fluidity of a liquid phase.' As a consequence of the orientational order present, liquid crystals exhibit anisotropic behavior. That is, measurements having to do with elastic, electric, magnetic, and optical properties of the material will give different results depending on the direction along which it is measured. Examples of such properties are index of refraction, magnetic susceptibility, and dielectric constant. Contrastly, liquid phases 11

13 exhibit isotropic behavior, where the lack of molecular order allows such measurements to be equivalent from any direction. The combined crystal-like anisotropy and liquid-like fluidity of liquid crystals allows them to be oriented in the presence of electric and magnetic fields, which is the basis of a large number of practical applications. 2 The formation of a mesophase requires a delicate balance between attractive and dispersive forces between neighboring molecules. While there is no way to definitively predict whether or not a molecule will exhibit a liquid crystal phase, there are certain structural and electronic guidelines often followed to ensure that there is sufficient interaction between neighboring molecules. Such factors include the geometrical shape, rigidity, polarity, and polarizability of a molecule. In general, a mesogen will possess some rigid, structural core responsible for the stabilizing, attractive forces, as well as aliphatic chains that are responsible for introducing dispersive forces. 1.2 Classification of Liquid Crystals There are two broad classifications for liquid crystalline phases: lyotropics and thermotropics. Lyotropic liquid crystals 3 form anisotropic aggregates when combined with a solvent, typically water, and the phase behavior is dependent on the concentration Figure 1.1. Examples of lyotropic liquid crystals. Pictured are (a) sodium stearate or soap and (b) a phospholipid. O C6r0 C 17 H 35 O 0 O I = C15H31.o- Na(D (a Na C 17 H 3 5 -o) O O0O~, (a) ( (b)s~o'n0 (b) 12

14 and polarity of solvent and temperature. Molecules which form lyotropic phases are usually amphiphilic, having non-polar, hydrophobic "tails" at one end with a polar, hydrophilic "head" at the other end. Some examples are sodium stearate (soap) and phospholipids. (Figure 1.1) The concentration of material in the solvent and the response of the amphiphile to the solvent environment dictate the type of lyotropic phase formed. For example, in a polar solvent like water, micelles are formed in which the hydrophobic tails assemble together and the hydrophilic heads groups are presented to the solvent. (Figure 1.2a) When combined with a non-polar solvent such as hexane, an inverse micelle is formed where the hydrophobic tails shield the hydrophilic head groups from the non-polar environment. (Figure 1.2b) Under certain conditions, these micelles Figure 1.2. Micellar aggregates and phases formed by Iyotropic liquid crystals. jib a.) micelle b.) inverse micelle c. ) lamellar I "I"saw 4?0 7'W"IF 4?_16 0""'weir 4?10 d.) hexagonal phase (Hi) e.) inverse hexagonal phase (H 2 ) 13

15 further aggregate to form more complicated assemblies, such as lamellar and hexagonal phases, which generate lyotropic liquid crystal phases. (Figure 1.2c-e) Lamellar phases are particularly significant as they form the structural basis for biological membranes. In thermotropic liquid crystals, the mesophase exists only within a certain temperature range. When a thermotropic liquid crystal phase is observed upon both heating and cooling processes, the phases are thermodynamically stable and the behavior is referred to as enantiotropic. Thermodynamically unstable, kinetically formed phases that only appear upon cooling and are referred to as monotropic. Molecules which form thermotropic liquid crystals typically have large shape anisotropy (or high aspect ratio) and consist of some rigid, aromatic core to provide dipolar attractive forces and pendant aliphatic sidechains to provide highly dynamic motion and fluidity. The most common thermotropic liquid crystals are formed by calamitic or rodshaped molecules. Calamitic mesogens 4 typically consist of some rigid, elongated, linearly-linked ring system that provides the shape anisotropy needed to produce interactions that favor alignment. Usually, a number of alkyl or alkoxy sidechains are Figure 1.3. Examples of calamitic liquid crystals. C4H XG/CN C5H1 CN C5H N_-CH1 CH C -CN NC ~ -oc8h17 O 14

16 placed at either or both ends of the mesogen to provide dispersive forces. Some examples of calamitic mesogens are shown in Figure 1.3. There are two types of phases formed by calamities: nematic and smectic (or lamellar) mesophases. The nematic phase is the simplest and least ordered thermotropic phase, as molecules freely diffuse throughout the sample but, on average, align their long axes in the same direction. (Figure 1.4a) Nematics are named for the "thread-like" features when viewed through a polarizing microscope. Smectic mesophases show a higher degree of order than nematics, as the molecules are not only aligned in one direction, but are further organized into layers. Smectic phases exhibit polymorphism, with each phase differing in the degree of order present within and between layers. For example, in more fluid smectic phases, the director n may lie perpendicular to the layer plane as in smectic A phases, or it may be tilted with respect to the layer plane, as in smectic C phases. (Figure 4b-c) Higher order smectic phases also exist, wherein molecules have more restricted mobility and three-dimensional order is present. Discotics 5 are another type of thermotropic liquid crystal. Discotic mesogens traditionally involve molecules with a flat, rigid, symmetrical, disc-shaped aromatic core Figure 1.4. Some phases formed by calamitic liquid crystals. a.) nematic (N) b.) smectic A (SA) c.) smectic C (Sc) 15

17 surrounded by a periphery of aliphatic chains. Some examples of discotic mesogens are show in Figure 1.5. Discotics can form either nematic or columnar mesophases. The discotic nematic phase is analogous to the nematic phase formed by calamitics in that molecules freely diffuse throughout the sample, yet the short axes of the molecules have a preferred orientation along a single direction. (Figure 1.6a) However, the most commonly found discotic phases are columnar phases, wherein molecules aggregate in columns that further organize to give different two-dimensional columnar assemblies. In the nematic columnar phase (Figure 1.6b), columns mimic calamitic mesogens, aligning the long axes of the columns along the same average direction. Some other examples of columnar phases include rectangular, hexagonal, and tetragonal phases, based on the symmetry of the two-dimensional lattice of columns. (Figure 1.6c-e) In recent years, liquid crystal research has expanded beyond small, purely organic molecules to include polymers, 6 organometallic complexes (further discussed in section 1.5), and hydrogen-bonded supramolecular assemblies. 7 Also, there has been an increasing number of mesogens reported having molecular shapes that do not adhere to Figure 1.5. Examples of discotic liquid crystals. C 7 H, 5 C 7 H 1 5 H1 5 H 15 16

18 Figure 1.6. Phases formed by discotic liquid crystals. A w 4EW p a.) nematic A n4 b.) nematic columnar c.) rectangular d.) hexagonal e.) tetragonal the classic calamitic or discotic model. Some of these structural motifs include cyclic compounds and cyclophanes, swallow-tailed compounds, calamitic-discotic dimers, epitaxygens, bowlic compounds, dendrimers, and bent-core liquid crystals. 8 Many new classes of liquid crystals have been created, each revealing new insights into ways in which mesogens can interact and aggregate to support a liquid crystal phase Metallomesogens Metallomesogens, or metal-containing liquid crystals, combine the properties of liquid crystals (fluidity, anisotropy) with those of metal atoms (magnetic, electrical, optical, electro-optical properties). 9 The metal centers can serve to induce, modify, or enhance the liquid crystalline behavior of the free organic ligand. Metallomesogens that 17

19 mimic calamitics and discotics in shape anisotropy and phase behavior have been described, as well as ones that largely deviate from the classic rod-shaped and diskshaped prototypes. The diverse array of coordination geometries and polydentate ligands available has allowed researchers to study new types of molecular organization previously inaccessible with purely organic mesogens. Additionally, metallomesogens provide a reliable method for the ordered aggregation of metal centers coupled with the long range orientation and ease of alignment in the mesophase, making them attractive candidates for technologically useful materials. 1.4 Chirality in Liquid Crystals When a liquid crystal phase contains molecules having one or more stereogenic centers, the molecular chirality is translated to chirality of the macroscopic mesophase, forming a helical, chiral assembly. The pitch of the formed helix is temperature dependent, and the handedness of the helical structure will depend on the stereogenic center present, as one enantiomer generates a left-handed helix and the other enantiomer generates a right-handed helix. Introduction of chirality into a mesophase results in a reduction in the symmetry when compared to analogous achiral phases. In general, chiral mesophases have reduced phase stability and lower clearing points (temperature at which the transition from mesophase to isotropic phase occurs), often due to the steric effects caused by the chiral center. Chiral phases are most often formed by thermotropic liquid crystals. A chiral mesophase can be formed in two ways. First, the phase can be composed of only chiral molecules. That is, the mesogen itself has one or more stereogenic centers, found either 18

20 along the terminal chain of the mesogen or in the central core. Most often, the chiral center is found in the terminal chain of the molecule due to relative ease of synthesis and the number of commercially available, chiral alkyl chains. Second, a chiral dopant can be added to an otherwise achiral phase. Although the chiral dopant need not be liquid crystalline itself, ideally it will have a mesogenic-like structure, preferably similar to the host phase in order to preserve the properties of the original mesophase. Chiral mesophases formed by rod-shaped mesogens are analogous to their achiral, calamitic counterparts. (Figure 1.7) The chiral nematic (or cholesteric) phase is much like the achiral nematic phase, except that the presence of the chiral unit causes a gradual rotation of the director n in the form of a helix along the long molecular axis. Helical structures are also formed by several chiral smectic phases, but the most commonly found phase is the chiral smectic C phase (Sc*).l As in the achiral Sc phase, molecules within a given layer are tilted with respect to the layer plane, yet, in the Sc* phase, there is a gradual change in tilt direction from layer to layer in the form of a helix. The reduction in phase symmetry causes a spontaneous polarization of molecules within each layer, but Figure 1.7. Some chiral mesophases formed by calamitic mesogens. )"""I\\ ) I,,,, a.) chiral nematic (N*) b.) smectic C* (Sc*) 19

21 due to the helical arrangement of the layers, the polarization direction is rotated from layer to layer and the bulk polarization of the material is zero. Frustrated chiral phases are formed when competition between different structural features of the mesogens prevents a continuous phase from forming, giving rise to a periodic array of defects. Blue phases form when molecules adopt double twist helices which pack in a cubic manner. (Figure 1.8a) Twist grain boundary phases also exist, where blocks of smectic phases (smectic A for TGBA*, smectic C for TGBC*) are arranged in a helical fashion, broken by screw dislocations which abruptly twist the director of the next block. (Figure 1.8b) Frustrated phases such as these exist only in very narrow temperature ranges. Discotic molecules also form chiral phases. Analogous to the structure of the Figure 1.8. Frustrated chiral phases. a.) blue phase screw dislocation where blocks of smectic A meet bloceks of smectic A zi =1 4 zi b.) twist grain boundary phase 20

22 calamitic chiral nematic phase, the chiral discotic nematic phase has a gradual rotation of the molecular director in the form of a helix. However, there are only a few examples of the chiral discotic nematic, as chiral columnar phases are more commonly found. The chirality of a columnar phase can be defined by the chirality within a given column and within the lattice of columns. In either case, the loss of mirror symmetry can arise from a helical twist in the molecular director (Figure 1.9a), a spiraling of molecular position (Figure 1.9b), or the introduction of tilt and polarization in the molecules, analogous to the smectic C* phase (Figure 1.9c). Figure 1.9. Examples of chirality in columnar phases. (a) (b) (c) 1.5. Characterization of Liquid Crystals Liquid crystal phases are typically characterized using three techniques: polarized microscopy, differential scanning calorimetry, and X-ray diffraction. Other techniques include miscibility studies with materials with known mesophases, neutron scattering studies (usually of partially deuterated systems), and NMR studies (useful for studying lyotropic systems), but will not be discussed here. 21

23 1.5.1 Polarized Microscopy When an isotropic liquid is placed between polarizers crossed at 90 to each other, the polarized light is unaffected by the sample and no light passes through the second polarizer. However, when an anisotropic, birefringent medium such as a liquid crystal is present, light interacts with the medium and a complex pattern or texture is observed. Analysis of the defects and deformations in the texture can give information relating to the molecular arrangement of the mesophase. 1 ' 12 Typically, a thin sample of material is sandwiched between a glass microscope slide and a glass cover slip and placed on a temperature-controlled heating stage between two polarizers, and the mesophase behavior is observed upon several cycles of heating and cooling. Nematics normally give rise to schlieren textures, identified by black bands or "brushes" that meet at point singularities or disclinations. Smectics can give a variety of textures including focal conic fans, mosaic, schlieren, and homeotropic. Fan textures, linear birefringent defects, and large areas of uniform extinction are common for columnar hexagonal phases, while rectangular phases typically show wedge-shaped domains Differential Scanning Calorimetry Differential scanning calorimetry (DSC) detects the presence of a liquid crystal phase by measuring the enthalpy change associated with a phase transition. A DSC instrument measures the energy absorbed or released by a sample as it is heated or cooled, indicating at which temperatures endothermic melting processes and exothermic crystallization processes occur. The magnitude of the enthalpy change is proportional to 22

24 the change in structural ordering. As such, solid to liquid phase transitions are relatively drastic in terms of structural change, as reflected by high enthalpy values. Liquid crystal to liquid crystal and liquid crystal to liquid phase transitions are subtle, as evidenced by the relatively small enthalpy changes. DSC alone cannot identify the exact nature of the phase present, but can indicate the degree of molecular order within the phase 3 and should be used in combination with other methods like optical microscopy and X-ray diffraction X-Ray Diffraction X-ray diffraction (XRD) is the technique most often used for unambiguous characterization of liquid crystal phases. Reflected X-rays can be carried out on either a "powder" sample, consisting of polydomains with random director orientation, or aligned samples, usually obtained by application of an electric or magnetic field or mechanical shearing of the viscous mesophase. Only "powder" or unaligned samples will be discussed in the following text. Figure Low (I) and wide (w) angle maxima for a.) calamities and b.) discotics. I i k I A I I~lr M III 4 n W a.) calamities W b.) discotics 23

25 Low angle maxima correspond to long distances between molecules (tens of Angstroms) while wide angle maxima correspond to short distances (between 3-6 Angstroms). Periodic distances d are calculated from these maxima using Bragg's law: nx = 2dsin 0 For calamitics, low angle maxima are measured along the director, and d roughly corresponds to molecular length (or interlayer spacing). (Figure 1.10a) Wide angle maxima, on the other hand, are measured perpendicular to director, and correspond to roughly the molecular width. For nematic phases, low angle maxima are diffuse since there is no periodic structure and positional order is short range. Wide angle maxima are also broad since the phase is liquid-like in the direction perpendicular to the director. In smectics, sharp low angle peaks (Bragg peaks) are observed in the scattered intensity due to periodic arrangement of layers. Wide angle maxima are diffuse for smectic A and C, where molecular packing perpendicular to the director is liquid-like, whereas they are Figure Periodicities within the hexagonal lattice which give rise to low angle peaks. The lattice constant a corresponds to the distance between neighboring columns, while the distance d corresponds to planes of columns. (1 (100) 24

26 sharp for smectics other than A and C, in which there is two-dimensional order within the layer. For discotics, low angle maxima are measured perpendicular to the director and d roughly corresponds to the molecular diameter, while wide angle maxima are measured along the director and correspond to molecular thickness. (Figure 1.10b) In columnar phases, Bragg peaks are observed in the scattered intensity due to periodic arrangement of columns. The spacing ratio of the low angle maxima reflects the type of columnar packing present. Hexagonal phases, for example, show spacing with ratios of 1: 3: N4 for the (100): (110): (200) reflections. (Figure 1.11) Typically, a hexagonal phase has a strong, sharp (100) peak and two weak peaks related to the (110) and (200) reflections, as well as a broad peak around 4.5 angstroms due to the diffuse scattering from the flexible, alkyl side changes. While the (100) peak is always observed, the (110) and (200) peaks may not be present if the columnar lattice is sufficiently disordered. Rectangular phases typically have two sharp, low angle peaks relating to the (100) and (200) reflections, and, like the hexagonal phase, a broad halo at 4.5 angstroms. Additional mid-angle peaks are needed to determine which type of rectangular symmetry is present. The lattice constant a, which corresponds to the separation between nearest neighboring columns, is calculated based on the symmetry of the two-dimensional lattice of columns. The lattice constant for hexagonal phases, for example, can be calculated from the distance d, which corresponds to the separation between planes of columns, using the equation, a = d/cos30 = d213, where d is calculated from the (100) peak using Bragg's law. 25

27 Finally, columnar phases can be ordered or disordered with respect to molecules within a given column, depending on the length scale of molecular correlations within the columns. (Figure 1.12) Ordered columnar phases will exhibit an additional broad peak at A corresponding to the distance between neighboring cores within the individual column caused by dense packing of molecules within the columns. Figure Order (a) and disorder (b) within a column. b 4 (a) (b) 1.6. Outlook on Future Applications Until now, the hallmark application for liquid crystals has been restricted to the field of displays, in large part since, historically, the majority of known liquid crystal phases involved solely calamitic mesogens, which can be aligned in the presence of an electric or magnetic field. It was in the 1970s that discotic mesogens and their phases began to receive considerable attention, introducing more diverse modes of molecular organization and providing new direction towards a wide range of potential technological applications. In particular, columnar phases have been suggested to be useful as sensors, charge transport materials, and other conducting materials. With an array of chiral mesomorphic assemblies at our disposal, this thesis investigates the prospect of utilizing chiral columnar liquid crystals and polymers as asymmetric heterogeneous catalysts, 26

28 exploring the influence that supramolecular chirality may have on the stereochemical outcome of a chemical reaction. Such materials would have a tremendous impact on the fields of liquid crystals, polymers, and catalysis. References 1 Collings, P.J. and Hird, M. Introduction to Liquid Crystals: Chemistry and Physics Taylor and Francis: Philadelphia, 1997; pp Collings, P. J. Liquid Crystals: Nature's Delicate Phase of Matter; Princeton University Press: Princeton, 1990; pp Collings, P.J. and Hird, M. Introduction to Liquid Crystals: Chemistry and Physics ; Taylor and Francis: Philadelphia, 1997; pp Collings, P.J. and Hird, M. Introduction to Liquid Crystals: Chemistry and Physics ; Taylor and Francis: Philadelphia, 1997; pp Collings, P.J. and Hird, M. Introduction to Liquid Crystals: Chemistry and Physics ; Taylor and Francis: Philadelphia, 1997; pp Collings, P.J. and Hird, M. Introduction to Liquid Crystals: Chemistry and Physics ; Taylor and Francis: Philadelphia, 1997; pp Some recent examples include: (a) Lee, K.-M.; Lee, Y.-T.; Lin, I. J. B.; J. Mater. Chem. 2003, 13(5), (b) Song, X.; Li, J.; Zhang, S.; Liq. Cryst. 2003, 30(3), 331. (c) Li, M.; Guo, C.; Wu, Y.; Liq. Cryst. 2002, 29(8), (d) Chen, D.; Wan, L.; Fang, J.; Yu, X.; Chem. Lett. 2001, 11, (d) Lee, H.-K.; Lee, K.; Ko, Y. H.; Chang, Y. J.; Oh, N.-K.; Zin, W.-C.; Kim, K.; Angew. Chem., Int. Ed. 2001, 40,

29 8 Demus, D. In Handbook of Liquid Crystals; Demus, D., Goodby, J., Gray, G.W., Spiess, H.-W., Vill, V. Eds.; Wiley-VCH: Weinheim, 1998; Vol 1, pp For reviews of metallomesogens, please see: (a) Metallomesogens: Synthesis, Properties, and Applications; Serrano, J. L., Ed.; VCH: New York, (b) Donnio, B.; Bruce, D. W.; Liquid Crystals II, Vol. 95: Berlin, 1999; pp (c) Hudson, S. A.; Maitlis, P. M.; Chem. Rev. 1993, 93, 861. (d) Espinet, P.; Esteruelas, M. A.; Oro, L. A.; Serrano, J. L.; Sola, E.; Coord. Chem. Rev. 1992, 117, 215. (e) Inorganic Materials, 2nd ed.; Bruce, D. W., O'Hare, D., Ed.; John Wiley & Sons: New York, (f) Giroud- Godquin, A. M.; Maitlis, P. M.; Angew. Chem., Int. Ed. Engl. 1991, 30, 375. l0 Gray, G.W. and Goodby, J.W.G. Smectic Liquid Crystals: Textures and Structures Leonard Hill: Glasgow and London, 1984; pp " Demus, D.; Richter, L. Textures of Liquid Crystals; Verlag Chemie, Weinheim, Gray, G.W.; Goodby, J.W. Smectic Liquid Crystals: Textures and Structures ; Leonard Hill, Glasgow, Collings, P.J. and Hird, M. Introduction to Liquid Crystals: Chemistry and Physics Taylor and Francis: Philadelphia, 1997; pp

30 Chapter 2 In Situ Polymerization of Columnar Liquid Crystals using Acyclic Diene Metathesis Polymerization: Iron(III) Diketonate Complexes Adapted from: Villazor, K. R.; Swager, T. M. Mol. Cryst. Liq. Cryst. 2004, 410,

31 2.1. Introduction Mesomorphic organizations represent the most powerful and efficient method for the preorganization of molecules to create nanometer-scale ordered synthetic systems.' 2 The incorporation of polymerizable groups within liquid crystals is effective for the synthesis of anisotropic molecular networks by in situ polymerization, wherein reactive monomers are crosslinked in an ordered mesomorphic state with retention of molecular order. The use of such polymerizable liquid crystals as self-assembling building blocks provides a versatile method for processing anisotropic polymeric films with control over both the order and symmetry of the material. Using the appropriate liquid crystal phase as a template, "designer" organic materials can be tailored to suit a specific function. For example, aligned smectic C* phases have been crosslinked in order to make noncentrosymmetric polymer networks, either using a chiral polymerizable mesogen 3 or mixtures containing achiral polymerizable mesogens and chiral dopants. 4 (Figure 2.la) Such materials have been found to exhibit pyroelectric, piezoelectric, and nonlinear optical properties. 3 g' 4Also, lyotropic liquid crystals exhibiting inverse hexagonal phases have been crosslinked to produce nanoporous structures with hexagonally ordered, hydrophilic pores. 2 (Figure 2. lb) Gin and co-workers have applied such materials as heterogeneous Lewis acid 5 and Br0nsted acid 6 catalysts, as well as molecular filters.2a In the crosslinking of liquid crystal phases, the polymerizable group should undergo rapid and efficient crosslinking with minimal perturbation of the liquid crystal phase. Ideally, the reactive group should be synthetically accessible and stable to a wide range of reaction conditions. Photopolymerization of acrylate-containing mesogens has been the most common method of crosslinking with retention of the original mesophase. 7 30

32 Figure 2.1. Schematic representations of in situ crosslinking of (a) an aligned smectic C* phase where p = direction of polarization, and (b) an inverted hexagonal phase. a.) P %P %%%% aligned smectic phase cross-linked network with bulk C 2 symmetry b.) crosslink C > inverse hexagonal phase cross-linked network with hydrophilic pores Typically, a photoinitiator and thermal inhibitor are added to decouple the polymerization event from temperature, allowing for the ordering of the mesophase prior to irradiation. While an efficient and reliable method for polymerization, the use of acrylate groups presents certain drawbacks as well. A highly reactive functional group, acrylates are typically introduced at the final step of a given synthesis, a limitation that can be problematic for mesogens with more complex syntheses. Furthermore, introduction of the polar and sterically bulky acrylate groups often precludes formation of the mesophase. 8 The addition of the branched functionality and intermolecular dipolar interactions effectively destabilizes the mesophase, preventing the side chains from 31

33 efficiently filling space in the liquid crystal phase when compared to mesogens containing only aliphatic side chains. In order to circumvent this problem, Gin and co-workers have had success employing 1,3-dienes, 9 and to a lesser degree, styrene 'O and isoprene " groups, within the sides chains of lyotropic monomers. Photopolymerization of the terminal dienes in an inverted hexagonal phase proceeded with little perturbation to the liquid crystalline order. 9 However, while eliminating the steric bulk and polarity found in acrylate groups, the syntheses of 1,3-diene-containing monomers still require several additional steps to incorporate the polymerizable functional groups within the mesogen. Acyclic Diene Metathesis Polymerization Acyclic diene metathesis polymerization 1 2 (ADMET) is a step-growth polycondensation reaction in which the production and expulsion of ethylene gas drives the polymerization. An application of olefin metathesis, ADMET has proven to be a powerful synthetic route to high molecular weight unsaturated polymers through the polymerization of terminal olefins.' 3 (Figure 2.2) The general mechanism involves two metallocyclobutane intermediates in the reaction cycle, as show in Scheme 2.1, and the Figure 2.2. Acyclic diene metathesis polymerization of terminal olefins. ADMET - C 2 H 4 32

34 Scheme 2.1. Mechanism of ADMET polymerization. R' LnM=\ R' iiw===nft= VR \I L,== 0. 1 L'M R 1%_ LnM=\ R L-M- R 11 Rl R LM= A R active metal species is released from the polymer chain during each propagation step. Similar to catalysts for ring-opening metathesis polymerization (ROMP), catalysts for ADMET include ruthenium-based Grubbs-type carbenes, as well as tungsten-based and molybdenum-based Schrock-type alkylidenes, pictured in Figure 2.3. Resembling the general reaction conditions of other polycondensation reactions, ADMET is often carried out in neat monomer to maximize monomer concentration and drive the reaction towards polymer formation. Additionally, the reaction is carried out under reduced pressure to remove the generated ethylene, again to shift the equilibrium irreversibly towards polymer formation and to accelerate monomer conversion. 33

35 Figure 2.3. Grubbs' "first generation" catalyst (a), "second generation" catalyst (b), and Shrock's molybdenum alkylidene (c) for olefin metathesis. Ci. PCy 3 I CI I Ph PCy 3 LDr 0I r Er I 1-rI N II H 3 C(F 3 C) 2 C -O-Mo% (CH3)2 : P C(CF3)2CH3 h (a) (b) (c) To date, there have been no examples of the utilization of ADMET for the in situ crosslinking of liquid crystal phases with retention of mesophase order. However, there are limited examples of the use of ADMET in the polymerization of liquid crystals to make main-chain liquid crystalline oligomers and polymers. 4 In ease case, terminal olefins were easily incorporated into the side chains of the mesogen using commercially available bromoalkenes. Herein we describe the incorporation of terminal olefins within a metal-containing liquid crystalline monomer and the use of ADMET polymerization to crosslink with retention of the original mesophase order. This approach is particularly attractive since the olefin crosslinking groups more closely resemble typical alkyl side chains of the mesogens in size, hydrophobicity, and thermal stability, yet are reactive towards olefin metathesis. Another advantage of this method is that terminal olefins do not require additional synthetic steps as bromoalkenes of various chain lengths are commercially available. Iron(III) Diketonate Complexes Previous work in the Swager group focused on octahedral iron(iii) diketonate complex 1.15 (Figure 2.4) In the liquid crystal phase, these low aspect ratio complexes 34

36 Figure 2.4. Iron(III) octahedral complexes. la R = (CH 2 )nh, n = 6, 12, 15, 18 lb R = 1c R= I align in columnar arrangements with hexagonal and rectangular packing of columns. When the side chains are chiral (lb-c),' 6 the complexes resolve into single optical isomers and segregate into microdomains of net chirality.' 7 This allows for interdigitation of the aromatic rings of nearest neighbors within a column and the most efficient packing arrangement. In the isotropic phase, 1 is fluxional, rapidly interconverting between optical isomers (A and A). However, in the case of lb-c, examination of the circular dichroism (CD) spectra as a function of temperature shows that the chiral sidechains provide enough perturbation in the mesophase to favor one optical isomer and to effectively induce helicity within a given column. No CD signal was observed for complexes with achiral sidechains. Using polymerizable analogues of these iron(iii) tris(diketonate) complexes, we have developed a method to create robust, polymeric materials from columnar liquid crystals. As demonstrated by Gin and co-workers, columnar phases can act as templates for ordered, porous materials having a variety of potential functions such as ion transport, 35

37 molecular filtration, and catalysis. By employing ADMET as a means of crosslinking, we have prepared anisotropic materials using polymerizable columnar hexagonal liquid crystals with the retention of the original mesophase. (Figure 2.5) We have also employed chiral columnar hexagonal phases to synthesize materials having bulk chirality, potentially for use in asymmetric catalysis and chiral separation technologies. Figure 2.5. In situ polymerization of columnar hexagonal liquid crystals. MEUU* 36

38 2.2. Results and Discussion The liquid crystalline monomers were synthesized following similar procedures as complex 1.14 (Scheme 2.2.) Compound 2 was synthesized via a Williamson etherification of ethyl 3,4-dihydroxybenzoate and the appropriate alkyl bromide. Subsequent hydrolysis of the ethyl benzoate to carboxylic acid salt 3 followed by treatment with >2.0 equivalents of CH 3 Li gave the methyl ketone 4. C-acylation of 4 with the appropriate ethyl benzoate using NaH in anhydrous THF gave the -diketone 5. The iron tris([-diketonate) complexes were synthesized from reaction of the appropriate ligand with Fe(acac) 3. Scheme 2.2. Synthesis of iron(iii) complexes. HO O 0 j OEt i, OEt RO OH OR ii 0 %e%~ OH RO -O OR ii 2a,b 3a,b F,,e O iv O OH v RO [ OR RO OR OR' OR' RO R OR' OR OR' 4a,b 5a,b 6a,b 2a,3a,4a: R= 5a, 6a: R=m 2b,3b,4b: R = (CH )9 2 R' = (CH2)9 5b, 6b: R = R' = (CH 2 ) 9 " (i) RBr, K 2 CO3, KI, 2-butanone, %; (ii) KOH, EtOH/H 2 0, 97-99%; (iii) CH 3 Li, THF, 0 C, 90%; (iv) 2a or 2b, NaH, THF, 68-72%; (v) Fe(acac) 3, benzene, 50-55%. 37

39 The phase behavior is summarized in Table 1. Complexes 6a and 6b exhibit enantiotropic columnar hexagonal (Colh) mesophases as identified by polarized microscopy and X-ray diffraction. When viewed by polarized microscopy, these compounds exhibited linear birefringent defects and large areas of uniform extinction, characteristic of columnar phases. (Figure 2.6) The Colh phases were characterized by the observation of sharp (100) peaks in the low angle region of X-ray diffraction patterns. The wide-angle regions all display broad halos at approximately 4.5 A, which correspond to the distance between liquid-like sidechains, confirming that the phases are indeed liquid crystalline as opposed to crystal or plastic phases. Table 2.1. Phase Behavior of 6a and 6b. The phase behavior for complexes lb-c has been previously reported [ref 16] and is included here for clarity. The transition temperatures and the enthalpies (in parentheses) are given in *C and kcal/mol, respectively, and were determined by differential scanning calorimetry (10 *C / min). Phase Behavior lb Col h 81.0 (2.1) _ - I 73.8 (-2.1) lc Colh 83.8 (2.4) _- I 76.5 (-2.4) 6a Colh 62.4(1.1) I 54.0 (-1.1) 6b Colh 68.8 (7.5) _ - I 61.0 (-7.6) 38

40 Figure 2.6. Microphotographs of the columnar hexagonal texture of 6a. Samples were sandwiched between untreated glass slides and viewed through crossed polarizers. 39

41 For the in situ crosslinking of polymerizable mesogens 6a and 6b, Grubbs' "second-generation" catalyst (Figure 2.3b) was chosen for its stability over a wide range of temperatures and high degree of tolerance for a wide variety of functional groups. 12 Also, an induction period has been observed for the second-generation catalyst, making it relatively slow at the initial stage of the reaction, attributed to the slower rate of phosphine dissociation. g This induction period is particularly attractive for crosslinking liquid crystals, as it allows the mesophase to form before polymerization occurs. Crosslinking can be performed at any given temperature within range of the mesophase. For this particular system, the mesophase is conveniently accessible at ambient temperature. Polymerization studies were carried out on thin films of the appropriate mesogenic monomer and catalyst at room temperature. Film preparation was performed in a glove box under nitrogen atmosphere. Hexane solutions of 6a or 6b containing 1.0 mol % catalyst were drop cast on aluminum plates for X-ray diffraction measurements and spin cast onto a quartz plates for circular dichroism measurements. 9 The films were then annealed to 90 oc to order the mesophase and cooled to room temperature. The annealed films were then placed under vacuum at room temperature for 24 hours to drive the polymerization, resulting in heavily crosslinked free-standing films which were rinsed with hexanes to remove any un-crosslinked material. Table 2.2 lists the XRD lattice constants of the hexagonal phases for 6a and 6b, before and after cross-linking, and the XRD patterns are pictured in Figure 2.7. The XRD patterns of the polymerized films show slightly reduced peak intensities but closely resemble the XRD patterns for the unpolymerized films, indicating that the columnar hexagonal organization remains intact upon crosslinking. Also, circular dichroism (CD) 40

42 confirms that the post-polymerization film of 6a retains its chiral structure (Figure 2.8). The achiral complex 6b showed no CD signal, verifying that the CD signal for 6a was not a result of the chiral ruthenium catalyst, but from the bulk chirality of the mesophase. Table 2.2. X-ray Diffraction Data for 6a and 6b Before and After Crosslinking. Lattice o Spacing Miller Constant (A) observed () indices 6a (Before crosslinking) (100) (110) halo 6a (After crosslinking and extraction) (100) (110) halo 6b (Before crosslinking) 28; (100) halo 6b (After crosslinking and extraction) (100) halo 6b + chiral dopant (30 mol %) (Before crosslinking) (100) halo 6b + chiral dopant (30 mol %) (After crosslinking and extraction) (100) halo 41

43 Figure 2.7. Top: X-ray diffraction profiles of 6a on aluminum plates (a) before polymerization and (b) after polymerization. Bottom: X-ray diffraction profiles of 6b on aluminum plates (a) before polymerization and (b) after polymerization., a ns5 L. IV theta o n4 0 UIV theta 42

44 In an attempt to introduce porosity into the materials, the achiral complex 6b was combined with varying amounts of lb or lc as a chiral dopant. It is well known that small chiral perturbations in liquid crystalline phases, often in the form of a chiral dopant, can induce a strong, cooperative chiral response in the mesophase. 20 Here we attempt to synthesize chiral porous materials by using a chiral dopant to form a chiral hexagonal phase with 6b, then extracting the dopant upon crosslinking. Figure 2.8. Circular dichroism of 6a on aluminum plates (a) before polymerization and (b) after polymerization. 10 i Wavelength (nm) 43

45 Figure 2.9. Circular dichroism of mixtures of 6b with chiral dopants, (a) lb or (b) Ic '0.R Wavelength (nm) 12 E 0% 00 Cn t cu 6 ~-- 0% dopant 11 ae % dopant (,' Oclopatll 2-50% dopant Mole % chiral dopant % dopant 90% dopant 44

46 Before crosslinking, the CD spectra of thin films of mixtures of 6b with chiral dopant were measured and a non-linear dependence on the concentration of dopant was observed, suggesting cooperative chiral induction in the mesophase. (Figure 2.9) Interestingly, addition of chiral (S)-3,7-dimethyloctyl bromide as a chiral dopant does not induce chirality in the mesophase, indicating the importance of a covalent linkage between the mesogenic core and the chiral alkyl chain. The mixtures of achiral 6b and chiral dopant (lb or c) were crosslinked as described above and rinsed with hexanes to wash away the chiral dopant. XRD profiles show that the peak intensity is slightly diminished upon crosslinking, yet the hexagonal phase is retained. Table 2.2 lists representative XRD spacing of the un-crosslinked and crosslinked hexagonal phases of chirally-doped 6b, and the XRD patterns are pictured in Figure Circular dichroism confirmed the chirality of the doped polymerized networks in contrast to the lack of chirality in the undoped network. (Figure 2.10) Attempts were made to determine the extent to which the chiral dopants were successfully extracted from the crosslinked films. UV measurements of crosslinked films before and after hexane extraction of the chiral dopant were made, but the observed decrease in optical density did not correspond to the amount of chiral dopant that was presumed to be extracted. Also, attempts were made to incorporate a guest chromophore within the crosslinked films following extraction of the chiral dopant. To maximize film porosity, mixtures containing 70% chiral dopant or higher were crosslinked as previously described and rinsed with hexanes to remove the dopant. The films were immersed in solutions containing either chromophore 7 or 8 to allow the guest chromophore to diffuse into the porous networks. The chromophores are relatively small molecules with potential ability to diffuse within the pores of the crosslinked film. The hope was that the 45

47 addition of these chromophores within the crosslinked films would be observable in the UV spectrum and, ideally, would give rise to a new CD signal if the chromophores were affected by the bulk chirality of the films. However, upon examination of the UV and CD spectra, no change was observed to denote the inclusion of the chromophores within the networks. These results were attributed to the densely crosslinked nature of the films, wherein each monomer bears at least six polymerizable groups in three-dimensions, making it difficult to extract any guest molecules trapped within the crosslinked network. Figure Left: X-ray diffraction profiles of 6b with 30% chiral dopant on aluminum plates (a) before polymerization and (b) after polymerization Right: CD spectra of crosslinked films of 6b on aluminum plates with (a) 30% chiral dopant and (b) 0% chiral dopant on M theta Wavelength (m) 46

48 Figure Guest chromophores for porous networks.,n /~NSO 2F Concluding Remarks In summary, we have demonstrated that the use of ADMET polymerization is a viable and attractive route towards the synthesis of supramolecular polymeric materials. Incorporation of terminal olefins within the side chains of mesogenic monomers is synthetically straightforward using commercially available bromoalkenes. The addition of the olefin groups within iron(iii) tris(diketonate) complexes does not impede mesophase formation, and the liquid crystalline monomers exhibit columnar hexagonal phases over a wide temperature range. Upon in situ crosslinking using ADMET polymerization, retention of the original liquid crystal phase order is achieved. This method has been used to synthesize both achiral and chiral polymer networks. Attempts to synthesize porous networks were unsuccessful due to the densely crosslinked nature of the films. 47

49 Experimental Section General Methods. Tetrahydrofuran was dried by passing through activated alumina columns. (S)-(+)-Citronellyl bromide and (R)-(+)-citronellyl bromide were purchased from Aldrich (>99% purity) and hydrogenated to give (S)-3,7-dimethyloctyl bromide and (R)-3,7-dimethyloctyl bromide, respectively, using literature procedure.21 All other chemicals were of reagent grade and were used as received, unless otherwise specified. The dialkoxy ethyl benzoate derivatives acetophenone derivatives, 22 as well as complexes lb and c, were synthesized using modified literature procedures. 'H and ' 3 C NMR spectra were obtained on Varian Inova-500 spectrometers. All chemical shifts are referenced to residual CHC1 3 (7.27 ppm for H, ppm for 1 3 C). Multiplicities are indicated as s (singlet), d (doublet), t (triplet), and m (multiplet). DSC investigations were carried out on a Perkin Elmer DSC-7. Optical microscopy was performed on a Leica polarizing microscope in combination with a Mettler FP 80HT/FB 82HT hot stage. Spin cast films were made on quartz plates using a Laurell Spin Processor WS-400-6NPP- LITE at 500 rpm. X-ray diffraction studies were carried out on unoriented samples on aluminum plates with an INEL diffractometer with a 2kW Cu K-a X-ray source fitted with an INEL CPS-120 positive-sensitive detector. The detector was calibrated using a silver behenate standard which was produced by Eastman Kodak and supplied by The Gem Dugout. 3,4-Di-[(S)-3,7-dimethyloctyloxy]-benzoic acid ethyl ester (2a). (S)-3,7-dimethyloctyl bromide (17.6 g, 95.7 mmol) and K 2 CO 3 (19.7 g, 198 mmol) were added to a 2-butanone solution (135 ml) of 3,4-dihydroxybenzoic acid ethyl ester (5.28 g, 38.1 mmol) containing a catalytic amount of potassium iodide. The mixture was heated to reflux at 48

50 80 C under an argon atmosphere for three days. The excess salts were removed by filtration, and the filtrate was washed successively with 0.5M NaOH (aq), water, and brine, and extracted with dichloromethane. The organic fraction was dried over MgSO 4 and the solvents were removed by rotary evaporation to give a yellow-tinted oil. Excess alkyl bromide was removed by vacuum distillation, and the remaining residue was further purified by filtering through a plug of silica gel (1% ethyl acetate/hexane) to afford the product (13.4 g, 100%) as a clear oil. 1 H NMR (CDC13, 500 MHz) 6: 0.87 (d, J = 6.5 Hz, 12H, CH 3 ), 0.96 (dd, J = 6.5, 3.0, 6H, CH 3 ), (m, 12H, CH 2 ), 1.39 (t, J = 7.0 Hz, 3H, CH 3 ), (m, 2H, CH 2 ), (m, 4H, CH, CH 2 ), (m, 2H, CH), (m, 4H, OCH 2 ), 4.35 (q, J = 14.0; 7.0, Hz, 2H, CH 2 ), 6.87 (d, J = 8.0 Hz, 1H, Ar-H), 7.55 (d, J = 2.0 Hz, 1H, Ar-H), 7.65 (dd, J = 8.5, 2.0 Hz, 1H). 13C NMR (CDC1 3, 500 MHz) 8: 14.60, 19.87, 19.91, 22.79, 22.89, 24.90, 24.92, 28.16, 30.09, 30.10, 36.16, 36.30, 37.49, 37.52, 39.41, 39.42, 60.87, 67.50, 67.72, 111.9, 114.2, 122.9, 123.6, 148.6, 153.2, HRMS-ESI (m/z): [M+H] + calcd for C 29 H , found ,4-Di-(10-undecen-l-ol-oxy) benzoic acid ethyl ester (2b). The title compound was prepared using the same procedure as above except that -bromoundec-1-ene was used instead of (S)-3,7-dimethyloctyl bromide (90%). 1 H NMR (CDC13, 500 MHz) 6: (m, 20H, (CH 2 ) 5 ), 1.38 (dd, J = 7.0, 1.5Hz, CH 3 ), (m, 4H, CH 2 ), (m, 4H, CH 2 ), (m, 4H CH 2 ), 4.05 (t, J = 6.5 Hz, 4H, OCH 2 ), 4.35 (q, J = 14.0, 7.0, Hz, 2H, CH 2 ), 4.94 (dd, J = 10.0, 1.0 Hz, 2H, CHCH 2 ), 5.00 (dd, J = 17.0, 1.5 Hz, 2H, CHCH 2 ), (m, 2H, CH), 6.87 (d, J = 8.5 Hz, 1H, Ar-H), 7.55 (s, 1H, Ar-H), 7.65 (dd, J = 8.5, 1.5 Hz, 1H). 13 C NMR (CDC1 3, 500 MHz) : 14.61, 26.14, 26.18, 49

51 29.12, 29.13, 29.24, 29.33, 29.35, 29.36, 29.55, 29.57, 29.62, 29.63, 29.73, 29.75, 34.01, 60.89, 69.12, 69.39, 112.0, , , 122.9, 123.6, 139.4, 148.6, 153.2, HRMS-ESI (m/z): [M+H] + calcd for C 31 H , found ,4-Di-[(S)-3,7-dimethyloctyloxy]-benzoic acid (3a). A solution of 2a (2.01 g, 4.36 mmol) and potassium hydroxide (1.31 g, 23.4 mmol) in ethanol (15 ml) and deionized water (15 ml) was heated to reflux at 80 C for four hours. The solution was then poured into 100 ml of 1N HC1 to form a white precipitate, which was filtered and washed with ethanol to afford the product (1.85 g, 97% yield) as a white solid. H NMR (CDC13, 500 MHz) 8: 0.88 (dd, J = 6.5, 1.0 Hz, 12H, CH 3 ), 0.97 (dd, J = 6.5, 1.0 Hz, 6H, CH 3 ), (m, 4H, CH 2 ), (m, 8H, CH 2 ), (m, 2H, CH 2 ), (m, 4H, CH, CH 2 ), (m, 2H, CH), (m, 4H, OCH 2 ), 6.91 (d, J = 8.5 Hz, 1H, Ar- H), 7.61 (d, J = 2.0 Hz, 1H), Ar-H), 7.75 (dd, J = 8.5, 2.0 Hz, 1H, Ar-H). 3 C NMR (CDC13, 500 MHz) : 19.91, 19.94, 22.83, 22.92, 22.93, 24.93, 24.95, 28.20, 28.21, 30.13, 36.12, 36.26, 37.51, 37.53, 39.43, 39.45, 67.59, 67.75, 111.9, 114.4, 121.5, 124.7, 148.7, 154.1, HRMS-ESI (m/z): [M+Na] + calcd for C 27 H , found ,4-Di-(10-undecen-l-ol-oxy) benzoic acid (3b). The title compound was prepared using the same procedure as above except that 2b was used instead of 2a (99%). H NMR (CDC13, 500 MHz) 6: (m, 20H, (CH 2 ) 5 ) (m, 4H, CH 2 ), (m, 4H, CH 2 ), 2.05 (q, J = 7.0 Hz, 4H, CH 2 ), 4.07 (q, J = 7.0, 6.5 Hz, 4H, OCH 2 ), 4.94 (d, J= 1.0 Hz, 2H, CHCH 2 ), 5.00 (d, J = 17.0 Hz, 2H, CHCH 2 ), (m, 2H, CH), 6.90 (d, 50

52 J = 8.5 Hz, 1H, Ar-H), 7.60 (d, J = 1.5 Hz, Ar-H), 7.74 (dd, J = 8.5, 2.0, 1H, Ar-H). 13 C NMR (CDC13, 500 MHz) 6: 26.15, 26.19, 29.14, 29.15, 29.21, 29.33, 29.35, 29.37, 29.56, 29.59, 29.64, 29.66, 29.74, 29.77, 34.03, 34.04, 69.19, 69.41, 112.0, 114.3, 114.6, 121.5, 124.7, 139.4, 148.7, 154.1, HRMS-ESI (m/z): [M-H]- calcd for C 29 H , found ,4-Di-[(S)-3,7-dimethyloctyloxy]-acetophenone (4a). A solution of 3a (1.35 g, 3.11 mmol) and dry THF (30 ml) was cooled to 0 C under an argon atmosphere. A 1.4M solution of methyllithium in ether (7.0 ml) was added dropwise via syringe, and the solution was allowed to stir overnight, warming to room temperature. After being poured into 100 ml of N HC1 and extracted with dichloromethane, the solution was dried over MgSO 4 and the solvents were removed by rotary evaporation. The remaining residue was purified by column chromatography using 5% ethyl acetate/hexane as the eluant to afford the product (1.22 g, 91%) as a clear oil. H NMR (CDC13, 500 MHz) : 0.86 (d, J = 6.5 Hz, 12H, CH 3 ), 0.95 (d, J = 6.5 Hz, 6H, CH 3 ), (m, 4H, CH 2 ), (m, 8H, CH 2 ), (m, 2H, CH 2 ), (m, 4H, CH, CH 2 ), (m, 2H, CH), 2.55 (s, 3H, CH 3 ), (m, 4H, OCH 2 ), 6.86 (d, J = 8.0 Hz, 1H, Ar-H), 7.52 (s, 1H, Ar-H), 7.53 (d, J = 8.5 Hz, 1H, Ar-H). 1 3 C NMR (CDC1 3, 500 MHz) 6: 19.84, 19.87, 22.76, 22.85, 22.86, 24.86, 24.88, 26.36, 28.13, 30.05, 30.06, 36.08, 36.24, 37.45, 37.46, 39.36, 39.38, 67.49, 67.62, 111.5, 112.2, 123.3, 130.3, 149.0, 153.6, HRMS-ESI (mlz): [M+Na] + calcd for C 28 H , found

53 3,4-Di-(10-undecen-l-ol-oxy)-acetophenone. (4b). The title compound was prepared using the same procedure as above except that 3b was used instead of 3a (90%). 'H NMR (CDC13, 500 MHz) 6: (m, 20H, (CH 2 ) 5 ) (m, 4H, CH 2 ), (m, 4H, CH 2 ), (m, 4H, CH 2 ), (m, 4H, CH 2 ), 2.55 (s, 3H, CH 3 ), 4.07 (q, J = 6.5, 6.0 Hz, 4H, OCH 2 ), 4.93 (d, J = 10.0 Hz, 2H, CHCH 2 ), 5.00 (dd, J = 17.0, 1.5 Hz, 2H, CHCH 2 ), (m, 2H, CH), 6.86 (d, J = 8.5 Hz, 1H, Ar-H), 7.52 (d, J = 2.0 Hz, Ar-H), 7.54 (dd, J = 8.5, 2.0, 1H, Ar-H). 13 C NMR (CDC13, 500 MHz) 8: 26.11, 26.15, 26.40, 29.10, 29.11, 29.19, 29.32, 29.52, 29.55, 29.60, 29.61, 29.70, 29.73, 33.98, 33.99, 69.15, 69.33, 111.6, 112.4, 114.3, 123.4, 130.4, 139.3, 149.0, 153.6, HRMS-ESI (m/z): [M+H] + calcd for C 30 H , found [3',4'-((S)-3,7-Dimethyloctyloxy)phenyl]-3-[3",4"-(10-undecen-1-ol-oxy)phenyl]- propan-1,3-dione (5a). A solution of 2b (1.67 g, 3.53 mmol) and 4a (1.02 g, 2.35 mmol) in anhydrous THF (10 ml) was added via cannula to a 3-neck flask containing sodium hydride (0.624 g, 26.0 mmol) and 20 ml dry THF at 0 C under an argon atmosphere and was stirred for two hours, warming to room temperature, then heated to reflux at 80C for four hours. The resulting dark orange solution was cooled to room temperature, and water was added to quench excess NaH. The diketone was neutralized using N HC1 and was extracted with dichloromethane and dried over MgSO 4. The solvents were removed by rotary evaporation to give a dark orange oil, which was purified by column chromatography using 5% ethyl acetate as the eluant to afford the product (2.68 g, 74.0%) as a bright yellow oil. H NMR (CDC13500 MHz) 6: 0.97 (dd, J = 6.5, 2.0 Hz, 12H, CH 3 ), 1.06 (dd, J = 6.5, 2.0 Hz, 6H, CH 3 ), (m, XH, CH 2 ), 52

54 (m, 4H CH 2 ), (m, 8H, OCH 2 ), 5.03 (dd, J = 10.0, 1.0 Hz, 2H, CHCH 2 ), (m, 2H, CHCH 2 ), (m, 2H, CH), 6.78 (s, 1H, CH), 7.02 (d, J = 8.0 Hz, 2H, Ar-H), 7.36 (s, 2H, Ar-H), 7.66 (dd, J = 7.5, 2.0 Hz, 2H, Ar-H). 3 C NMR (CDC MHz) 8: 19.91, 19.96, 22.83, 22.93, 24.94, 24.96, 26.27, 26.30, 28.20, 20.16, 29.19, 29.37, 29.41, 29.60, 29.68, 29.76, 29.77, 29.80, 29.88, 30.14, 30.16, 30.55, 34.04, 34.06, 36.19, 36.32, 36.36, 37.53, 37.56, 39.44, 39.46, 67.65, 67.99, 69.62, 73.80, 112.2, 114.3, 121.4, 128.4, 130.7, 139.4, 142.3, 149.2, 153.1, 184.4, HRMS-ESI (m/z): [M-H]- calcd for C 57 H , found ,3-Bis[3',4'-(10-undecen-1-ol-oxy)phenyl]-propan-1,3-dione (5b). The title compound was prepared using the same procedure as above except that 4b was used instead of 4a (68%). 'H NMR (CDC MHz) 8: (m, 40H, (CH 2 ) 5 ), 1.50 (m, 8H, CH 2 ), (m, 8H, CH 2 ), (m, 8H CH 2 ), (m, 8H, OCH 2 ), 4.94 (dd, J= 10.0, 1.0 Hz, 4H, CHCH 2 ), 5.00 (d, J= 17.0 Hz, 4H, CHCH 2 ), (m, 4H, CH), 6.73 (s, 1H, CH), 6.92 (d, J = 8.5 Hz, 2H, Ar-H), 7.55 (s, 2H, Ar-H), 7.57 (d, J = 8.5 Hz, 2H, Ar-H). ' 3 C NMR (CDC13, 500 MHz) : 26.18, 26.21, 29.15, 29.28, 29.35, 29.37, 29.43, 29.58, 29.61, 29.64, 29.66, 29.75, 29.78, 34.03, 69.23, 69.58, 91.86, 112.3, 114.3, 121.2, 128.4, 139.4, 149.1, 153.1, HRMS-ESI (m/z): [M-H]- calcd for C 59 H , found Tris[1-[3',4'-((S)-3,7-dimethyloctyloxy)phenyl]-3-[3",4"-(1-undecen-1-ol-oxy)- phenyl]-propanedionato]iron(iii). (6a) A suspension of 5a (1.05g, 1.20 mmol), iron trisacetylacetonate (0.14, 0.40 mmol), and 5 ml benzene was heated to reflux at 100 C 53

55 for 12 hours under argon. The solvent was removed using vacuum rotary evaporation, affording a red oil. To purify, the red oil was dissolved in hot acetone and placed in the refrigerator until red solids form at the bottom of the flask. The solvent was decanted away from the red solids, which was then redissolved in hot acetone, and the purification procedure was repeated again to yield the product as a waxy, red solid in 50% yield. HRMS-MALDI (m/z): [M+Na] + calcd for C 177 H 273 FeO , found Tris[1,3-di-(3,4-di-10-undecenoxyphenyl)-propanedionatoliron(III). (6b) The title compound was prepared using the same procedure as above except that 5b was used instead of 5a (55%). HRMS-MALDI (mlz): [M+Na] + calcd for C 171 H 273 FeO , found

56 References 'For reviews on polymerizable thermotropic liquid crystals, please see: (a) Kelly, S. M. ; J. Mater. Chem. 1995, 5, (b) Hikmet, R. A. M.; Lub, J.; Broer, D. J.; Adv. Mater. 1991, 3, For reviews of polymerizable lyotropic liquid crystals, please see: (a) Gin, D. L.; Gu, W.; Pindzola, B. A.; Zhou, W.-J.; Acc. Chem. Res. 2001, 34, 973. (b) Miller, S. A.; Ding, J. H.; Gin, D. L.; Curr. Opin. Colloid Interfac. Sci. 1999, 4, 338. (c) O'Brien, D. F.; Armitage, B.; Benedicto, A.; Bennett, D. E.; Lamparski, H. G.; Lee, Y.-S.; Srisiri, W.; Sisson, T. M.; Acc. Chem. Res. 1998, 31, 861. (d) Ringsdorf, H.; Schlarb, B.; Venzmer, J.; Angew. Chem., Int. Ed. Engl. 1988,27, (a) Stupp, S. I.; Son, S.; Li, L. S.; Lin, H. C.; Keser, M.; J. Am. Chem. Soc. 1995, 117, (b) Trollsas, M.; Sahlen, F.; Gedde, U. W.; Hult, A.; Hermann, D.; Rudquist, P.; Komitiv, L.; Lagerwall, S. T.; Stebler, B.; Lindstrom, J.; Rydlund, O. Macromolecules 1996, 29, (c) Lub, J.; Van Der Veen, J. H.; Van Echten, E.; Mol. Cryst. Liq. Cryst. Sci. Technol., A 1996,287, 205. (d) Kitzerow, H. S.; Schmid, H.; Ranft, A.; Heppke, G.; Hikmet, R. A. M.; Lub, J.; Liq. Cryst. 1993, 14, 911. (f) Trollsas, M.; Orrenius, C.; Sahlen, F.; Gedde, U. W.; Norin, T.; Hult, A.; Hermann, D.; Rudquist, R.; Komitov, L.; Lagerwall, S. T.; Lindstrom, J.; J. Am. Chem. Soc. 1996, 118, (a) Guymon, C. A.; Hoggan, E. N.; Bowman, C. N.; Clark, N. A.; Rieker, T. P.; Walba, D. M.; Science 1997, 275, 57. (b) Kurihara, S.; Ishii, M.; Nonaka, T.; Macromolecules 1997, 30, 313. (c) Hikmet, R. A. M.; Michielson, M.; Adv. Mater. 1995, 7, 300. (d) Hikmet, R. A. M.; Zwerver, B. H.; Liq. Cryst. 1993, 13, 561. (e) Hikmet, R. A. M.; Macromolecules 1992, 25, (f) Heynderickyx, I.; Broer, D. J.; Mol. Cryst. Liq. 55

57 Cryst. 1991, 203, 113. (g) Hikmet, R. A. M.; Zwerver, B. H.; Mol. Cryst. Liq. Cryst. 1991, 200, 197. (h) Broer, D. J.; Heynderickyx, I.; Macromolecules 1990, 23, Gu, W.; Zhou, W.-J.; Gin, D. L.; Chem. Mater. 2001, 13, XU, Y.; Gu, W.; Gin, D. L.; J. Am. Chem. Soc. 2004, 126, (a) Favre-Nicolin, Christine D.; Lub, Johan; Van Der Sluis, P.; Mol. Cryst. Liq. Cryst. 1997, 299, 157. (b) Favre-Nicolin, C. D.; Lub, J.; Macromolecules 1996, 29, (c) Keum, C.-D.; Kanazawa, A.; Ikeda, T.; Adv. Mater. 2001, 13(5), 321. (d) Sanchez, C.; Villacampa, B.; Alcala, R.; Martinez, C.; Oriol, L.; Pinol, M.; Serrano, J. L.; Chem. Mater. 1999, 11, (e) Ogiri, S.; Nakamura, H.; Kanazawa, A.; Shiono, T.; Ikeda, T.; Nishiyama, I.; Macromolecules 1999, 32, (f) Hikmet, R. A. M.; Michielsen, M.; Adv. Mater. 1995, 7, 300. (g) Gray, David H.; Gin, Douglas L.; Chem. Mater. 1998, 10, (h) Baxter, B. C.; Gin, D. L.; Mol. Cryst. Liq. Cryst. 1999, 332, (a) Dwer, M. J., Goldberg, R. S.; J. Am. Chem. Soc. 1970, 92, (b) Takenaka, S.; Morita, H.; Iwano, M.; Sakurai, Y.; Ikemoto, T.; Kusabayashi, S.; Mol. Cryst. Liq. Cryst. 1990, 182, 325. (c) Schroeder, J. P. Mol. Cryst. Liq. Cryst. 1980, 61, 229. (d) Kossmehl, G.; Gerecke, B.; Harmsen, N.; Schroeder, F.; Vieth, H. M.; Mol. Cryst. Liq. Cryst. 1994, 269, 39. (e) Marcot, L.; Maldivi, P.; Marchon, J.-C.; Mol, G.; Chem. Mater. 1997, 9, (f) Kelly, S. M.; Liq. Cryst. 1996, 20, (a) Pindzola, B. A.; Hoag, B. P.; Gin, D. L.; J. Am. Chem. Soc. 2001, 123, (b) Pindzola, B. A.; Jin, J.; Gin, D. L.; J. Am. Chem. Soc. 2003, 125, (c) Hoag, B. P.; Gin, D. L.; Macromolecules 2000, 33, Reppy, M. A.; Gray, D. H.; Pindzola, B. A.; Smithers, J. L.; Gin, D. L.; J. Am. Chem. Soc. 2001, 123(3),

58 Hoag, B. P.; Gin, D. L.; Liq. Cryst. 2004, 31, For a recent review on ADMET, please see: Schewendeman, J. E.; Church, A. C., Wagener, K. B.; Adv. Synth. Catal. 2002, 344, 597. '3 (a) Lindmark-Hamberg, M.; Wagener, K. B.; Macromolecules 1987, 20,2949. (b) Wagener, K. B.; Boncella, J. M.; Nel, J. G.; Duttweiler, R. P.; Hilllmyer, M. A.; Makromol. Chem. 1990, 191, 365. (c) Wagener, K. B.; Nel, J. G.; Konzelman, J.; Boncella, J. M.; Macromolecules 1990, 23, (d) Brzezinsak, K.; Wagener, K. B.; Macromolecules 1991, 24, (e) Wagener, K. B.; Smith, D. W., Jr.; Macromolecules 1991, 24, (a) Walba, D. M.; Keller, P.; Shao, R.; Clark, N. A.; Hillmyer, M.; Grubbs, R. H.; J. Am. Chem. Soc. 1996, 118, (b) Joo, S.-H.; Yun, Y.-K.; Jin, J.-I.; Kim, D.-.; Zin, W.-C.; Macromolecules 2000, 33, (c) Qin, H.; Chakulski, B. J.; Rousseau, I. A.; Chen, J.; Xie, X.-Q.; Mather, P. T.; Constable, G. S.; Coughlin, E. B.; Macromolecules 2004, 37, '5 Zheng, H.; Swager, T. M.; J. Am. Chem. Soc. 1994, 116(2), Trzaska, S. T.; Hsu, H. F.; Swager, T. M.; J. Am. Chem. Soc. 1999, 121, Recent studies of discoid molecules have also established the preference for a single chiral conformer in a columnar stack: Palmans, A. R. A.; Vekemans, J. A. J. M.; Havinga, E. E.; Meijer, E. W.; Angew. Chem., Int. Ed. Engl. 1997, 36, (a) Sanford, M. S.; Love, J. A.; Grubbs, R. H.; J. Am. Chem. Soc 2001, 123, (b) Sanford, M. S.; Ulman, M.; Grubbs, R. H.; J. Am. Chem. Soc 2001, 123, 749. '9 Circular dichroism is measured on spin-case films with an optical density ranging from

59 9 Goodby, J. W. In Handbook of Liquid Crystals: Fundamentals; Demus, D.; Goodby, J. W.; Gray, G. W.; Spiess, H. W.; Vill, V., Eds.; Wiley-VCH: Weinheim, 1998; Vol.l, Chapter Trzaska, S. T.; Zheng, H.; Swager, T. M.; Chem. Mater. 1999, 11, Zheng, H.; Xu, B.; Swager, T. M.; Chem. Mater. 1996, 8,

60 Chapter 3 In Situ Polymerization of Columnar Liquid Crystals using Acyclic Diene Metathesis Polymerization: Dioxomolybdenum Complexes

61 3.1. Introduction In the previous chapter, in situ crosslinking of a columnar hexagonal phase was successfully carried out using acyclic diene metathesis polymerization (ADMET). The mesophase was essentially "frozen" in place, affording a free-standing, densely crosslinked, anistropic film. The octahedral iron tris(diketonate) system studied, however, exhibited a wide phase range and was liquid crystalline at room temperature, two advantages not typically available with other mesophases. Also, the monomers contained terminal olefins within each of its twelve alkyl chains, a relatively high number of polymerizable groups per monomer, resulting a densely crosslinked film. In order to explore the applicability of this method to other columnar liquid crystals, systems with different phase behavior and number of polymerizable groups required investigation. Previous work in the Swager group focused on the dioxomolybdenum pyridine 2,6-dimethanolate complex 1, which forms a tapered columnar phase.' (Figure 3.1) While the free ligand is not itself mesogenic, the polymeric (--Mo=O--Mo=O--)n interaction of complex 1 provides the organizational force needed to direct the mesophase assembly. The polymeric metal-oxygen coordination lies within the central axis of a column, with the ligands tapered around columnar core in order to effectively fill space and stabilize the columnar structure. (Figure 3.2) When the sidechains are sufficiently Figure 3.1. Dioxomolybdenum liquid crystals. 0O RO IR(CH)Hn=1O, 12,14 ROO 60

62 long (n a 10), the complexes exhibit enantiotropic liquid crystal behavior at temperatures higher than - 80 C. Our interest in this particular molybdenum system stemmed from not only from its ability to form columnar phases, but also for its potential to become a heterogeneous catalyst upon crosslinking of the mesophase. Dioxomolybdenum complexes have been well-established as catalysts for olefin epoxidation when treated with hydrogen peroxide or t-buooh to form peroxomolydenum. 2 (Scheme 3.1) Activation of the dioxomolybdenum metal center within a chiral columnar phase would result in a chiral arrangement of catalytic metal centers within the axis of a column, providing a potential medium for the asymmetric epoxidation of olefins. Figure 3.2. Tapered columnar phase formed by dioxomolydenum complexes. RO OR RO RO RO RO O -Mo:O Y I! RO OR :, RSide View Top View Side View 61

63 Utilizing the methods developed to achieve the in situ crosslinking of liquid crystals, we have synthesized ordered networks from the columnar hexagonal phase formed by dioxomolybdenum complexes. Incorporation of terminal olefins within the side chains of the mesogenic monomers affords a monomer with three polymerizable groups, anchoring the mesogens at the periphery of the column upon polymerization. Also, the effectiveness of the dioxomolybdenum mesogens in the epoxidation of olefins is evaluated. Scheme 3.1. Peroxomolybdenum-catalyzed olefin epoxidation. 4? t-buooh LnMo LnMo RoR/ Results and Discussion Variations on the general synthetic route previously developed by Swager and Serrette afforded the target mesogens 7a-b. As depicted in Scheme 3.2, Williamson etherification of methyl 3,4,5-trihydroxybenzoate with the appropriate alkyl bromide gave methyl benzoate 2. Reduction of 2 with lithium aluminum hydride or diisobutyl aluminum hydride followed by treatment with phosphorus tribromide gave 4 in 91% yield. Williamson etherification of 4-hydroxypyridine-2,6-dicarboxylic acid dimethyl 62

64 ester 3 with benzylic bromide 4 followed by reduction of the ester groups at the C-2 and C-6 positions afforded ligand 6. Finally, complexes 7a-b were synthesized by reaction of the appropriate ligand 6 with MoO 2 (acac) 2. Scheme 3.2. Synthesis of dioxomolydenum complexes. O OCH 3 o OCH 3 ~~~~~~i HO-OH OH RO OR OR iii OR iv 2a,b 3a,b - i 4a,b RO.OCH3 vi RO 5a,b 6a,b 7a R = (CH2) RO RO 7b(R) R = 7b(S) R = (i) RBr, K 2 C0 3, KI, MEK, 94-98%; (ii) DIBAL-H or LAH, THF, 0 C, 93-97%; (iii) PBr 3, toluene, 91%; (iv) 4-hydroxy-pyridine-2,6-dicarboxylic acid methyl ester, K 2 C0 3, KI, MEK, 78%; (v) NaBH 4, CHCI3/CH 3 0H, 64-87%; (vi) MoO 2 (acac) 2, CHCI3/CH 3 0H, 65-80%. 63

65 The phase behavior is summarized in Table 3.1. Mesogens 7a-b display enantiotropic liquid crystalline behavior, with phases appearing at temperatures above 80 C. The optical textures viewed through a polarizing microscope are characteristic of hexagonal columnar phases and display linear birefringent defects and large areas of uniform extinction. The mesophase-to-isotropic transition enthalpies are small (1.0 to 1.3 kcal mol'), in accordance with a highly disordered phase. When compared to the mesogens with unbranched, achiral, aliphatic chains, the introduction of either terminal olefins or chiral branching groups in the side chains of the mesogens destabilizes the phase and results in lower clearing points and narrower phase ranges. Examination of the X-ray diffraction (XRD) patterns reveals low angle peaks corresponding to the (100) and (110) reflections of a hexagonal lattice. A broad halo at wide angle is also observed, indicating the presence of weak, liquid-like interactions between alkyl chains. (Table 3.2) Table 3.1. Phase Behavior of 7a-b. The transition temperatures and the enthalpies (in parentheses) are given in given in C and kcal/mol, respectively, and were determined by differential scanning calorimetry (10 C / min). Phase Behavior 94.3 (15.5) (1.2) 7a K Colh - I 84.8 (-15.1) 98.3 (-1.3) 91.1 (14.3) (1.0) 7b (R) K - Colh I 84.6 (-14.1) (-1.2) 92.6 (14.4) (1.0) 7b (S) K Colh - I 87.9 (-14.2) (-1.3) 64

66 Table 3.2. X-ray diffraction data for 7a-b. Lattice o Spacing. Miller Constant (A) observed (A) indices 7a (at 95 C) (100) (110) halo 7a (at 25 C, after crosslinking and extraction) (100) (110) (200) halo 7b (R) (at 95 C) (100) (110) halo 7b (S) (at 95 C) (100) (110) halo Crosslinking this liquid crystal system required different conditions than in the case of the octahedral complexes (Chapter 1). The mesophase is only available at higher temperatures, requiring that polymerization be performed above at least 85 C. Also, a greater amount of Grubbs' catalyst is needed, as initial attempts to crosslink neat films of 7a using 1 mole % catalyst 95 oc were not successful. Therefore, under nitrogen atmosphere, a solution of 7a and 5 mole % Grubbs' catalyst in dichloromethane is drop cast onto an aluminum plate. The film is placed on a hot plate at 95 oc for 24 hours, resulting in a heavily crosslinked free-standing film, which is then rinsed with 65

67 Figure 3.3. X-ray diffraction pattern of crosslinked film of 7a k liu) "A'lo O.oJ A , (1 10) 16.4 A ) (200) 14.3 A 4.55 A I ~~~~~~~~~~~~~~~~~~I theta dichloromethane to remove any un-crosslinked material. Table 3.2 lists the XRD lattice constants of the hexagonal phases, before and after cross-linking, while Figure 3.3 shows the X-ray diffraction pattern of the crosslinked material. Upon polymerization, the mesogens are locked in place at the periphery of the columns, resulting in retention of the columnar hexagonal organization. The crosslinked material displays the (100), (110), and (200) reflections of a hexagonal lattice, as well as a broad halo at wide angle. Chiral phases were formed using mixtures of 7a and various amounts of 7b(R) or 7b(S) as a chiral dopant. DSC measurements of the mixtures are shown in Figure 3.4. With addition 50 mole % or less of chiral dopant, the clearing and crystallization points 66

68 Figure 3.4. Phase behavior of mixtures of 7a with 7b(S) as chiral dopant. * Columnar hexagonal phase 03 a E ae Percent Chiral Dopant both occur at a lower temperatures, indicating destabilization of the mesophase. However, with the addition of 50 mole % or more, the clearing points are raised and the phase ranges are broadened, signifying a higher degree of stabilization. The mixtures were crosslinked as described above and the resulting anisotropic materials again retain the original columnar mesophase order. Attempts to obtain circular dichroism spectra on the films proved to be challenging due to the lack of homogeneity in the drop cast films. Also, at higher temperatures the mesophase is highly fluid, resulting in highly irreproducible spectra. Spin cast films of sufficient thickness and homogeneity were difficult to obtain. Initial evaluation of 7b(S) in the solution phase epoxidation of crotyl alcohol with t-buooh 4 indicated that the monomeric mesogen was not catalytically active (Scheme 67

69 3.3) and only starting materials were recovered. In an effort to enhance the reactivity of the molybdenum center, complex 8 was synthesized by hydrolysis of 5b(S), followed by complexation to MoO 2. However, the replacement of hydroxymethyl groups with more electronegative carboxylate groups did not provide sufficient activation for the metal center and complex 8 was found to be catalytically inactive in the epoxidation of crotyl alcohol. Scheme 3.3. Attempted epoxidation of crotyl alcohol. HOJ MoO 2 L, tbuooh HO P MoO 2 L = 7b(S) Concluding Remarks In summary, we have demonstrated that the use of ADMET polymerization can be used in the in situ crosslinking of liquid crystals at higher temperature ranges and with fewer number of polymerizable groups per monomer. The addition of terminal olefins or chiral, branched sidechains within dioxomolybdenum complexes does not impede 68

70 mesophase formation, although the phase ranges are narrowed relative to the complexes with aliphatic side chains. Retention of the original liquid crystal phase order is achieved indicating that the weak, polymeric (--Mo=O--Mo=O--)n interaction remains intact. An initial evaluation of the catalytic activity of the mesogens indicated the metal complex is not catalytically active in the epoxidation of crotyl alcohol Experimentals General Methods. (S)-(+)-Citronellyl bromide and (R)-(-)-Citronellyl bromide were purchased from Aldrich (>99% purity) and were hydrogenated using literature procedure. 5 All other chemicals were of reagent grade and were used as received, unless otherwise specified. 'H and ' 3 C NMR spectra were obtained on Varian Inova-500 spectrometers. All chemical shifts are referenced to residual CHC1 3 (7.27 ppm for 'H, 77.3 ppm for 3 C). Multiplicities are indicated as s (singlet), d (doublet), t (triplet), and m (multiplet). DSC investigations were carried out on a Perkin Elmer DSC-7. Optical microscopy was performed on a Leica polarizing microscope in combination with a Mettler FP 80HT/FB 82HT hot stage. X-ray diffraction studies were carried out on unoriented samples on aluminum plates with an INEL diffractometer with a 2kW Cu K-a X-ray source fitted with an INEL CPS-120 positive-sensitive detector. The detector was calibrated using a silver behenate standard which was produced by Eastman Kodak and supplied by The Gem Dugout. 69

71 3,4,5-Tri-[3,7-dimethyloctyloxy]-benzoic acid methyl ester, (R) and (S). (2b) 3,4,5- Trihydroxybenzoic acid methyl ester (2.22 g, 12.1 mmol), (R)- or (S)-3,7-dimethyloctyl bromide (10.7 g, 48.3 mmol), potassium carbonate (6.68 g, 48.3 mmol), and a catalytic amount of potassium iodide were combined in 60 ml of 2-butanone and the mixture was heated to reflux at 80 0 C under an argon atmosphere for 72 hours. The excess salts were removed by filtration, and the filtrate was washed successively with 0.5M NaOH (aq), water, and brine, and extracted with dichloromethane. The organic fraction was dried over MgSO 4 and the solvents were removed by rotary evaporation to give a yellow-tinted oil. Excess alkyl bromide was removed by vacuum distillation, and the remaining residue was further purified by filtering through a plug of silica gel (5% ethyl acetate/hexane) to afford the product (7.30 g, 94.0%) as a clear oil. 'H NMR (CDC13, 500 MHz) : 0.87 (dd, J = 6.5, 2.0 Hz, 18H, CH 3 ), 0.95 (d, J = 6.5 Hz, 9H, CH 3 ), (m, 6H, CH 2 ), (m, 12H, CH 2 ), (m, 4H, CH 2 ), (m, 2H, CH 2 ), (m, 3H, CH), (m, 3H, CH), 3.89 (s, 3H, OCH 3 ), (m, 6H, OCH 2 ), 7.27 (s, 2H, Ar-H). ' 3 C NMR (CDC13, 500 MHz) 8: 19.73, 19.76, 22.79, 22.81, 22.90, 24.90, 24.93, 28.17, 29.79, 29.98, 36.47, 37.52, 37.67, 39.44, 39.53, 52.28, 67.56, 71.84, 108.0, 124.8, 142.4, 153.0, HRMS-ESI (m/z): [M+H] + calcd for C 38 H , found ,4,5-Tri-(10-undecen-l-ol-oxy)-benzoic acid methyl ester. (2a) The title compound was prepared using the same procedure as above using 11-bromoundec-1-ene instead of (R)- or (S)-3,7-dimethyloctyl bromide (98.1%). H NMR (CDC1 3, 500 MHz) 6: (m, 30H, (CH 2 ) 5 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, 70

72 CH 2 ), 3.89 (s, 3H, CH 3 ), (m, 6H, OCH 2 ), (m, 3H, CHCH(H)), (m, 3H, CHCH(H)), (m, 3H, CH), 7.26 (s, 2H, Ar-H). 1 3 C NMR (CDC1 3, 500 MHz) 6: 26.23, 26.25, 29.13, 29.15, 29.34, 29.38, 29.47, 29.55, 29.64, 29.68, 29.73, 29.76, 29.80, 29.85, 30.50, 31.79, 34.01, 34.02, 52.26, 69.27, 73.61, 108.1, 114.3, 124.8, 139.3, 142.4, 153.0, HRMS-ESI (m/z): [M+H] + calcd for C 41 H , found ,4,5-Tri-[3,7-dimethyloctyloxy]-benzyl alcohol, (R) and (S). (3b) A solution of 3a (4.39 g, 7.26 mmol) and dry THF (25 ml) was added to a stirring solution of LAH (0.69 g, 18.2 mmol) and THF (50 ml) at 0 C. The suspension was allowed to stir for four hours, warming to room temperature, then cooled back to 0 C. A small amount of cold distilled water was added slowly to quench the excess LAH, then 1.OM HC1 was added to break up the formed aluminum salts. The white solution was extracted with dichloromethane, and the organic layer was dried over MgSO 4. The solvents were removed by rotary evaporation to yield the product (4.20 g, 97.4%) as a white solid. H NMR (CDC13, 500 MHz) 8: 0.88 (d, J = 6.5 Hz, 18H, CH 3 ), 0.93 (t, J = 6.5 Hz, 9H, CH 3 ), (m, 6H, CH 2 ), (m, 12H, CH 2 ), (m, 6H, CH 2 ), (m, 3H, CH), (m, 3H, CH), (m, 6H, OCH 2 ), 4.59 (s, 2H, CH 2 ), 6.56 (s, 2H, Ar-H). 13 C NMR (CDC1 3, 500 MHz) : 19.77, 22.80, 22.83, 22.91, 24.91, 24.94, 28.18, 29.88, 30.00, 36.60, 37.51, 37.54, 37.73, 39.47, 39.56, 65.81, 67.49, 71.84, 105.3, 136.3, 137.6, HRMS-ESI (m/z): [M+Na]+ calcd for C 3 7 H , found

73 3,4,5-Tri-(10-undecen-1-ol-oxy)-benzyl alcohol. (3a) The title compound was prepared using the same procedure as above using 2a instead of 2b (92.5%). H NMR (CDC1 3, 500 MHz) 6: (m, 30H, (CH 2 ) 5 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (mn, 6H, OCH 2 ), 4.58 (d, J = 6.0 Hz, 2H, CH 2 ), (m, 3H, CHCH(H)), (m, 3H, CHCH(H)), (m, 3H, CH), 6.55 (s, 2H, Ar-H). 3 C NMR (CDC13, 500 MHz) : 26.27, 26.31, 29.12, 29.15, 29.34, 29.39, 29.58, 29.65, 29.73, 29.77, 29.86, 30.39, 34.00, 34.02, 65.75, 69.19, 73.58, 105.4, 114.3, 136.3, 137.6, 139.4, HRMS-ESI (m/z): [M+H] + calcd for C4OH , found ,4,5-Tri-[3,7-dimethyloctyloxy]-benzyl bromide, (R) and (S). (4b) To a solution of 3b (3.71 mmol) in toluene (20 ml) was added phosphorus tribromide (0.35 ml) and the solution was heated to reflux at 100 C for three hours. The clear solution was decanted away from the inorganic salts and was poured slowly into 100 ml of water. The organic layer was extracted with dichloromethane and dried over MgSO 4 and the solvents were removed in vacuo to yield the product (95%) as a clear oil. The product was used without further purification. For analytical measurements, the material was purified by filtration through silica gel (5:95 ethyl acetete: hexane). 1 H NMR (CDC13, 500 MHz) : 0.90 (d, J = 6.5 Hz, 18H, CH 3 ), 0.95 (t, J = 6.5 Hz, 9H, CH 3 ), (m, 6H, CH 2 ), (m, 12H, CH 2 ), (m, 6H, CH 2 ), (m, 3H, CH), (m, 3H, CH), (m, 6H, OCH 2 ), 4.45 (s, 2H, CH 2 ), 6.61 (s, 2H, Ar-H). 13 C NMR (CDC13, 500 MHz) : 19.74, 22.78, 22.80, 22.89, 24.89, 24.92, 28.16, 29.86, 29.98, 72

74 36.59, 37.49, 37.53, 37.70, 39.45, 39.54, 53.66, 67.45, 71.82, 107.3, 133.3, 138.5, HRMS-ESI (m/z): [M+H]+ calcd for C37H 68 BrO , found ,4,5-Tri-(10-undecen-1l-ol-oxy)-benzyl bromide. (4a) The title compound was prepared using the same procedure as above using 3a instead of 3b. 'H NMR (CDC1 3, 500 MHz) 6: (m, 30H, (CH 2 ) 5 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), 4.44 (d, J = 6.0 Hz, 2H, CH 2 ), (m, 3H, CHCH(H)), (m, 3H, CHCH(H)), (m, 3H, CH), 6.55 (s, 2H, Ar-H). 13 C NMR (CDC1 3, 500 MHz) 6: 26.22, 26.24, 29.08, 29.11, 29.30, 29.34, 29.49, 29.53, 29.60, 29.62, 29.65, 29,69, 29.72, 29.82, 30.46, 33.96, 33.98, 34.74, 53.60, 69.16, 73.52, 107.5, 114.3, 132.7, 138.4, 139.3, HRMS-ESI (m/z): [M+H] + calcd for , found [3,4,5-Tri-(3,7-dimethyloctyloxy)-benzyloxy]-pyridine-2,6-dicarboxylic acid methyl ester, (R) and (S). (5b) A mixture of 4b (2.46 g, 3.84 mmol), 4-hydroxypyridine-2,6-dicarboxlyic acid methyl ester (0.65 g, 3.08 mmol), K 2 CO 3 (0.82 g, 5.93 mmol) and a catalytic amount of KI in 2-butanone was heated to reflux at 80 C for 12 hours. The mixture was poured into 0.5M NaOH (aq) and extracted with ethyl acetate. The combined organic layers were dried over MgSO 4 and the solvents were removed in vacuo. Purification by column chromatography in 1:1 ethyl acetate:hexane gave the product (2.30 g, 78.0%) as a clear oil. 'H NMR (CDC13, 500 MHz) : 0.86 (d, J = 6.5 Hz, 18H, CH 3 ), 0.93 (t, J = 7.0 Hz, 9H, CH 3 ), (m, 18H, CH 2 ), (m, 6H, CH 2 ), (m, 3H, CH), (m, 3H, CH), 3.89 (s, 3H, OCH 3 ), (m, 73

75 6H, OCH 2 ), 4.01 (s, 6H, OCH 3 ), 5.12 (s, 2H, OCH 2 ), 6.62 (s, 2H, Ar-H), 7.91 (s, 2H, Ar- H). 13 C NMR (CDC1 3, 500 MHz) 6: 19.76, 22.79, 22.81, 22.90, 22.91, 24.91, 24.92, 28.17, 29.86, 29.97, 31.13, 36.55, 37.51, 37.53, 37.70, 39.44, 39.54, 53.47, 67.63, 71.43, 71.87, 106.4, 115.0, 129.6, 138.6, 150.0, 153.7, 165.3, HRMS-ESI (m/z): [M+H] + calcd for , found [3,4,5-Tri-(10-undecen-1-ol-oxy)-benzyloxy]-pyridine-2,6-dicarboxylic acid methyl ester. (5a) The title compound was prepared using the same procedure as above using 4a instead of 4b. H NMR (CDC13, 500MHz) 6: (m, 30H, (CH 2 ) 5 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), 3.99 (s, 6H, OCH 3 ), (m, 3H, CHCH(H)), (m, 3H, CHCH(H)), 5.11 (s, 2H, OCH 2 ), (m, 3H, CH), 6.60 (s, 2H, Ar-H), 7.88 (s, 2H, Ar-H). ' 3 C NMR (CDC1 3, 500 MHz) 6: 26.20, 26.22, 29.05, 29.08, 29.27, 29.32, 29.48, 20.50, 29.57, 29.66, 29.69, 29.79, 30.44, 33.93, 33.96, 53.39, 69.25, 71.31, 73.53, 106.3, 114.3, 115.0, 129.6, 138.5, 139.3, 149.9, 153.6, 165.2, [M+H] + calcd , found {6-Hydroxymethyl-4-[3,4,5-tri-(3,7-dimethyloctyloxy]-pyridin-2-yl}methanol, (R) and (S). (6b) Sodium borohydride (0.40 g, 10.6 mmol) was added in small portions to a solution of 5b (0.82 g, 1.06 mmol) in CHC1 3 :CH 3 OH (1:1) (15 ml) at 0 C. The solution was then stirred for 1 hour, warming to room temperature, and heated to reflux at 70 C for 72 hours. The solution was then cooled to room temperature, and water was added to quench excess NaBH 4. The mixture was extracted with dichloromethane and washed 74

76 successively with 1.OM HC1 (aq), water, and brine, and the organic layer was dried over MgSO 4. The solvents were removed in vacuo to yield the product as a white solid, which was recrystallized in CHC1 3 /MeOH to yield the pure product in 74% yield. 'H NMR (CDC13, 500 MHz) 6: 0.86 (d, J = 6.5 Hz, 18H, CH 3 ), 0.93 (t, J = 7.0 Hz, 9H, CH 3 ), (m, 18H, CH 2 ), (m, 6H, CH 2 ), (m, 3H, CH), (m, 3H, CH), (m, 6H, OCH 2 ), 4.98 (s, 2H, OCH 2 ), 6.60 (s, 2H, Ar-H), 6.80 (s, 2H, Ar-H). 1 3 C NMR (CDC13, 500 MHz) 6: 19.74, 22.78, 22.80, 22.89, 24.92, 28.16, 29.87, 29.96, 36.56, 37.51, 37.54, 37.70, 39.44, 39:53, 64.61, 67.59, 70.60, 71.87, 106.1, 106.2, 130.6, 138.3, 153.6, 160.9, HRMS-ESI (m/z): [M+H] + calcd , found {6-Hydroxymethyl-4-[3,4,5-tri-(10-undecen-1-ol-oxy)]-pyridin-2-yl}methanol. (6a) The title compound was prepared using the same procedure as above using 5a instead of 5b. (87%) IH NMR (CDC13, 500MHz) 6: (m, 30H, (CH 2 ) 5 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), 4.70 (s, 4H, CH 2 ), 4.93 (d, J = 10.0 Hz, 3H, CHCH(H)), 4.99 (dd, J = 17.0, 2.0 Hz, 3H, CHCH(H)), 4.99 (s, 2H, OCH 2 ), (m, 3H, CH), 6.58 (s, 2H, Ar-H), 6.79 (s, 2H, Ar-H). ' 3 C NMR (CDC13, 500 MHz) 6: 26.27, 26.29, 29.12, 29.15, 29.34, 29.39, 29.43, 29.56, 29.64, 29.68, 29.73, 29.76, 29.80, 29.86, 30.50, 32.79, 34.00, 34.02, 64.59, 69.32, 70.60, 73.63, 106.0, 106.3, 114.3, 130.6, 138.3, 139.4, 153.6, 160.7, HRMS-ESI (mlz): [M+H] + calcd , found

77 MoO 2 (6b), (R) and (S). (7b) Bis(acetylacetonato)dioxomolybdenum(VI) (0.51 g, 1.57 mmol) was added to a stirring solution of 6b (1.12 g, 1.57 mmol) in CHCl 3 :MeOH (1:1) at room temperature. The mixture was heated to reflux at 80 C for 12 hours, during which the orange suspension becomes a clear solution. After cooling to room temperature, the solvents were removed in vacuo, and the product (80%) was recrystallized in CHCl 3 :MeOH. 1 H NMR (CDC1 3, 500 MHz) 6: 0.87 (d, J = 6.5 Hz, 18H, CH 3 ), 0.94 (t, J = 6.5 Hz, 9H, CH 3 ), (m, 12H, CH 2 ), (m, 6H, CH 2 ), (m, 4H, CH 2 ), (m, 2H, CH 2 ), (m, 3H, CH), (m, 3H, CH), (m, 6H, OCH 2 ), 5.15 (s, 2H, OCH 2 ), 5.86 (s, 4H, OCH 2 ), 6.61 (s, 2H, Ar-H), 6.96 (s, 2H, Ar-H). 1 3 C NMR (CDC1 3, 500 MHz) 8: 19.77, 22.82, 22.84, 22.93, 24.93, 24.95, 28.20, 29.89, 30.00, 36.57, 37.54, 37.58, 37.72, 39.47, 39.56, 67.74, 71.94, 72.48, 80.95, 104.9, 106.5, 128.9, 139.0, 153.8, 168.0, HRMS-ESI (m/z): [M+H] + calcd , found MoO 2 (6a). (7a) The title compound was prepared using the same procedure as above using 6a instead of 6b. (65%) H NMR (CDC13, 500MHz) 6: (m, 30H, (CH 2 ) 5 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), (m, 3H, CHCH(H)), 5.00 (dd, J = 17.0, 2.0 Hz, 3H, CHCH(H)), 5.14 (s, 2H, OCH 2 ), (m, 3H, CH), 5.86 (s, 4H, CH 2 ), 6.58 (s, 2H, Ar-H), 6.94 (s, 2H, Ar-H). 13 C NMR (CDC1 3, 500 MHz) : 26.30, 29.14, 29.18, 29.35, 29.41, 29.46, 29.58, 29.61, 29.67, 29.76, 29.78, 29.89, 30.54, 34.02, 34.05, 69.49, 72.43, 73.71, 80.02, 104.9, 106.6, 114.4, 128.8, 131.8, 139.4, 153.8, 168.0, HRMS-ESI (mlz): [M+Na]+ calcd , found

78 References Serrette, A. G.; Swager, T. M.; Angew. Chem., Int. Ed. Engl. 1994, 33, (a) Rossiter, B. E.; Verhoeven, T. R.; Sharpless, K. B.; Tetrahedron Lett. 1979, (b) Arcoria, A.; Ballistreri, F. P.; Tomaselli, G. A.; Di Furia, F.; Modena, G.; J. Org. Chem. 1986, 51, (c) Sharpless, K. B.; Michaelson, R. C.; J. Am. Chem. Soc. 1973, 95, hydroxypyridine-2,6-dicarboxylic acid dimethyl ester is obtained from acid-catalyzed esterification of commercially available chelidamic acid monohydrate. 4 Adam, W.; Mitchell, C. M.; Saha-Mller, C. R.; J. Org. Chem. 1999, 64, Trzaska, S. T.; Zheng, H.; Swager, T. M.; Chem. Mater. 1999, 11,

79 Chapter 4 Liquid Crystals containing Catalytic Ligands

80 4.1. Introduction The success of an asymmetric catalyst relies on its ability to enhance the enantioselectivity for a chemical reaction. While the focus has primarily been on the clever design and choice of chiral ligands, researchers have also continued to explore other methods of enhancing asymmetric induction by undertaking a more supramolecular approach. In certain cases, the aggregation of multiple catalytic moieties has been shown to facilitate a bimetallic cooperative mechanism of catalysis, l wherein the catalyst plays a dual role in the catalytic cycle, such as simultaneous activation of both nucleophile and electrophile. As such, researchers have attempted to bring multiple metal centers in close proximity to each other by incorporation of chiral, catalytic complexes within dimeric, oligomeric, and dendritic frameworks. 2 Such efforts have resulted in significant enhancements in both rate and enantioselectivity when compared to the monomeric counterparts. The observed improvements in stereochemical communication are attributed in part to the greater effective molarity of catalytic units, as well as their relative orientation to one another. Metallomesogens or metal-containing liquid crystals represent a unique supramolecular platform for the controlled aggregation of metal complexes. In chiral columnar liquid crystal phases formed by metallomesogens, the metal centers can be distributed in a helical fashion along the columnar axis. This type of supramolecular array of catalytic metal complexes could potentially facilitate a cooperative mechanism of catalysis and exhibit improved reactivity relative to the monomeric complex. In this chapter we describe our efforts towards the incorporation of well-known chiral catalytic 79

81 ligands into liquid crystal phases. Systems under investigation include chiral pyridine bis(oxazoline) ligands as well as pincer ligands Pyridine bis(oxazoline) Ligands Background Chiral, C 2 -symmetric pyridine bis(oxazoline) or "pybox" ligands are one of the most versatile and widely used systems in asymmetric catalysis. 3 (Figure 4.1) First synthesized by Nishiyama in 1989, 4 these tridentate ligands are conformationally constrained once chelated to a metal, minimizing the number of possible substratecatalyst arrangements and transition states in a particular reaction. 5 Substituents at the stereogenic centers of the oxazoline rings are in close proximity to the metal center, directly influencing the stereochemical outcome of the reaction. The chirality in pybox is derived from a wide variety of commercially available optically active natural and unnatural amino alcohols, allowing for flexibility in ligand design as well as availability of both enantiomeric forms. Pybox ligands have been utilized in a vast array of asymmetric reactions and have been the subject of numerous reviews. 3 Some examples include various additions to C=O and C=N double bonds (aldol, reduction of ketones, silylcyanations) and formation Figure 4.1. C 2 -symmetric pyridine bis(oxazoline) ligand..o N " RI R 80

82 Scheme 4.1. Example of bimetallic catalysis observed in system using pybox ligands. X s (pybox)yb/. 0 pybox ligand, M = YbC1 3 Lx YbLy(pybox) TMSO PN TMSCN, CHCI 3 CN R R R R of three-membered rings from olefins and imines (cyclopropanation, aziridination, epoxidation). Also, several pericyclic reactions have been investigated (Diels-Alder and hetero Diels-Alder, 1,3-dipolar cycloadditions, [2,3]-sigmatropic rearrangements). In certain cases, cooperative bimetallic catalysis has been observed as evidenced by a positive nonlinear effect and a second-order dependence on catalyst. Studies on the asymmetric ring opening of meso epoxides with cyanide, for example, indicate that the pybox catalyst performs the dual tasks of nucleophilic delivery and activation of the electrophile via Lewis acidity. 6 (Scheme 4.1) The incorporation of chiral pybox ligands within supramolecular platforms has been mainly restricted to immobilization on polymeric supports. 7 To date, there have been no reports of a mesomorphic system containing chiral pybox ligands, but there are limited examples of systems containing a chiral oxazoline ring within the mesogenic core. In their studies on helical columnar superstructures, Serrano and co-workers have investigated mesogens containing a chiral, methyl-substituted oxazoline ring. Ligands containing three alkoxy side chains were complexed to either a copper(ii) or palladium(ii) metal center to give phasmid-shaped complexes which did not exhibit liquid crystalline phases unless combined in certain proportions with an electron acceptor such as trinitrofluorenone (TNF).8(Figure 4.2a) Typically, placing the stereogenic center 81

83 on the central core as opposed to the peripheral side chains introduces steric repulsions between neighboring molecules and often precludes formation of a liquid crystal phase. Without the addition of TNF, the methyl groups at the stereogenic centers of the oxazoline rings provide sufficient steric bulk to prevent the aromatic cores from assembling into a stable columnar phase. However, when the ligand has an expanded aromatic core and six alkoxy chains, the negative steric effect of the methyl groups is overcome and a columnar mesophase is formed without need for any additive. (Figure 4.2b) Columns within the phase have a helical organization and a 60 rotation between neighboring molecules, an arrangement that allows for the even distribution of the alkyl side chains around the central core of the column. Figure 4.2. Previously studied chiral oxazoline liquid crystals. (a) NO 2 02N - N02 PI l nematic and smectic phases formed (b) 82

84 Results and Discussion Building on the ligand design previously utilized for dioxomolybdenum complexes (Chapter 3), the target pybox ligands append chiral oxazoline rings at the C-2 and C-6 positions of a pyridine ring, with a trialkoxy-substituted benzyl group at the C-4 position. (Bis)methyl esters 1 and 2 were synthesized using methods developed for our studies with dioxomolybdenum complexes. 9 Direct condensation of the aminoalcohol with diester or 2 in refluxing xylenes gave the bis(hydroxy)amides 3 and 4, respectively. Conversion of the hydroxy groups to chlorides with SOC12 was performed in the presence of 2,6-di-t-butyl-4-methylpyridine as a proton scavenger in order to prevent cleavage of the benzylic bond. Treatment of bis(chloromethyl)amides 5 and 6 Scheme 4.2. Synthesis of pyridine bis(oxazoline) ligand. O O x X x H iii 1 R = C 14 H29 2 R = (CH 2 ) 9 CHCH 2 For Y = OH: 3a X = CH 3, R = C 14 H 29 3b X = H, R = C 1 4 H29 4a X = CH 3, R = (CH 2 ) 9 CHCH 2 4b X = H, R = (CH 2 ) 9 CHCH 2 7a X = CH 3, R = C 14 H29 7bX = H, R = C 14 H 2 9 8a X = CH 3, R = (CH 2 ) 9 CHCH 2 8b X = H, R = (CH 2 ) 9 CHCH 2 For Y = CI: 5a X = CH 3, R = C 14 H 29 5b X = H, R = C 14 H29 6a X = CH 3, R = (CH 2 ) 9 CHCH 2 6b X = H, R = (CH 2 ) 9 CHCH 2 (i) (S)-alaninol or ethanolamine, xylenes, 57-64%; (ii) SOCI 2, 2,6-di-t-butyl-4-methylpyridine, THF, 60 C, 42-86%; (iii) NaH, THF, 1 hour, 76-94%. 83

85 with base gave the oxazoline ligands 7 and 8. Ligands 7 and 8 did not exhibit mesomorphic behavior. As such, a metal center was needed to provide a sufficient driving force for mesophase formation. Copper and palladium pybox complexes are two of the most common metal-pybox complexes utilized and have been shown to catalyze a wide variety of reactions. However, complexation of ligands 7a-b to CuC1 2, Cu(BF 4 ) 2, CuOAc 2, CuOTf, PdC1 2, and Pd[CH 3 CN] 4 (BF 4 ) 2 resulted in non-mesomorphic materials which melted directly into the isotropic phase. However, CuCl(7a) and CuCl(7b) showed bright birefringence when viewed under crossed polarizers, but no clear mesophase was evident. To promote mesomorphic behavior, dodecylsulfate (DOS) chains were introduced into the fourth coordination site of the metal center. Previous work by Bruce and co-workers with silver complexes of stilbazoles found that the replacement of BF4-, NO3, or CF 3 SO 3 anions with DOS anions resulted in stabilized mesophases, lower clearing points and broadened temperature range of the phase. Thus, ligands 7a and 7b were first complexed to CuCl, followed by treatment with AgDOS in the absence of light to extract the chloride, affording CuDOS(7a) and CuDOS(7b), respectively. (Scheme 4.3) Scheme 4.3. Synthesis of Cu(DOS)(7). 7a, 7b 1. CuCI, EtOH/CH 2 CI 2 2. AgDOS, CH 2 C12 CuDOS(7a): X = CH 3 CuDOS(7b): X = H 84

86 When viewed under a polarized microscope, achiral CuDOS(7b) showed birefringence and appeared to be forming a columnar phase. However, upon heating, a dark reddish brown color began to appear at temperatures above 200 C and the material decomposed before reaching the clearing point. In the case of CuDOS(7a), the chiral methyl groups significantly lower the melting point of the complex. When viewed through crossed polarizers, regions of a columnar phase were observed, yet, upon repeated heating and cooling cycles, the regions disappeared and only disordered birefringence was observed. (Figure 4.3) We therefore investigated the effect that the addition of TNF would have on the phase behavior of CuDOS(7a). As described above, the "sandwiching" of an electron acceptor such as TNF between neighboring mesogens has been known to stabilize liquid Figure 4.3. Microphotographs of the columnar hexagonal texture of CuDOS(7a). Samples were sandwiched between untreated glass slides and viewed through crossed polarizers. 85

87 crystal phases, creating a supramolecular array of charge transfer complexes. Contact preparations were performed, in which the two materials are placed on the same glass slide and the phase behavior in the region where the two materials meet is observed. CuDOS(7a) forms a charge transfer complex with TNF, as evidenced by the reddish brown color change in the contact region in the isotropic phase. However, upon cooling, the two materials separate as TNF crystallizes and no mesophase is observed under polarized microscopy. Interestingly, it was observed that the columnar phase seemed to be stabilized by the presence of coordinating solvents like acetone. (Figure 4.5a) Large regions of columnar phase were observed and persisted upon numerous cycles of heating and cooling. Still, the phase was not uniform throughout the sample. (Figure 4.5b) In an attempt to uniformly stabilize the phase, several coordinating a-ketones were added. The a-ketone solvents contained long, aliphatic chains to lower the volatility of the solvent and to also facilitate formation of the mesophase. (Figure 4.4) Contact preparations were performed, with the best results obtained in the mixture between (R)-4,8-dimethyl-2- nonanone and CuDOS(7a). (Figure 4.5c-d) Clear columnar phases were observed by polarized microscopy as characterized by fan shaped textures and large domains of uniform extinction. However, subsequent contact preparations with the same material Figure 4.4. a-ketone solvents used as additives for CuDOS(7a). 10-decanone (R)-DMN (S)-DMN DMN = 4,8,-dimethyl-2-nonanone 86

88 gave inconsistent results and mesophase formation was not observed. Upon the study of specific ratios of CuDOS(7a):solvent, inconsistent phase behavior was again observed. Multiple samples from the same mixture showed drastically different behavior, often displaying no mesophase. It became apparent that the material was in some way decomposing, as evidenced by broad melting transitions observed by DSC. One possible explanation for the inconsistency of the columnar phase could be the instability of the Cu(I) metal center, Figure 4.5. Microphotographs of the columnar hexagonal texture of CuDOS(7a). Samples were sandwiched between untreated glass slides and viewed through crossed polarizers. a.) b.) c.) d.) 87

89 which readily oxidizes to Cu(II) at high temperatures. In order to determine whether or not oxidation was indeed occurring, Cu(DOS) 2 (7a) was synthesized and its phase behavior was observed. Cu(DOS) 2 (7a) was an isotropic liquid at room temperature and no birefringence was observed when viewed through crossed polarizers, indicating that oxidation of the metal center to form Cu(DOS) 2 (7a) was unlikely. Another possibility for decay of the columnar phase is metal leaching, as catalytic copper(i) complexes of tridentate pybox ligands are typically generated in situ and not isolated.l' The proton NMR of CuDOS(7a) only showed peaks for the aliphatic side chains and the 3,4,5-alkoxy substituted phenyl ring and none for the pybox ring. This could be explained by oxidation of Cu(I) to some Cu(II) species, which can have a strong disproportionate effect, even in small quantities, dampening the NMR signals of protons in close proximity to the paramagnetic metal center by electron transfer between Cu(I) and Cu(II) centers. Another explanation would involve cleavage of the weak benzylic linkage, given the introduction of electron-deficient oxazoline substituents on the pyridine ring and the electron-rich nature of the trialkoxy-substituted benzyl group. In fact, the instability of the benzylic linkage was observed in separate attempts to polymerize the free ligand 7a via ADMET polymerization with Grubbs' second generation catalyst. No polymerization occurred, as proton NMR revealed decomposition of the ligand by cleavage of the benzylic bond. The ruthenium catalyst likely binds the tridentate pybox moiety, effectively diminishing catalyst activity and catalyzing cleavage of the benzylic linkage. The difficulties experienced with this particular system stemmed not from the chiral oxazoline groups, but largely from the instability of both the benzylic linkage and 88

90 the Cu(I) metal center with the tridentate pybox ligand. Nonetheless, a metastable columnar phase was observed, indicating that there is potential for C 2 -symmetric pyboxes to form stable mesophases. Modification of the linkage between the pybox entity and the trialkoxy-substituted appendage should stabilize the ligand and facilitate formation of a stable, columnar phase. Furthermore, other metal centers forming more stable complexes with pybox ligands should be explored Pincer Liquid Crystals Background "Pincer" complexes are comprised of an aryl anion bound to a metal center via a metal-carbon o bond, with substituents ortho to the metal-carbon bond that coordinate to the metal. 12 (Figure 4.6) Chelation of the two neutral donor groups (E) results in the formation of two five-membered metallacycles. The rigid terdentate binding mode substantially stabilizes the metal-carbon bond, preventing metal leaching. Pincers are stable to air and moisture, and are thermally robust. Also, a range of steric and electronic modifications to the pincer framework can be achieved without substantially affecting the properties of the metal site. This excellent stability of the pincer complex has made it particularly attractive for various applications in materials science. Pincer complexes have been incorporated into various supramolecular platforms, including polymers, Figure General structure of pincer ligands. RAII R IiXnLn 89

91 macrocycles, dendrimers, sensors, and switches, and immobilized on gold surfaces, fullerenes, silica, and various soluble and insoluble polymeric supports.l2a The unique and highly protective environment for the metal site coupled with the ability to fine tune electron density around the metal has made pincers ideal system for catalysis. The stability of the metal-carbon a bond prevents metal leaching, a problem common to many catalysts in which the metal is coordinated solely to heteroatoms. Pincers have found application in a wide array of reactions, including Heck, Suzuki, transfer hydrogenation, alkane dehydrogenation, asymmetric aldol, Michael addition, allylation of aldehydes. Also, chiral modifications can be made on the benzylic positions or on the donor atoms to produce chiral catalysts. Previous work in the Swager group took an unconventional approach to creating a chiral pincer catalyst.' 3 As shown in Figure 4.7a, two C 2 -symmetric pincer units were linked using a chiral spacer derived from O-isopropylidene-L-threitol. While the stereogenic center is remote from the active site, it was hoped that interaction of a substrate with both metal centers would create a highly chiral pocket and influence the Figure 4.7. Bimetallic pincer catalyst (a) and grafted onto silica support (b) where R = phenyl, t-butyl. 3F 4 ) 2 (a) (b) 90

92 enantioselectivity. Studies on the aldol condensation of isocyanoacetates and aldehydes or ketones proceeded with <1% ee, suggesting that the catalytic centers behave independently and no cooperative catalysis occurs. In a further attempt to promote interaction of adjacent pincer moieties, the bimetallic pincer compounds were grafted onto silica support in order to achieve a densely packed array of catalysts with constricted conformational mobility. (Figure 4.7b) However, only enantiomeric excesses of 2-3% were observed. Herein we describe our initial efforts towards the synthesis of pincer liquid crystals. In order to achieve the desired aggregation of pincer complexes, we sought to incorporate the pincer moiety into a liquid crystalline columnar phase, which would give rise to a one-dimensional array of metal centers. The high level of stability of the pincer ligand with substitution in the 4-position makes it a better candidate for appendage with an electron rich, alkoxy-substituted benzyl group. The only example of mesomorphic pincers are based on pyridine-2,6-bis(carboxylate) and pyridine-2,6-bis(thiocarboxylate) Figure 4.8. Previously studied pincer liquid crystals. (a) 1r~(sO) ~~ O I OCoH2 10H 2 'NLO ~ (b) OC OH

93 ligands, which formed smectic, nematic, and in one case, columnar, phases when another mesomorphic ligand is placed in the fourth coordinate site of the metal center. (Figure 4.8) Results and Discussion The design for the target pincer ligands places a trialkoxy-substituted benzyl group at the 4-position of the pincer ring. 3,5-Bis-thiophenylmethyl-anisole 9 was prepared in a series of steps that has been described in literature starting from 5- hydroxyisophthalate, with the exception that a methyl group was used to protect the phenol. 14 Treatment with BBr 3 gave phenol 10. Alkylation of 10 via a Williamson ether synthesis gives ligand 11, which was then metallated with Pd(CH 3 CN) 4 (BF 4 ) 2 in anhydrous acetonitrile to give complex 12. Scheme 4.4. Synthesis of Pincer Complexes. CO 2 CH 3 j jj -SPh /SPh iii, iv H3C Ho -~ H 3 CO -HO CO 2 CH 3 SPh SPh 9 10 SPh SPh RO RO I RO A v I O o0 I -NCC-NCC H 3 (BF 4 ) SPh SPh RO RO 11 R = C 4 H R = C 14 H29 (i) CH 3 1, K 2 CO 3, KI, 2-butanone, reflux 4 hrs; (ii) LAH, THF, 0C; (iii) PBr 3, toluene, reflux 3 hours; (iv) thiophenol, ADOGEN 464, toluene/h 2 0, 96%; (v) BBr 3, THF, 0 C, 94%; (vi) 3,4,5-tritetradecyloxybenzyl bromide, K 2 CO 3, KI, 2-butanone, reflux 4 hrs, 80%; (vii) Pd(CH 3 CN)4(BF 4 ) 2, CH 3 CN, reflux 14 hours. 92

94 No mesophase is observed for ligand 11 or complex 12, upon both heating and cooling. Due to the C 2 symmetry of the pincer complex, the phenyl substituents are in a trans conformation with respect to the square planar palladium coordination plane, causing a large degree of steric repulsion between neighboring complexes and preventing effective aggregation of the mesogens. Replacement of the acetonitrile ligand with a mesogenic alkyl-substituted cyanobiphenyl ligand, as shown in Scheme 4.5, indicated no improvement of mesomorphic behavior. Based on these preliminary results, future work should include the attachment of smaller substituents on the donating groups to facilitate mesogen aggregation. Scheme 4.5. Addition of 4'-Pentyl-4-biphenyl-carbonitrile to NC 'CH1 I CH 2 CI 2 RO Ph I-PhNC Ph C5H, 4.4. Concluding Remarks Incorporation of catalytic moieties within supramolecular platforms has been shown to enhance catalytic behavior, prompting the investigation of metallomesogens containing well-established catalytic moieties. Chiral bis(oxazoline) ligands displayed a metastable columnar phase when complexed to Cu(I) center. However, while instability of the metal-ligand complex as well as the benzylic linkage of the ligand caused the phase to readily decompose, there is still potential for stable mesophase formation. By 93

95 appropriate modification of the ligand. Pincer ligands were also investigated as a system offering a more robust metal-ligand sigma bond. Preliminary results indicate that phenyl groups on the donating sulfur groups provide significant steric repulsion, precluding formation of a liquid crystal phase. The incorporation of C 2 -symmetric ligands within liquid crystal phases remains promising. From our studies, it was observed that while the phenyl substituents on the pincer ligand caused significant steric repulsion between mesogens, the methyl groups on the pybox ligand did not impede formation of a metastable mesophase. Optimization of these systems requires tailoring the substituents at the stereogenic centers as well as determining a suitable metal center for complexation. Modifications such as these can lead to successful formation of a liquid crystalline phase containing catalytic moieties Experimental Section General Methods. Compounds 3-8 were synthesized using modified literature procedures.' 5 Tetrahydrofuran was dried by passing through activated alumina columns. AgDOS was synthesized following literature procedures.' 6 All chemicals were of reagent grade and were used as received, unless otherwise specified. H and 13 C NMR spectra were obtained on Varian Inova-500 spectrometers. All chemical shifts are referenced to residual CHC1 3 (7.27 ppm for 'H, ppm for ' 3 C). Multiplicities are indicated as s (singlet), d (doublet), t (triplet), and m (multiplet). High resolution mass spectra were obtained at the MIT Department of Chemistry Instrumentation Facility (DCIF) on a Finnigan MAT 820 or on a Bruker Daltonics Apex II 3T FT-ICR MS. DSC 94

96 investigations were carried out on a TA Instruments DSC-Q10. Optical microscopy was performed on a Leica polarizing microscope in combination with a Mettler FP 80HT/FB 82HT hot stage. Pybox Coumpounds: 4-[3,4,5-Tri-tetradecyloxy-benzyloxy]-pyridine-2,6-dicarboxylic acid bis-[(2'-(r)- hydroxy-l'-methyl-ethyl)-amide]. (3a) (S)-alaninol (0.46 ml, 5.90 mmol) was added to a stirring solution of 1 (1.85 g, 1.97 mmol) in xylenes (14 ml) and the solution was heated at 100 C for three hours under argon atmosphere. The solvents were removed by rotary evaporation and the resulting material was purified by column chromatography (10:90 methanol:ethyl acetate) to afford the product (1.30 g, 64.0%) as a white solid. 'H NMR (CDC13, 500 MHz) 8: (m, 9H, CH 3 ), (m, 60H, (CH 2 ), 0 ), 1.30 (d, J = 6.5 Hz, 6H, CH 3 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.69 (dd, J = 10.5, 5.0, Hz, 2H, CH(H)), (m, 2H, CH(H)), (m, 6H, OCH 2 ), (m, 2H, CH), 5.06 (s, 2H, OCH 2 ), 6.59 (s, 2H, Ar-H), 7.85 (s, 2H, Ar-H), 8.13 (d, J = 8.0 Hz, 2H, NH). 1 3 C NMR (CDC1 3, 500 MHz) 8: 14.33, 17.18, 22.90, 26.32, 29.58, 29.60, 29.66, 29.84, 29.87, 29.88, 29.90, 29.93, 29.97, 29.98, 30.54, 32.13, 47.91, 66.44, 69.31, 71.16, 73.64, 106.2, 111.6, 129.9, 138.4, 150.9, 153.6, 163.8, HRMS-ESI (m/z): [M+H] + calcd for C 62 H, 09 N , found [3,4,5-Tri-(undec-10-enyloxy)-benzyloxy]-pyridine-2,6-dicarboxylic acid bis-[(2'- (R)-hydroxy-l'-methyl-ethyl)-amide]. (4a) The title compound was prepared using the same procedure as above except that 2 was used instead of 1 (57.0%). 'H NMR (CDC1 3, 95

97 500 MHz) 6: (m, 30H, (CH 2 ) 5 ), 1.32 (d, J = 7.0 Hz, 6H, CH 3 ), 1.47 (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 2H, CH(H)), (m, 2H, CH(H)), (m, 6H, OCH 2 ), 4.25 (m, 2H, CH), 4.93 (d, J = 10.0 Hz, 3H CHCH(H)), 4.99 (d, 3H, CHCH(H)), (m, 3H, CHCH(H)), 5.08 (s, 2H, OCH 2 ), (m, 3H, CHCH 2 ), 6.60 (s, 2H, Ar-H), 7.87 (s, 2H, Ar-H), 8.11 (d, J= 8.0 Hz, 2H, NH). 3 C NMR (CDC1 3, 500 MHz) 8: 26.29, 26.31, 29.14, 29.17, 29.36, 29.40, 29.45, 20.58, 29.60, 29.66, 29.75, 29.79, 30.52, 32.12, 32.81, 34.01, 47.91, 66.58, 69.32, 71.16, 73.63, 106.2, 111.7, 114.3, 124.7, 130.0, 131.8, 138.4, 139.4, 150.9, 153.6, , HRMS-ESI (m/z): [M+H]+ calcd for C 53 H 85 N , found (3,4,5-Tri-tetradecyloxy-benzyloxy)-pyridine-2,6-dicarboxylic acid bis-[(2'- hydroxyethyl)-amide]. (3b) Ethanolamine (0.06 ml, 0.99 mmol) was added to a stirring solution of 4-[3,4,5-tri-(tetradecyloxy)-benzyloxy]-pyridine-2,6-dicarboxylic acid methyl ester (0.33 g, 0.35 mmol) of xylenes (3.5 ml) and the solution was heated at 100 C for three hours under argon atmosphere. The solvents were removed by rotary evaporation and the resulting material was purified by column chromatography (10:90 methanol:ethyl acetate) to afford the product (0.20 g, 57.4%) as a white solid. 'H NMR (CDC13, 500 MHz) 6: (m, 9H, CH 3 ), (m, 60H, (CH 2 ), 0 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.66 (q, J = 5.0 Hz, 4H, CH 2 ), 3.86 (t, J = 5.0 Hz, 4H, CH 2 ) (m, 6H, OCH 2 ), 5.07 (s, 2H, OCH 2 ), 6.61 (s, 2H, Ar-H), 7.83 (s, 2H, Ar-H), 8.46 (t, J = 6.0 Hz, 2H, NH). ' 3 C NMR (CDC13, 500 MHz) 6: 14.32, 22.90, 26.35, 29.58, 29.60, 29.62, 29.69, 29.86, 29.88, 29.94, 29.96, 29.97, 29.99, 30.56, 32.13, 32.14, 42.33, 96

98 61.81, 69.30, 71.20, 73.65, 106.3, 111.4, 129.9, 138.4, 150.6, 153.6, 164.4, HRMS-ESI (m/z): [M+H] + calcd for C60H 05 N , found [3,4,5-Tri-(undec-10-enyloxy)-benzyloxy]-pyridine-2,6-dicarboxylic acid bis-[(2'- hydroxyethyl)-amide]. (4b) The title compound was prepared using the same procedure as above except that 4-[3,4,5-tri-(undec- 10-enyloxy)-benzyloxy]-pyridine-2,6- dicarboxylic acid methyl ester was used instead of 4-[3,4,5-tri-(tetradecyloxy)- benzyloxy]-pyridine-2,6-dicarboxylic acid methyl ester (59.6%). H NMR (CDC13, 500 MHz) : (m, 36H, (CH 2 ) 6 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.66 (q, J = 5.0 Hz, 4H, CH 2 ), 3.86 (t, J = 5.0 Hz, 4H, CH 2 ), (m, 6H, OCH 2 ), 4.93 (d, J = 10.0 Hz, 3H, CH(H)), 4.99 (dt, J = 17.0, 2.5 Hz, 3H, CH(H)), 5.07 (s, 2H, OCH 2 ), (m, 3H, CH), 6.61 (s, 2H, Ar-H), 7.83 (s, 2H, Ar-H), 8.47 (t, J = 6.0 Hz, 2H, NH). 3 C NMR (CDC1 3, 500 MHz) 8: 26.32, 29.15, 29.18, 29.38, 29.42, 29.61, 29.63, 29.68, 29.77, 29.81, 29.90, 30.55, 34.03, 34.05, 42.40, 62.07, 69.32, 71.21, 73.64, 106.3, 111.6, 114.3, 130.0, 138.4, 139.4, 150.7, 153.6, 164.5, HRMS-ESI (m/z): [M+H]+ calcd for C 51 H 8 ln , found (3,4,5-Tri-tetradecyloxy-benzyloxy)-pyridine-2,6-dicarboxylic acid bis-[(2'- chloro-1'-methyl-ethyl)-amide]. (5a) SOC12 (0.04 ml, 0.55 mmol) was added dropwise to a stirring solution of 3a (0.205 g, 0.20 mmol) and di-t-butyl-methylpyridine (0.13 g, 0.70 mmol) in THF (4 ml) at room temperature under argon atmosphere. The solution was heated to 60 C for four hours and then poured into water. The aqueous phase was extracted with dichloromethane and dried over MgSO 4. Purification by column 97

99 chromatography (30:70 ethyl acetate:hexane) afforded the product in 66.0% yield. 1 H NMR (CDC13, 500 MHz) : (m, 9H, CH 3 ), (m, 60H, (CH 2 ) 10 ), 1.39 (d, J = 7.0 Hz, 6H, CH 3 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.70 (dd, J = 11.0, 3.0 Hz, 2H, CH(H)), 3.81 (dd, J = 11.0, 4.0 Hz, 2H, CH(H)), (m, 6H, OCH 2 ), (m, 2H, CH), 5.09 (s, 2H, OCH 2 ), 6.59 (s, 2H, Ar-H), 7.89 (s, 2H, Ar- H), 8.06 (d, J = 9.0 Hz, 2H, NH). ' 3 C NMR (CDC13, 500 MHz) 6: 14.35, 18.31, 22.92, 26.32, 26.34, 29.60, 29.61, 29.65, 29.84, 29.87, 29.89, 29.92, 29.94, 29.97, 29.99, 30.55, 32.15, 45.51, 49.97, 69.34, 71.23, 73.65, 106.2, 111.7, 129.9, 138.4, 150.6, 153.6, 162.7, HRMS-ESI (m/z): [M+H] + calcd for C 62 HI 07 C1 2 N , found [3,4,5-Tri-(undec-10-enyloxy)-benzyloxy]-pyridine-2,6-dicarboxylic acid bis-[(2'- chloro-l'-methyl-ethyl)-amide]. (6a) The title compound was prepared using the same procedure as above except that 4a was used instead of 3a (42.0%). H NMR (CDC13, 500 MHz) : (m, 30H, (CH 2 ) 5 ), 1.42 (d, J = 6.5 Hz, 6H, CH 3 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m; 6H, CH 2 ), (m, 2H, CH(H)), (m, 2H, CH(H)), (m, 6H, OCH 2 ), (m, 2H, CH), 4.93 (dd, J = 10.0, 1.5 Hz, 3H CHCH(H)), (m, 3H, CHCH(H)), 5.13 (s, 2H, OCH 2 ), (m, 3H, CHCH 2 ), 6.61 (s, 2H, Ar-H), 7.91 (s, 2H, Ar-H), 8.02 (d, J = 8.5 Hz, 2H, NH). 3 C NMR (CDC13, 500 MHz) : 26.28, 26.32, 29.15, 29.18, 29.37, 29.41, 29.57, 20.61, 29.67, 29.76, 29.79, 29.89, 30.53, 34.03, 34.06, 45.51, 49.96, 69.32, 71.22, 73.62, 106.2, 111.7, 114.3, 129.9, 139.4, 150.6, 153.6, 162.7, H NMR (CDC13, 500 MHz) a: 3.73 (dd, J = 11.0, 3.0, 2H, CH(H)), 6.61 (s, 2H, Ar-H), 7.91 (s, 2H, Ar-H),

100 (d, J = 8.5 Hz, 2H, NH), HRMS-ESI (m/z): [M+H] + calcd for C 53 H 83 N , found (3,4,5-Tri-tetradecyloxy-benzyloxy)-pyridine-2,6-dicarboxylic acid bis-[2'-chloroethyl)-amide]. (5b) The title compound was prepared using the same procedure as above except that 3b was used instead of 3a (73.6%). 'H NMR (CDC13, 500 MHz) 8: (m, 9H, CH 3 ), (m, 60H, (CH 2 ) 0 ); (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.75 (t, J = 5.5 Hz, 4H, CH 2 ), 3.85 (q, J = 6.0 Hz, 4H, CH 2 ) (m, 6H, OCH 2 ), 5.11 (s, 2H, OCH 2 ), 6.60 (s, 2H, Ar-H), 7.93 (s, 2H, Ar-H), 8.26 (t, J = 6.0 Hz, 2H, NH). ' 3 C NMR (CDC13, 500 MHz) 8: 14.33, 22.90, 26.31, 26.33, 29.58, 29.59, 29.64, 29.83, 29.88, 29.90, 29.92, 29.95, 29.97, 30;54, 32.13, 32.14, 41.42, 44.08, 69.36, 71.25, 73.65, 106.3, 112.0, 129.9, 138.5, 150.7, 153.6, 163.7, HRMS-ESI (m/z): [M+H] + calcd for C60H 0 3 Cl2N , found [3,4,5-Tri-(undec-10-enyloxy)-benzyloxy]-pyridine-2,6-dicarboxylic acid bis-[(2'- chloro-ethyl)-amide]. (6b) The title compound was prepared using the same procedure as above except that 4b was used instead of 3a (86.0%). H NMR (CDC13, 500 MHz) 6: (m, 36H, (CH 2 ) 6 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.77 (t, J = 5.5 Hz, 4H, CH 2 ), 3.87 (q, J = 5.5 Hz, 4H, CH 2 ), (m, 6H, OCH 2 ), 4.93 (d, J = 10.0 Hz, 3H, CH(H)), 4.99 (dd, J= 17.5, 1.5 Hz, 3H, CH(H)), 5.13 (s, 2H, OCH 2 ), (m, 3H, CH), 6.61 (s, 2H, Ar-H), 7.94 (s, 2H, Ar-H), 8.18 (t, J = 6.0 Hz, 2H, NH). ' 3 C NMR (CDC1 3, 500 MHz) : 26.32, 29.15, 29.19, 29.37, 29.42, 29.58, 29.61, 29.67, 29.76, 29.79, 29.89, 30.53, 34.03, 34.06, 41.40, 44.15, 69.34, 71.25, 73.63, 106.2, 112.0, 99

101 114.3, 129.9, 138.5, 139.4, 150.6, 153.6, 163.6, HRMS-ESI (m/z): [M+H] + calcd for C 51 H 79 C1 2 N , found MgSO 4. Concentration of the organic layer afforded the product (93.5%) as a white solid. 'H NMR (CDC1 3, 500 MHz) : (m, 9H, CH 3 ), (m, 30H, (CH 2 ), 0 ), 1.36 (d, J = 6.0 Hz, 6H, CH 3 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.95 (q, J = 6.5 Hz, 6H, OCH 2 ), 4.06 (t, J = 8.0 Hz, 2H, CH(H)), (m, 2H, CH(H)), (m, 2H, CH(H)), 5.09 (d, J = 1.5 Hz, 2H, CH 2 ), 6.58 (s, 2H, Ar-H), 7.78 (s, 2H, Ar-H). 1 3 C NMR (CDCl 3, 500 MHz) : 14.30, 21.56, 22.87, 26.28, 26.30, 29.55, 29.57, 29.60, 29.79, 29.82, 29.85, 29,87, 29.89, 29.93, 29.95, 30.51, 32.11, 62.35, 69.27, 70.87, 73.60, 74.93, 106.0, 112.5, 130.2, 138.3, 148.6, 153.5, 162.5, HRMS-ESI (m/z): [M+H] + calcd for C 62 H, 05 N , found [3,4,5-Tris-(tetradecyloxy)-benzyloxy]-2,6-bis-[(4-methyl-4,5-dihydro-oxazol-2- yl)]-pyridine. (7a) To a suspension of NaH (10.4 mmol) in anhydrous THF (5 ml) was added a solution containing 5a (.76 mmol) and 5 ml of THF. The mixture was stirred at room temperature under argon atmosphere for 1 hour and was then poured over ice to quench excess NaH. The residue was extracted with dichloromethane and dried over 4-[3,4,5-Tri-(undec-10-enyloxy)-benzyloxy]-2,6-bis-[(4-methyl-4,5-dihydro-oxazol-2- yl)]-pyridine. (8a) The title compound was prepared using the same procedure as above except that 6a was used instead of 5a (94.0%). 'H NMR (CDC1 3, 500 MHz) 6: (m, 36H, (CH 2 ) 6 ), 1.35 (d, J = 7.0 Hz, 6H, CH 3 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), 4.06 (t, J = 8.0 Hz, 2H, CH(H)), (m, 2H, 100

102 CH), (m, 2H, CH(H)), 4.92 (dd, J = 10.0, 1.0 Hz, 3H, CHCH 2 ), 4.98 (dd, J = 17.0, 1.0 Hz, 3H, CHCH 2 ), 5.08 (s, 2H, CH 2 ), (m, 3H, CHCH 2 ), 6.58 (s, 2H, Ar-H), 7.77 (s, 2H, Ar-H). 13 C NMR (CDC1 3, 500 MHz) 8: 21.53, 26.23, 26.26, 29.09, 29.12, 29.31, 29.35, 29.52, 29.54, 29.61, 29.70, 29.73, 29.83, 30.47, 33.97, 33.99, 62.32, 69.25, 70.86, 73.56, 74.91, 106.0, 112.5, , , 130.2, 138.3, , , 148.5, 153.5, 162.5, HRMS-ESI (m/z): [M+H] + calcd for C 53 H 8 N , found ,6-Bis-(4,5-dihydro-oxazol-2-yl)-4-[3,4,5-tri-(tetradecyloxy)-benzyloxy]-pyridine. (7b) The title compound was prepared using the same procedure as above except that 5b was used instead of 5a (76.0%). 'H NMR (CDC1 3, 500 MHz) 8: (m, 9H, CH 3 ), (m, 30H (CH 2 ) 10 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), 4.11 (t, J = 10.0 Hz, 4H, CH 2 ), 4.53 (t, J = 9.5 Hz, 4H, CH 2 ), 5.09 (s, 2H, OCH 2 ), 6.60 (s, 2H, Ar-H), 7.77 (s, 2H, Ar-H). 3 C NMR (CDC1 3, 500 MHz) 6: 14.34, 22.91, 26.31, 26.33, 29.58, 29.60, 29.64, 29.83, 29.64, 29.88, 29.90, 29.93, 29.96, 29.98, 30.54, 32.14, 55.18, 68.59, 69.34, 70.98, 73.65, 106.2, 112.5, 130.1, 138.4, 148.4, 153.6, 163.7, HRMS-ESI (m/z): [M+H] + calcd for C60H 1 ON , found ,6-Bis-(4,5-dihydro-oxazol-2-yl)-4-[3,4,5-tri-(undec-10-enyloxy)-benzyloxy]- pyridine. (8b) The title compound was prepared using the same procedure as above except that 6b was used instead of 5a (93.2%). 'H NMR (CDC13, 500 MHz) 6: (m, 36H, (CH 2 ) 6 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, 101

103 OCH 2 ), 4.11 (t, J = 10.0 Hz, 4H, CH 2 ), 4.53 (t, J = 9.5 Hz, 4H, CH 2 ), 4.92 (d, J = 10.0 Hz, 3H, CH(H)), 4.99 (dd, J = 17.0, 1.0 Hz, 3H, CH(H)), 5.08 (s, 2H, OCH 2 ), (m, 3H, CH), 6.59 (s, 2H, Ar-H), 7.75 (s, 2H, Ar-H). 3 C NMR (CDC1 3, 500 MHz) 6: 26.25, 26.28, 29.11, 29.14, 29.33, 29.38, 29.53, 29.56, 29.63, 29.72, 29.76, 29.85, 30.32, 30.49, 33.99, 34.01, 55.12, 68.57, 69.28, 70.96, 73.60, 106.2, 112.5, 114.3, 130.1, 138.3, 139.4, 148.3, 153.5, 163.7, HRMS-ESI (m/z): [M+H] + calcd for C 5 sh 77 N , found Pincer Compounds: 3,5-Bis-thiophenylmethyl-anisole. (9) A solution of NaOH (0.81 g, 20.3 mmol) in 25 ml of water was added to a solution of 3,5-bis-bromomethyl-anisole (1.50 g, 5.10 mmol) in 75 ml of toluene and a catalytic amount of ADOGEN 464. Thiophenol (1.50 ml, 14.6 mmol) was added, and the solution was heated to reflux for 2 hours under argon. The solution was cooled to room temperature and poured into dichloromethane, washed three times with 0.5M NaOH(aq) to remove excess thiophenol, and extracted with ether. The organic layer was dried over MgSO 4, and the solvents were removed. Purification by column chromatography on silica gel using ethyl acetate/hexane (5/95) as eluant yielded the product as a white solid in 95.7% yield. H NMR (CDC13, 500 MHz) 6: 3.65 (s, 3H, CH 3 ), 4.00 (s, 4H, CH 2 ), 6.68 (d, J = 1.5 Hz, 2H, Ar-H), 6.81 (s, 1H, Ar-H), (m, 2H, Ar-H), (m, 4H, Ar-H), (m, 4H, Ar-H). C NMR (CDC13, 500 MHz) 6: 38.93, 55.21, 113.3, 121.8, 126.5, 129.0, 129.9, 136.4, 139.2, HRMS-ESI (m/z): [M+H] + calcd for C 21 H 20 OS , found

104 3,5-Bis-thiophenylmethyl-phenol. (10) A 1.OM solution of BBr 3 in dichloromethane (2 ml) was added slowly via syringe to a stirring solution of 3,5-bis-thiophenylmethylanisole (1.07g, 3.31 mmol) and dichloromethane (50 ml) at -78 C. After stirring overnight and warming to room temperature, the solution was slowly poured over ice to quench excess BBr 3. The organic layer was extracted with ether. was dried over MgSO 4, and the solvents were removed to afford the product in 93.5% yield. Characterization of the title compound agrees with reported literature. 13 3,5-Bis-thiophenylmethyl-1-[3,4,5-tri-tetradecyloxy-benzyloxy]-benzene. (11) A mixture of 10 (0.35 g, 1.03 mmol) 3,4,5-tri-tetradecyloxy-benzyl bromide (0.92 g, 1.14 mmol), K 2 CO 3 (0.21 g, 1.50 mmol), and a catalytic amount of KI in 2-butanone (25 ml) was heated to reflux at 80 C for 12 hours. The mixture was poured into 0.5M NaOH (aq) and extracted with ethyl acetate. The solution was washed successively with water and brine, and the combined organic layers were dried over MgSO 4. The solvents were removed in vacuo, followed by purification by column chromatography in 5:95 ethyl acetate:hexane to give the product (80%) as a clear oil. H NMR (CDC13, 500 MHz) b: (m, 9H, CH 3 ), 1.27 (m, 60H, (CH 2 ) 10 ),1.47(m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), 4.04 (s, 4H, SCH 2 ), 4.85 (s, 2H, OCH 2 ), 6.59 (s, 2H, Ar- H), 6.82 (s, 2H, Ar-H), 6.84 (s, 1H, Ar-H), (m, 2H, Ar-H), (m, 8H, Ar-H). 13 C NMR (CDC1 3, 500 MHz) 6: 14.30, 26.33, 29.59, 29.61, 29.62, 29.66, 29.89, 29.91, 29.94, 29.97, 29.99, 30.55, 32.15, 39.19, 55.29, 69.03, 70.57, 73.63, 106.3, 114.3, 122.2, 126.6, 129.1, 130.0, 131.8, 136.4, 137.6, 139.3, 153.5, HRMS-ESI (m/z): [M+H] + calcd for C 6 9 HI S , found

105 Pd(ll)(CH 3 CN). (12) A solution of 11 (0.05 g, in dichloromethane (2 ml) is added dropwise to a stirring solution of commercially available palladiumtetrakis(acetonitrile) bis(tetrafluoroborate) in anhydrous acetonitrile. The yellow solution was heated at 60 C for 12 hours and was then filtered through a pad of Celite. The solution was diluted with dichloromethane and washed with water. The organic layer was dried over MgSO 4, and the solvents were removed in vacuo. The material was purified by precipitation in ether. 'H NMR (CDC13, 500 MHz) 8: (m, 9H, CH 3 ), 1.26 (m, 60H, (CH 2 ) 0 O),1.49 (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), 4.55 (broad s, 4H, SCH 2 ), 4.88 (s, 2H, OCH 2 ), 6.57 (s, 2H, Ar-H), 6.69 (s, 2H, Ar-H), 7.52 (m, 8H, Ar-H), 7.81 (m, 2H, Ar-H). 13 C NMR (CDC1 3, 500 MHz) : 14.35, 26.33, 29.59, 29.61, 29.62, 29.66, 29.89, 29.91, 29.94, 29.97, 29.99, 30.55, 32.15, 39.19, 55.29, 69.03, 70.57, 73.63, 106.3, 111.4, 118.9, 131.3, 132.4, 132.8, 133.1, 136.4, 137.6, 152.8, 153.5,

106 References 1 Girard, C.; Kagan, H. B.; Angew. Chem. Int. Ed. 1998, 37, a) ( a) White, D. E.; Jacobsen, E. N.; Tetrahedron: Asymmetry 2003, 14, (b) Ready, J. M.; Jacobsen, E. N. Angew. Chem., Int. Ed. 2002, 41, (c) Ready, J. M.; Jacobsen, E. N.; J. Am. Chem. Soc. 2001,123, (d) Breinbauer, R.; Jacobsen, E. N.; Angew. Chem., Int. Ed. 2000, 39, (e) Konsler, R. G.; Karl, J.; Jacobsen, E. N.; J. Am. Chem. Soc. 1998, 120, For recent reviews on bis(oxazoline) ligands in catalysis, please see: (a) McManus, H. A.; Guiry, P. J.; Chem. Rev. 2004, 104, (b) Ghosh, A. K.; Mathivanan, P.; Cappiello, J.; Tetrahedron: Asymmetry 1998, 9, 1. (c) Johnson, J. S.; Evans, D. A.; Acc. Chem. Res. 2000, 33, Nishiyama, H.; Sakaguchi, H.; Nakamura, T.; Horihata, M.; Kondo, M.; Itoh, K.; Organometallics 1989, 8, Whitesell, J. K.; Chem. Rev. 1989, 89, Schaus, S. E.; Jacobsen, E. N.; Org. Lett. 2000, 2, (a) Cornejo, A.; Fraile, J. M.; Garcia, J. I.; Garcia-Verdugo, E.; Gil, M. J.; Legarreta, G.; Luis, S. V.; Martinez-Merino, V.; Mayoral, J. A.; Org. Lett. 2002, 4, (b) Lundgren, S.; Lutsenko, S.; Jonsson, C.; Moberg, C.; Org. Lett. 2003, 5, Lehmann, M.; Sierra, T.; Barbera, J.; Serrano, J. L.; Parker, R.; J. Mater. Chem. 2002, 12, See Chapter 3. '0 Bruce, D. W.; Acc. Chem. Res. 2000, 33,

107 11 (a) Doyle, M. P.; Protopopova, M. N.; Tetrahedron 1998, 54, (b) Ghosh, A. K.; Mathivanan, P.; Cappiello, J.; Tetrahedron: Asymmetry 1998, 9, 1. (c) Wei C.; Li C.-J.; J. Am. Chem. Soc. 2002, 124, For reviews on pincer ligands, please see: (a) Albrecht, M.; van Koten, G.; Ang. Chem, Int. Ed. 2001, 40, (b) Singleton, J. T.; Tetrahedron 2003, 59, (c) Gossage, R. A.; van de Kuil, L. A.; van Koten, G.; Acc. Chem. Res. 1998, 31, Gimenez, R.; Swager, T. M.; J. Mol. Catal. A 2001, 166, Huck, W. T. S.; van Veggel, F. C. J. M.; Kropman, B. L.; Blank, D. H. A.; Keim, E. G.; Smithers, M. M. A.; Reinhoudt, D. N.; J. Am. Chem. Soc. 1995, 117, Motoyama, Y.; Kurihara, O.; Murata, K.; Aoki, K.; Nishiyama, H. Organometallics, 2000, 19, Aqueous solutions of AgNO 3 and NaDOS were combined in the absence of light until AgDOS precipitated as a white crystalline solid, which was filtered and dried under vacuum for 48 hours in the absence of light. Bruce, D.W.; Dunmur, D. A.; Hudson, S. A.; Lalinde, E.; Maitlis, P. M.; McDonald, M. P.; Orr, R.; Styring, P.; Cherodian, A. S.; Richardson, R. M.; Feijoo, J. L; Ungar, G.; Mol. Cryst., Liq. Cryst. 1991, 206,

108 Chapter 5 Immobilized Chiral Monodentate Oxazolines: Heterogeneous Catalysis within an Organic Polymer Network

109 5.1. Introduction Although homogeneous asymmetric catalysts offer more versatility and viability in the synthesis of chiral molecules, l achiral heterogeneous catalysts are still the most widely used systems in the industrial production of fine chemicals. 2 Heterogeneous systems are appealing for a number of practical reasons such as ease of separation, handling and recovery, and a higher potential for regeneration and reuse. As such, the heterogenization of chiral homogeneous catalysts has been an active area of research, though the levels of activity, enantioselectivity, and recyclability that are required for application in industry have yet to be reached. Various methods exist for the immobilization of homogeneous catalysts including covalent or non-covalent bonding to organic and inorganic polymers, and soluble and insoluble polymers. The work relevant to this chapter involves covalent bonding to insoluble, organic supports. The strategy for the preparation of chiral heterogeneous catalysts typically begins with a well-established and efficient homogenous system. Structural modifications are then made in order to allow for incorporation into a polymer matrix and, ideally, the catalytic activity of the homogeneous system is preserved upon immobilization and after numerous catalytic cycles. In such a process, it is often hoped that the polymeric backbone will serve as an inert matrix to which the active catalytic moiety is merely attached. However, the nature of the support and the method of immobilization have been shown to have profound influence on the activity, stability, and selectivity of the catalyst. More often than not, the polymeric support is seen as having a deleterious effect on catalytic behavior. Examination of ligand systems whose catalytic behavior could 108

110 Scheme 5.1. Copper-catalyzed cyclopropanation of styrene with ethyl diazoacetate. Ph~ + N'COE 2 t *~ H... A.CO 2 Et Hi AH Ph H Ph CO 2 Et Ph Cu catalyst trans(is,2s) cis(1r,2s) Phi A H Ph, A"Co 2 Et H C0 2 Et H H trans(1r,2r) cis(is,2r) potentially benefit from the presence of a polymeric support would lead to improved design and use of heterogeneous catalysts. One of the most studied and well-established catalytic systems is the coppercatalyzed cyclopropanation reaction between styrene and ethyl diazoacetate. 3 (Scheme 5.1) The postulated mechanism involves formation of a copper(i) carbene complex, followed by cyclopropanation of the double-bonded substrate. First reported in 1966, this reaction represents the first use of a chiral catalyst to impart control over the stereochemical outcome of a reaction. 4 Pfaltz and co-workers then pioneered the use of Cu(II)-semicorrin complexes for enantioselective cyclopropanation, determining that the Cu(I) oxidation state was responsible for catalytic activity. 5 Structurally related yet more synthetically accessible bis(oxazoline) ligands later emerged as excellent catalysts for asymmetric cyclopropanation and have been extensively studied by Masamune, 6 Evans, 7 and Pfaltz. 8 Evans first described direct access to the catalytically active species by in situ mixing of the bis(oxazoline) ligand with a stoichiometric amount of CuOTf, achieving enantiomeric excesses of >99%

111 As such, the immobilization of bis(oxazoline) cyclopropanation catalysts onto various heterogeneous supports has received considerable attention. 9 Heterogenization methods used have included grafting chiral ligands onto commercially available resins or direct polymerization of a monomer containing the chiral ligand. One recent example from Mayoral and co-workers involved the homopolymerization of a styrenefunctionalized bis(oxazoline) monomer followed by Cu(OTf) 2 loading. 0 (Scheme 5.2) Enantioselectivities approaching and even slightly surpassing those of the homogeneous parent bis(oxazoline) ligand were achieved. Furthermore, enantioselectivities were only slightly reduced in the second cycle of catalyst use. Scheme 5.2. Immobilization of bis(oxazoline)s. 1. homopolymerization 2. excess Cu(OTf) 2 3. washing with CH 3 0H In the interests of exploring the effects of heterogenization on catalytic behavior, we examined the immobilization of a chiral, monodentate oxazoline ring on an insoluble, organic polymer. Monodentate nitrogen ligands are generally less effective as asymmetric catalysts when compared with the bidentate and tridentate counterparts in asymmetric cyclopropanation. However, incorporation of such ligands within a crosslinked polymeric network could create a sufficiently chiral microenvironment to 110

112 favorably impact the enantioselectivity of the cyclopropanation reaction. A flexible, swellable polymer system is required for any reaction to occur within a polymeric support. Incorporation of a long, flexible spacer between the oxazoline ring and the polymerizable group would provide a more solution-like availability of the chiral ligands. In this chapter we describe the synthesis of a chiral oxazoline monomer and its polymerization using ruthenium-catalyzed acyclic diene metathesis. l The catalytic behavior of both the homogeneous system and the heterogeneous system in the cyclopropanation of styrene with ethyl diazoacetate is examined Results and Discussion The synthesis of the chiral oxazoline monomer is shown in Scheme 5.3. The target monomer possesses long, aliphatic chains as the spacer between the oxazoline ring and the polymerizable functionality to allow for a more flexible polymer network. Terminal olefins provide the polymerizable functionality needed for ADMET Scheme 5.3. Synthesis of chiral oxazoline monomer. RO RO RO RO X - * RO HN*. RO RO RO YRO 1 X=OH 3Y=OH 5 ii iii 2X=CI ' 4Y=CI ii (i) SOCI2, CHC1 3 ; (ii) (S)-alaninol, NEt 3, CH 2 CI 2, 85%; (iii) SOCI2, THF, reflux 4 hours, 78%; (iv) NaH, THF, 0 C, 81%. R = (CH 2 ) 9 CHCH 2 111

113 Scheme 5.4. Preparation of polymeric copper oxazoline catalysts. f\n Ms-N NMs 1. * 2. CuOTf Route A l Route B Route B 1. CuOTf 2. I' MsNyN.Ms CIV,. - T polymerization. Acid 1 is synthesized by the hydrolysis of the corresponding methyl benzoate, whose synthesis is described in Chapter 3. Condensation of the chiral aminoalcohol with acid chloride 2 gives the bis(hydroxy)amide 3. Treatment of the amide with thionyl chloride affords the chloride 4, which affords the oxazoline monomer 5 when treated with base. Two methods to generate the polymeric copper catalyst from monomer 5 were explored. (Scheme 5.4) Following Route A, films of the chiral monomer were polymerized via ADMET polymerization, followed by treatment with CuOTf. Due to the presence of three terminal olefins per monomer, there is a wide range of possible 112

114 intermolecular and intramolecular linkages that can be made between monomers. (Scheme 5.5) The resulting free-standing film was easily peeled off the glass slide and was slightly discolored by a dark green tint due to degradation of the ruthenium catalyst. Insolubility of the films indicated that the polymers possess a sufficient degree of crosslinking to anchor the polymer chains and prevent the configurational entropy required to form a solution. The swelling capability of the polymer was investigated to estimate the degree of cross-linking and to ensure good mass transport such that the CuOTf and subsequent substrates could readily diffuse through the polymer network. As the degree of crosslinking increases, the polymer becomes more rigid and swelling becomes difficult. For example, styrene-divinylbenzene co-polymers which contain 20% or higher degree of crosslinking exhibit no swelling with toluene. l2 Systems with relatively dilute crosslinking (>1.0%) can give expanded polymer networks having reduced chain entanglements resulting in higher mobility and good swelling capability, but mechanical stability is often sacrificed. The films were examined in solvents relevant to the conditions for the cyclopropanation of styrene with ethyl diazoacetate: styrene, the solvent in which cyclopropanation is typically performed, and toluene, whose structures and properties are similar to that of styrene. (Figure 5.1) In both styrene and toluene, the polymer size increased to 150% of its original size, indicating an estimated 5-10% degree of crosslinking.l3 This indicates the presence of a large amount of linear polymer within the network, allowing for good swelling properties, yet the polymer network is sufficiently crosslinked to maintain good mechanical stability. Other hydrophobic solvents such as 113

115 hexane also cause the films to swell, but to a lesser degree, while in polar solvents such as methanol, the polymer does not swell. Scheme 5.5. Polymerization of monomer 5 and the potential linkages present in the resulting polymer network. ~~,,,,_ossnsr Ms-N CIT N-Ms C" =Rue CIU Ph PCy 3 (5 mol %) 100 C, 24 hrs ~- 0 n-bw 0 I d, n NX""""0" N #%~NO\/ 0 ( = crosslinked polymer network 114

116 Figure 5.1. Swelling behavior of polymer films obtained by Route A. a.) non-swollen polymer swollen with toluene b.) non-swollen polymer swollen with toluene c.) non-swollen polymer swollen with styrene 115

117 The oxazoline polymer was then converted into a copper catalyst by treatment with CuOTf. First, the polymer was ground to a fine powder and suspended in toluene with an excess of CuOTf and stirred for 24 hours under argon atmosphere. The insoluble material was filtered and washed successively with toluene, dichloromethane, and methanol to remove any excess copper triflate, and dried under vacuum. Elemental analysis confirmed the presence of copper ions within the polymer network. The second strategy for generating a polymeric copper catalyst involved formation of the metal complex first, followed by polymerization. (Route B) The presence of the CuOTf seemed to inhibit metathesis polymerization, and a longer reaction time was required. The resulting films were dark brown and brittle, and elemental analysis confirmed that copper ions were included in the polymer network. The copper catalysts were then tested in the cyclopropanation of styrene with ethyl diazoacetate and the results are summarized in Table 5.1. For catalysts prepared via Route A (Table 5.1, Entries 4-7), the method of copper loading proved to be a significant factor in the success of the catalyst. When methanol was used as the solvent during copper loading, the polymer network does not swell and the copper ions are prevented from diffusing into the polymer network. As a result, the catalyst is not active and only starting materials are recovered. (Table 5.1, Entry 4) However, when toluene is used during copper loading, the polymer swells significantly and a sufficient amount of copper ion is bound within the polymer and catalytic activity is exhibited. (Table 5.1, Entries 4-7) Additionally, slow diffusion of CuOTf is needed. Sonication of the polymer network with CuOTf in toluene for 30 minutes did not result in sufficient copper loading, and the cyclopropanation reaction did not proceed. (Table 5.1, Entry 5) 116

118 Table 5.1. Results of cyclopropanation reactions. Entry Catalyst Catalyst Prep Yield Time trans/cis Cis Trans (%) (h) (%ee) (%ee) 1 CuOTf alone /31 <1 < CuOTf / Polymer alone 20 4 Polymer (Route A) 5 Polymer (Route A) Stir in MeOH with CuOTf Sonicate in toluene with CuOTf, 30 min a Polymer, Run 1 (Route A) Stir in toluene with CuOTf, 24 hours / b Polymer, Run 2 (Route A) Reuse catalyst from Entry 6a / Polymer (Route B) /

119 Enantiomeric excesses of the products were determined by gas chromatography as previously described.' For the homogeneous systems studied (Table 5.1, Entries 1-2), the presence of monomer 5 increases the trans/cis ratio and the enantioselectivities of both trans and cis isomers, more significantly in the case of the trans isomer. As is typical for heterogeneous catalysts, lower yields are observed for the polymeric catalysts when compared to the homogeneous ligand 5. Also, the trans/cis ratio is generally decreased in the heterogeneous systems. However, the enantioselectivities for the cis products are higher for heterogeneous systems than the homogeneous system, (Table 5.1, Entry 2 vs. Entries 6-7) demonstrating a favorable effect of the immobilization on this particular selectivity. The polymeric support clearly exerts influence on the energy of the four diastereomeric transition states, although elucidation of such effects requires further investigation. One possibility for the enhanced stereoselectivity is the spatial constraint induced by the polymer matrix, which may increase the influence of the chiral ligands. In homogeneous reactions, the chiral directing ligand and the catalytic metal center influence the transition state of a reaction. In heterogeneous reactions, the spatial confinement of the immobilized catalyst adds additional parameter that often enhances the selectivity of the reaction. An interesting factor that calls for further investigation is the effect of copper loading on the stereochemical outcome of the reaction. Interaction of multiple Cu(I) catalytic centers often has a detrimental effect on activity and enantioselectivity, 9 and the polymeric catalysts used in this study possessed high copper loading. However, complexation of multiple chiral monodentate oxazoline ligands to a single Cu(I) center has been shown to increase enantioselectivities when compared to a 1:1 metal:ligand 118

120 complex. 4 Decreasing the copper loading of the polymer catalysts may encourage interaction of multiple chiral ligands with a single metal center, creating a local chiral environment in which the reaction can take place. Interestingly, upon reuse of the catalyst (Table 5.1, Entry 6b), the level of enantioselectivity remains essentially the same, although the trans/cis ratio and yield are decreased, possibly due to coordination of impurities or metal leaching. Another possible alteration of the original catalyst is cyclopropanation of the polymer backbone, although the reaction is performed in excess styrene to prevent such side reactions. With the polymer obtained by Route B, the translcis ratio obtained is the same as in the homogeneous case, but lower levels of enantioselectivity of the cis isomer are observed Concluding Remarks The preliminary results presented here open the way for the design of heterogeneous catalysts based on chiral monodentate oxazoline ligands. Immobilization of chiral oxazoline ligands using ADMET polymerization gives flexible polymer networks that swell in hydrophobic solvents such as toluene and styrene. When charged with copper(i) triflate, the polymers catalyze the cyclopropanation of styrene with ethyl diazoacetate with higher enantioselectivity than the corresponding homogeneous phase reaction. Elucidation of the nature of the effects of the polymeric support and methods to benefit from such effects require further study, involving investigation of the effects of copper loading on the catalytic behavior of the polymeric material. Also, co-monomers 119

121 can be employed to control the amount of chiral ligand within the material, as well as to explore the effects of polymer morphology on the system. Furthermore, the use of Cu(OTf) 2 to form a supported precatalyst should also be explored, with in situ reduction of the metal center to attain the catalytically active Cu(I) species. Studies such as these would provide useful information for the optimization of oxazoline-containing polymers as catalysts for asymmetric cyclopropanation. 120

122 5.4. Experimental Section General Methods. All chemicals were of reagent grade and were used as received, unless otherwise specified. H and 13 C NMR spectra were obtained on Varian Inova-500 spectrometers. All chemical shifts are referenced to residual CHC1 3 (7.27 ppm for 'H, ppm for 1 3 C). Multiplicities are indicated as s (singlet), d (doublet), t (triplet), and m (multiplet). High resolution mass spectra were obtained at the MIT Department of Chemistry Instrumentation Facility (DCIF) on a Finnigan MAT 820 or on a Bruker Daltonics Apex II 3T FT-ICR MS. GC analysis was performed on a Varian CP-3800 gas chromatograph equipped with FID detector and Cyclodex B capillary columns. 3,4,5-Tri-(10-undecen-1-ol-oxy)-benzoic acid (1). A solution of 3,4,5-tri-(10-undecen- 1-ol-oxy)-benzoic acid methyl ester 5 (5.01 g, 7.82 mmol) and potassium hydroxide (2.19 g, 39.1 mmol) in ethanol (80 ml) and deionized water (40 ml) was heated to reflux at 80 C for four hours. The solution was then poured into 100 ml of 1N HC1 to form a white precipitate, which was filtered and washed with ethanol to afford the product (4.80 g, 98% yield) as a white solid. H NMR (CDC13, 500 MHz) 8: (m, 30H, (CH 2 ) 5 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, OCH 2 ), (m, 3H, CHCH(H)), (m, 3H, CHCH(H)), (m, 3H, CH), 7.34 (s, 2H, Ar-H). 13 C NMR (CDC13, 500 MHz) 8: 26.23, 26.27, 29.14, 29.17, 29.36, 29.41, 29.46, 29.57, 29.67, 29.74, 29.78, 29.86, 30.52, 34.03, 34.05, 69.33, 73.73, 108.7, 114.3, 123.9,139.4, 143.3, 153.0, HRMS-ESI (m/z): [M-H]- calcd for C 40 H , found

123 N-(2'-(R)-Hydroxy-1 '-methyl-ethyl)-3,4,5-tri-(undec-10-enyloxy)-benzamide. (3) To a solution of 1 (0.55 g, 0.88 mmol) in anhydrous THF (8.0 ml) was added SOC12 (1.0 ml), and the solution was heated to reflux for two hours. The solution was cooled to room temperature, and then excess SOC12 and solvent were removed by vacuum distillation. The resulting acid chloride was dissolved in anhydrous CH 2 C12 (4.0 ml) and was added slowly via cannula to a stirring solution of (S)-alaninol (0.20 ml), a catalytic amount of NEt 3, and anhydrous CH 2 C12 (4.0 ml) at 0 C under argon atmosphere. The solution was allowed to stir overnight, warming to room temperature. Water was added to quench any excess acid chloride, and the reaction was extracted with CH 2 C12 and the organic layer was dried over MgSO 4. The solvents were removed in vacuo, and the product (85% yield) was taken onto the next step without further purification. For analytical purposes, a small amount of material was purified by column chromatography using 50:50 ethyl acetate: hexane as eluant, affording the product as a white solid. ' H NMR (CDC1 3, 500 MHz) 8: 1.7 (d, J = 6.5 Hz, 3H, CH 3 ), (m, 30H, (CH 2 ) 5 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.62 (dd, J = 11.0, 6.0 Hz, 1H, CH(H)), 3.75 (dd, J = 11i.0, 3.5 Hz, 1H, CH(H)), (m, 6H, OCH 2 ), (m, 1H, CH), (m, 3H, CHCH(H)), 4.99 (dd, J = 17.0, 1.5 Hz, 3H, CHCH(H)), (m, 3H, CHCH 2 ), 6.37 (d, J = 7.0 Hz, 2H, NH), 6.95 (s, 2H, Ar-H). 13 C NMR (CDC13, 500 MHz) : 26.24, 26.29, 29.11, 29.14, 29.29, 29.33, 29.37, 29.53, 29.56, 29.59, 29.71, 29.73, 29.75, 29.80, 30.47, 31.11, 33.99, 48.41, 67.12, 69.52, 73.14, 73.64, 105.9, 114.3, 129.4, 139.3, 141.4, 153.2, HRMS-ESI (m/z): [M+H] + calcd for C 43 H 73 NO, , found

124 N-(2'-(R)-Chloro-l'-methyl-ethyl)-3,4,5-tri-(undec-10-enyloxy)-benzamide. (4) Thionyl chloride (0.10 ml) was added dropwise to a stirring solution 3 (0.31 g, 0.45 mmol) in THF (5 ml) at 0 C under argon atmosphere. The solution was heated to reflux at 75 C for four hours and was then poured into water. The mixture was extracted with dichloromethane, and washed successively with 0.5M NaOH (aq), water, and brine. The organic layer was separated and dried over MgSO 4. Purification by column chromatography (30:70 ethyl acetate:hexane) afforded the product as a white solid in 78% yield. 'H NMR (CDC13, 500 MHz) 8: (m, 30H, (CH 2 ) 5 ), 1.37 (d, J = 6.5 Hz, 3H, CH 3 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.67 (dd, J = 11.5, 3.5 Hz, 1H, CH(H)), 3.83 (dd, J = 11.0, 4.0 Hz, 1H, CH(H)), (m, 6H, OCH 2 ), (m, 1H, CH), (m, 3H, CHCH(H)), (m, 3H, CHCH(H)), (m, 3H, CHCH 2 ), 6.17 (d, J = 8.5 Hz, 2H, NH), 6.95 (s, 2H, Ar-H). ' 3 C NMR (CDC1 3, 500 MHz) 6: 18.20, 26.26, 29.13, 29.16, 29.35, 29.39, 29.54, 29.57, 29.65, 29.73, 29.74, 29.77, 29.85, 30.49, 34.01, 34.03, 45.92, 49.79, 69.57, 73.68, 105.9, 114.3, 129.4, 139.4, 141.5, 153.3, HRMS-ESI (mlz): [M+H] + calcd for C 43 H 72 CINO , found (R)-Methyl-2-[3,4,5-tri-(undec-10-enyloxy)-phenyl)]-4,5-dihydro-oxazole. (5) To a suspension of NaH (0.06g, 2.46 mmol) in THF (5 ml) was added a solution containing 4 (0.15 g, 0.21 mmol) and 5 ml of THF. The mixture was stirred at room temperature under argon atmosphere for 1 hour and was then poured over ice to quench excess NaH. The residue was extracted with dichloromethane, and washed successively with 0.5M NaOH (aq), water, and brine. The organic layer was separated and dried over MgSO

125 Removal of the solvents in vacuo afforded. the product (81%) as a clear oil. 'H NMR (CDC13, 500 MHz) 6: (m, 30H, (CH 2 ) 5 ), 1.34 (d, J = 6.5 Hz, 3H, CH 3 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), (m, 6H, CH 2 ), 3.93 (t, J= 15.5 Hz, 1H, CH(H)), (m, 6H, OCH 2 ), (m, 1H, CH), 4.49 (t, J = 17.0 Hz, 1H, CH(H)), 4.92 (dd, J = 10.0, 1.5 Hz, 3H, CHCH(H)), 4.98 (dd, J = 17.5, 1.5 Hz, 3H, CHCH(H)), (m, 3H, CHCH 2 ), 7.15 (s, 2H, Ar-H). ' 3 C NMR (CDC13, 500 MHz) : 21.63, 26.20, 26.21, 29.09, 29.12, 29.30, 29.35, 29.46, 29.51, 29.61, 29.69, 29.70, 29.72, 29.81, 30.45, 33.97, 33.99, 62.07, 69.22, 73.56, 74.23, 106.7, 114.3, 122.6, 139.3, 140.9, 153.0, HRMS-ESI (m/z): [M+H] + calcd for C 43 H 71 NO , found Polymerization Procedure (Route A) A solution of monomer 5 (0.01 g, 0.02 mmol) and 5 mole % of Grubbs' catalyst' 6 (0.15 ml, 5.0 x 10-3 M in CH 2 Cl 2 ) is drop cast onto a glass slide under argon atmosphere. The film is placed on a hot plate at 100 C.for 12 hours, and the resulting material was washed with dichloromethane. The green-tinted, free-standing film was easily peeled off the glass slide and was dried under vacuum overnight. Preparation of Catalyst (Route A) The Cu complexes were prepared by adding the polymer to a solution of excess Cu(I)OTfotoluene, 2 in toluene. The suspension was stirred at room temperature for 24 hours. The solid was filtered, washed successively with toluene, methylene chloride, and 124

126 methanol, and dried under vacuum overnight. Anal. Cald. 7.57% Cu, Found 7.15%, 94% loading. Polymerization Procedure (Route B) To a solution of Cu(I)OTftoluenel,2 (0.01 g, 0.05 mmol) in a 1:1 mixture of CHC13:CH 3 OH was added monomer 5 (0.04 g, 0.05 mmol). The solution was stirred at room temperature for 30 minutes, and the solvents were removed by rotary evaporation. To the resulting material was added a solution of Grubbs' catalyst (0.55 ml, 5.0 x 10-3 M in CH 2 C1 2 ), and the solution was drop cast onto a glass slide under argon atmosphere. The film was placed on a hot plate for 60 hours at 100 C. The resulting polymer was washed with methylene chloride and dried under vacuum overnight. Anal. Cald. 7.57% Cu, Found 5.86%, 77% loading. General Procedure for Asymmetric Cyclopropanation Styrene (1000 eq.) was added to a stirring suspension of the appropriate catalyst (1.0 eq.) in dry CH 2 C1 2 (1 ml) at 0 C under argon. A CH 2 C1 2 solution (3.5 ml) of ethyl diazoacetate (100 eq.) was added slowly over 4 hours using a syringe pump. The reaction mixture was allowed to warm to room temperature and was stirred an additional 16 hours, and then was quenched with a 10% aqueous solution of NH 4 C1 (10 ml). For reactions with polymeric catalysts, the solution was filtered to remove heterogeneous materials. The solution was diluted with diethyl ether, washed with water, brine, and dried over MgSO4. The solvents were removed by rotary evaporation, affording the crude product as a mixture of cis and trans. For solution phase reactions, the crude 125

127 mixture was purified by flash chromatography (5% ethyl acetate in hexane). The ratio of trans to cis product was determined by H NMR spectroscopy. Enantiomeric excess was determined by gas chromatography using a Cyclodex B column, 15 m x 0.25 mm x 0.25 Gm, hydrogen as carrier gas, 20 p.s.i, injector temperature 200 C; oven temperature 200 C; 100 C isotherm, retention times (min) 60.7 (1S,2R), 62.5 (R, 2S), 76.1 (1R, 2R), 77.7 (S,2S). 126

128 References 1 (a) Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Comprehensive Asymmetric Catalysis, Springer-Verlag: Berlin-Heidelberg, (b) Noyori, R. Asymmetric Catalysis in Organic Synthesis; Wiley: New. York, De Vos, D. E.; Vankelecom, I. F. J.; Jacobs, P. A., Eds.; Chiral Catalyst Immobilization and Recycling, Wiley-VCH: Weinheim, (a) Doyle, M. P.; Protopopova, M. N.; Tetrahedron 1998, 54, (b) Ghosh, A. K.; Mathivanan, P.; Cappiello, J.; Tetrahedron: Asymmetry 1998, 9, 1. 4 Nozaki, H.; Morituri, S.; Takaya, H.; Noyori, R.; Tet. Lett. 1966, S Fritschi, H.; Leutenegger, U.; Pfaltz, A.; Helv. Chim. Acta 1988, 71, (b) Pfaltz, A.; Acc. Chem. Res. 1993, 26, Lowenthal, R. E.; Abiko, A.; Masamune, S.; Tet. Lett. 1990, 31, (a) Evans, D. A.; Woerpel, K. A.; Hinman, M. M.; Faul, M. M.; J. Am. Chem. Soc. 1991, 113(2), (b) Evans, D. A.; Woerpel, K. A.; Scott, M. J.; Angew. Chem. Int. Ed. Engl. 1992, 31, Muller, D.; Umbricht, G.; Weber, B.; Pfaltz, A.; Helv. Chim. Acta 1991, 74, For papers discussing immobilization of copper-mediated asymmetric cyclopropanation catalysts, please see: (a) Rechavi, D.; Lemaire, M.; Chem. Rev. 2002, 102, 3467, and references therein. (b) Cornejo, A.; Fraile, J. M.; Garcia, J. I.; Gil, M. J.; Luis, S. V.; Martinez-Merino, V.; Mayoral, J. A.; C. R. Chimie 2004, 7, 161, and references therein. (c) Altava, B.; Burguete, M. I.; Garcia-Verdugo, E.; Luis, S. V.; Vicent, M. J.; Mayoral, J. A.; Reactive & Functional Polymers 2001, 48,

129 10 Burguete, M. I.; Fraile, J. M.; Garcia, J. I.; Garcia-Verdugo, E.; Herrerias, C. I.; Luis, S. V.; Mayoral, J. A.; J. Org. Chem. 2001, 66, Grubbs' second generation catalyst is used. See Chapters 2 and Davankov, V. A.; Pastukhov, A. V.; Tsyurupa, M. P.; J. Polym. Sci. B 2000, 38, Estimated by comparison with swelling behavior of polystyrene-divinylbenzene polymers in toluene. Rana, S.; White, P.; Bradley, M.; J. Comb. Chem. 2001, 3, 9. '4 Dakovic, S.; Liscic-Tumir, L.; Kirin, S. I.; Vinkovic, V.; Raza, Z.; Suste, A.; SunJic, V.; J. Mol. Catal. A 1997, 118, 27. '5 See 2a in Chapter Grubbs' second generation catalyst = 1,3-(Bis(mesityl)-2-imidazolidinylidene)dichloro- (phenylmethylene)(tricyclohexyl-phosphine)ruthenium. 128

130 Appendix 1: 1 H and 1 3 C NMR Spectra for Chapter 2

131 Chapter 2 NMR Spectra I I I I I I ' I I ' pp 'H NMR of 2a (500 MHz, CDC1 3 ) ppa 13C NMR of 2a (500 MHz, CDC1 3 ) 130

132 Chapter 2 NMR Spectra :H ppm 1H NMR of 2b (500 MHz, CDC1 3 ) pa ' 3 C NMR of 2b (500 MHz, CDC1 3 ) 131

133 Chapter 2 NMR Spectra 0 I I L IV A AM V _ K pp 'H NMR of 3a (500 MHz, CDC1 3 ) i-l/ill//i/il -- w ---- im IIll I I'l I... I I I I i I IiiNii1I I -...,...,,l II I pp ' 3 C NMR of 3a (500 MHz, CDC1 3 ) 132

134 Chapter 2 NMR Spectra I$ 1 11 A... p 'kf X.X 7 7 I 6 I I 5 4 I.. I pi 'H NMR of 3b (500 MHz, CDC1 3 ) 1WI I -.,....,...' I,.. a I I,, i... ~~Y~~' ~~~~""'"""~~~~~"'" ~~WII"' ' '1' ppm 13 C NMR of 3b (500 MHz, CDC1 3 ) 133

135 Chapter 2 NMR Spectra Li I AA _ v L ' I I - I... I. '..' ' T...' I l I ' I I 7 I ' I I ppm th NMR of 4a (500 MHz, CDC1 3 ) ppm 13 C NMR of 4a (500 MHz, CDC1 3 ) 134

136 Chapter 2 NMR Spectra 0 I.. I. l'.i... 8 pp 7 6 S ]PI= 'H NMR of 4b (500 MHz, CDC1 3 ) YI Y-. -rn--i ~L rn-yi--y mm 11-. _~w r-- I ni o ppm 13 C NMR of 4b (500 MHz, CDC1 3 ) I I. 1. I I -...Y c...,I.L

137 Chapter 2 NMR Spectra I!. : li, Z : i :~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ H~~~~~~~~~~~~~~~~~ i C_~_ r~_ -- _ r---r r---r- r---m--_t----_r----r~-or A O--s ~-~----_ ~-----~~~-~~-~~ ; 7 -_~ ~ ~ pim ii z. - It-i U 'H NMR of 5a (500 MHz, CDC1 3 ) ppm 13 C NMR of 5a (500 MHz, CDC1 3 ) 136

138 Chapter 2 NMR Spectra O OH I.,I I i 6 ] ppm a 7 d b ppmr 'H NMR of 5b (500 MHz, CDC1 3 )..I i -~ r~u~u ; ;. uli~ip Y-IY~II.1' YLNI ll1~i, 1. '-,".'.;-,III II-1 I T ; l_.... I Nlmllllf A, I -uuc-- u uulurcur-,.l I I'--... I : ; I I l;.... TT.' - 4,. -'-"-; --'- - : - T L ' T-j... -; I '' ". I. ;:: r.v-7 _!J ; I o o80 60o ppm 13C NMR of 5b (500 MHz, CDC1 3 ) 137

139 Appendix 2: 1 H and 13 C NMR Spectra for Chapter 3

140 Chapter 3 NMR Spectra -- OCH, L I I _ -e I 6 5, 4 3 I i I Pm 'H NMR of 2a (500 MHz, CDC1 3 ) I I I I I I pp 13 C NMR of 2a (500 MHz, CDC1 3 ) 139

141 Chapter 3 NMR Spectra i pp 'H NMR of 2b (500 MHz, CDC1 3 ) ppm ' 3 C NMR of 2b (500 MHz, CDC1 3 ) 140

142 No l.. -~~... L IN Chapter 3 NMR Spectra CH 2 OH H 2 CHC(H 2 C)Oy O(CH 2 )CHCH 2 6(CH 2 ) 9 CHCH 2 I ii _ n in II w- 1 1I ijl ' 7 I po 'H NMR of 3a (500 MHz, CDC1 3 ) - -_~~ $woo"_ Irlr C NMR of 3a (500 MHz, CDC1 3 ) ~ mr I - Irr - -.; _.~~ t..! [[Ld all - II," I ppm 141

143 T - _ Chapter 3 NMR Spectra 0 OH I A I j h I AAA V v / v _ I I.. I I Pp l 1 H NMR of 3b (500 MHz, CDC1 3 ) t i : i : tf : t I i : I l I -rl W1YL i-l.r- -- u L i.ulc--r -r rr y,.l L -- LI-.l r- {wals-mmomm"" ' C NMR of 3b (500 MHz, CDC1 3 ) Y _-. - I-V- I ~ II ow : 1.. i.' ''0 '' ''' I ' ': [I II I ppm 142

144 Chapter 3 NMR Spectra rbr H 2 CHC(H 2 CO)gO O(CC O(CH 2 )gci 4 L_J i I I... p nic I p 'H NMR of 4a (500 MHz, CDC1 3 ) ppl 1 3 C NMR of 4a (500 MHz, CDC1 3 ) 143

145 l - -- r~- ~ Chapter 3 NMR Spectra I ' s I AAA V I 1 'H NMR of 4b (500 MHz, CDC1 3 ) I I r- m ' N woo I I ki,-----' --- I I-I l WANORMONVANNOO I I I I ii.-i..,,.i, i,, I I I, ' ' '.... I I.,,, o pp ~ 13C NMR of 4b (500 MHz, CDC1 3 ) 144

146 Chapter 3 NMR Spectra H 2 CHC(H 2 C)O/ H 2 CHC(H 2 C)O ~ 0'N CO 2 CH 3 H 2 CHC(H 2 C)O CH 3 i I i A JALAJ S I 5 3 I I. pp= 'H NMR of 5a (500 MHz, CDC1 3 ) S. z z a' i! :1 l L Ii I I, '---' ' ''."----t--' T'". -'-T T ' '-- ' ' '-' ""' " "* '"'-''--,'-:"T-.-'--r-?-r-: '' - 1..'' '- -'--T '-' '-r--v ppm ' 3 C NMR of 5a (500 MHz, CDC1 3 ) 145

147 Chapter 3 NMR Spectra CO 2 CH 3 orc C02CH J ~... 7 I8 7 I 6 6 I 5 / I I i 4 AAJJl Ivv I Pa v 'H NMR of 5b (500 MHz, CDC1 3 ) Y'- - _L _L - - I Ad... Ill.. I^rU I I ~Aal Y _l.k i. & in pa 13 C NMR of 5b (500 MHz, CDC1 3 ) U.. I I k~ ~J i Ill _.Y.IY.- IU I d r.. L In IL ill., II I I YI1 L - I_ 1_ 1-I _" Has_ 1111 I I I Ace En., it 146

148 Chapter 3 NMR Spectra H 2 CHC(H 2 C) 9,0, CH20H H 2 CHC( I i, I, -- ~~I i ii i, i il ~~~~~~~~~~~~~~~~ i! ~ , I I 4,.,., I I I I I I m PPa 'H NMR of 6a (500 MHz, CDC1 3 ) ~r.~ -,~~ ~r~...~yr~~~. i., t,,,.. I II - I. YL... I.~- rl. L.' I1 zi ppm 3 C NMR of 6a (500 MHz, CDC1 3 ) 147

149 -_,,~-.-, j -, - - ~,,..,,, Chapter 3 NMR Spectra L Jl 7 6 S.~~~~..vx AXk I ~-~~ ~` I 1 I pp 1A 'H NMR of 6b (500 MHz, CDC1 3 ).. t.. --l Y L-IY YL _r ---- lrl-- yyll 1.1 LI-- I _~ UY - [ [. -VYCI LY Y --I -I-- mi1l _'""- &i.i.i ~" " -" '"'~ I-?m-r--,,-,,-r,,,,,,,-,,.,,, P 1I C NMR of 6b (500 MHz, CDC1 3 ) 80 so POP 148

150 Chapter 3 NMR Spectra H 2 CHC(H 2 C) -' H 2 CHC(H 2 C) 9 0 _ - H 2 CHC(H 2 C) 9 I].,~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.i i I i~~~~ i I i i 1 I.- '*.- I ' T" - - T ''-"---' -- T r ppi 'H NMR of 7a (500 MHz, CDC1 3 ) i 1.., I... I i I -.''I i z.ii Ii: zi: II.1.Ii ppm 13 C NMR of 7a (500 MHz, CDC1 3 ) 149

151 Chapter 3 NMR Spectra I 7 r T I 5I I I ' I I I I I T I I I I I PI 'H NMR of 7b (500 MHz, CDC1 3 ) -'-! -r--r- 60 :- W ;I. *I~,-rW--~....- I. Ii -.. r.l rru -. ri. i-~ly iwri~l~l-l~~ ppl 1 3 C NMR of 7b (500 MHz, CDC1 3 ) 150

152 Appendix 3: 1 H and 13 C NMR Spectra for Chapter 4

153 Chapter 4 NMR Spectra 0 HOJ.N NO H H 0 H 2 gci40 0C14H2 OC 14 H 2 9 Al, I I AL A) I.1 -I - - S a I 7I I I I 6 I I I I I I 5 3 2I 4 32 I I I1I I II I.. 'H NMR of 3a (500 MHz, CDC1 3 ) ppm so P 13 C NMR of 3a (500 MHz, CDC1 3 ) 152

154 Chapter 4 NMR Spectra 0 0 HO-NH, N-,,OH HI1 H H 2 9 C 14 O OC4H 29 0C 1 4 H 2 9 I~ I I I..... Il... l. l. l.x l I ill ' l IA) \ L IC PPm 'H NMR of 3b (500 MHz, CDC1 3 ) '.. '- - ' -... ' " '-T -, , : T - '- - r ' 3 C NMR of 3b (500 MHz, CDC1 3 ). I ~--- _L- _ -~ -Y--I--_--LL_-_I_ -_I- ~-.- _ ~I-- --~ -_ _.~1_-I ~L _---_ ~ I I--iL._ILI - _~.- I I I l ld.. J. 1iI. i i i i n... - ' ' 20' ' r - - T pp! P 153

155 Chapter 4 NMR Spectra OH pp 'H NMR of 4a (500 MHz, CDC1 3 ) i i i i I I I ppm 13 C NMR of 4a (500 MHz, CDC1 3 ) 154

156 , Chapter 4 NMR Spectra OH HN 0 N t~o HN OH I; L, i! u: I'\ 1 ) ` I - ' I r-- r p--r 1 ppm 1 H NMR of 4b (500 MHz, CDC1 3 ) I i ii I I I 1 I 1.. I.1 I 1.,1, I 1.. I II I,.. I I. ", I.. II Ill ]., I "ujdui~iiiuui~iliujt LrYhIlW~kL",WA YlU iw.. I..... I....' ' I I I C NMR of 4b (500 MHz, CDC1 3 ) I lillAlhL~~h"Ly I '. I ' '.. I.. I. ". ' I ppm 155

157 Chapter 4 NMR Spectra 0 0 : H H 0o o H2g140 OC14H29.1-4H29 LJL. 1 i 1 I I A IIi _ A-JV' I I8 7 6 S I ppm 'H NMR of 5a (500 MHz, CDC1 3 ) I inml r -LLInm YYY I~~-LIYIC m Y L-L m I(L LL LL I mml~yc~ nm L I I~_l~ _I~-L- -- u~y-i~liy- Im_I Lr I'YY -- - n rr 0 I m mm. I TT T T r r r r 120 r r 100 r ppm ' 3 C NMR of 5a (500 MHz, CDC1 3 ) 156

158 - - Chapter 4 NMR Spectra o o HI H H 29 C 1 40 )OC 14 H 29 0C 14 H 29 A a.iv I II 6 A) [ I ikiv,-,.... I...._.. _ I I 3 2 I PPa 1 T- N4PR f 1h nf M4T-T7 rnri ). I I ppm 13 C NMR of 5b (500 MHz, CDC1 3 ) 157

159 Chapter 4 NMR Spectra HN N 0~~~~~~~ N0~~ N~~HN 1,,, ' ' I ' I I I I 4 ' I I ' I...' I I p I I S P]E 1 FT NMR nf a OMR7 Mnn rnrl A i. i z ;: 1.. i~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ : I.i : I i I I I L z ; I I I..,..!.,,. I ' I..I :. I. z i I "-, ' -I, '' ' ''' ' pepm ' 3 C NMR of 6a (500 MHz, CDC1 3 ) 158

160 Chapter 4 NMR Spectra CI HN HN : i, Ti pp 'H NMR of 6b (500 MHz, CDC1 3 ) t11.i 1, pp 13 C NMR of 6b (500 MHz, CDC1 3 ) 159

161 Chapter 4 NMR Spectra *' N' No H 29 C 14 0O OC14H 2 9 OC 14 H 29 I I i I J I I An )U I It I I 7 I I 4 2 II 7 S 4 i a I P"r t 'H NMR of 7a (500 MHz, CDC1 3 ) I I I. _ I _I_ C l. al ' 3 C NMR of 7a (500 MHz, CDC1 3 ) : ppm 160

162 Chapter 4 NMR Spectra N N- H 2 9C OC14H C OC1 4 H 2 9 I ' II L. A I I 1I J I J " w I ' I I I '.I I I I. i I - ~ - ~ -~ ~ ~ I -. * I I I ppa i -J-- v 1. 'H NMR of 7b (500 MHz, CDC1 3 ).I i z ppm 13 C NMR of 7b (500 MHz, CDC1 3 ) 161

163 Chapter 4 NMR Spectra 0 ll a pm 'H NMR of 8a (500 MHz, CDC1 3 ) - - f -1 J,. I,... -, <, J,..I II Y1L1I,.-ruyiLu Y-Y inmnm r LJ~Lyrr~r:, l l~r ~. Lluy-l um-msin lialfms ' '- l I -n ~, ~r,,. I, ppm ' 3 C NMR of 8a (500 MHz, CDC1 3 )... - ; : y Tv,5st-r~ l -y-mr A I. 162

164 Chapter 4 NMR Spectra 0 k~~ ~ ~~~ 0-0N i,, 1 I 7 I I I ' 6 I I I I, 7 6 S 4 I 3 I,, I 2 I 1 ppm 'H NMR of 8b (500 MHz, CDC1 3 ) z1., pap 13 C NMR of 8b (500 MHz, CDC1 3 ) 163

165 Chapter 4 NMR Spectra O's sio OCH3 J I L.1 Y L pl 1 H NMR of 9 (500 MHz, CDC1 3 ) ppn 1 3 C NMR of 9 (500 MHz, CDC1 3 ) I.. I

166 _ Chapter 4 NMR Spectra C1 4 H 29 0,-SC6H5 C14H290-~ '-~SC 6 H 5 C 14 H 29 0 l - _ r I 5 I I 4. A +LI'J l JL --- I pp 'H NMR of 11 (500 MHz, CDC1 3 ) i I i I It.l II.. 11 N ON1 do -U- inmm..,..ulimi iu l. a i ~ f....!~~~~~~~~~~. ' '' ` '' '". r.~ ~ - ~ "~'' "t lp t -' r"w 1-- '"" "'' I1irm r r s- -_- rvf"" I I I... t... I I i 1.,- N I, I,... I 'l I. I ' 3 C NMR of 11 (500 MHz, CDC1 3 ) I.. I... I ppi 165

167 Chapter 4 NMR Spectra C,.H,.O l1 CSH C 6 H 5 1s ppa 'H NMR of 12 (500 MHz, CDC1 3 ) i ALL i I Ii 1 1 i: J ''~~~~~~~~~~~~~ '' - 1II -L-_--L ----_LI _--_-Y_-L -I- - YY-YI ---YL_-I- _L..LI YILY_ --- -I-rY i-: X -- m ;=. :..., ,-..,... _... _._.'......! I, _ - T' _ r-... ', ppm t 3 C NMR of 12 (500 MHz, CDC1 3 ) 166

168 Appendix 4: 1 H and 13C NMR Spectra for Chapter 5

169 Chapter 5 NMR Spectra -~,,~~ x - n ppm 'H NMR of 1 (500 MHz, CDC1 3 ) al-n O Y LlrrlYIYU II " I , - - I r- ' ,r ~ 1--l~--,,--, --,-,T-r~.--~-1- T--, Tr.,, -~--,-..T'.,--,,-, YLLIIII L-- -C jj Yir IIIILYIIL 1Y(IL- -UILCLIUIWL-I wimmmomms" C NMR of 1 (500 MHz, CDC1 3 ) _t l ppmp 168

170 - Chapter 5 NMR Spectra - H N ' _ ^ A I-- YV, ll I I A J%. F I, I pa I i JLJ V 1 H NMR of 3 (500 MHz, CDC1 3 ) I Ift" - 1 omr I -s a le w I M..... i i ' 3 C NMR of 3 (500 MHz, CDC1 3 ) - I o I %momlow I w 4 u-41l~ ~rl~ 20 pi= 169

171 Chapter 5 NMR Spectra I i A I L l ' L IJ,,--~-- I. I I I I I i I I I ppm I 'H NMR of 4 (500 MHz, CDC1 3 ) ppm ' 3 C NMR of 4 (500 MHz, CDC1 3 ) 170

172 Chapter 5 NMR Spectra A 1 I 'I 6511'II I I' I I I I 1I I ' I I I I I NM= 'H NMR of 5 (500 MHz, CDC1 3 ) I Ii,-,.-._,. -l.y,..-_.. "W"~LII 1m.. _,, I-L_-- -Ly--l N mm - a-msmorv NMIw "-O.., ',' I..., i. i so PPa 13 C NMR of 5 (500 MHz, CDC1 3 ) 171

173 Curriculum Vitae Karen Villazor Martin ACADEMIC INTERESTS Organic chemistry, liquid crystals and liquid crystalline materials, supramolecular chemistry, chiral materials, heterogeneous catalysis EDUCATION Massachusetts Institute of Technology Candidate for Ph.D., Organic Chemistry Advisor: Professor Timothy M. Swager Boston College B.S., Chemistry, cum laude Advisor: Professor Lawrence T. Scott Thesis title: "Synthesis of [8]-Circulene" Cambridge, MA Chestnut Hill, MA RESEARCH EXPERIENCE Massachusetts Institute of Technology Cambridge, MA Graduate Research Assistant * Designed and synthesized several series of organometallic liquid crystals for potential applications in chiral separation technology and asymmetric catalysis * Applied a variety of techniques for the study of new liquid crystal phases * Developed method to polymerize liquid crystal phases in situ using metathesis Massachusetts Institute of Technology Cambridge, MA Chemistry Outreach Volunteer * Conducted science experiments for local high school students * Designed chemistry demonstrations to promote interest in scientific careers Boston College Undergraduate Research Assistant * Designed syntheses of curved polycyclic aromatic hydrocarbons * Synthesized fragments of C60 using flash vacuum pyrolysis Chestnut Hill, MA TEACHING EXPERIENCE Teaching Assistant, Massachusetts Institute of Technology * Lectured recitation sections for introductory organic chemistry * Prepared recitation materials and graded problem sets and exams 172

174 TECHNICAL PROFICIENCIES Synthetic organic chemist: small molecule purification and characterization Materials design, synthesis, and characterization Liquid crystal design, synthesis, and characterization Variable temperature X-ray diffraction Polarized microscopy of liquid crystal defect textures Inert atmosphere and Schlenk techniques PRESENTATIONS AND PUBLICATIONS Villazor, K. R.; Swager, T. M. "Chiral Supramolecular Materials from Columnar Liquid Crystals" Mol. Cryst. Liq. Cryst. 2004, 410, K. R. Villazor and T. M. Swager, "Materials with Supramolecular Chirality," presented at the Gordon Research Conference on Liquid Crystals, New London, NH (16-20 June 2003). K. R. Villazor and T. M. Swager, "Chiral Supramolecular Materials: Polymerization of Chiral Columnar Liquid Crystals with Retention of Mesophase Order," presented at the Materials Research Symposium, Boston, MA (2-6 December 2002). K. R. Villazor and T. M. Swager, "Chiral Supramolecular Materials from Columnar Liquid Crystals," presented to the Organic Division of the American Chemical Society at the 224 h Nation Meeting, Boston, MA (18-22 August 2002) K. R. Villazor and T. M. Swager, "Incorporating Catalytic Function into Chiral Supramolecular Materials," presented at the 19" h International Liquid Crystals Conference, Edinburgh UK (30 June - 5 July 2002). K. R. Villazor and T. M. Swager, "Chiral Supramolecular Materials from Columnar Liquid Crystals," presented at the 19" International Liquid Crystals Conference, Edinburgh UK (30 June - 5 July 2002). K. R. Villazor and T. M. Swager, "Chiral Supramolecular Materials from Columnar Liquid Crystals," presented at the Gordon Research Conference on Liquid Crystals, New London, NH (24-29 June 2001). K. R. Villazor and T. M. Swager, "Chiral Supramolecular Materials from Columnar Liquid Crystals," presented at the 7" International Symposium on Metallomesogens, Nagano, Japan (6-9 June 2001). 173

175 AWARDS AND HONORS Wyeth Scholar, MIT (2003) International Liquid Crystal Conference Poster Winner (2002) Copithorne Scholar, Boston College (2002) Scholar of the College, Boston College (1999) Golden Key National Honor Society (1998) AFFILIATIONS Member, Materials Research Society Member, American Chemical Society 174

176 Acknowledgements First and foremost, I would like to thank my advisor, Tim Swager, for spoiling me with innumerable acts of kindness over the past five years. From funding me when there was no funding, to sending me to conferences all over the world, to giving me the freedom to work on my own terms, his faith in me, and in all of his students, is both relentless and inspiring. A true mentor and educator, he empowers his students to develop their skills in ways that are unique to them, rather than some prescribed model. He pursues science with levels of enthusiasm, imagination and fearlessness that never cease to amaze, and yet, despite all his achievements and accolades, he begs for a level of irreverence that his group members so gladly grant him. His unassuming, good-natured, and humorous demeanor provides the foundation for a relaxed, open, and collaborative atmosphere in the lab. I could not imagine experiencing (or surviving) graduate school in any other environment. Tim is also someone who shows appreciation for the nontangible contributions of his students, those achievements that cannot be published in literature nor itemized on a resume. I have received a compliment or even a bottle of wine for simple group tasks that would have gone unacknowledged in any other setting. For the past five years, I have felt privileged and immensely proud to be part of the Swager group and have been grateful for every opportunity I had to represent Tim, and I thank him for that. I can only hope that our paths will continue to cross. Over the years, I have had the opportunity to work and play with so many wonderful people in the Swager lab. I could not have asked for a warmer, friendlier, and more welcoming environment to spend five years. We laughed together, teased each other, harassed each other, shamelessly inhaled PPST pizza together, and battled mice together. Oh, and we also did some research occasionally. I would like to thank a number of former group members for giving me a lot of guidance back in the day, when we had no windows in the lab but a big lunchroom table and lots of time to kill. Tyler McQuade, my personal favorite, always pushed me to do better, to try harder, and to think bigger that I had ever thought possible. Never have I enjoyed debating someone as much as him, and I am forever grateful for his friendship. J. D. Tovar always seemed to put things in perspective for me in his own unique way, typically through the immortal words of Snoop or Dre. Zhengguo ("ZZ") Zhu offered me a lot of synthetic advice, as well as a freakishly strong arm to open various bottles and pry loose any of my stuck glassware. Vance ("Wance") Williams made me feel right at home in the lab and helped me get acclimated quickly. I am convinced that Hindy Bronstein followed me from BC for the sole purpose of looking after me those first few years. Steffen Zahn happily showed me how to use the CD and always had time to discuss my research, and in return received much heckling for his red cargo pants and special VS deliveries. Shige Yamaguchi had to endure working with me in such close quarters in old , but generously acted as my personal travel agent for my trip to Japan. I especially thank Alex Paraskos, who taught me everything about liquid crystals, DSC, X-ray diffraction, optical microscopy, and Minesweeper, and answered every question I had no matter how many times I asked them. I think our first conversations consisted of my timid questions about the microscope, but over the years evolved into cynical wisecracks and pestering comments about his lovely wardrobe. Alex eventually became a permanent fixture in the "Somerville Shuttle" that was my car, and, oddly 175

177 enough, became just one of the girls. I wish him, Stacie, and their beautiful daughter Georgia all the best, and hope they find reasons to make their way back to Boston. And to Phoebe Kwan... what can I say?? We barely knew each other before we joined the lab, but for the past five years, there is hardly an MIT memory that she is not a huge part of. Although we have finally broken free, I will miss horrifying the Dali waiters with how much food we can eat, taking "coffee breaks" at Legal Seafoods, and sharing an inappropriate joke and a devious laugh every now and then. The lab may be a little more politically correct upon our departure, but nonetheless, I am proud of the impact that we have made. Also, thanks to Gigi Bailey for her friendship and support, and for always making sure my French was pronounced properly (Au Bon Pain?). Although I am confident that my leaving the group does not equate to a goodbye by any means, I wish her all the best for the remainder of her MIT run, and I remind her that "being nice is overrated." To Juan (and all her heavenly baked goods), Paul (P-Diddy, no more broken bones), Craig (what could have been...), "Professor" Sam (I'd join your group in a heartbeat), John (Provo, Spain?), Andrew (don't worry, I'll still hit on you), Dahui (thanks for the free therapy sessions), Hyuna, Scott, and the rest of the current Swager group, thanks for all the laughs and memories. I'm not sure I would have survived my first year at MIT without Aimee Crombie. Attached at the hip from day one, we took comfort in the fact that we both felt entirely clueless and were able to find humor in all situations. Although our careers have taken us in different directions, I do not doubt that we will remain strong friends. Thanks to Dave and Mark, and to Li Li for their help with all the DCIF instruments. Also, thank you to our lab manager, Becky Bjork, for keeping the lab running smoothly and for helping me with the random essentials that popped up over the course of the past year. Finally, there are a number of people outside of MIT who have helped me stay afloat throughout this experience. Dr. Larry Scott at Boston College has had an indelible impact on my life, from the day he pulled me out of his class and stuck me in front of a hood. He made applying to MIT sound like a given rather than a reach for me. I owe a special thank you to Jolynn, Janet, and Tara, for being a great group of cheerleaders who kept the lab phone number on speed dial. To my parents, Rodney, Rose, Reese, Paul, Gail, and Nick, I thank them for not knowing a blessed thing about chemistry but for caring the most about what I did each day in lab. Finally, and most notably, thank you to my husband Chris, who sees me at my best and at my very worst, but who sees me through it all. Thanks for never, ever letting me quit. I love you and know I could not have made it here without you. And now, onto the next chapter