Sigma Bond Metathesis

Transcription

1 Sigma Bond Metathesis eporter: Changliang Sun Supervisor: Zhangjie Shi Outline Introduction Mechanism Examples and Applications Summary and Outlook Acknowledgements OPSS 2

2 Introduction The Nobel Prize in Chemistry 2005 : for the development of metathesis method in organic synthesis Yves Chauvin obert. Grubbs ichard. Schrock A Dance Changing Partners! OPSS 3 Alkene Metathesis Introduction L n M L n M L n M Mes N N Mes Alkyne Metathesis u PCy 3 Ph L nm L nm L nm ML n (O) 3 W C t-bu Alkane Metathesis L n M L n M ML n? OPSS 4

3 Introduction Natural Gas Methane Liquefied Natural Gas OPSS 5 Introduction C 4 higher alkanes OPSS 6

4 Introduction Chemical conversions of methane Syngas CO, 2 Steam reforming & partial oxidation Transiton metal activation of C- bond C 4 [Pt], [Pd] O 2 C 3 O, COO C 4 + C m 2m superacid OM cat. eaction with olefins for higher alkanes Coupling with silanes - + -Si 3 cat. C m+1 2(m+1)+2 Alkanes Metathesis -Si C 4 + C n 2n+2 [TM] cat. C m 2m+2 + C (n+1-m) 2(n+1-m)+2 Alkanes' Dehydropolymerization [TM] cat. C m 2m+2 + C n 2n+2 C m+n 2(m+n) Jean-Marie Basset, Angew. Chem. Int. Ed. 2004, 43, OPSS 7 Alkane Metathesis Introduction Significant Unreactive C-C, C- Metathesis Non-selective Ineffective σ Bond Metathesis General Direct Unique OPSS 8

5 Outline Introduction Mechanism Examples and Applications Summary and Outlook Acknowledgements OPSS 9 General Define Mechanism The idea of sigma bond metathesis was developed for the progress of σbond cleavage and formation that catalyzed by alkyl or hydride complexes of early transition metals with d 0 electronic configurations. Extensive experimental and theoretical studies have led to the concept of the general four-center transition state. M E M E M E' E' E' E M= Sc,Y,Ln;Ti, f, Zr,W,etc OPSS 10

6 Mechanism d 0 Metals 1. Electropositive, very easy to lose all their valence electrons---highest permissible oxidation state (d 0 configuration complexes). Oxidative addition and reductive elimination are impossible! 2. Electron-deficient metal center with one or more vacant orbitals would provide a low-energy means of approach for -, C- bond to M- bond OPSS 11 Ligand Mechanism Me Me Me Sc Zr Me Me Cp Cp* 1. anionic ligands: necessary for d 0 metal center 2. η 5 ligands: more stable for the complex 3. bulky ligands: able to prevent dimerization or oligomerization able to block approach of the π-orbital from substituted olefins. John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, OPSS 12

7 Mechanism (Cp* 2 )Sc (Cp* 2 )Sc (Cp* 2 )Sc Three steps: (i) (ii) Approach of the - or C- bond to the vacant orbital of Cp* 2 Sc ; Formation of the transition state described above with occupying the central β position in all cases; (iii) Departure of the new - or C- σbond from the opposite side of the orbital. Steigerwald, M. L.; Goddard, W. A., III. J. Am. Chem. Soc. 1984, 106, 308. John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, OPSS 13 Agostic Interaction Mechanism The word agostic is derived from the Greek word for to hold on to oneself.( 元结作用, 抓氢作用 ) It most commonly refers to a C- bond on a ligand that undergoes an interaction with the metal complex. Three-center, two-electron bridging interaction. This interaction closely resembles the transition state of an oxidative addition or reductive elimination reaction. The bonding could also be described as closely resembling a sigma complex. Me Et C B P CO Co N Mo 3 P N CO P Ti C N N first example α-agostic interaction β-agostic interaction Cotton, F. A.; LaCour, T.; Stanislowski, A. G. J. Am. Chem. Soc.1974, 96, OPSS 14

8 Mechanism Cp* Cp* Sc 1. The C- group acts as an electron donor in an interaction with an electron deficient metal center. 2. One condition for the interaction to be effective is that the hydrogen and the metal can be brought into contact without straining the system too much. 2 C C 2 3. Typical agostic metal-hydrogen distances are Å. 4. The determination of agostic bond strengths is often not possible at all and only approximate values are proposed. These difficulties lead to uncertain estimations of those interaction strengths between 1 and 20 kcal. mol -1. Jorg Grunenberg, et al., Organometallics 2006, 25, Bjorn O. oos, et al., J. Phys. Chem. A 2007, 111, OPSS 15 Transition State Mechanism E 1.86 A Cp 2 Sc 1.97 A 1.53 A 2.11 A 0.81 A Cp 2 Sc 1.92 A Cp 2 Sc 1.85 A 1.02 A [Cp 2 Sc] + 2 [Cp 2 Sc] + 2 Kite-Shaped Transition State T. Ziegler, E. Folga, A. Berces, J. Am. Chem. Soc. 1993, 115, OPSS 16

9 Mechanism Selectivity (Cp* 2 )Sc (Cp* 2 )Sc Thermodynamic control? Cp* 2 Sc-C 3 + -C 6 5 Cp* 2 Sc-C C 3 Cp* 2 Sc- + C 3 -C 6 5 (1) (2) θ = θ (2)- θ (1)= 4 kcal. mol -1 Consistent with the observed experimental results, but only slightly selective. Many reactions with other substituents showed a roughly equalδ θ values. Steigerwald, M. L.; Goddard, W. A., III. J. Am. Chem. Soc. 1984, 106, 308. John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, OPSS 17 Steric effect control? Mechanism A bulky group, rather than atom, seems favored atβ position. Even when =Me, no C-C coupling product (ethane) was found! Electronic effect control? Difference of electronegativity between C and. Much poorer overlap provided by the sp 3 C orbital of in the crucial center β position results in an overriding, unfavorable electronic effect. (Cp* 2 )Sc (Cp* 2 )Sc Unfavored Steigerwald, M. L.; Goddard, W. A., III. J. Am. Chem. Soc. 1984, 106, OPSS 18

10 Outline Introduction Mechanism Examples and Applications Summary and Outlook Acknowledgements OPSS 19 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr 2. IVB Metals: Ti Zr f 3. VB Metals: V Nb Ta OPSS 20

11 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr M(η 5 -Cp*) 2 C C 4 M = Lu, Y cyclohexane 70 o C M(η 5 -Cp*) 2 13 C 3 + C 4 + C 4 Lu C 3 Lu - C 4 3 C C 3 Patricia L. Watson, J. Am. Chem. Soc. 1983, 105, OPSS 21 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr Cp* 2 MC 3 -C 4 M 13 C 4 M 13 C 3 Cp* 2 M 13 C 3 Aaron D. Sadow and T. Don Tilley, J. Am. Chem. Soc. 2003, 125, Carol M. Fendrick and Tobin J. Marks, J. Am. Chem. Soc. 1984, 108, OPSS 22

12 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr Th 2 C C 2 C(C 3 ) 3 closed container Th C(C 3 ) 2 + -C 2 C(C 3 ) 3 cyclohexane, 50 o C C 2 C(C 3 ) 3 C 2 ( 3 C) 3 C 2 C 2*CpTh 2 C C 2 C(C 3 ) 2 Carol M. Fendrick and Tobin J. Marks, J. Am. Chem. Soc. 1984, 106, OPSS 23 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr Th 2 C C 2 C(C 3 ) 2 + cyclohexane, 30 o C 80±10% yield by NM Th Cp* Th Cp* C 3 C 3 C 3 Th 2 C C(C 3 ) 2 C 2 + cyclohexane, 30 o C Th Unstable β-c elimination! Carol M. Fendrick and Tobin J. Marks, J. Am. Chem. Soc. 1984, 108, OPSS 24

13 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr L n Sc- + - δ- δ+ L n Sc δ+ δ-, =, alkyl, alkenyl, aryl, alkynyl L n Sc- + - An appropriate model for the transition states of such σ bond metathesis reactions must accommodate the observed order of reactivity of - bonds with Cp* 2 Sc- bonds : = = >> =, = alkyl >> - = sp C-, = alkyl > - = sp 2 C-, = alkyl > - = sp 3 C-, = alkyl. John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, OPSS 25 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr 80 o C Cp* 2 ScC 3 + C 2 =CMe 2 σ-bond metathesis Cp 2 *Sc C + C 4 CMe 2 Cp* 2 ScC 3 C 2 =CMe 25 o C Cp* 2 ScC 2 CMe 2 C 2 =CMe 80 o C, -C 3 CMe 2 Cp 2 *Sc C CMe olefin insertion σ-bond metathesis Bulky Cp* ligands block approach of the π-orbitals from substituted olefins! ow about other less sterically encumbered ligands? John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, OPSS 26

14 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr [OpSc-] OpSc- = Me 2Si Sc (n+2) [(Cp*SiN)(PMe 3 )Sc] X 25 o C ; -PMe 3 (Cp*SiN)Sc 2 -[(Cp*SiN)Sc] n slow β- elim. -[(Cp*SiN)Sc] [(Cp*SiN)(PMe 3)Sc] = Me 2Si Sc PMe 3 n n Me 3C N Ziegler-Natta Catalysts John E. Bercaw, Pure & Appl. Chem., 1990, 62, OPSS 27 Examples and Applications 1. IIIB Metals: Sc Y La-Lu Ac-Lr Initial investigation in σbond metathesis III B group metal complex catalysts: Stoichiometric amount of complex, rather than catalystic reaction! Providing the general models of investigation on theoretical calculation. Unknown Lanthanide series and Actinium series OPSS 28

15 Examples and Applications 2. IVB Metals: Ti Zr f Catalytic dehydrogenative polymerization of silanes by Ti and Zr metallocene derivatives Cp 2 M 2 n Si 3 Si Significance: n + (n-1) 2 A number of applications for polysilanes: photoresists, photoconductors, semiconductors, nonlinear optical meterials. As an investigation ahead for methane (alkanes) dehydropolymerization, which probably shares the same mechanism. ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, OPSS 29 Examples and Applications 2. IVB Metals: Ti Zr f Cp*CpZr hν + PhSi 3 Cp*CpZr Si(SiMe 3 ) 3 benzene-d 6 Si 2 Ph + Si(SiMe 3 ) 3 Failed to isolate! (-SiPh-) n + [CpCp*Zr] Cp*Cpf heat or hν + PhSi 3 Cp*Cpf Si(SiMe 3 ) 3 benzene-d 6 Si 2 Ph + Si(SiMe 3 ) 3 M Si Si ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, OPSS 30

16 Examples and Applications 2. IVB Metals: Ti Zr f ydrolysis Cp 2 M 2 n Si 3 Si + (n-1) 2 n M Si + M M + Si ydrogen exchange ' M + ' Si M Si M ' + Si Silane exchange Si' M Si + Si' M M Si' + Si Si Si-Si bond cleavage/formation Si M + Si Si M Si M Si + Si ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, OPSS 31 Si Examples and Applications 2. IVB Metals: Ti Zr f ydrolysis 2 Cp*CpM Cp*CpM Si(SiMe 3 ) 3 Si (SiMe 3 ) 3 2 should be excess absolutely! - Si(SiMe 3 ) 3 Cp*CpM M = Zr, f everse Cp*Cpf PhSi 3 Cp*Cpf Si Ph - 2 Cp*Cpf Si 2 Ph Silanes should be excess absolutely! ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, OPSS 32

17 Examples and Applications 2. IVB Metals: Ti Zr f Silane exchange Cp*Cpf Si(SiMe 3 ) 3 A Si 2 Cp*Cpf Si Si (SiMe 3 ) 3 - Si(SiMe 3 ) 3 Cp*Cpf Si Occur when the starting complex possesses a bulky, easily displaced silyl group! A : A good starting material!!! ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, OPSS 33 Examples and Applications 2. IVB Metals: Ti Zr f Si-Si bond cleavage/formation Cp*Cpf A SiPh 2 PhSi 3 Cp*Cpf SiPh 2 Si Ph Cp*Cpf + Ph 2 SiSiPh 2 B SiPh 3 should be excess absolutely! B is a crucial complex in this process! A or B PhSi 3 (SiPh) n ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, OPSS 34

18 Examples and Applications 2. IVB Metals: Ti Zr f Dehydropolymerization Catalytic Mechanism (Si) m (Si) n M (Si) n Si(Si) n-1 M Si(Si) m-1 Si-Si bond formation Si(Si) n-1 M dehydrogenation (Si) m M(Si) n 2 ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, OPSS 35 Examples and Applications 2. IVB Metals: Ti Zr f Notes: 1. This polymerization involves step growth of polymer rather than chain growth. So the relatively low molecular weights are produced, and high monomer concentration and high vacuum to remove hydrogen can increased MW. 2. It is well-known that Si has an lower electronegativity to and can form stable compounds with expanded 3d coordination spheres. So the Si atom can occupy the β position in transition state. But C atom seems very difficult! Electronegativity: Si: 1.9 : 2.2 C: 2.5 ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, ee-gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, OPSS 36

19 Examples and Applications 3. VB Metals: V Nb Ta The silica-supported transition metal hydrides: Si-O Si Si-O Ta 2 C n 2n+2 C n+i 2(n+i)+2 + C n-i 2(n-i)+2 with i = 1, 2,...n-1, but where i = 1 is generally favored. Successful metathesis of alkanes! V. Vidal, A. Theolier, J. Thivolle-Cazat, J.-M. Basset, Science 1997, 276, OPSS 37 Examples and Applications 3. VB Metals: V Nb Ta V. Vidal, A. Theolier, J. Thivolle-Cazat, J.-M. Basset, Science 1997, 276, OPSS 38

20 Examples and Applications 3. VB Metals: V Nb Ta [Ta] S C 3 C 3 2 C [Ta] S C 2 C 4 3 C 3 C 3 C 3 C 2 C 3 C 3 [Ta] S C 3 [Ta] S CC 3 C3 C 3 [Ta] S C 3 C 3 C 2 C 3 V. Vidal, A. Theolier, J. Thivolle-Cazat, J.-M. Basset, Science 1997, 276, OPSS 39 Examples and Applications 3. VB Metals: V Nb Ta cat. 2 C 2 6 C 4 + C o C ΔG θ = kj mol -1.(at 150 C driven by the formation of methane) everse direction : C 4 + C 3 8 cat. 2 C C 3 8 C 4 + C 2 6 C / 2 C / 2 C 4 10 methane/propane = 1250:1 Jean-Marie Basset, Angew. Chem. Int. Ed. 2004, 43, OPSS 40

21 Examples and Applications 3. VB Metals: V Nb Ta [( Si O ) x Ta( CCMe 3 )(C 2 CMe 3 ) (3-x) ] x=1, or 2 C 3 C 3 C 2 C 2 Ta C 3 Ta Ta C 2 Ta Ta Ta C-C bond activation C- bond activation(alkane exchange) Jean Thivolle-Cazat, Jean-Marie Basset, Angew. Chem. Int. Ed. 2001, 40, OPSS 41 Examples and Applications 3. VB Metals: V Nb Ta Ta C- bond activation Ta C C-C bond activation C 1 C 2 C Ta 2 Ta C 1 Ta > > >> reverse C- bond activation C C 1 larger than C 2 not abserved Jean Thivolle-Cazat, Jean-Marie Basset, Angew. Chem. Int. Ed. 2001, 40, OPSS 42

22 Examples and Applications 3. VB Metals: V Nb Ta Notes: Silica-supported catalysts have special properties and have already been used in industrial applications. Selectivity needs more improvement. Still difficult for formation of higher alkanes. Jean Thivolle-Cazat, Jean-Marie Basset, Angew. Chem. Int. Ed. 2001, 40, OPSS 43 Outline Introduction Mechanism Examples and Applications Summary and Outlook Acknowledgements OPSS 44

23 Summary and Outlook Sigma bond metathesis is a kind of mechanism applied in the progress of σbond cleavage and formation that catalyzed by alkyl or hydride complexes of early transition metals with d 0 electronic configurations. Initial investigation Stoichiometric reaction Dehydropolymerization of Silanes Silica-supported alkane metathesis Where is the future of sigma bond metathesis? OPSS 45 Summary and Outlook O P 2 3 C (C 2 ) n C C (C 2 ) n C 3 3 C (C 2 ) n+m-x C C (C 2 ) x C 3 X O P 2 1: = t-bu, X= L= C 2 4, 2 Ir(L) P 2 2M 2M olefin metathesis X Ir(L) P 2 2M 2 2M 2a: =t-bu, X= 2b: =i-pr, X=OMe L= 2 and/or C C C C 3 A new idea for alkane metathesis! i -Pr N Mo ( 3C)(F 3C)CO ( 3C)(F 3C)CO 3 i -Pr CC(C 3) 2Ph A. S. Goldman, et al, Science 2006, 312, OPSS 46

24 Summary and Outlook A. S. Goldman, et al, Science 2006, 312, OPSS 47 Summary and Outlook This system involves a single metal with dual properties in contrast to the Goldman Brookhart system! i-pr i-pr t-bu N Mo t-bu O O O Si O O Si O O There are also new methods to afford alkane metathesis, and sigma bond metathesis is just a kind of them! C. Copret,* J. T.Cazat, and J.M. Basset, Angew. Chem. Int. Ed. 2006, 45, OPSS 48

25 Summary and Outlook This represents a great step forward for green chemistry, reducing potentially hazardous waste through smarter production. Metathesis is an example of how important basic science has been applied for the benefit of man, society and the environment, the committee s comment on 2005 Nobel Prize in Chemistry. Next Nobel Prize in Organic Chemistry? OPSS 49 Outline Introduction Mechanism Examples and Applications Summary and Outlook Acknowledgements OPSS 50

26 Acknowledgements PKU, CCME, OPSS Prof. Zhangjie Shi All members in my group All professors and students here OPSS 51