Rh-Catalyzed Hydroformylation of 1,3-Butadiene to Adipic Aldehyde: Revealing Selectivity and Rate Determining Steps

Transcription

1 Rh-Catalyzed Hydroformylation of,3-butadiene to Adipic Aldehyde: Revealing Selectivity and Rate Determining Steps Sebastian Schmidt, Eszter Baráth, Christoph Larcher, Tobias Rosendahl, and Peter Hofmann,,* Organisch-Chemisches Institut, University of Heidelberg, Im Neuenheimer Feld 270, D-6920 Heidelberg, Germany Catalysis Research Laboratory (CaRLa), University of Heidelberg, Im Neuenheimer Feld 584, D-6920 Heidelberg, Germany Supporting Information Contents In situ IR Experiments...S2 2 In situ NMR Experiments...S6 3 Additional Spectra of (L4)Rh(η3-crotyl)(3CO)...S7 4 Additional Spectra for the Hydroformylation of Butadiene with (L2)RhH(CO)2...S8 5 Kinetic Experiments...S9 6 Deuterioformylation...S 7 Computational Details...S2 8 Cartesian Coordinates...S4 S

2 In situ IR Experiments In situ Study of (L2)Rh(η3-crotyl) under CO and Syngas Pressure 74 mg (0.079 mmol) (L2)Rh(η3-crotyl) were dissolved in ml toluene and added to 9 ml of pretempered toluene (60 C) in the ReactIR autoclave. After injection of this solution the measurement was started with 32 scans at min intervals (Figure S). After several minutes the autoclave was pressurized with 20 bar CO. After 55 min additional 20 bar H2 were added, so that the reaction ran at 40 bar (H2:CO approx. :) and 60 C for another.5 h. After cooling down to r.t. and releasing the pressure, the reaction mixture was analyzed by GC. Figure S. In situ IR spectra of the reaction of (L2)Rh(η3-crotyl) with CO and H2. a) The solution of (L2)Rh(η3-crotyl) in toluene as background under atm. argon; b) After addition of 20 bar CO; c) After addition of additional 20 bar H2. After addition of CO the formation of at least one dinuclear species with bridging CO ligands can be seen by the bands at 82 and 797 cm in spectrum b (Figure S). We tentatively assign these bands to species D in Scheme 2 in the main text, since it has already been observed in previous studies. D can be formed from two hydrido dicarbonyl complexes (L)RhH(CO) 2 under liberation of H2. When a Haji, S.; Erkey, C. Tetrahedron 2002, 58, S2

3 sufficient amount of H2 is present, however, D is easily cleaved again as can be seen in spectrum c. In the region of terminal CO ligands several overlapping bands were observed which can not be assigned unambiguously. Bands belonging to acyl species that would be expected around 700 cm were not observed. A strong band at 990 cm that could belong to the η3-crotyl CO complex, which was already observed as the main species with ligand L3, is present. When hydrogen was added, this band instantly increased slightly and then decreased again, but overlapped with another band so that it cannot be said if it completely vanished. This observation is in agreement with the expectation that the crotyl complex 7a is formed from the hydrido dicarbonyl complex (which is formed rapidly from D when hydrogen is added) and the liberated butadiene and then reacts slowly back to under aldehyde formation. Under syngas pressure, aldehyde (E-3-pentenal, confirmed by GC analysis) is formed, as was already observed in the analogous experiment with ligand L3 described in the main text. At the end of the reaction 4 bands in the region for terminal CO ligands were observed (2076, 2024, 2009 and 99 cm ) which are in good agreement with the bands of the hydrido dicarbonyl complex. Two other bands at 205 and 860 cm could not be assigned. The latter is again a sign of a dinuclear species. Under real hydroformylation conditions this band was not observed. Analysis of the Carbonyl Region of (L2)RhH(CO)2 The hydrido dicarbonyl complex (L)RhH(CO)2 is an important intermediate in hydroformylation reactions and appeared as an intermediate during the in situ IR (and NMR), kinetic, and deuterioformylation experiments in the IR autoclave. As discussed in the main text, it exists in a fast equilibrium of diastereomers, which results in overlapping bands from each isomer in the carbonyl region of the IR spectrum. A detailed analysis of such a spectrum is given here for ligand L2. With this CS-symmetric ligand there are three important isomers2: One with the chelating ligand in an axialequatorial position (ae) of the trigonal bipyramid (actually it is two enantiomers) and the other two with the ligand in equatorial-equatorial position (ee and ee2, Figure S2). 2 Schmidt, S.; Abkai, G.; Rosendahl, T.; Rominger, F.; Hofmann, P. Organometallics 203, 32, S3

4 Figure S2. General overview of the possible isomers of trigonal bipyramidal complexes with the chelating ligands used in this study. For compound with ligand L2 it is R=H, L=L2=CO. Therefore, the two ae isomers are enantiomers. We calculated the IR spectra of these three isomers with DFT (BP86/def2-SV(P)): Each isomer exhibits three coupled CO and Rh-H stretching vibrational modes in the region around 2000 cm. The corresponding frequencies are given in Table S. Table S. Computed Vibrational Frequencies in cm (BP86/def2-SV(P)) with Relative Intensities for the Three Relevant Isomers of Complex (L2)RhH(CO)2 ae ee ee2 993 (738) 979 (75) 954 (58) 2009 (42) 203 (452) 2002 (550) 2026 (209) 2068 (288) 2064 (303) We then simulated the spectrum of the mixture by linear combination of the three single component spectra. Each vibration is represented by a Lorentz function with a half-width of 5 cm. The isomer ratio was set to 3:: (ae:ee:ee2), which is close to the experimental 2 estimate. A comparison of this simulated spectrum with two experimental spectra is shown in Figure S3. The computed spectrum agrees very well with the two experimental spectra, which confirms the existence of three isomers in the mixture. The deuterated analogon of this compund, which could be observed in the deuterioformylation runs, was analyzed the same way (Figure S4). Here again the agreement is good. Each isomer contributes only two bands in this case and the remaining bands are shifted due to the missing coupling to the Rh-H vibration. S4

5 Figure S3. Carbonyl region of the simulated spectrum and experimental spectra of the hydrido complex (L2)RhH(CO)2. a pure compound in KBr at 298 K; preformed catalyst in toluene at 363 K (Figure 4 in the main text) 2 b Figure S4. Carbonyl region of the simulated and experimental spectrum of the deuterio complex (L2)RhD(CO)2. a preformed catalyst in toluene at 353 K S5

6 2 In situ NMR Experiments In situ Study of (L2)Rh(η3-crotyl) under CO and Syngas Pressure 7 mg of the known complex (L2)Rh(η3-crotyl) were dissolved in 0.5 ml toluene-d8 in a middle pressure NMR tube. The tube was pressurized with 3 bar CO and rigorously shaken. H and 3P{H} NMR spectra were recorded at r.t., 60 C, 80 C, 40 C and again at r.t. After 2 days 2 bar H2 were added so that the total pressure was 5 bar. The tube was heated to 70 C for 30 minutes and NMR spectra were recorded. The 3P{H} spectra are depicted in Figure S5. Two double doublets at 60.9 ppm (JP-P = 67.0 Hz, JP-Rh = Hz) and 63.4 ppm (JP-P = 65.8 Hz, JP-Rh = Hz) reveal the presence of the crotyl carbonyl complex (L2)Rh(η3-crotyl)(CO). At 80 C this signal clearly shows dynamic behavior, which points towards an isomerization process, most likely an η3-η-η3 coordination mode change of the crotyl moiety. The doublet at 65.4 ppm (JP-Rh = 20. Hz) belongs to (L2)RhH(CO)2. The broad signals between 5 and 48 ppm are tentatively assigned to dinuclear species. They slowly begin to appear already at room temperature, which means that β-h-elimination starts to take place at this temperature. The signals decrease when hydrogen is added to the mixture. Figure S5. 3P{H} NMR spectra (202.5 MHz, toluene-d8) of (L2)Rh(η3-crotyl) under different conditions. S6

7 3 Additional Spectra of (L4)Rh(η3-crotyl)(3CO) Figure S6. 3P{H} NMR spectrum (202.5 MHz, 298 K, C6D6) of the crotyl carbonyl complex (L4)Rh(η3-crotyl)(3CO) under 2 bar 3CO pressure. Signals of a diastereomer are marked with *. Figure S7. Carbonyl region of the 3C{H} NMR spectrum (25.8 MHz, 298 K, C6D6) of the crotyl carbonyl complex (L4)Rh(η3-crotyl)(3CO) under 2 bar 3CO pressure. Signals of a diastereomer are marked with *. S7

8 4 Additional Spectra for the Hydroformylation of Butadiene with (L2)RhH(CO)2 Figure S8. In situ IR spectra of the hydroformylation of butadiene with L2. (a) Rh(acac)(CO)2 and L2 dissolved in toluene at 90 C as background (b) after one hour preformation of the catalyst (c) after addition of butadiene at 00 C (d) after 90 minutes hydroformylation (A: aldehyde; B: butadiene). Figure S9. Full IR spectrum (left) and carbonyl region (right) of the hydroformylation of butadiene with (L2)RhH(CO)2 over time. S8

9 5 Kinetic Experiments At constant pressure, the reaction rate stayed constant throughout all hydroformylation and deuterioformylation runs even though the butadiene concentration decreased significantly (typically 6 mol/l at the beginning of the reaction and half of that or less when the reaction was stopped). Thus, in this range the reaction rate is independent of the butadiene concentration (saturation regime). Figure S0. Typical progress of the butadiene and aldehyde bands (at 05 and 730 cm ) during a hydroformylation run at constant pressure. The discontinuities of the butadiene band after 70 and 90 minutes were caused by interruptions of the mechanical stirrer which temporarily changed the butadiene concentration in solution. Figure S. Progress of the normalized absorption of the aldehyde and butadiene bands at 730 and 05 cm, respectively, during the kinetic experiments with stepwise increasing syngas pressure. S9

10 In order to investigate the dependence of the reaction rate on the syngas pressure, a kinetic hydroformylation experiment was performed as described in the main text. The total aldehyde concentration was determined with the calibration curve in Figure S2 for the cabonyl stretching band at 730 cm (Figure S). The relative reaction rate was determined with a linear regression for each of these pressure regions (Table S2). Figure S2. Calibration curve for the area of the aldehyde band at 730 cm with different concentrations of pentanal in toluene. The dotted line represents a linear Lambert-Beer-type fit for low concentrations. Table S2. Data for the Determination of the Relative Reaction Rate exp. time [min] pressure rel. reaction rate R bar 0.04 ± bar 0.23 ± bar 0.55 ± bar.00 ± bar.53 ± bar 2.24 ± bar 2.76 ± S0

11 6 Deuterioformylation Table S3. Reaction Conditions for the Deuterioformylation Experiments No. pressure butadiene butadiene : Rh reaction time conversion 20 bar 4.7 g min 7% 2 40 bar 4.8 g min 5% 3 60 bar 6.8 g min 4% Table S4: Relative Integrals of the 2H{H} NMR Signals for the Deuterioformylation runs signal 20 bar 40 bar 60 bar pathway -D-4-pentenal (not used) -D-3-pentenal (not used) Z--D-butadiene rev. iso-insertion E--D-butadiene rev. iso-insertion 2-D-butadiene rev. n-insertion 3-D-4-pentenal irrev. n-insertion 5-D-E-3-pentenal irrev. iso-insertion 5-D-Z-3-pentenal irrev. iso-insertion For the calculation of the degree of reversibility the ratio of reversible olefin insertions and total insertions (irrev. + rev.) was calculated according to the pathways given in Table S4. While doing that, the correction factors for statistical and isotope effects were included according to Table S5. Table S5: Correction Factors for the NMR Integrals for Different Kinetic Isotope Effects kh/kd = kh/kd = 3.4 kh/kd = 5-D-3-pentenal irrev. iso-insertion 3-D-4-pentenal irrev. n-insertion -D-butadiene.47.5 rev. iso-insertion 2-D-butadiene product S pathway rev. n-insertion

12 7 Computational Details All DFT calculations were carried out with the program package TURBOMOLE Geometries were fully optimized using the BP86 4 functional and the def2-sv(p) basis set 5 on all atoms together with a Stuttgart relativistic effective core potential6 on Rh in order to account for scalar relativistic effects. Frequency calculations were carried out to identify the stationary points as true minima with zero imaginary frequencies or transition states with exactly one imaginary frequency and to estimate the zero point vibrational energy (ZPE). All frequencies were scaled by a factor of as they appear to be slightly too large. 7 Single point energies were calculated at the optimized geometries with the def2-tzvp basis set4 on all atoms. In all calculations the RI approximation was used in order to speed up the calculation.8 Gibbs free energies (G) were obtained using standard statistical thermodynamics within the ideal gas, harmonic oscillator, rigid rotor approximations. If not otherwise noted, G-values refer to 0 C and 40 bar pressure. Kinetic isotope effects were estimated with Eyring-Theory (kh/kd = exp{ (GH GD)/RT}) where GH and GD are the free energies of the corresponding transition states for β-elimination with migrating hydrogen or deuterium atom. The results for the most important isomers of these transition states are listed in Table S6. The nomenclature of the isomers is described in a recent9 publication. 3 (a) Ahlrichs, R.; Bär, M.; Häser, M.; Horn, H.; Kölmel, C. Chem. Phys. Lett. 989, 62, (b) Häser, M.; Ahlrichs, R. J. Comput. Chem. 989, 0, 04. (c) Treutler, O.; Ahlrichs, R. J. Chem. Phys. 995, 02, (d) von Arnim, M.; Ahlrichs, R. J. Chem. Phys. 999,, (e) Deglmann, P.; Furche, F.; Ahlrichs, R. Chem. Phys. Lett. 2002, 362, (f) Deglmann, P.; Furche, F. J. Chem. Phys. 2002, 7, (a) Becke, A. D. Phys. Rev. A 988, 38, (b) Perdew, J. P. Phys. Rev. B 986, 33, (c) Perdew, J. P. Phys. Rev. B 986, 34, Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, Andrae, D.; Häußermann, U.; Dolg, M.; Stoll, H.; Preuß, H. Theor. Chim. Acta 990, 77, Scott, A. P.; Radom, L. J. Phys. Chem. 996, 00, (a) Eichkorn, K.; Treutler, O.; Öhm, H.; Häser, M.; Ahlrichs, R. Chem. Phys. Lett. 995, 240, (b) Eichkorn, K.; Treutler, O.; Öhm, H.; Häser, M.; Ahlrichs, R. Chem. Phys. Lett. 995, 242, (c) Eichkorn, K.; Weigend, F.; Treutler, O.; Ahlrichs, R. Theor. Chem. Acc. 997, 97, Schmidt, S.; Deglmann, P.; Hofmann, P. ACS Catal. 204, 4, S2

13 Table S6: Calculated Kinetic Isotope Effects of the β-elimination in Alkenyl Complexes of the Type (L2)Rh(alkenyl)(CO) a isomer replaced atom for replaced atom for GH GD ΔG in kj/mol KIE n aes n ae2s n ees n ee2s iso aes iso ae2s iso ees iso ee2s a for the nomenclature of the isomers see Figure S2, where R=H/D, L =butadiene, L =CO. Only the favored parallel orientation of the biphenyl side groups (s) has been regarded. Table S7: Calculated Relative Energies of the Most Important Isomers of (L3)Rh(η3-crotyl)(CO) a isomer a E (BP86/def2TZVP) in H rel. E in kj/mol L3-7a eea_a L3-7a eea_b L3-7a ees_a L3-7a ees_b L3-7a ee2a_a L3-7a ee2a_b L3-7a ee2s_a L3-7a ee2s_b for the nomenclature of the isomers see Figure S2, where R-L =crotyl, L =CO. Parallel (s) and orthogonal (a) orientations of the biphenyl side groups have been regarded. "_a" and "_b" refer to the crotyl unit with the methyl group near the axial or the equatorial coordination site, respectively. S3

14 8 Cartesian Coordinates The supplemental file coordinates.xyz contains the computed Cartesian coordinates of all of the molecules reported in this study. The file may be opened as a text file to read the coordinates, or opened directly by a molecular modeling program such as Mercury (version 3.3 or later, for visualization and analysis. S4