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Functional Theory Study
Luca Schiaffino, Gianfranco Ercolani
To cite this version:
Luca Schiaffino, Gianfranco Ercolani. Rhodium Catalyzed Hydrogenation of Enamides with Mon- odentate Phosphorous Ligands. A Density Functional Theory Study. Journal of Physical Organic Chemistry, Wiley, 2010, 24 (3), pp.257. �10.1002/poc.1756�. �hal-00599796�
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Rhodium Catalyzed Hydrogenation of Enamides with Monodentate Phosphorous Ligands. A Density Functional
Theory Study
Journal: Journal of Physical Organic Chemistry Manuscript ID: POC-10-0010.R1
Wiley - Manuscript type: Research Article Date Submitted by the
Author: 17-May-2010
Complete List of Authors: Schiaffino, Luca; Università degli Studi di Roma Tor Vergata, Scienze e Tecnologie Chimiche
Ercolani, Gianfranco; Università degli Studi di Roma Tor Vergata, Scienze e Tecnologie Chimiche
Keywords: asymmetric catalysis, density functional calculations, hydrogenation, P ligands, rhodium
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Rhodium Catalyzed Hydrogenation of Enamides with Monodentate Phosphorous Ligands. A Density Functional Theory Study
Short title: Rhodium-Catalyzed Hydrogenation of Enamides with Monodentate P-ligands.
Luca Schiaffino,* and Gianfranco Ercolani
Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Via della Ricerca Scientifica, 00133 Roma, Italy. Fax: (+39) 0672594328. E-mail: [email protected]
Abstract
The hydrogenation of enamides catalyzed by rhodium complexes of monodentate phosphorous ligands has been studied by density functional theory. The role of trans intermediates, made accessible by the non chelating nature of the ligand, has been taken into account. The findings here reported show that cis intermediates play the major role in the mechanism of the reaction, suggesting that data obtained with chiral monodentate phosphorous ligands or with a mixture of them should be interpreted excluding the intervention of structures with trans phosphine arrangement. Thus, results observed with monodentate phosphorous ligands must be interpreted in the light of the exclusive intervention of cis intermediates, without involvement of structures with trans phosphine arrangements.
Keywords: asymmetric catalysis / density functional calculations / hydrogenation / P ligands / rhodium
Introduction
The rhodium-catalyzed enantioselective hydrogenation of enamides (Scheme 1) is one of the most important methods in the synthesis of chiral amino acids.[1] The reaction is clean, efficient, and atom- economical. Moreover it can be carried out under very mild conditions in a variety of organic solvents.
Due to its broad applications and central role in the field of asymmetric catalysis, it has been the object of a large number of mechanistic studies up to become one of the best known transition metal catalyzed reactions.
Although the first pioneering studies focused on the use of chiral monophosphines as ligands for the rhodium metal ion,[2] after the introduction of the bidentate ligand DIOP by Kagan in 1971,[3] it has been customarily assumed that bidentate diphosphines are required to achieve high enantioselectivities.
The underlying idea is that the rigidity introduced by the use of chelating ligands is necessary for optimal transfer of chirality in the catalytic reaction. The syntheses of bidentate ligands, however, are often demanding thus limiting the access to the vast libraries necessary for large scale screenings. In the
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2 last decade, evidences have accumulated showing that the use of chelating diphosphines is not essential to obtain high enantioselectivities.[1g,4] Chiral monodentate phosphines,[5] phosphonites,[6] phosphites,[7]
phosphoramidites,[8] and mixtures of them[9] have proven to be excellent ligands in the hydrogenation of a variety of olefins, affording enantioselectivities that are comparable or even better than those observed with traditional bidentate ligands. A striking difference between bidentate and monodentate ligands is that the former can only coordinate in a cis fashion, whereas the latter can coordinate in both a cis and a trans fashion. There are even examples of monodentate ligands, such as the so-called TRAP ligands, which can only coordinate in a trans fashion.[10] In spite of the growing importance of monodentate phosphorous ligands, a detailed computational study of the reaction mechanism with non chelating ligands has never been reported. Only computational studies with bidentate diphosphine ligands in the cis arrangement, or models of them, can be found in the literature.[11]
Here we report the results of a computational study on model achiral catalytic systems 2a and 2b aimed at investigating also the competing trans mechanistic pathway that is potentially available when monodentate ligands are employed. This study is propaedeutic to any computational investigation of the enantioselectivities observed in the reaction with a chiral monodentate phosphorous ligand[4-8] or with a mixture of two such ligands.[9]
Results and Discussion
The accepted mechanism for the rhodium-catalyzed hydrogenation of enamides, elaborated on the basis of extensive experimental[1e,12] and theoretical[11,13] studies using bidentate diphosphine ligands, is shown in Scheme 2. In the first step the substrate chelates the rhodium ion to give a square planar complex, which can interact with molecular hydrogen to form a weakly bound ion induced dipole species IID. The latter intermediate transforms into a trigonal bipyramidal molecular hydrogen complex MOLH2, which subsequently undergoes oxidative addition to form a six coordinate octahedral alkyl metal hydride complex DIHY. Migratory insertion of an olefin carbon into a Rh-H bond within the DIHY complex produces a five-coordinate alkyl hydride ALHY. The cycle is completed by fast reductive elimination of the alkyl hydride to yield the hydrogenated product that readily dissociates and regenerates the catalyst.
Bidentate diphosphine ligands give rise to four diastereomeric pathways, corresponding to the four DIHY intermediates in Figure 1. In the Figure the original notation A, B, C, and D introduced by Landis and coworkers is used.[11a,b] Pathways B and D involve the same trigonal bipyramidal molecular hydrogen complex MOLH2-B/D (Figure 1). It has been found that barriers to the formation of this intermediate from the two IIDs are very high, precluding any significant contribution of these pathways
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to the overall reaction. This result has been rationalized on the basis of the least motion principle,[11a,14]
since conversion of both IIDs into MOLH2-B/D requires a large ligand reorganization within the complex.
When substrates with electron withdrawing groups at the α carbon (1, R=EWG), usually employed in experimental practice, are considered, the migratory insertion of DIHY-C has a very high barrier and pathway C is blocked at this stage. On the other hand, migratory insertion of DIHY-A is much faster, so that A is the only productive pathway. [11a] This has been recently rationalized on the basis of charge distribution in the transition states connecting DIHY to ALHY intermediates.[11e] Summing up, the electron withdrawing effect of the amide and of the R substituent polarize the double bond and favours the Michael type hydride addition at the β carbon atom, which takes place in the A pathway. Conversely, pathway C involves hydride addition at the α carbon atom and is disfavoured. The relative barriers for oxidative addition and migratory insertion in pathway A are sensitive to the stereoelectronic environment, so that the turnover limiting step depends on the nature of the phosphorous ligand in an unpredictable manner.[11b] When the electron withdrawing substituent at the α position is replaced by an electron-donating methyl group (1, R=CH3), the effects of methyl and amide cancel each other out and pathways A and C are found to be almost equivalent in energy.[11e]
The model system 2a, chosen to investigate the mechanism with monodentate ligands, consists of a cationic rhodium with two ligated trimethylphosphines and a coordinated N-(3,3,3-trifluoroprop-1-en-2- yl)acetamide (1, R=CF3, R'=H). Trimethylphosphine was chosen as it is the simplest trialkylphosphine ligand. The choice of the substrate was dictated by the fact that the typical enamide used in previous computational studies, namely N-(1-cyanovinyl)acetamide (1, R=CN, R'=H), coordinates the rhodium ion with the nitrogen atom of nitrile rather than with the double bond in the DIHY-E trans structure (vide infra). In view of the importance of the electronic properties of the substituent on the double bond remarked by Wiest,[11e] we replaced the nitrile group with an electron-withdrawing non coordinating trifluoromethyl substituent. Calculations on the methyl derivative 2b were also performed in order to investigate the possible role of electronic effects.
All calculations were carried on with the program Gaussian 03[15] with all structures optimized at the M05-2X level of theory[16] using the basis set LANL2DZ ECP[17] for rhodium and the 6-31G(d,p) for all other atoms. The M05-2X functional was chosen because it has been demonstrated to outperform the popular B3LYP functional,[16] whereas the basis set was chosen in analogy with those previously used by Landis,[11a-d] and Wiest.[11e] The nature of all stationary points was checked by frequency calculations.
Computed relative electronic energies of all relevant intermediates and transition states are reported in Table 1.
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4 It has been unambiguously demonstrated[4c,18] that the catalytically active species has two phosphorous ligands bound to the rhodium ion, so the possible intervention of mono coordinated and/or tri coordinated intermediates was excluded. Under this restriction, in principle five octahedral intermediates are possible: the four cis DIHY A, B, C, and D and the trans DIHY E.
Since the phosphine ligands are achiral, Re and Si-face coordination of the double bond to the rhodium ion in 2 give rise to enantiomers rather than to diastereomers and thus there is only one energetically distinct 2 species to consider. The intermediates IID-A/B and IID-C/D differ by the face approached by H2, the two stereoisomers being almost isoenergetic in the case of model system 2b. In model system 2a we did not find any minimum corresponding to the IID-C/D intermediate. Attempts at optimizing such a structure led to MOLH2-C.
The pentacoordinated MOLH2 complexes are stable intermediates with trigonal bipyramidal geometry.
When the phosphorous ligands are kept in a cis arrangement the amido oxygen always occupies an axial position, so that there are only three possible isomers.[11a] Monodentate ligands could in principle allow a new structure MOLH2-E, in which both phosphines occupy the axial positions. However, we found that this geometry does not represent a minimum in the potential energy surface and all attempts at optimizing such a structure invariably led either to the already known MOLH2-B/D isomer or to the DIHY-E intermediate. In agreement with previous findings,[11a] we found that the MOLH2-B/D isomer is not kinetically accessible, the barriers for its formation from either IID-A/B or IID-C/D being equal or larger than 14.7 kcal mol-1 for both substrates. Accordingly, we did not consider the successive steps of pathways B and D.
For both model systems 2a and 2b, the activation barriers to reach the transition states TS(MOLH2- A→DIHY-A) and TS(MOLH2-C→DIHY-C) are lower than 9 kcal mol-1. We succeeded in optimizing a stable trans DIHY-E structure, somewhat more stable than its A and C isomers. Since pathways B and D are not productive, we wondered if this isomer could directly form from intermediates MOLH2-A and MOLH2-C. Transition states for direct formation of DIHY-E from MOLH2-A and MOLH2-C were located and characterized. The corresponding activation barriers were in all cases much greater than the highest barriers in pathways A and C (Table 1). This finding can be rationalized by the principle of least motion.[14] In order for a MOLH2 intermediate to transform into the DIHY-E structure, both phosphine ligands must move in coordination sites perpendicular to the coordination plane of the chelating substrate and the hydrogen atoms of H2 simultaneously move in the same plane. It appears that such rearrangements require a very large structural reorganization and generate a very high barrier even though the final product of the transformation is the most stable DIHY intermediate.
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It is also conceivable that DIHY-E can originate from DIHY-A or DIHY-C by a mechanism involving dissociation and reassociation of a phosphine ligand. In order to study the energetic of phosphine dissociation in our model system 2a, we performed a scan along the coordinative bond between the rhodium atom and the phosphine trans to hydride in the DIHY-A intermediate.[19] We found that electronic energy grows very steeply with bond distance. When the bond is elongated by just 1 Å, from 2.49 to 3.49 Å, the energy increases by as much as 20 kcal mol-1, a value much higher than the 5-15 kcal mol-1 barriers of the migratory insertion calculated from the data in Table 1. This result should not be significantly affected by the solvent on the basis of the Hughes Ingold solvation rules[20] and in view of the fact that the metal and the ligand are still close enough to exclude the assistance of coordinating solvent molecules. Complete phosphine dissociation in the gas phase requires about 30 kcal mol-1. On the basis of these results, a dissociation-reassociation pathway involving the Rh-P bonds can be excluded.[21] Since other isomerisation pathways between DIHY intermediates, namely Bailar twist and dissociation of the alkene ligand, have already been ruled out in Landis original work,[11a] it can be safely concluded that a cis to trans isomerisation cannot take place. Accordingly, DIHY-E is an unlikely intermediate in the enamide reduction and only DIHY-A and DIHY-C are produced even when monodentate ligands are involved. These intermediates undergo migratory insertion of an olefin carbon into a Rh-H bond, yielding the alkyl hydrides ALHY. As previously stated,[11e] DIHY-A intermediates form an ALHY-Aα product with a formal negative charge on the α carbon atom of the substrate and thus the reaction is strongly favoured by an electron-withdrawing substituent on the same position. This behaviour is observed also in model system 2a. The energy barrier for migratory insertion in DIHY-A is 4.9 kcal mol-1, and the transition state is much lower in energy than the analogous transition state for migratory insertion within DIHY-C (Figure 2) to form ALHY-C/Dβ. When the electron withdrawing trifluoromethyl group in α is replaced by an electron-releasing methyl group as in model system 2b, the behaviour is significantly modified and the two barriers are more levelled out. Indeed, since the energies of the two transition states differ by just 0.5 kcal mol-1 and since they are the highest-energy transition states in both pathways, pathways A and C have about the same probability of occurrence (Figure 3).
In Table 1 are also reported in parentheses the ZPE corrected electronic energies of the intermediates and transition states discussed so far. Even if the general trends are not substantially modified, it should be noted that in the first steps of pathways A and C some energy barriers disappear. In particular, in the case of the model system 2a, there is no barrier for the conversion of IID-A/B into MOLH2-A, thus no stable ion induced dipole intermediate is formed upon approach of H2 on both sides of its mean plane.
Even more interestingly, in model system 2b the ZPE-corrected energy of MOLH2-A is higher than that of the transition state for its production from IID-A/B, so that the octahedral intermediate DIHY-A forms directly from IID-A/B. However, since the relative stabilities of the highest energy transition
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6 states remain unchanged, the above differences do not alter the general conclusions on the competition between stereoisomeric pathways already derived from the analysis of the electronic energy profiles.
Conclusions
In summary, the mechanism of hydrogenation of enamides by rhodium catalysts with monodentate phosphorous ligands has been computationally investigated by means of the recent functional M05-2X, considering two model substrates bearing substituents with opposite electronic effects in the α position.
Trans intermediates have been taken into account and their stabilities and ease of formation compared with the corresponding cis structures. We have found that the trans structure of the octahedral DIHY intermediate is significantly more stable than all of the four cis isomers. Nevertheless its formation from the kinetically accessible MOLH2-A and MOLH2-C precursors is highly unfavoured with respect to the already known DIHY-A and DIHY-C cis isomers. Isomerization between DIHY structures by virtue of a dissociation-reassociation pathway, made viable by the monodentate nature of the investigated ligand, has also been explored and ruled out on the basis of comparison with the energy barriers required for conversions of DIHY-A and DIHY-C into the corresponding ALHY intermediates. These findings indicate that reactions with monodentate ligands follow the same cis pathways A and C available to bidentate ligands. Accordingly, intermediate structures with trans phosphine arrangements do not need to be considered in the interpretation of data obtained with monodentate phosphorous ligands or with a mixture of them.[9]
References
[1] a) W. S. Knowles, Acc. Chem. Res. 1983, 16, 106-112. b) M. J. Burk, Acc. Chem. Res. 2000, 33, 363-372. c) W. Tang, X. Zhang, Angew. Chem. Int. Ed. 2002, 41, 1612-1614. d) J.-P. Genet, Acc.
Chem. Res. 2003, 36, 908-918. e) I. D. Gridnev, T. Imamoto, Acc. Chem. Res. 2004, 37, 633-644. f) J. Wu, A. S. C. Chan, Acc. Chem. Res. 2006, 39, 711-720. g) A. J. Minnaard, B. L. Feringa, L.
Lefort, J. G. de Vries Acc. Chem. Res. 2007, 40, 1267-1277. h) W. Zhang, Y. Chi, X. Zhang, Acc.
Chem. Res. 2007, 40, 1278-1290.
[2] a) W. S. Knowles, M. J. Sabacky, Chem. Commun. 1968, 1445-1446. b) W. S. Knowles, Acc. Chem.
Res. 1983, 16, 106-112.
[3] a) T. P. Dang, H. B. Kagan, J. Chem. Soc., Chem. Commun. 1971, 481. b) H. B. Kagan, T. P. Dang, J. Am. Chem. Soc. 1972, 94, 6429-6433.
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[4] a) I. V. Komarov, A. Börner, Angew. Chem. Int. Ed. 2001, 40, 1197-1200. b) T. Jerphagnon, J.-L.
Renaud, C. Bruneau, Tetrahedron: Asymmetry 2004, 15, 2101-2111. c) M. T. Reetz, A. Meiswinkel, G. Mehler, K. Angermund, M. Graf, W. Thiel, R. Mynott, D. G. Blackmond, J. Am. Chem. Soc.
2005, 127, 10305-10313.
[5] F. Guillen, J.-C. Fiaud, Tetrahedron Lett. 1999, 40, 2939-2942.
[6] a) M. T. Reetz, T. Sell, Tetrahedron Lett. 2000, 41, 6333-6336. b) C. Claver, E. Fernandez, A.
Gillon, K. Heslop, D. J. Hyett, A. Martorell, A. G. Orpen, P. G. Pringle, Chem. Commun. 2000, 961-962.
[7] M. T. Reetz, G. Mehler, Angew. Chem. Int. Ed. 2000, 39, 3889-2890.
[8] a) M. van den Berg, A. J. Minnaard, E. P. Schudde, J. van Esch, A. H. M. de Vries, J. G. de Vries, B. L. Feringa J. Am. Chem. Soc. 2000, 122, 11539-11540. b) H. Bernsmann, M. van den Berg, R.
Hoen, A. J. Minnaard, G. Mehler, M. T. Reetz, J. G.. De Vries, B. L. Feringa, J. Org. Chem. 2005, 70, 943-951.
[9] a) M. T. Reetz, T. Sell, A. Meiswinkel, G. Mehler, Angew. Chem. Int. Ed. 2003, 42, 790-793. b) M.
T. Reetz, G. Mehler, Tetrahedron Lett. 2003, 44, 4593-4596. c) M. T. Reetz, X. Li, Tetrahedron 2004, 60, 9709-9714. d) M. T. Reetz, G. Mehler, A. Meiswinkel, T. Sell, Tetrahedron: Asymmetry 2004, 15, 2165-2167. e) M. T. Reetz, Y. Fu, A. Meiswinkel, Angew. Chem. Int. Ed. 2006, 45, 1412- 1415. f) M. T. Reetz, O. Bondarev, Angew. Chem. Int. Ed. 2007, 46, 4523-4526. g) M. T. Reetz, Angew. Chem. Int. Ed. 2008, 47, 2556–2588.
[10] Z. Freixa, P. W. N. M. van Leeuwen, Coord. Chem. Rev. 2008, 252, 1755–1786.
[11] a) C. R. Landis, P. Hilfenhaus, S. Feldgus, J. Am. Chem. Soc. 1999, 121, 8741-8754. b) S. Feldgus, C. R. Landis, J. Am. Chem. Soc. 2000, 122, 12714-12727. c) C. Landis, S. Feldgus, Angew. Chem., Int. Ed. 2000, 39, 2863-2866. d) S. Feldgus, C. R. Landis, Organometallics 2001, 20, 2374-2386. e) P. J. Donoghue, P. Helquist, O. Wiest, J. Org. Chem. 2007, 72, 839-847.
[12] a) J. Halpern, D. P. Riley, A. S. C. Chan, J. J. Pluth,. J. Am. Chem. Soc. 1977, 99, 8055-8057. b) A.
S. C. Chan, J. J. Pluth, J.; Halpern, J. Am. Chem. Soc. 1980, 102, 5952-5954. c) J. M. Brown, P. A.
Chaloner, J. Am. Chem. Soc. 1980, 102, 3040-3048. d) J. Halpern, Science 1982, 217, 401-407. e) C. R. Landis, J. Halpern, J. Am. Chem. Soc. 1987, 109, 1746-1754. f) J. M. Brown, P. L. Evans, Tetrahedron 1988, 44, 4905-4916. g) B. McCulloch, J. Halpern, M. R. Thompson, C. R. Landis,
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8 Organometallics 1990, 9, 1392-1395. h) I. D. Gridnev, T. Imamoto, Chem. Commun. 2009, 7447–
7464.
[13] a) C. Daniel, N. Koga, J. Han, X. Y. Fu, K. Morokuma, J. Am. Chem. Soc. 1988, 110, 3773-3787.
b) N. Koga, K. Morokuma, Chem. Rev. 1991, 91, 823-842. c)S. Mori, T. Vreven , K. Morokuma, Chem. Asian J. 2006, 1, 391 – 403.
[14] J. Hine, Adv. Phys. Org. Chem. 1978, 15, 1–61.
[15] Gaussian 03, Revision E.01, M. J. Frisch et al.; Gaussian, Inc., Wallingford CT, 2004.
[16]a) Y. Zhao, D. G. Truhlar, Acc. Chem. Res. 2008, 41, 157-167. b) C. J. Cramer, D. G. Thrular, Phys.
Chem. Chem. Phys. 2009, 11, 10757-10816.
[17] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 299-310.
[18] I. D. Gridnev, C. Fan, P. G. Pringle, Chem. Commun. 2007, 1319-1321.
[19] The dissociation of the phosphine trans to hydride in DIHY-A is faster than dissociation of the other phosphine because the bond is weakened by a stronger trans effect.
[20] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, 3rd ed., Wiley-VCH, Weinheim, 2003, p. 163ff.
[21] a) The dissociation of phosphorous ligands in an octahedral rhodium intermediate of the Wilkinson reduction has been experimentally investigated (ref. 20b). The rate constant for the dissociative site exchange of two phosphines bound to the central rhodium was measured as 0.2 s-1 at 303 K, corresponding to a free energy barrier of ca. 19 kcal mol-1. This value is well higher than the activation energy for the conversion of DIHY-A and DIHY-C into the corresponding ALHYs, indicating that the conclusion derived from calculations in the gas phase can be safely extended to the reaction in solution. b) J. M. Brown, P. L. Evans, A. R. J. Lucy, Chem. Soc. Perkin Trans. II 1987, 1589-1596
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Chart.
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Scheme 1. Rh-catalyzed hydrogenation of enamides.
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Scheme 2. General mechanistic scheme for the rhodium catalyzed hydrogenation of enamides.
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Figure 1. Diastereomeric pathways for the rhodium-catalyzed hydrogenation of enamides when the coordinating phosphorus ligands are kept in the relative cis arrangement.
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Figure 2. Energy profiles for model system 2a over pathways A(●) and C (○).
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Figure 3. Energy profiles for model system 2b over pathways A(●) and C (○).
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Table 1. Computed relative electronic energies (kcal mol-1) of all relevant intermediates and TSs in the hydrogenation of model systems 2a and 2b. ZPE energies are also reported in parentheses.
Structure 2a 2b
2 + H2 0.0 (0.0) 0.0 (0.0)
IID-A/B -2.4 (-0.8) -2.4 (-0.5)
IID-C/D - - -1.8 (0.4)
TS(IID-A/B→MOLH2-A) -2.0 (-1.1) -0.6 (0.5)
TS(IID-A/B→MOLH2-B/D) 23.5 (26.1) 20.8 (22.7)
TS(IID-C/D→MOLH2-C) - - 1.3 (2.9)
TS(IID-C/D→MOLH2-B/D) 18.9 (21.0) 12.9 (15.1)
MOLH2-A -4.4 (-1.4) -1.3 (1.8)
MOLH2-B/D 7.7 (11.1) 10.2 (13.4)
MOLH2-C -5.3 (-2.2) -1.0 (2.2)
TS(MOLH2-A→DIHY-A) 4.1 (7.3) 7.5 (10.1)
TS(MOLH2-C→DIHY-C) 3.4 (5.9) 5.1 (7.2)
TS(MOLH2-A→DIHY-E) 11.4 (14.8) 18.4 (21.1)
TS(MOLH2-C→DIHY-E) 23.1 (26.7) 16.1 (19.5)
DIHY-A 0.2 (5.2) 0.6 (4.9)
DIHY-B 5.6 (9.3) 1.7 (5.4)
DIHY-C -1.3 (3.1) -3.3 (0.4)
DIHY-D -0.2 (4.0) -3.9 (0.1)
DIHY-E -5.0 (-0.3) -7.0 (-2.6)
TS(DIHY-A→ALHY-Aα) 5.1 (8.5) 10.8 (13.9)
TS(DIHY-C→ALHY-C/Dβ) 12.6 (15.4) 11.3 (13.8)
ALHY-Aα -23.6 (-17.4) -13.4 (-7.8)
ALHY-C/Dβ -12.7 (-6.3) -12.6 (-6.2)
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The hydrogenation of enamides catalyzed by rhodium complexes of monodentate
phosphorous ligands has been studied by DFT.
The role of trans intermediates, made accessible by the non chelating nature of the ligand, has been taken into account. The findings here reported show that cis intermediates play the major role in the reaction mechanism.
DIHY-A Rh O HN
H
P H P
DIHY-B Rh O HN
H
P P H
DIHY-C Rh O HN
P
H H P
DIHY-D Rh O HN
P
H P H
DIHY-E Rh O HN
P
P H
H Rhodium Catalyzed Hydrogenation of Enamides with Monodentate Phosphorous
Ligands. A Density Functional Theory Study
Luca Schiaffino,* and Gianfranco Ercolani
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Supporting Information
Rhodium Catalyzed Hydrogenation of Enamides with Monodentate Phosphorous Ligands. A Density Functional Theory Study
Luca Schiaffino* and Gianfranco Ercolani
Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Via della Ricerca Scientifica, 00133 Roma, Italy. E-mail: [email protected]
Contents
Full author listing for ref. 14 S2
Atomic coordinates, structures, and energies of optimized structures S2
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S2 Full author listing for ref. 14
Gaussian 03, Revision E.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J.
R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J.
Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S.
Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and J.
A. Pople, Gaussian, Inc., Wallingford CT, 2004.
Atomic coordinates, structures, and energies of optimized structures
(pictures created with Molden: G. Schaftenaar, J. H. Noordik J. Comput.-Aided Mol. Design 2000, 14, 123-134)
H2
EE (hartrees) = -1.167738 ZPE (hartrees) = 0.010302
H 0.000000 0.000000 0.029667 H 0.000000 0.000000 0.770333 2a model system
Square planar complex
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EE (hartrees) = -1655.025024 ZPE (hartrees) = 0.352002
C 0.572061 2.581327 -1.589565 P -0.416669 2.123240 -0.109060 C 0.300162 3.157523 1.225240 Rh 0.103644 -0.195922 0.284004 C 0.929053 -2.594562 -1.432042 C 1.326005 -1.877226 -0.172782 C 0.790787 -2.126051 1.084194 C -2.016151 2.967399 -0.448551 P -2.055386 -0.957968 0.068670 C -2.658206 -0.967791 -1.661885 O 2.105961 0.640679 0.464499 C 2.998741 -0.147246 0.088065 C 4.436638 0.269106 0.065899 C -2.503487 -2.630095 0.690470 C -3.297524 0.044763 0.976991 N 2.678139 -1.387416 -0.290229 F 0.800210 -1.755729 -2.466851 F 1.879665 -3.489133 -1.758899 F -0.226649 -3.258773 -1.292471 H -2.578440 2.447417 -1.223915 H -1.806507 3.982701 -0.788860 H -2.614939 3.025495 0.459417 H -3.704962 -1.272361 -1.703466 H -2.051764 -1.660532 -2.243370 H -2.551402 0.028513 -2.091039 H 4.764123 0.431071 1.093449 H 4.514145 1.218532 -0.461793 H 5.080234 -0.469080 -0.407619 H 3.394603 -2.039207 -0.574844 H -1.936237 -3.411627 0.193340 H -2.329357 -2.675034 1.766251 H -3.565675 -2.793809 0.503403 H 1.598293 2.252418 -1.439246 H 0.164839 2.086385 -2.471029 H 0.549908 3.662568 -1.734850 H -3.393128 1.030786 0.532163 H -4.267836 -0.452502 0.941394 H -2.985800 0.150310 2.016220 H 0.296487 4.208149 0.931026
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S4 H 1.320641 2.824806 1.405994
H -0.280951 3.034723 2.138808 H 1.392913 -1.918392 1.959796 H -0.033179 -2.810754 1.206776 IID-A/B
EE (hartrees) = -1656.196619 ZPE (hartrees) = 0.364822
C -0.647799 2.571329 1.638264 P 0.374888 2.125795 0.177579 C -0.321982 3.155456 -1.170956 Rh -0.106651 -0.192181 -0.263645 P 2.058674 -0.931226 -0.028652 C 2.524777 -2.582048 -0.691279 C 1.960860 2.981575 0.547364 O -2.120177 0.615837 -0.454168 C -3.000653 -0.178419 -0.062627 N -2.662259 -1.409340 0.330814 C -1.306913 -1.887532 0.200477 C -0.893351 -2.609733 1.451936 C -4.443727 0.219424 -0.037864 C 2.645056 -0.974953 1.706720 C 3.300430 0.110453 -0.893402 C -0.782273 -2.130236 -1.062751 F -0.748900 -1.776601 2.489117 F 0.260102 -3.274191 1.291613 F -1.840097 -3.505026 1.786897 H 3.588309 -2.740666 -0.507921 H 1.964512 -3.381267 -0.214575 H 2.350705 -2.599065 -1.768046 H 1.738345 3.995887 0.882436 H 2.512104 2.466023 1.333560 H 2.575207 3.041881 -0.349937 H -5.074760 -0.520253 0.450033 H -4.531101 1.175455 0.476166 H -4.779073 0.361854 -1.065804 H -3.369369 -2.066660 0.625947 H 0.048118 -2.805259 -1.195084 H -1.393867 -1.925413 -1.932476 H 0.643218 0.340353 -3.471196 H 0.436119 0.146102 -2.779614
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H 2.981258 0.281498 -1.921327 H 4.266455 -0.396163 -0.895703 H 3.409550 1.065796 -0.388610 H 2.040634 -1.685358 2.267732 H 2.524457 0.011385 2.154776 H 3.694341 -1.270077 1.750836 H -1.333275 2.810191 -1.379099 H 0.283738 3.039616 -2.069510 H -0.338777 4.205742 -0.876061 H -1.669913 2.243228 1.460056 H -0.630405 3.651341 1.792604 H -0.261838 2.069044 2.524979 TS(IID-A/B→MOLH2-A)
EE (hartrees) = -1656.195948 ZPE (hartrees) = 0.363776
C -0.684542 2.262885 1.719421 P 0.327295 2.042864 0.201061 C -0.408271 3.236379 -0.983062 Rh -0.062122 -0.232420 -0.528970 O -2.064914 0.549596 -0.866290 C -2.936837 -0.124980 -0.278631 N -2.587676 -1.231785 0.383732 C -1.249327 -1.764989 0.263649 C -0.803092 -2.330558 1.582803 C 1.901482 2.888514 0.649362 C -0.818138 -2.241978 -0.979634 P 2.078589 -0.957650 -0.135744 C 2.547633 -2.647216 -0.678111 C 2.667941 -0.879451 1.597507 C 3.291167 0.047973 -1.076923 C -4.378320 0.277941 -0.313924 F -0.545976 -1.376425 2.486707 F 0.298973 -3.085080 1.455318 F -1.774977 -3.109217 2.092855 H 3.620796 -2.779521 -0.532907 H 2.018730 -3.404170 -0.105070 H -3.288856 -1.808003 0.826043 H 0.323788 0.021385 -2.741194 H 0.599180 0.572879 -3.170273 H 2.487168 3.084727 -0.248515
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S6 H -4.985957 -0.278917 0.396194
H -4.447544 1.344333 -0.106896 H -4.756877 0.109126 -1.323162 H 2.317174 -2.762055 -1.737749 H -0.027487 -2.973364 -1.040563 H -1.496962 -2.186087 -1.821042 H 1.665625 3.844247 1.120221 H 2.496159 2.294620 1.342060 H 3.065181 -0.025289 -2.140639 H 4.300673 -0.325205 -0.898023 H 3.236600 1.090655 -0.775895 H 2.115276 -1.599027 2.197506 H 2.490403 0.115445 2.002982 H 3.733730 -1.107425 1.643509 H -1.406269 2.892617 -1.248534 H 0.201941 3.274000 -1.885917 H -0.459373 4.232271 -0.540557 H -1.705720 1.950368 1.504238 H -0.683629 3.307114 2.035894 H -0.288337 1.634374 2.516664 TS(IID-A/B→MOLH2-B/D)
EE (hartrees) = -1656.155313 ZPE (hartrees) = 0.366460
Rh 0.121966 0.064055 0.084926 O -0.041977 0.018307 2.389264 C 1.052819 -0.089609 2.966320 N 2.161558 -0.424197 2.282144 C 2.117182 -0.801632 0.907893 C 1.277227 -1.807460 0.471945 H 0.654735 -2.340467 1.178069 H 1.466226 -2.273468 -0.485694 C 3.412848 -0.555590 0.195025 F 3.957584 0.616229 0.551454 F 3.259651 -0.582637 -1.136748 F 4.307350 -1.505023 0.520657 H 3.045483 -0.477864 2.765268 C 1.184844 0.145664 4.442444 H 2.220652 0.164181 4.775831 H 0.653543 -0.647073 4.970082 H 0.703000 1.090815 4.687436
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P -1.975036 0.953356 0.290031 P 0.943459 2.024127 -1.095537 C -2.118133 2.313368 1.501401 C -2.987890 -0.374878 1.035962 C -2.924221 1.448917 -1.193974 H -1.670409 3.229576 1.126596 H -1.594777 1.994598 2.401891 H -3.170683 2.489501 1.728191 H -2.483759 -0.713737 1.940653 H -3.983885 -0.002718 1.282045 H -3.071730 -1.207631 0.338164 H -3.935821 1.740199 -0.908041 H -2.976518 0.598754 -1.875010 H -2.446352 2.279945 -1.709284 C 0.625512 1.780671 -2.895291 C 0.168566 3.675493 -0.805931 C 2.703423 2.566866 -1.145352 H 1.200488 0.919545 -3.237870 H -0.432072 1.581513 -3.070184 H 0.925853 2.662293 -3.464291 H -0.911292 3.645474 -0.938181 H 0.581012 4.397378 -1.512826 H 0.393667 4.007213 0.207949 H 3.340506 1.768974 -1.514601 H 2.774735 3.425102 -1.815600 H 3.039124 2.853878 -0.150925 H -0.356063 -0.695530 -1.486976 H -0.734104 -1.202317 -0.969379 TS(IID-C/D→MOLH2-B/D)
EE (hartrees) = -1656.162669 ZPE (hartrees) = 0.365658
Rh 0.020481 -0.001313 0.032193 O -0.005664 0.063795 2.944482 C 1.187348 0.027826 3.199817 N 2.079005 -0.649543 2.396345 C 1.739198 -1.384572 1.258657 C 0.599213 -2.094067 1.061378 H -0.126842 -2.167988 1.851067 H 0.537424 -2.756135 0.208713 C 2.949428 -1.624231 0.377329
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S8 F 3.614414 -0.484875 0.129918
F 2.620835 -2.190948 -0.780512 F 3.791944 -2.435197 1.032325 H 3.062978 -0.517250 2.572678 C 1.798685 0.690126 4.404905 H 2.771512 1.128986 4.182544 H 1.930223 -0.056123 5.191180 H 1.117145 1.457194 4.761078 P -2.276094 -0.454992 0.846822 P -0.578211 1.948268 -0.994336 C -3.051471 0.959099 1.733248 C -2.541931 -1.791852 2.083581 C -3.510867 -0.928026 -0.432687 H -3.156775 1.828599 1.086009 H -2.410338 1.216102 2.576759 H -4.038935 0.675056 2.100136 H -1.939980 -1.590137 2.968757 H -3.596149 -1.809108 2.363859 H -2.278196 -2.762542 1.663946 H -4.497371 -1.043165 0.019005 H -3.207427 -1.877209 -0.874744 H -3.561041 -0.184424 -1.224245 C 0.590416 2.464252 -2.309036 C -2.197746 2.139567 -1.831509 C -0.512564 3.338029 0.199405 H 1.596041 2.528878 -1.894904 H 0.587478 1.725688 -3.110619 H 0.298541 3.435591 -2.710349 H -2.291200 1.388089 -2.615542 H -2.253602 3.132907 -2.279787 H -3.019267 2.025784 -1.126969 H 0.498804 3.402585 0.600325 H -0.767721 4.276808 -0.295110 H -1.200424 3.161081 1.024855 H 1.476584 0.431529 -0.435969 H 0.977439 -0.166965 -1.184292 MOLH2-A
EE (hartrees) = -1656.199783 ZPE (hartrees) = 0.367026
C -3.202756 0.529585 1.210757
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P -2.209841 -0.544146 0.102835 C -2.789262 -0.113876 -1.580393 Rh 0.021695 -0.298526 0.571685 O 2.139996 -0.001124 0.946970 C 2.853810 -0.629331 0.134481 N 2.281937 -1.424322 -0.774024 C 0.876078 -1.749622 -0.649833 C 0.308301 -2.058113 -2.001259 C -2.967043 -2.184651 0.413633 C 0.445662 -2.403457 0.534993 P 0.132116 2.003730 -0.243810 C -1.258329 3.212905 -0.323850 C 1.351396 2.977797 0.727934 C 0.808113 2.068561 -1.951610 C 4.345699 -0.509335 0.170166 F 1.115664 -2.915010 -2.655606 F -0.904469 -2.628908 -1.911113 F 0.190306 -0.968423 -2.773663 H 1.190475 -2.658952 1.278201 H -0.425257 -3.040875 0.505803 H 2.850899 -1.991919 -1.385745 H -0.413841 0.522380 2.353553 H -0.376590 -0.236895 2.511907 H -3.068611 0.199625 2.240945 H -4.049473 -2.101872 0.304860 H 1.526443 3.944691 0.253909 H 1.703347 1.448704 -2.003923 H 0.077658 1.663504 -2.651005 H 1.054638 3.094305 -2.230268 H 2.283053 2.422673 0.806855 H 0.961653 3.135004 1.734344 H -2.881105 1.565415 1.127594 H -4.259018 0.456848 0.948151 H -2.732673 -2.505041 1.428926 H -2.595012 -2.920283 -0.295116 H -3.879467 -0.144094 -1.608726 H -2.389030 -0.826579 -2.296369 H -2.448574 0.883093 -1.853151 H -0.905644 4.132164 -0.794384 H -1.593673 3.448732 0.686656 H -2.102075 2.830247 -0.896078 H 4.820950 -0.953299 -0.702010 H 4.708926 -1.005528 1.071249 H 4.611026 0.544117 0.241728 MOLH2-B/D
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