Hydrogenation of tris(triphenylphosphine)chlororhodium(I)

Halpern, Jack; Wong, C. S.

doi:10.1039/c39730000629

Cited by 130 publications

(46 citation statements)

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“…The accepted mechanism for hydrogenation of alkenes by Wilkinson's catalyst involves the addition of dihydrogen prior to coordination of the alkene, followed by migratory insertion [31]. The new demonstrations of the existence of solvate dihydride complexes inevitably raise the question as to whether the same mechanism can apply in rhodium enantioselective hydrogenation.…”

Section: Transient and Reactive Intermediates In Rhodium Enantioselecmentioning

confidence: 99%

“…The rhodium catalyst is frequently introduced as a cationic diphosphine dialkene complex which requires an initial hydrogenation of the dialkene before an active catalyst is formed. All of the described intermediates give well-defined and distinctive NMR spectra in which 1 H, 31 P and 13 C (with enrichment) are all informative. Hydrogenation of the first double bond in situ may be followed by a sequential hydrogenation of the now freely dissociating mono-alkene.…”

Section: Introductionmentioning

confidence: 96%

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Mechanism of Enantioselective Hydrogenation

Brown¹

2006

The Handbook of Homogeneous Hydrogenation

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John M. Brown IntroductionThe discovery of the first practical catalyst for homogeneous hydrogenation by Wilkinson, Osborn, Jardine and Young in 1965 [1] occurred at around the same time that others, especially Mislow and Horner [2], were demonstrating that chiral trivalent phosphorus compounds were capable of existing as stable, noninterconverting enantiomers. With suitable adaptation of Wilkinson's catalyst, a prostereogenic alkene could be hydrogenated with preferential formation of one enantiomer of the reduced product. The possibility of such enantioselective hydrogenation was recognized by both Horner [3] and Knowles [4], but it was Knowles who won the race to demonstrate the first example in 1968. This led rapidly to a period of seminal discoveries: the application of chelate biphosphine ligands came from Kagan [5], and the development of a full-scale enantioselective hydrogenation of a dehydroamino acid to provide a rhodium-complex-based catalytic synthesis of l-Dopa by Knowles' team at Monsanto [6]. For many years this provided a substantial part of the supply of the main drug active in the control of Parkinson's disease. Kagan was also the first to demonstrate, in his synthesis and application of DIOP (derived very simply from RR-or SS-tartaric acid), that the difficult synthesis of enantiomerically pure phosphines was unnecessary for effective enantioselective hydrogenation, since a suitable chelate backbone could provide the necessary level of stereochemical control. For many years the development of enantioselective hydrogenation converged on the preparation of enantiomerically pure chelate diphosphines and the application of their rhodium complexes to the hydrogenation of dehydroamino acids, enamides and closely related reactants [7]. Although both ruthenium [8] and iridium catalysts [9] for homogeneous hydrogenation were known at an early stage, the development of effective enantioselective hydrogenation in these two spheres occurred much later. For ruthenium enantioselective hydrogenation, the spectacular efficiency of BINAP catalysts [10] developed by Noyori's group was first demonstrated for alkenes, and then in rather greater depth for ketones [11]. The high efficiency of iridium complexes in hydrogenation had been demonstrated 1073The Handbook of Homogeneous Hydrogenation. Edited by J. G. de Vries and C. J. Elsevier

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Section: Transient and Reactive Intermediates In Rhodium Enantioselecmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Mechanism of Enantioselective Hydrogenation

Brown¹

2006

The Handbook of Homogeneous Hydrogenation

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“…[6] Despite the resultant low concentration of [RhCl(PPh 3 ) 2 ], [7,8] it remains kinetically significant since H 2 addition to it is 10 4 times faster than that to [RhCl(PPh 3 ) 3 ]. [9] Indeed, based on results with [RhCl[P(p-tolyl) 3 . [10] A number of related species have been synthesised using bulky phosphines that mimic the H 2 addition product [RhCl(H) 2 (PPh 3 ) 2 ] and these culminated in a crystal structure for [RhCl(H) 2 (PtBu 3 ) 2 ].…”

Section: Introductionmentioning

confidence: 98%

Hydrogenation Studies Involving Halobis(phosphine)–Rhodium(i) Dimers: Use of Parahydrogen Induced Polarisation To Detect Species Present at Low Concentration

Colebrooke

Duckett

Lohman

et al. 2004

Chemistry A European J

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Reaction of [RhCl(PPh3)2]2 with parahydrogen revealed that the binuclear dihydride [Rh(H)2(PPh3)2mu-Cl)2Rh(PPh3)2] and the tetrahydride complex [Rh(H)2(PPh3)2(mu-Cl)]2 are readily formed. While magnetisation transfer from free H2 into both the hydride resonances of the tetrahydride and [Rh(H)2Cl(PPh3)3] is observable, neither transfer into [Rh(H)2(PPh3)2(mu-Cl)2Rh(PPh3)2] nor transfer between the two binuclear complexes is seen. Consequently [Rh(H)2(PPh3)2(mu-Cl)]2 and [Rh(H)2(PPh3)2(mu-Cl)2Rh(PPh3)2] are not connected on the NMR timescale by simple elimination or addition of H2. The rapid exchange of free H2 into the tetrahydride proceeds via reversible halide bridge rupture and the formation of [Rh(H)2(PPh3)2(mu-Cl)RhCl(H)2(PPh3)2]. When these reactions are examined in CD2Cl2, the formation of the solvent complex [Rh(H)2(PPh3)2(mu-Cl)2Rh(CD2Cl2)(PPh3)] and the deactivation products [Rh(Cl)(H)PPh3)2(mu-Cl)(mu-H)Rh(Cl)(H)PPh3)2] and [Rh(Cl)(H)(CD2Cl2)(PPh3)(mu-Cl)(mu-H)Rh(Cl)(H)PPh3)2] is indicated. In the presence of an alkene and parahydrogen, signals corresponding to binuclear complexes of the type [Rh(H)2(PPh3)2(mu-Cl)(2)(Rh)(PPh3)(alkene)] are detected. These complexes undergo intramolecular hydride interchange in a process that is independent of the concentration of styrene and catalyst and involves halide bridge rupture, followed by rotation about the remaining Rh-Cl bridge, and bridge re-establishment. This process is facilitated by electron rich alkenes. Magnetisation transfer from the hydride ligands of these complexes into the alkyl group of the hydrogenation product is also observed. Hydrogenation is proposed to proceed via binuclear complex fragmentation and trapping of the resultant intermediate [RhCl(H)2PPh3)2] by the alkene. Studies on a number of other binuclear dihydride complexes including [(H)(Cl)Rh(PMe3)2(mu-H)(mu-Cl)Rh(CO)(PMe3)], [(H)2Rh(PMe3)2(mu-Cl)2Rh(CO)(PMe3)] and [HRh(PMe3)2(mu-H)(mu-Cl)2Rh(CO)(PMe3)] reveal that such species are able to play a similar role in hydrogenation catalysis. When the analogous iodide complexes [RhIPPh3)2]2 and [RhI(PPh3)3] are examined, [Rh(H)2(PPh3)2(mu-I)2Rh(PPh3)2], [Rh(H)2(PPh3)2(mu-I)]2 and [Rh(H)2I(PPh3)3] are observed in addition to the corresponding binuclear alkene-dihydride products. The higher initial activity of these precursors is offset by the formation of the trirhodium phosphide bridged deactivation product, [[(H)(PPh3)Rh(mu-H)(mu-I)(mu-PPh2)Rh(H)(PPh3)](mu-I)2Rh(H)2PPh3)2]

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“…Of course there was already a tradition in place, based largely on careful kinetic studies of catalytic processes. This tradition was largely established through the study of enzymes [3], and although the experimental problems are distinct, the principles derived from enzymology can be applied to kinetic studies of homogeneous catalysis [4]. The results were, and continue to be, a central plank in understanding of the discipline.…”

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confidence: 99%

Mechanism in homogeneous catalysis; NMR as a prime mover

Brown

2004

Journal of Organometallic Chemistry

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Hydrogenation of tris(triphenylphosphine)chlororhodium(I)

Cited by 130 publications

References 0 publications

Mechanism of Enantioselective Hydrogenation

Mechanism of Enantioselective Hydrogenation

Hydrogenation Studies Involving Halobis(phosphine)–Rhodium(i) Dimers: Use of Parahydrogen Induced Polarisation To Detect Species Present at Low Concentration

Mechanism in homogeneous catalysis; NMR as a prime mover

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