The preparation and properties of tris(triphenylphosphine)halogenorhodium(I) and some reactions thereof including catalytic homogeneous hydrogenation of olefins and acetylenes and their derivatives
01 Jan 1966-Journal of The Chemical Society A: Inorganic, Physical, Theoretical (The Royal Society of Chemistry)-pp 1711-1732
TL;DR: In this paper, the tris(triphenylphosphine) complexes are exceedingly active catalysts for the rapid and homogeneous hydrogenation, at ca. 1 atmosphere of hydrogen pressure and room temperature, of unsaturated compounds containing isolated olefinic and acetylenic linkages.
Abstract: Tris(triphenylphosphine)chlororhodium(I), RhCl(PPh3)3, has been prepared by the interaction of an excess of triphenylphosphine with rhodium(III) chloride hydrate in ethanol; the corresponding bromide and iodide are also described. The dissociation of the complex in various solvents has been investigated, and its reactions with hydrogen, ethylene, and carbon monoxide and aldehydes studied. Dihydrido- and ethylene complexes have been isolated and studied by nuclear magnetic resonance (n.m.r.) spectroscopy. Approximate values for the formation constants of ethylene and propylene complexes have been obtained; the latter is lower by a factor of over 103. By electron spin resonance spectroscopy, the complex RhCl(PPh3)3 has been shown to contain trace amounts of a paramagnetic species, probably a rhodium(II) complex.In homogeneous solution the tris(triphenylphosphine) complexes are exceedingly active catalysts for the rapid and homogeneous hydrogenation, at ca. 1 atmosphere of hydrogen pressure and room temperature, of unsaturated compounds containing isolated olefinic and acetylenic linkages.The rates of hydrogenation of hept-1-ene, cyclohexene and hex-1-yne have been studied quantitatively and the dependence on factors such as substrate and catalyst concentration, temperature, and pressure determined. The data can be accommodated by a rate expression of the form: Rate =Kp[S][A]//1 +K1p+K2[S] where [S] and [A] are the olefin and catalyst concentrations, respectively, and p is the concentration of hydrogen in solution.From the data for cyclohexene the activation energy for the rate determining step is Ea= 22·9 kcal. mole–1(ΔH‡= 22·3 kcal. mole–1) and the value of ΔS‡= 12·9 e.u.It is shown that the rate of hydrogen–deuterium exchange under selected conditions is quite slow compared with the rates of hydrogenation of olefins and, furthermore, that when H2–D2 mixtures are used in the reactions, alkanes and dideuteroalkanes are the major products. Reductions of maleic and fumaric acids with deuterium shows that cis-addition occurs preferentially. Similarly, in the reduction of hex-2-yne to n-hexane, cis-hex-2-ene is found to be the major olefin intermediate.A mechanism for the hydrogenation is proposed in which the metal complex serves as a template to which a hydrogen molecule and an olefin molecule are briefly co-ordinated before transfer of one to the other takes place. The low kinetic isotope effect (rate H2/rate D2= 0·9) suggests that synchronous breaking of Rh–H bonds and making of C–H bonds takes place in the transition state involving two simultaneous three-centre interactions.
Citations
More filters
TL;DR: The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies, and asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines has become one of the most efficient methods for constructing chiral compounds.
Abstract: The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.1,2 Among all asymmetric catalytic methods, asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines, have become one of the most efficient methods for constructing chiral compounds.3 The development of homogeneous asymmetric hydrogenation was initiated by Knowles4a and Horner4b in the late 1960s, after the discovery of Wilkinson’s homogeneous hydrogenation catalyst [RhCl(PPh3)3]. By replacing triphenylphosphine of the Wilkinson’s catalystwithresolvedchiralmonophosphines,6Knowles and Horner reported the earliest examples of enantioselective hydrogenation, albeit with poor enantioselectivity. Further exploration by Knowles with an improved monophosphine CAMP provided 88% ee in hydrogenation of dehydroamino acids.7 Later, two breakthroughs were made in asymmetric hydrogenation by Kagan and Knowles, respectively. Kagan reported the first bisphosphine ligand, DIOP, for Rhcatalyzed asymmetric hydrogenation.8 The successful application of DIOP resulted in several significant directions for ligand design in asymmetric hydrogenation. Chelating bisphosphorus ligands could lead to superior enantioselectivity compared to monodentate phosphines. Additionally, P-chiral phosphorus ligands were not necessary for achieving high enantioselectivity, and ligands with backbone chirality could also provide excellent ee’s in asymmetric hydrogenation. Furthermore, C2 symmetry was an important structural feature for developing new efficient chiral ligands. Kagan’s seminal work immediately led to the rapid development of chiral bisphosphorus ligands. Knowles made his significant discovery of a C2-symmetric chelating bisphosphine ligand, DIPAMP.9 Due to its high catalytic efficiency in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids, DIPAMP was quickly employed in the industrial production of L-DOPA.10 The success of practical synthesis of L-DOPA via asymmetric hydrogenation constituted a milestone work and for this work Knowles was awarded the Nobel Prize in 2001.3k This work has enlightened chemists to realize * Corresponding author. 3029 Chem. Rev. 2003, 103, 3029−3069
1,995 citations
1,358 citations
673 citations
TL;DR: The intent is to provide a comprehensive overview of all work in the field up to December 2016, organized according to reaction class, which allows for comparison of similar reactions catalyzed by ArMs constructed using different metallocofactor anchoring strategies, cofactors, protein scaffolds, and mutagenesis strategies.
Abstract: The incorporation of a synthetic, catalytically competent metallocofactor into a protein scaffold to generate an artificial metalloenzyme (ArM) has been explored since the late 1970’s. Progress in the ensuing years was limited by the tools available for both organometallic synthesis and protein engineering. Advances in both of these areas, combined with increased appreciation of the potential benefits of combining attractive features of both homogeneous catalysis and enzymatic catalysis, led to a resurgence of interest in ArMs starting in the early 2000’s. Perhaps the most intriguing of potential ArM properties is their ability to endow homogeneous catalysts with a genetic memory. Indeed, incorporating a homogeneous catalyst into a genetically encoded scaffold offers the opportunity to improve ArM performance by directed evolution. This capability could, in turn, lead to improvements in ArM efficiency similar to those obtained for natural enzymes, providing systems suitable for practical applications and ...
504 citations