Ruthenium catalysis Noyori asymmetric hydrogenation

The first transition metal catalysis using BINAP-ruthenium complex in homogeneous phase for enantioselective hydrogenation of P-ketoesters was developed by Noyori and co-workers [31]. Genet and co-workers described a general synthesis of chiral diphosphine ruthenium(II) catalysts from commercially available (COD)Ru(2-methylallyl)2 [32]. These complexes preformed or prepared in situ have been found to be very efficient homogeneous catalysts for asymmetric hydrogenation of various substrates such as P-ketoesters at atmospheric pressure and at room temperature [33]. 

The mechanism of the catalysis (Scheme 20.8) is quite unlike that of the rhodium-DuPhos catalysis of prochiral olefins described above, since the ketone substrate does not bind to the metal (ruthenium) atom. When a substrate binds the metal, as in the rho-dium-DuPhos systems, there are opportnnities for unwanted pathways that terminate the catalysis. On the other hand, a conseqnence of the metal being protected by its ligands in the Noyori-Ikariya catalysis in principle rednces the likelihood of catalyst deactivation and increases the expectation for achieving very high catalyst utilization (substrate/catalyst ratios). Thus, in the asymmetric hydrogenation of acetophenone to (i )-l-phenylethanol, Noyori et al. reported an astounding molar snbstrate/catalyst ratio of 2,400,000 1. ... 

Review. Noyori has reviewed homogeneous asymmetric catalysis, particularly by complexes of (R)- and (S)-BINAP with ruthenium. He suggests possible reasons for the high efficiency of Ru-BINAP complexes in catalytic hydrogenation (40 references). 

The present interest in asymmetric catalysis was demonstrated by awarding Nobel prizes to three winners W. S. Knowles (USA) for elaboration of rhodium complex catalysts effective in asymmetric synthesis of anti-Parkinson medicine, R. Noyori (Japan) for elaboration of a new catalytic system based on chiral ruthenium-phosphine complex catalysts that are very effective in hydrogenation reactions, and B. Sharpless (USA) for elaboration of epoxidation and other reactions under the action of chiral titanium complexes. 

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