Enantioselective hydrogenation of olefins with phosphinooxazoline-iridium catalysts

Cationic iridium complexes with chiral phosphinooxazoline ligands are effic ient catalysts for the enantioselective hydrogenation of olefins. The compl exes are readily prepared, air-stable, and easy to handle. In contrast to c hiral rhodium- and ruthenium-phosphine catalysts, they do not require the p resence of a polar coordinating group near the C=C bond. In the hydrogenati on of unfunctionalized trisubstituted 1,2-diaryl-olefins, high enantioselec tivities of >95% ee with full conversion and turnover frequencies of >7,000 h(-1) can be achieved, using 0.1 mol% of catalyst with tetrakis[3,5-bis(tr ifluoromethyl)phenyl] berate (TFPB or BARF) as the counterion. The correspo nding hexafluorophosphate or tetrafluoroborate salts give low conversion du e to deactivation of the catalyst during the reaction. Substrates with pola r substituents such as allylic alcohols, on the other hand, afford better r esults with the hexafluorophosphate salts. (C) 2000 Wiley-Liss, Inc.