Iridium(III) hydride complexes for the catalytic enantioselective hydrogenation of imines

Considerable research during the past 20 years has produced remarkable catalysts based on Rh and Ru for enantioselective homogeneous hydrogenation of olefins and ketones where in many cases optical yields > 95% have been observed. On the other hand, few publications have appeared that deal with asymmetric hydrogenation of the C{double bond}N bond of imines to form chiral amines, the greatest success having been obtained by using in situ mixtures of M/chiral diphosphine/X (M = Rh{sup I} or Ir{sup I}, X = NEt{sub 3} or halide) but the nature and the mechanism of action of the catalyst is not well-defined. The authors report herein the discovery of a new class of iridium(III)-diphosphine-monohydrido complexes that are effective for asymmetric reduction of prochiral imines to the corresponding amine with high turnover numbers and moderate to good enantioselectivity.