Cationic iridium complexes with chiral P,Nligands and tetrakis [3,5-(trifluoromethyl)phenyl]borate (BAr F ) as the counterion are efficient homogeneous catalysts for the enantioselective hydrogenation of olefins. The complexes are readily prepared, air-stable, and easy to handle. In contrast to chiral rhodium-and ruthenium-phosphine catalysts, they do not require the presence of a polar coordinating group near the C C bond. In the hydrogenation of unfunctionalized arylolefins, high enantioselectivities of > 95% ee with turnover numbers of up to 5000 and turnover frequencies of > 5000 h À1 have been achieved.

Iridium complexes derived from chiral P,N ligands are efficient catalysts for the enantioselective hydrogenation of 2-aryl-substituted terminal alkenes. Using 0.1 -1 mol % of catalyst at room temperature and ambient hydrogen pressure, high enantioselectivities (88 -94% ee), full conversions after short reaction times and essentially quantitative yields were obtained for a range of differently substituted 2-arylalkenes. Among six iridium complexes that were tested, the most selective catalyst was a complex with a phosphinite-oxazoline ligand derived from threonine (IrThrePHOX). In contrast to the hydrogenation of trisubstituted alkenes, a strong pressure effect was observed for this class of substrates. Lowering the hydrogen pressure from 50 to 1 bar resulted in a strong increase of the ee values.

Organic chemistryOrganic chemistry Z 0200 Iridium-Catalyzed Enantioselective Hydrogenation of Olefins. -[ca. 40 refs.]. -(PFALTZ*, A.; BLANKENSTEIN, J.; HILGRAF, R.; HOERMANN, E.; MCINTYRE, S.; MENGES, F.; SCHOENLEBER, M.; SMIDT, S. P.; WUESTENBERG, B.; ZIMMERMANN, N.; Adv. Synth. Catal. 345 (2003) 1-2, 33-43; Dep. Chem., Univ. Basel, CH-4056 Basel, Switz.; Eng.) -Lindner 18-253