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.

Asymmetric hydrogenation of olefins is one of the most useful reactions for the synthesis of optically active compounds, especially in industry. However, the application range of the catalysts developed so far is limited to alkenes with a coordinating functional group or an aryl substituent next to the double bond. We have found a class of chiral iridium catalysts that give high enantioselectivity in the hydrogenation of unfunctionalized, trialkyl-substituted olefins. Because these catalysts do not require the presence of any particular functional group or aryl substituent in the substrate, they considerably broaden the scope of asymmetric hydrogenation.

[reaction: see text] A series of chiral phosphino-imidazolines (PHIM ligands) 1a-j with different substituents at the stereogenic center, the nitrogen atom of the imidazoline ring, and at the phosphorus atom were synthesized. Iridium complexes derived from these ligands have been evaluated as catalysts for the enantioselective hydrogenation of unfunctionalized olefins. In several cases, higher enantiomeric excesses were observed than with analogous phosphino-oxazoline ligands.

[reaction: see text] New Ir-SimplePHOX complexes Ir-6-Ir-9 catalyze the quantitative, highly enantioselective hydrogenation of a range of unfunctionalized and functionalized olefins. Synthesis, catalytic results, and X-ray crystal structures are presented here.

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.