Chiral complexes of RhI containing binaphthalene-core P,S-heterobidentate ligands - Synthesis, characterization, and catalytic activity in asymmetric hydrogenation of α,β-unsaturated acids and esters

The enantiopure complexes 3a and 3b [Rh(NBD)(P,S)]+BF4- [P,S = (S)-2-(diphenylphosphanyl)-2′-(methylthio)-1,1′-binaphthalene (a); (S)-2-(diphenylphosphanyl)-2′-(isopropylthio)-1,1′-binaphthalene (b) have been prepared from [Rh(NBD)(THF)2]+BF4- by reaction with a stoichiometric amount of the appropriate P,S-heterobidentate ligand. Single-crystal X-ray analysis of the S-methyl derivative shows that the seven-membered chelate ring is locked in a boat-like conformation with the methyl group in the equatorial position. Variable-temperature NMR measurements confirm that this conformation is maintained in solution and that the dynamic behaviour displayed by the complex is due to pseudo-rotation of the diolefin. Complexes 3 have been tested in the asymmetric hydrogenation of α,β-unsaturated acids and esters. Enantioselectivities of up to 60% ee have been recorded. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.