CHIRAL POISONING OF RAC-DIOP IRIDIUM COMPLEXES IN THE CATALYTIC ENANTIOSELECTIVE HYDROGENATION OF IMINES

Dimeric Ir(III) complexes [Ir(P-P)HI2](2) (P-P = enantiopure bisphosph ine) have previously been shown to be efficient catalysts for the enan tioselective hydrogenation of imines, In the present study we have pre pared the analogues using rac-diop. Among the possible dimers, there w as only a slight preference for the mu-I-2 heterodimer {[Ir(R,R)-diopH I(2)][Ir(S,S)-diopHI(2)]}. Although this mixture of dimers was a moder ately good catalyst for the hydrogenation of imines, it showed no enan tioselectivity, as expected, Addition of the readily available aminoph osphinephosphinite ligand, (+)-(S)-pronop, to this dimer mixture in a ratio of [(S)-pronop]:[Ir](tot) = 1:1 produced a poor catalyst which e ffected only a few turnovers in 100h. However, addition of (+)-(S)-pro nop to this dimer mixture in a ratio of [(S)-pronop]:[Ir](tot) = 1:2 p roduced an effective catalyst for the enantioselective hydrogenation o f imines, Significant chiral amplification was not observed in catalys is with dimers prepared from nonracemic diop.