Synthesis and asymmetric catalytic application of chiral imidazolium-phosphines derived from (1R,2R)-trans-diaminocyclohexane

Reaction between a chiral imidazole-amine precursor derived from (1R,2R)-trans-diaminocyclohexane and (PCl)-Cl-1 (where P-1 = PPh2, P(1,3,5-Me3C6H3)2, P(2,2'-O,O'-(1,1'-biphenyl), P((R)-(2,2'-O,O'-(1,1'-binaphthyl))) and P((S)-(2,2'-O,O'-(1,1'-binaphthyl)))) followed by RX (where R = Pr-n, Pr-i, CHPh2, X = Br; R = Pr-i, X = 1), respectively, gives a selection of chiral imidazolium-phosphine compounds. Deprotonation of the imidazolium Salt gives the corresponding NHC-P ligands that can be used in metal-mediated asymmetric catalytic applications. Catalytic reactions show that NHC-P ligands give a significantly greater rate of reaction for a palladium catalysed allylic substitution reaction in comparison to analogous di-NHC or NHC-imine ligands and that NHC-P hybrids are also effective for iridium catalysed transfer hydrogenation. (c) 2005 Elsevier B.V. All rights reserved.