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

Abstract

Reaction between a chiral imidazole–amine precursor derived from (1 R,2 R)- trans-diaminocyclohexane and P 1Cl (where P 1 = PPh 2, P(1,3,5-Me 3C 6H 3) 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 = n Pr, i Pr, CHPh 2, X = Br; R = i Pr, X = I), 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.