Asymmetric hydroformylation of styrene with rhodium complexes of sulfonated diphosphines in aqueous systems

Abstract

Hydroformylation of styrene has been performed using as catalyst precursor [Rh(μ-OMe)(cod)] 2 (cod=1,5-cyclooctadiene) associated with the sulfonated diarylphosphines dpppts [tetrasulfonated 1,3-bis(diphenylphosphino)propane], dppbts [tetrasulfonated 1,4-bis(diphenylphosphino)butane], ( R, R)-CBDTS [1,2-bis(diphenylphosphinomethyl)cyclobutane] and ( S, S)-BDPPTS [2,4-bis(diphenylphosphino)pentane] in aqueous solutions. The best results were obtained with the dpppts system using water–methanol as the solvent at 14 atm, a [P]/[Rh] ratio of 4 and a temperature range of 50–80°C. Under these conditions, the rhodium–dpppts catalyst gives regioselectivities up to 93% in 2-phenylpropanal. The rhodium–dppbts system gives higher conversions (up to 91%), but lower regioselectivity in 2-phenylpropanal (89%). The asymmetric hydroformylation of styrene using CBDTS as the ligand provided one of the highest enantioselectivity reported up to now for this reaction using sulfonated diphosphines (17% e.e. in S-2-phenylpropanal), although BDPPTS gives a slightly lower enantioselectivity of 14%, but with a very low conversion.