New Chiral Phosphine−Phosphite Ligands in the Enantioselective Rhodium-Catalyzed Hydroformylation of Styrene

Abstract

A series of chiral phosphine−phosphite ligands 1a−g have been synthesized from monophosphines 2−4, enantiomerically pure propene oxide or styrene oxide, and 3,3‘,5,5‘-tetra(tert-butyl)-2,2‘-bisphenol phosphorochloridite or enantiomerically pure 3,3‘-bis(trimethylsilyl)-2,2‘-binaphthol phosphorochloridites. These phosphine−phosphites have been used in the rhodium-catalyzed asymmetric hydroformylation of styrene. The structures of the active catalysts, [HRh(L−L)(CO)2] complexes (L−L = ligands 1a−g), have been studied using high-pressure NMR and IR spectroscopy. The obtained spectroscopic data show that the ligands coordinate in an equatorial−apical fashion to the rhodium center with the phosphine in apical position. Systematic variation in configuration of the stereocenters at both the ligand bridge and the phosphine moiety revealed a remarkable cooperative effect on the selectivity of the hydroformylation reaction. Under mild reaction conditions ee’s of 63% and regioselectivities up to 92% toward 2-phenylp...