Development of phosphapalladacycles as potential catalysts for asymmetric synthesis

Abstract

A series of chiral tertiary phosphine ligands have been prepared via two synthetic approaches, namely through the optical resolution of racemic phosphines, and the asymmetric hydrophosphination reaction of enones with secondary phosphines promoted by chiral palladacycles. The ortho-palladation of the chiral phosphine ligands resulted in the formation of optically active CP-palladacycles containing a five-membered ring structure. The properties of the newly synthesized phosphapalladacycles were studied by NMR spectroscopy and single crystal X-ray crystallography. The potential use of the phosphapalladacycles as catalysts was explored in the enantioselective addition of various diarylphosphines to benzoquinone for generating P-stereogenic diarylphosphinites readily convertible into various phosphines and their derivatives.