Hammett 13C NMR and X-ray studies of π-allylpalladium phosphinooxazoline chiral ligand complexes

Abstract

The transmission of substituent effects across the palladium center to the allyl carbons is monitored by 13C NMR and X-ray crystallography as a way to probe electronic asymmetry in chiral ligand design. Based on their similar chemical shift trends and X-ray structures, the π-allylpalladium intermediates provide a good model for early transition state reactions, which are less sensitive to electronic perturbations. Hammett analysis supports an electronic basis for enantioselection that increases as the transition state becomes later.