Ligand-Dependent Diastereoselectivity in the Palladium-Catalyzed Copolymerization of Styrene with Carbon Monoxide

Abstract

[(LL′)Pd(H2O)](OTf)2 complexes, in which LL′ is a chelate ligand containing the chiral 4-benzyl-4,5-dihydrooxazole moiety and either pyridin-2-yl or 2-(diphenylphosphino)phenyl substituents, catalyze the copolymerization of styrene with carbon monoxide with an isotactic or prevailingly syndiotactic microstructure, respectively. The chiroptical properties of the copolymers and model studies for carbon monoxide and olefin insertion on related Pd complexes suggest that the reason for the different stereochemistry of the copolymers is a site-selective coordination of the olefin in the intermediates containing the PN ligand; a lower regioselectivity in the coordination and a different coordination site lead to the different diastereoselectivity for the copolymer formation by the complex containing the NN′-ligand.