Ligand effects in the non-alternating CO–ethylenecopolymerization by palladium(ii) catalysis

Abstract

In this paper we report on a comparative study of the non-alternating CO–C₂H₄ copolymerization catalyzed by neutral Pd^II complexes with the phosphine–sulfonate ligands bis(o-methoxyphenyl)phosphinophenylenesulfonate and bis(o-methoxyphenyl)phosphino-ethylenesulfonate. The former ligand, featuring a lower skeletal flexibility, has been found to form more active catalysts as well as produce polyketones with higher molecular weight and higher extra-ethylene incorporation. Operando high-pressure NMR studies have allowed us to intercept, for the first time, Pd^II(phosphine–sulfonate) β-chelates in the non-alternating copolymerization cycle, while model organometallic reactions have contributed to demonstrate that Pd^II (phosphine–sulfonate) fragments do not form stable carbonyl complexes. The opening of the β-chelates has been found to be a viable process by either comonomer, which contrasts with the behaviour of Pd^II (chelating diphosphine) catalysts for the perfectly alternating copolymerization.