Ligand effects in the non-alternating CO-ethylene copolymerization by palladium(ii) catalysis

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.