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 PdII 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, PdII(phosphine-sulfonate) b-chelates in the non-alternating copolymerization cycle, while model organometallic reactions have contributed to demonstrate that PdII (phosphine-sulfonate) fragments do not form stable carbonyl complexes. The opening of the b-chelates has been found to be a viable process by either comonomer, which contrasts with the behaviour of PdII (chelating diphosphine) catalysts for the perfectly alternating copolymerization.