Palladium(II)-Assisted Copolymerization of Ethylene and CO: Influence of the Chain End on the Regularity of the Polymer

Abstract

A theoretical study based on nonlocal density functional theory has been carried out on the Pd(II)-assisted homogeneous catalytic copolymerization of olefin and carbon monoxide, where the catalytic center is modeled by Pd(II) coordinated to PH2CHCHPH2 and the olefin is modeled by C2H4. The investigation concentrated on the energetics of the chain propagation mechanism in the presence of a copolymer chain end with a carbonyl group coordinated to the metal center. With CO misinsertion ruled out in a previous work,1 the present investigation rules out ethylene misinsertion into a growing polyketone chain due to the lack of a thermodynamically stable ethylene π-complex and the high barrier (+78 kJ/mol) associated with insertion of ethylene into the Pd−C2H4COR bond. On the other hand, insertion of CO into a Pd−C2H4COR bond is favored by a rather stable CO precursor complex (−32 kJ/mol) and by a low activation barrier (+49 kJ/mol).