Palladium(II)-assisted copolymerization of ethylene and CO: Influence of the chain end on the regularity of the polymer

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 PH2CH=CHPH2 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 pi-complex and the high barrier (+78 kJ/mol) associated with insertion of ethylene into the Pd-C(2)H(4)COR bond. On the other hand, insertion of CO into a Pd-C(2)H(4)COR bond is favored by a rather stable CO precursor complex (-32 kJ/mol) and by a low activation barrier (+49 kJ/mol).