Drent et al. have recently reported on a neutral Pd(II)-based complex with a bidentate sulfonate ligand that is able to copolymerize ethylene (E) and methacrylate (MA) into linear EMA polymers. We report here on a theoretical study that examines the Drent system and compares it to the cationic Brookhart catalyst, which affords branched EMA polymers with MA units at the end of the branches.

Drent et al. [Chem. Commun. 2002, 9, 964] have recently shown that a neutral (P−O)Pd(II) catalyst based on o-alkoxy derivatives of diphenylphosphinobenzene sulfonic acid (1a) can perform nonalternating CO/C2H4 copolymerization in which the resulting polyketone can have one or more subsequent ethylene units. We have analyzed this catalyst by comparing it to a cationic palladium catalyst, [(P−P)Pd(II)+] (1c), (P−P) = dppp = Ph2P−(CH2)3−PPh2, that affords polyketones with strictly alternating CO and C2H4 units. We have also investigated a derivative (1b) of 1a in which the o-methoxy substituents were replaced by a o-isopropyl group in order to investigate whether increasing the steric bulk enhances the degree of nonalternation.