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.

The oxidative carbonylation of styrene has been achieved in MeOH with known and new palladium(II) catalysts of general formulae [Pd(P–P)(MeCN)₂][PF₆]₂, [Pd(P–P)(bipy)][PF₆]₂, Pd(P–P)(OAc)₂, [Pd₂(cyclo-tetraphos)(MeCN)₄][PF₆]₄, [Pd₂(cyclo-tetraphos)(bipy)₂][PF₆]₄, Pd₂(cyclo-tetraphos)(OAc)₄ (P–P = 1,2-bis(diphenylphosphino)ethane), meso-2,3-bis(diphenylphosphino)butane or rac-2,3-bis(diphenylphosphino)butane; cyclo-tetraphos = cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane; bipy = 2,2′-bipyridine; OAc = acetate). The influence of various catalytic parameters on the overall conversion of styrene into carbonylated products and on the product selectivity has been studied by systematically varying the type of palladium initiator, the concentrations of organic oxidant (1,4-benzoquinone) and protic acid ( p-toluenesulfonic acid), and the CO pressure. This investigation has allowed a partial optimization of the process so as to obtain the largely predominant formation of either methyl cinnamate (highest selectivity 99%) or dimethyl phenylsuccinate (highest selectivity 88%).