Palladium-catalysed methoxycarbonylation of ethene with bidentate diphosphine ligands: a density functional theory study.

ABSTRACT

Catalytic methoxycarbonylation of ethene with a bidentate tertiary phosphine (DTBPX) and palladium has been explored at the B3PW91-D3/PCM level of density functional theory. Three different pathways for formation of methyl propanoate (MePro) have been studied, namely carbomethoxy (A), ketene (B) and hydride-hydroxyalkylpalladium pathways (C), the latter of which is favoured because it has the lowest overall kinetic barrier. After intermolecular methanolysis, a hydroxyalkylpalladium complex has been characterised on pathway C, which eventually leads to the low overall barrier to produce MePro. The possibility of copolymerisation leading to oligo-/polymers has also been considered. With a computed selectivity of >99% towards the formation of MePro and a reasonably low overall kinetic barrier of 23.0 kcal mol-1, pathway C appears to be the most plausible one. Consistent with experimental data, the overall barrier increases to 30.1 kcal mol-1 for a less bulky bidentate phosphine.