Deuterium labelling evidence for a hydride mechanism in the formation of methyl propanoate from carbon monoxide, ethene and methanol catalysed by a palladium complex

Reaction of ethene with CO in CH3OD in the presence of a catalyst prepared in situ from [Pd(DBPMB)(DBA)] (DBPMB=1,2-bis[(di-tert-butyl)phosphinomethyl] benzene, DBA=dibenzylideneacetone) and methanesulfonic acid under conditions of good gas mixing gives a 1:1 mixture of CH2DCH2CO2Me and CH3CHDCO2Me with no H incorporated into the CH3OD. If the gas mixing is less efficient, the methyl propanoate has 0-5 D atoms incorporated in the ethyl group, CH3OD exchanges to give increasing amounts of CH3OH throughout the reaction and there is a slight increase in the less deuteriated products with reaction time. Significant D incorporation into unreacted ethene is also observed. These results are interpreted in terms of a hydride mechanism with the rates of the individual steps under conditions of good mixing being: reversible H migration to coordinated ethene >CO coordination much greater thanC(2)H(4) exchange >H/D exchange.