Evidence for the hydride mechanism in the methoxycarbonylation of ethene catalysed by palladium-triphenylphosphine complexes

Analysis of the phosphorus containing by-products from the catalytic methox ycarbonylation of ethene using a palladium triphenylphosphine complex with a combination of High Performance Liquid Chromatography (HPLC) and Mass Spe ctrometry (MS) indicated increasing levels of phosphonium salts through the course of the reaction, major ones being methyltriphenylphosphonium, ethyl triphenylphosphonium and 3-oxopentyltriphenylphosphonium (CH3CH2C(=O)CH2CH2 PPh3) cations, isolated as the sulfonate salts. The latter are shown to be produced by metal mediated pathways and believed to be indicative of the op eration of the hydride mechanism.