Methoxycarbonylation versus Hydroacylation of Ethene; Dramatic Influence of the Ligand in Cationic Palladium Catalysis

The palladium-catalysed carbonylation of ethene in methanol shows acute sensitivity towards the diphosphine ligand used. Systems based on 1,3-bis(di-t-butylphosphino)propane afford catalysts for fast, selective methoxycarbonylation to methyl propionate; the corresponding catalyst based on 1,2-bis(di-t-butylphosphino)ethane hydroacylates ethene to diethyl ketone at high rates. The use of less sterically demanding ligands, hydrogen and auxiliary acid are explored and mechanistic implications discussed.