Mechanism of the palladium-catalysed electrosynthesis of diethyl carbonate from carbon monoxide and ethanol

摘要

A mechanism is proposee for the PdBr_2(PPh_3)_2-catalysed electrosynthesis of diethyl carbonate from carbon monoxide and ethanol,proceeding at room temperature and atmospheric CO pressure.The mechanism is investigated by cyclic voltammetry and ~31P NMR spectroscopy.The active Pd~O complex able to coordinate CO is generated by the chemical reduction of PdBr_2(PPh_3)_2 by EtO~-ions generated from EtOH at the cathode.After reaction of EtO~-ions with Pd~O(PPh_3)_2(CO),the ensuing anionic complex [(PPh_3)_2Pd~O-COOEtr is oxidized at the anode in a key step leading to BrPd1I-COOEt(PPh_3)_2.A nucleophilic attack of ethoxide on the latter generates diethyl carbonate and the Pd~O complex active in the catalytic cycle.