Isolation and characterization of an iodide bridged dimeric palladium complex in carbonylation of methanol

Palladium-catalyzed carbonylation of methanol in presence of iodide promoters was investigated. Iodide bridged palladium dimeric complex, [PPh3CH3]2[Pd2I6] was isolated from the carbonylation reaction mixture and characterized using X-ray crystallography. Reaction mechanism was proposed based on IR and UV spectroscopic characterizations of catalytic species involved in the catalytic cycle. The isolated dimeric palladium species, [Pd2I6]2− underwent carbonylation to give monomeric species [PdI3CO]− at atmospheric pressure of carbon monoxide. It was also observed that PPh3 plays an important role to avoid catalyst deactivation at higher temperatures. Turnover frequency (TOF) of 1052 h−1 was achieved using Pd(OAc)2–HI–PPh3 catalyst system at 175 °C.