Reaction of CO with a Methylpalladium Heterocyclic Carbene Complex: Product Decomposition Routes - Implications for Catalytic Carbonylation Processes

The methylpalladium-heterocyclic carbene dimer [PdMe(tmiy)(μ-Cl]2 (1) (tmiy = 1,3,4,5-tetramethylimidazolin-2-ylidene) reacts with CO to yield [PdMeCl(tmiy)CO] (2) through cleavage of the Cl bridge. Complex 2 decomposes in solution to yield the 1,2,3,4,5-pentamethylimidazolium ion (I) along with a small amount of 2-acyl-1,3,4,5-tetramethylimidazolium (II). In the presence of AgBF4 the dimer reacts with CO to give II as the major product. The reaction sequence is interpreted as evidence for CO insertion into the Pd-Me bond of 2 and also represents a possible mode of deactivation for potential CO/ethylene copolymerization catalysts based on heterocylic carbene complexes.