Effect of the Ancillary Ligand on the Mechanism for CO Migratory Insertion in High-Valent Oxorhenium Complexes

Several oxorhenium complexes bearing an SSS pincer ligand were isolated and characterized, and their reactivity with carbon monoxide was explored. The corresponding oxorhenium­(V) acyl derivatives were also isolated and characterized. Carbonylation reactions required high pressures (400 psi) and temperatures (50 °C). The mechanism for carbonylation was explored with DFT (M06) calculations and revealed that the most likely mechanism for carbonylation involved stepwise formation of CO adducts followed by migration of the carbonyl ligand to the alkyl/aryl groups.