Insertion of Carbon Monoxide into the Terminal Co–O Bond in a Methoxocobalt(III) Complex via a Tuneable Mechanism

The insertion of CO into the terminal Co–OMe bond in (Salophent-Bu)(MeOH)Co(III)(OMe), which led to the formation of (Salophent-Bu)(MeOH)Co(III)(COOMe), was investigated without and with the addition of free MeO–. The free MeO– concentration in the reaction system showed a nonlinear influence on the carbonylation rate, and the fastest rate was observed upon the addition of 1.8 equiv of MeO–, referred to as the methoxocobalt complex. Two classical migratory insertion-based pathways and a direct CO insertion-based pathway were envisioned to occur in the reaction system and be responsible for the production of (Salophent-Bu)(MeOH)Co(III)(COOMe). Two of these three reaction pathways could be promoted by the addition of MeO–, thus yielding an overall mechanism that could be tuned based on the concentration of free MeO– in the reaction system. Furthermore, the anionic [(Salophent-Bu)Co(III)(OMe)2]−, a key intermediate in the direct CO insertion-based pathway, was independently synthesized and characterized. The reactivity of (Salophent-Bu)(MeOH)Co(III)(COOMe) as a potential methoxy carbonyl radical-yielding reagent under light irradiation was also examined.