Cooperative Heterobimetallic CO Activation Involving a Mononuclear Aluminum(II) Intermediate.

Molecular chemistry of aluminum most commonly involves Al ions due to their noble gas electronic configurations. In contrast, the chemistry of Al ions is underexplored and may contain undiscovered reaction manifolds. Here, we report the CO activation chemistry of a transient Al intermediate supported by a chelating, dianionic ligand and investigate the electronic structure details and reaction mechanisms required to access this reactivity. We found that a heterobinuclear complex, (NON)Al-FeCp(CO) (), undergoes Al-Fe bond homolysis at ambient conditions to reveal the [(NON)Al]/[CpFe(CO)] radical pair . The presence of predominantly Al-centered spin density (i.e., an Al ion) within this radical pair was established by quantum-chemical calculations and with experiments in which radical scavengers (TEMPO, benzophenone) induce Al-Fe bond homolysis. Exposure of to CO atmosphere resulted in insertion of CO into the Al-Fe bond. This net 2-electron CO reduction process was computationally modeled using density functional theory and direct dynamics simulations, revealing that reduction involves two 1-electron steps and, thus, depends on stabilization of high-energy [CO] by coordination to aluminum. This mechanism for CO activation is unexpected given the canonical predisposition of CO for multielectron reduction processes and demonstrates the possibility of discovering new reaction profiles using earth-abundant elements in unusual oxidation states.