[Co(NHC)(CO)3]: Isolation and Reactivity Study of a Model 17-Electron Species in the Oxo Process

[Co­(L)­(CO)3]2 (L = CO or PR3) catalyzed hydroformylation of olefins is among the most successful homogeneous organometallic catalysis. The bimetallic [Co­(L)­(CO)3]2 complex exists in equilibrium with its mononuclear 17-electron [Co­(L)­(CO)3] metalloradical. However, isolation of the mononuclear metalloradical is unknown, and hence the role of this species in the catalytic cycle is difficult to study. Herein, we report the isolation of [Co­(L)­(CO)3] using ring-expanded N-heterocyclic carbene (reNHC) ligands. Isolation of this complex enabled us to examine feasibility of putative termolecular H2 activation by the [Co­(L)­(CO)3] metalloradicals. The kinetic experiments revealed that [Co­(reNHC)­(CO)3] does not activate H2 via a previously proposed termolecular mechanism but via a bimolecular mechanism. The result obtained here will contribute to design a cobalt carbonyl complex that activates H2 under mild conditions and to develop a more energy efficient oxo process based on economical cobalt catalysts.