Isolation of a Bimetallic Cobalt(III) Nitride and Examination of Its Hydrogen Atom Abstraction Chemistry and Reactivity toward H.

Room temperature photolysis of the bis(azide)cobaltate(II) complex [Na(THF)][(guan)Co(N)] (guan = [(BuCN)C(NDipp)], Dipp = 2,6-diisopropylphenyl) () in THF cleanly forms the binuclear cobalt nitride Na(THF){[(guan)Co(N)](μ-N)} (). Compound represents the first example of an isolable, bimetallic cobalt nitride complex, and it has been fully characterized by spectroscopic, magnetic, and computational analyses. Density functional theory supports a Co═N═Co canonical form with significant π-bonding between the cobalt centers and the nitride atom. Unlike other group 9 bridging nitride complexes, no radical character is detected at the bridging N atom of . Indeed, is unreactive toward weak C-H donors and even cocrystallizes with a molecule of cyclohexadiene (CHD) in its crystallographic unit cell to give ·CHD as a room temperature stable product. Notably, addition of pyridine to or photolyzed solutions of [(guan)Co(N)(py)] () leads to destabilization via activation of the nitride unit, resulting in the mixed-valent Co(II)/Co(III) bridged imido species [(guan)Co(py)][(guan)Co](μ-NH)(μ-N) () formed from intermolecular hydrogen atom abstraction (HAA) of strong C-H bonds (BDE ∼ 100 kcal/mol). Kinetic rate analysis of the formation of in the presence of CH or CD gives a KIE = 2.5 ± 0.1, supportive of a HAA formation pathway. The reactivity of our system was further probed by photolyzing benzene/pyridine solutions of under H and D atmospheres (150 psi), which leads to the exclusive formation of the bis(imido) complexes [(guan)Co(μ-NH)] () and [(guan)Co(μ-ND)] (), respectively, as a result of dihydrogen activation. These results provide unique insights into the chemistry and electronic structure of late 3d metal nitrides while providing entryway into C-H activation pathways.