Isolation of a Bimetallic Cobalt(III) Nitride and Examination of Its Hydrogen Atom Abstraction Chemistry and Reactivity toward H₂

Room temperature photolysis of the bis­(azide)­cobaltate­(II) complex [Na­(THF)x]­[(ketguan)­Co­(N3)2] (ketguan = [(tBu2CN)­C­(NDipp)2]−, Dipp = 2,6-diisopropylphenyl) (3a) in THF cleanly forms the binuclear cobalt nitride Na­(THF)4{[(ketguan)­Co­(N3)]2(μ-N)} (1). Compound 1 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 CoIIINCoIII 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 1. Indeed, 1 is unreactive toward weak C–H donors and even cocrystallizes with a molecule of cyclohexadiene (CHD) in its crystallographic unit cell to give 1·CHD as a room temperature stable product. Notably, addition of pyridine to 1 or photolyzed solutions of [(ketguan)­Co­(N3)­(py)]2 (4a) leads to destabilization via activation of the nitride unit, resulting in the mixed-valent Co­(II)/Co­(III) bridged imido species [(ketguan)­Co­(py)]­[(ketguan)­Co]­(μ-NH)­(μ-N3) (5) formed from intermolecular hydrogen atom abstraction (HAA) of strong C–H bonds (BDE ∼ 100 kcal/mol). Kinetic rate analysis of the formation of 5 in the presence of C6H12 or C6D12 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 4a under H2 and D2 atmospheres (150 psi), which leads to the exclusive formation of the bis­(imido) complexes [(ketguan)­Co­(μ-NH)]2 (6) and [(ketguan)­Co­(μ-ND)]2 (6-D), 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.在室温下，对双叠氮合钴(II)酸盐配合物[Na(四氢呋喃(THF))ₓ][(ketguan)Co(N₃)₂]（其中ketguan = [(tBu₂CN)C(NDipp)₂]⁻，Dipp = 2,6-二异丙基苯基）（化合物3a）在四氢呋喃(THF)中的溶液进行光解，可高选择性地得到双核钴氮化物配合物[Na(THF)₄]{[(ketguan)Co(N₃)]₂(μ-N)}（化合物1）。化合物1是首例可分离的双金属钴氮化物配合物，且已通过光谱学、磁学及计算分析完成全面表征。密度泛函理论计算表明，该配合物存在Co(III)=N=Co(III)的经典共振结构，钴中心与氮原子之间存在显著的π成键作用。与其他第9族桥联氮化物配合物不同，化合物1的桥连氮原子未检测到自由基特性。事实上，化合物1与弱C-H供体均不发生反应，甚至可在其晶体学晶胞中与一分子环己二烯(CHD)共结晶，得到室温下稳定的产物1·CHD。值得注意的是，向化合物1或[(ketguan)Co(N₃)(吡啶(py))]₂（化合物4a）的光解溶液中加入吡啶，会通过活化氮桥单元导致体系不稳定，最终经由分子间氢原子提取(HAA)强C-H键（键解离能约100 kcal/mol），得到混合价态Co(II)/Co(III)的桥联亚氨基物种[(ketguan)Co(py)][(ketguan)Co](μ-NH)(μ-N₃)（化合物5）。在C₆H₁₂或C₆D₁₂存在下对化合物5的生成过程进行动力学速率分析，得到动力学同位素效应(KIE) = 2.5 ± 0.1，这一结果佐证了该反应通过HAA路径进行。我们进一步通过在氢气(H₂)和氘气(D₂)气氛（150 psi）下光解化合物4a的苯/吡啶溶液，对该体系的反应性进行了探究，结果分别专一性地生成了双亚氨基配合物[(ketguan)Co(μ-NH)]₂（化合物6）和[(ketguan)Co(μ-ND)]₂（化合物6-D），这一过程源于双氢活化反应。上述研究结果不仅为后过渡3d金属氮化物的化学性质与电子结构提供了独特的见解，同时也为C-H活化路径的研究提供了可行的切入点。