Synthesis and reactivity of cobalt dinitrogen complex supported by nonsymmetrical pincer ligand

Yuanjin Chen, Xianghui Shi, Dajiang Huang, Junnian Wei*, Zhenfeng Xi*

Chinese Chem. Lett., 2023. DOI: 10.1016/j.cclet.2023.109292.

        A nonsymmetrical PNN pincer ligand [6-(^tBu₂PNH)C₅H₄N-2-(3-Mes)C₃H₂N₂] and its corresponding cobalt-N₂ complex were synthesized and characterized. By the stoichiometric reaction of the PNN ligand lithium salt with CoCl₂, the complex 3, (PNN)CoCl, was obtained. Then, reduction of 3 with NaBHEt₃ under a dinitrogen atmosphere yielded complex 5, (PNN)Co(I)(η¹-N₂). Single-crystal X-ray analysis, IR spectrum, and DFT calculations revealed that the dinitrogen in 5 was only weakly reduced by the cobalt center. The reactions of 5 with carbon monoxide and 2,6-dimethylphenyl isocyanide gave carbonyl and isocyanide complexes 6 and 7 with the release of N₂, respectively. Furthermore, these cobalt complexes, especially complex 5, demonstrated the capacity to convert dinitrogen to N(TMS)₃ with moderate efficiency.