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

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.