A Three-Coordinate Cobalt(-I) Dinitrogen Complex

While most reported Co­(-I) complexes are coordinatively saturated, we report herein a 16e– Co­(-I) complex [(cyIDep)­Co­(η2-vtms)­(N2)­Na­(OEt2)]2 (where cyIDep = 1,3-di­(2′,6′-diethylphenyl)-4,5-(CH2)4-imidazol-2-ylidene; and vtms = vinyltrimethylsilane). The Co­(-I) complex is isolated from the reaction of [(cyIDep)­Co­(η2-vtms)2] with sodium under a dinitrogen atmosphere. It features short Co–N (1.695(3)/1.695(3) Å) and long N–N bonds (1.166(4)/1.168(3) Å). Theoretical study indicates the presence of 2-fold Co-to-N2 π-backdonation interactions in the three-coordinate Co­(-I) species, which might lead to thermodynamic gains to the unusual alkene-to-N2 ligand exchange reaction that gives the Co­(-I) complex. The attempts to functionalize the dinitrogen ligand in the Co­(-I) complex with Me3SiCl and a N-heterocyclic silylene lead to the isolation of the cobalt­(I) alkyl complex [(cyIDep)­Co­(C­(SiMe3)2Me)] and the cobalt(0) complex [(t‑BuNHSi)­(cyIDep)­Co­(η2-vtms)] (t‑BuNHSi = 1,3-bis­(tert-butyl)-1,3-diaza-2-silacyclopent-4-en-2-ylidene), respectively, rather than the desired products.