Effects of silylene ligands on the catalytic activity of [PSiP] pincer cobalt(ii) chloride for N₂ silylation

Three silyl [PSiP] pincer cobalt(ii) chlorides 1-3 [(2-Ph2PC6H4)(2)MeSiCo(Cl)(PMe3)] (1), [(2-(Pr2PC6H4)-Pr-i)(2)MeSiCo(Cl)(PMe3)] (2) and [(2-Ph2PC6H4)(2)MeSiCo(Cl)(LSi:)] (LSi: = {PhC((NBu)-Bu-t)(2)}SiCl) (3) were synthesized and used as catalysts and their catalytic activity for dinitrogen silylation was studied. Among the three complexes complex 3 was new and was synthesized via the reaction of [PSiP] pincer preligand L1 with CoCl2 in the presence of chlorosilylene via Si-H bond cleavage. The molecular structure of 3 was determined by single crystal X-ray diffraction analysis. Compared to complex 1, complex 2 is the more effective catalyst for dinitrogen silylation and 363 equiv. of N(SiMe3)(3) could be reached per Co atom. Further study indicates that using the silylene ligand in complex 3 instead of the PMe3 ligand in complex 1, the catalytic activity of 3 is lower than that of 1. The catalytic mechanism for this catalytic system is proposed with the support of experimental evidence. The [PSiP] pincer cobalt(i) dinitrogen complex was proposed as the active catalyst for dinitrogen silylation.