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

Abstract

Three silyl [PSiP] pincer cobalt(II) chlorides 1–3 [(2-Ph₂PC₆H₄)₂MeSiCo(Cl)(PMe₃)] (1), [(2-ⁱPr₂PC₆H₄)₂MeSiCo(Cl)(PMe₃)] (2) and [(2-Ph₂PC₆H₄)₂MeSiCo(Cl)(LSi:)] (LSi: = {PhC(N^tBu)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.