Synthesis and structure of stable base-free dialkylsilanimines

Four isolable dialkylsilanimines R^H₂SiNR (R = CH ₂Ph (5a), Ph (5b), 1-adamantyl (5c) and SiMe₃ (5d), where R^H₂ = 1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl) were synthesized as air-sensitive crystals by the reaction of isolable dialkylsilylene 4 with the corresponding azides. X-ray analysis shows that 5a-5d are base-free silanimines and 5a and 5b have a remarkable bent SiN-R structure, while 5c and 5d have an almost linear structure. Distinct π(SiN) →π*(SiN) and n(N)→π*(SiN) transition bands of silicon-nitrogen double bonds were observed for 5a-5d in hexane. A mechanism for the formation of silanimine from the reaction of silylene and azide is discussed using theoretical calculations with the GRRM method for model reactions.