Synthesis and structure of stable base-free dialkylsilanimines

Four isolable dialkylsilanimines (R2Si)-Si-H=NR (R = CH2Ph (5a), Ph (5b), 1-adamantyl (5c) and SiMe3 (5d), where R-2(H) = 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 Si=N-R structure, while 5c and 5d have an almost linear structure. Distinct pi(Si=N) -> pi*(Si=N) and n(N) -> pi*(Si=N) 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.