TWISTED SI=N BONDS - MATRIX-ISOLATION OF BRIDGEHEAD SILANIMINES

We report the IR and UV-vis spectra of three bridgehead silanimines, 1-sila-2-azabicyclo[3.2.2]non-1(2)-ene, 1-sila-2-azabicyclo[3.2.1]oct-1(2)-ene, and 1-sila-2-azabicyclo[2.2.2]oct-1(2)-ene, prepared in matrix isolation by UV irradiation of bridgehead silyl azide precursors and characterized by chemical trapping with trimethoxymethylsilane with and without prior selective photodestruction with light of suitable wavelengths. The IR spectra of the N-14 and N-15 species and the n --> pi* transition in their UV-vis spectra arc in good agreement with ab initio computations. It is concluded that pi bonding plays a crucial role in determining the properties of silanimines.