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 matri x isolation by UV irradiation of bridgehead silyl azide precursors and characterized by chemical trapping with trimethoxymethylsilane with a nd without prior selective photodestruction with light of suitable wav elengths. 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 ini tio computations. It is concluded that pi bonding plays a crucial role in determining the properties of silanimines.