Abstract
The bicyclic amido-substituted silicon(I) ring compound Si(4) {N(SiMe(3) )Mes}(4) 2 (Mes=Mesityl=2,4,6-Me(3) C(6) H(2) ) features enhanced zwitterionic character and different reactivity from the analogous compound Si(4) {N(SiMe(3) )Dipp}(4) 1 (Dipp=2,6-(i) Pr(2) C(6) H(3) ) due to the smaller mesityl substituents. In a reaction with the N-heterocyclic carbene NHC Me4 (1,3,4,5-tetramethyl-imidazol-2-ylidene), we observe adduct formation to give Si(4) {N(SiMe(3) )Mes}(4) ⋅ NHC Me4 (3). This adduct reacts further with the Lewis acid BH(3) to yield the Lewis acid-base complex Si(4) {N(SiMe(3) )Mes}(4) ⋅ NHC Me4 ⋅ BH(3) (4). Coordination of AlBr(3) to 2 leads to the adduct 5. Calculated proton affinities and fluoride ion affinities reveal highly Lewis basic and very weak Lewis acidic character of the low-valent silicon atoms in 1 and 2. This is confirmed by protonation of 1 and 2 with Brookharts acid yielding 6 and 7. Reaction with diphenylacetylene only occurs at 111 °C with 2 in toluene and is accompanied by fragmentation of 2 to afford the silacyclopropene 8 and the trisilanorbornadiene species 9.