Silylenes complexes with Lewis bases, electronic

Since they have both a vacant low-energy orbital and a lone pair, silylenes might behave either as electron pair donors or acceptors. There is scant evidence for silylenes reacting as Lewis bases, but complexes of silylenes acting as Lewis acids are now well-established these complexes can also be described as silaylides, R2>Si —B+262. Trinquier has calculated that even SiLL should form a weak complex with 112S i , in which a silane hydrogen binds to the p-orbital of the silylene263. 

Table IV also shows that the Amax values of the complexes are influenced even more by the substituents at silicon than by the nature of the Lewis base. The smallest blue shift on complexation occurs with silylenes, which are substituted by electron-donating groups such as aryloxy groups. This may be explained by intramolecular stabilization of the silylene by back-bonding of the heteroatom substituent, thus reducing the electrophilicity of the silicon center and weakening the silylene-donor interaction.30...

---