Heavier analogs of carbene complexes: Syntheses of a new type of silylene and germylene complexes and their reactions with unsaturated organic compounds

In comparison with carbene complexes having reactive M C double bonds, their heavier analogs, i.e. silylene and germylene complexes, having M E E Si, Ge double bonds are also expected to show high reactivity. However, most of such complexes previously prepared have actually shown poor reactivity toward usual organic substrates, probably because their M E double bonds are sterically overprotected for stabilization. Recently, we have succeeded in synthesizing silylene and germylene complexes having hydrogen atoms on both the metal center and E atom. The M E double bonds of these complexes are indeed the least sterically protected in any known ones and can react smoothly with various substrates such as nitriles, ketones, heterocumulenes, etc. under mild conditions. Here we report the syntheses, structures, and novel reactions of these new silylene and germylene complexes.