Stability and Structure of Carbene-Derived Neutral Penta- and Hexacoordinate Silicon Complexes

The stability and structure of the penta- and hexavalent complexes of SiF4 and SiCl4 with different carbenes have been investigated computationally. Apart from the known carbene complexes containing a pentavalent silicon center, stable neutral bis-carbene complexes with hexavalent silicon are also predicted to be stable compounds. While the largest binding energies of the pentavalent structures are somewhat higher in the SiF4 derivatives (21-30 kcal mol(-1)) than those for the analogous SiCl4 compounds (17-19 kcal mol(-1)), the hexacoordinated compounds exhibit almost the same stabilities (40-60 kcal mol(-1)) for both the chlorine and the fluorine derivatives. These stabilities are significantly higher than those for the hitherto synthesized amino and phosphino complexes. Not only the imidazol-2-ylidene- type carbene complexes but also the hexavalent bis(diisopropylamino) cyclopropylen-3-ylidene complex of SiCl4 or SiF4 are suggested to be an appropriate synthetic target.