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

Abstract

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.