The reaction of the methimazolyl (mt, i.e., 2-mercapto-1-methylimidazolide) substituted silane Si(mt)4 with SnCl2 and GeCl 2 in dioxane affords the paddlewheel-shaped complexes [ClSi(μ-mt)4MCl] (M=Sn (1) and Ge (2), respectively). These compounds represent the first crystallographically characterized hexacoordinate silicon complexes comprising a Sn or Ge atom in the Si coordination sphere. An attempt to synthesize the related silicon compound 3 [ClSi(μ-mt) 4SiCl] instead afforded the trisilane [ClSi(μ-mt) 4Si-SiCl3] (3a), which provides the first crystallographic evidence for the feasibility of oligosilanes with adjacent hexacoordinate Si atoms. One of the hexacoordinate Si atoms of 3a features the unprecedented (Si2S4)Si skeleton. Natural bonding orbital (NBO) analyses of compounds 1, 2, 3a (and the target compound 3) revealed characteristics of MII→SiIV (for 2 and 3) or MI→Si IV (for 3a) dative bonding in the systems with M=Si and Ge, whereas compound 1 exhibits a covalent SnIII-SiIII bond. The first structurally evidenced oligosilane with two hexacoordinate Si atoms exhibits electronic features of a Cl3SiSi→SiCl dative bond, as shown by a natural bonding orbital analysis. Whereas the same features apply to a related methimazolide-bridged ClGeII→SiIVCl complex, the corresponding Sn-Si system exhibits pronounced features of a covalent Sn III-SiIII bond.
All Science Journal Classification (ASJC) codes
- Organic Chemistry