Ylenes in the M II →Si IV (M=Si, Ge, Sn) Coordination Mode

The reaction of the methimazolyl (mt, i.e., 2‐mercapto‐1‐methylimidazolide) substituted silane Si(mt) 4 with SnCl 2 and GeCl 2 in dioxane affords the paddlewheel‐shaped complexes [ClSi(μ‐mt) 4 MCl] (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) 4 SiCl] instead afforded the trisilane [ClSi(μ‐mt) 4 SiSiCl 3 ] ( 3 a ), which provides the first crystallographic evidence for the feasibility of oligosilanes with adjacent hexacoordinate Si atoms. One of the hexacoordinate Si atoms of 3 a features the unprecedented (Si 2 S 4 )Si skeleton. Natural bonding orbital (NBO) analyses of compounds 1 , 2 , 3 a (and the target compound 3 ) revealed characteristics of M II →Si IV (for 2 and 3 ) or M I →Si IV (for 3 a ) dative bonding in the systems with M=Si and Ge, whereas compound 1 exhibits a covalent Sn III −Si III bond.