Unexpected Formation of Ru2Sn2 Bicyclic Four-Membered Ring Complexes with Butterfly and Inverse-Sandwich Structures

Reactions of tetraethyldilithiostannole 1 with [Cp*RuCl]4 afforded not η5-stannole dianion complexes but two novel bis­(stannylene)-bridged dinuclear ruthenium complexes, which have butterfly and inverse-sandwich structures, respectively, depending on the stoichiometry of [Cp*RuCl]4 toward dilithiostannole. The redox behavior between the two complexes is found to be reversible. The molecular structures were determined by X-ray diffraction analysis. The Ru–Ru bond of the butterfly complex is 2.3428(6) Å, which is the shortest among those of dinuclear ruthenium complexes having Cp or Cp*Ru units. Theoretical calculations revealed that the very short Ru–Ru bond is due to the presence of one σ bond between the ruthenium atoms and two three-centered bonds delocalized over the two Ru2Sn rings.