Synthesis, Structures, and Electronic Properties of Triple- and Double-Decker Ruthenocenes Incorporated by a Group 14 Metallole Dianion Ligand

The neutral triple-decker ruthenocenes and anionic ruthenocene bearing a stannole dianion were successfully synthesized by the reactions of dilithiostannoles with [Cp*RuCl]₄. This is the first example of a transition-metal complex bearing a group 14 metallole dianion with μ–η⁵:η⁵ coordination mode. These complexes were fully characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. In the complexes, each of the ruthenium atoms is coordinated by the stannole ring in an η⁵-fashion. The aromaticity of the stannole dianion moieties is retained judging from no C–C bond alternation in the stannole rings. CH/π interaction was found in the packing structure of the SiMe₃ derivative, which leads to a well-ordered column-like structure. The oxidation wave of the triple-decker complex was observed at −0.43 V (vs ferrocene), which reveals that the triple-decker type heavy ruthenocene is oxidized more easily than the ferrocene. Comparison of the oxidation potential between the triple-decker complex and decamethylruthenocene (Cp*₂Ru, Cp* = η⁵-C₅Me₅) reveals that a stannole ligand functions as an electron-donating ligand much stronger than the conventional electron-rich Cp* ligand.