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.