Structures and Physical Properties of Chemically Reduced Diindenosiloles and Their π‑Extended Derivatives

Diindenosilole Si1,
a silicon-bridged fulvalene derivative,
was successfully reduced to its dianions using various alkali metals,
and the structures were characterized by X-ray crystallographic analysis.
Radical anions of Si1 as well as dianions of π-extended Si3 could also be synthesized, and the structural and physical
properties were systematically compared. It was also found that the
NMR spectra of dianions Si12– and Si32– show countercation and temperature
dependency for their signal broadness, indicating the possible existence
of thermal interconversion between closed-shell singlet states and
open-shell triplet states.