Synthesis and Properties of Benzofuran-Fused Silole and Germole Derivatives: Reversible Dimerization and Crystal Structures of Monomers and Dimers

Benzofuran-fused silole and germole
derivatives were synthesized
by the reactions of dilithiobi­(benzofuran) with R2SiCl2 and R2GeCl2, respectively. Dilithiobi­(benzofuran)
was prepared by treating diiodobi­(benzofuran) with n-BuLi. Optical and electrochemical measurements of the resulting
bis­(benzofurano)­metalloles and their DFT calculations indicated that
the introduction of a metallole unit enhanced the conjugation of bi­(benzofuran)
mainly by raising the HOMO energy level, similarly to the case of
bis­(benzothieno)­silole prepared previously. Interestingly, [2+2] dimers
were obtained by recrystallization of the bis­(benzofurano)­metalloles,
and the dimers readily reverted to the respective monomers upon dissolving
in solvent. The crystal structures of the dimers and the monomers
were determined by X-ray diffraction studies.