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

Abstract

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.