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.苯并呋喃稠合硅咯与锗咯衍生物，可分别通过二锂代二(苯并呋喃)与R₂SiCl₂、R₂GeCl₂的反应合成。二锂代二(苯并呋喃)则由二碘代二(苯并呋喃)与正丁基锂（n-BuLi）反应制得。对所得双(苯并呋喃并)金属咯开展光学与电化学测试，并结合密度泛函理论（DFT）计算结果分析可知：与此前报道的双(苯并噻吩并)硅咯体系类似，引入金属咯单元主要通过提升最高占据分子轨道（HOMO）能级，强化了二(苯并呋喃)的共轭效应。值得注意的是，对双(苯并呋喃并)金属咯进行重结晶可得到[2+2]二聚体，该二聚体在溶于溶剂后可快速解离为对应的单体。该类二聚体与单体的晶体结构，通过X射线衍射（X-ray diffraction）分析得以确定。