Neutral Homoaromatic Diboradisilacyclobutene: Synthesis, Structure, and Reactivity

A formally neutral homoaromatic diboradisilacyclobutene was prepared and structurally characterized via the reduction of borylaminobromosilane with potassium graphite, which represents the first neutral boron and silicon mixed analogue of the homocyclopropenylium ion. Single-crystal X-ray analyses revealed a folded four-membered B2Si2 ring (26.2°) and a remarkably short transannular B-Si distance of 2.306(3) Å. DFT calculations showed that two π-electrons delocalize over the BSi2 moiety. Both structural feature and DFT calculations show the significant 2π-homoaromatic nature of the diboradisilacyclobutene. Furthermore, diboradisilacyclobutene reacted readily with CuCl or HCl to afford the diboradisilacyclobutanes.