A donor-supported silavinylidene and silylium ylides: boroles as a flexible platform for versatile Si(ii) chemistry.

Electron-deficient, anti -aromatic 2,5-disilyl boroles are shown to be a flexibly adaptive molecular platform with regards to SiMe 3 mobility in their reaction with the nucleophilic donor-stabilised precursor dichloro silylene SiCl 2 (IDipp). Depending on the substitution pattern, selective formation of two fundamentally different products of rivalling formation pathways is achieved. Formal addition of the dichlorosilylene gives the 5,5-dichloro-5-sila-6-borabicyclo[2.1.1]hex-2-ene derivatives. Under kinetically controlled conditions, SiCl 2 (IDipp) induces 1,3-trimethylsilyl migration and adds exocyclically to the generated carbene fragment giving an NHC-supported silylium ylide. In some cases interconversion between these compound classes was triggered by temperature or NHC-addition. Reduction of silaborabicyclo[2.1.1]hex-2-ene derivatives under forcing conditions gave clean access to recently described nido -type cluster Si(ii) half-sandwich complexes of boroles. Reduction of a NHC-supported silylium ylide gave an unprecedented NHC-supported silavinylidene which rearranges to the nido -type cluster at elevated temperatures.