A Crystalline Mesoionic Diazasilole Featuring Low‐Valent Silicon

Abstract A 1,4,2‐diazasilole containing a low‐valent silicon atom has been synthesized employing a bulky imino N‐heterocyclic carbene ligand. This molecular structure is characterized by a mesoionic C 2 N 2 Si five‐membered ring, notable for its delocalized π electrons, intrinsic charge‐separated zwitterionic properties, and a distinctly nucleophilic silicon center, culminating in 6π aromaticity. This compound manifests either mesoionic silylene or silylone characteristics upon coordination with transition metals. Demonstrating extraordinary versatility, this compound engages in diverse reactions such as coordination with iron or iridium, oxidation by S 8 , intramolecular ring saturation under the coordination influence of iridium, silicon atom transfer facilitated by Ph 2 Se 2 , ring contraction induced by Ph 2 Te 2 , and skeletal rearrangement triggered by Et 3 N•HCl. These reactions culminate in the formation of a variety of unprecedented silicon‐based heterocycles, which are typically formidable to achieve using conventional methods. This study unveils previously unexplored facets of low‐valent 1,4,2‐diazasilole, positioning it as a promising foundational building block for future innovations in unique silicon compounds.