Chalcogen‐Expanded Unsaturated Silicon Clusters: Thia‐, Selena‐, and Tellurasiliconoids

Reactions of silylenes with heavier chalcogens (E) typically result in Si=E double bonds or their π‐addition products. In contrast, the oxidation of a silylene‐functionalized unsaturated silicon cluster (siliconoid) with Group 16 elements selectively yields cluster expanded siliconoids Si7E (E=S, Se, Te) fully preserving the unsaturated nature of the cluster scaffold as evident from the NMR signatures of the products. Mechanistic considerations by DFT calculations suggest the intermediacy of a Si6 siliconoid with exohedral Si=E functionality. The reaction thus may serve as model system for the oxidation of surface‐bonded silylenes at Si(100) by chalcogens and their diffusion into the silicon bulk. The first chalcogen‐expanded Si7E siliconoids are readily accessible from the silylene‐substituted Si6 siliconoid and elemental chalcogen (E=S, Se, Te). The cluster core incorporates two additional vertices in one step: a pentacoordinate silicon and the chalcogen atom (⋅=silicon).