A Silicon/Sulfur Analog of an Acyl Anion With Ambident Reactivity.

Acyl anion-based umpolung is a foundational strategy in synthetic chemistry that enables reversal of the intrinsic electrophilic polarity of carbonyl compounds. Although acyl anion chemistry has been well developed, translating this polarity-inversion concept to heavier main-group congeners has remained elusive. Here we report the synthesis of a silicon/sulfur analogu of an acyl anion through a distinctive four-electron reductive rearrangement of an arylthiotribromosilane precursor. Structural and computational analyses reveal a polarized Si═S interaction and lone pair at the silicon center, endowing it with acyl-anion-type electronic character. The resulting anion exhibits ambident nucleophilic reactivity of the silicon and sulfur centers. Reactions with Fe2(CO)9 and organic azides demonstrate chemically accessible lone-pair reactivity at silicon, whereas sulfur-centered functionalization with chlorophosphine and chlorosilane electrophiles affords neutral acyclic silylenes. These findings establish a strategy for translating classical carbonyl umpolung concepts into low-valent silicon chemistry and provide access to electronically cooperative main-group frameworks featuring dual reactive sites.