Synthesis and Characterization of Hypercoordinated Silicon Anions: Catching Intermediates of Lewis Base Catalysis

Anionic hypercoordinated silicates with weak donors were proposed as key intermediates in numerous silicon‐based reactions. However, their short‐lived nature rendered even spectroscopic observations highly challenging. Here, we characterize hypercoordinated silicon anions, including the first bromido‐, iodido‐, formato‐, acetato‐, triflato‐ and sulfato‐silicates. This is enabled by a new, donor‐free polymeric form of Lewis superacidic bis(perchlorocatecholato)silane 1. Spectroscopic, structural, and computational insights allow a reassessment of Gutmann's empirical rules for the role of silicon hypercoordination in synthesis and catalysis. The electronic perturbations of 1 exerted on the bound anions indicate pronounced substrate activation. The Lewis superacid bis(perchlorocatecholato)silane serves as a binding platform for weak anionic donors, providing the first characterized anionic bromido, iodido, formato, acetato, triflato, and sulfato silicates. This set allows to evaluate the structural and electronic perturbation of silicon species and substantiates their role in Lewis base catalysis.