T-Shaped Stibenium(III) Cation: Hydrostibination Without Sb─H Bond

The hydrostibination of alkenes represents a largely underdeveloped transformation, owing to the intrinsic lability of the required Sb─H reagents. We now show that an Sb─H bond is not needed. The structurally constrained, amidophenolato-pyridyl supported T-shaped stibenium(III) ion undergoes anti-Markovnikov hydrostibination of a broad range of alkenes in excellent yields. Spectroscopic and computational analyses reveal a polarizable, redox-confused Sb-π system in the cation, whereas its reactivity follows closed-shell ionic pathways characteristic of a Lewis-acidic Sb(III) center. Mechanistic studies support element-ligand cooperativity (ELC) with the hydride equivalent for hydrostibination originating from the ligand scaffold after substrate activation at antimony. The resulting stiba-alkanes can be transformed quantitatively into haloalkanes. This work establishes a viable strategy for hydroelementation with heavy p-block elements while circumventing weak and labile E─H bonds.