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.