Evidence for Extensive Single-Electron-Transfer Chemistry in Boryl Anions: Isolation and Reactivity of a Neutral Borole Radical

Despite the synthesis of a boryl anion by Yamashita et al. in 2006, compounds that show boron‐centered nucleophilicity are still rare and sought‐after synthetic goals. A number of such boryl anions have since been prepared, two of which were reported to react with methyl iodide in apparent nucleophilic substitution reactions. One of these, a borolyl anion based on the borole framework, has now been found to display single‐electron‐transfer (SET) reactivity in its reaction with triorganotetrel halides, which was confirmed by the isolation of the first neutral borole‐based radical. The radical was characterized by elemental analysis, single‐crystal X‐ray crystallography, and EPR spectroscopy, and has implications for the understanding of boron‐based nucleophilic behavior and the emergent role of boron radicals in synthesis. This radical reactivity was also exploited in the synthesis of compounds with rare BSn and BPb bonds, the latter of which was the first isolated and structurally characterized compound with a “noncluster” BPb bond. ReSETting perspectives: A borolyl anion displays single‐electron‐transfer (SET) processes in its reaction with triorganotetrel halides. This was confirmed by the isolation of the first neutral borolyl radical. This radical reactivity was exploited in the synthesis of compounds with rare BSn and BPb bonds, the latter of which is the first structurally characterized species with a “noncluster” BPb bond.