Carboranyl-B-Mg: synthesis, reactivity, and nucleophilicity

The reactivity of boron is most commonly defined by its Lewis acidity and its reactivity as an electrophile. Recently, nucleophilic boron anions have attracted tremendous research interest for offering alternative routes to a variety of boron compounds. Herein, we report the synthesis and structure of a nucleophilic boron anionic salt featuring an exo-polyhedral B–Mg bond, for the first time. In sharp contrast to the known borylmetals, this bottleable compound does not have any heterocyclic backbones or supporting π-ligands. Its structure has been confirmed by single-crystal X-ray analyses. The calculated NPA charge of –0.503 at B(4) represents the most negative boron center among the reported boron anions, indicating the highly polarized B–Mg bond. It is shown to act as an unambiguous reactive nucleophile through its reactions with a broad range of organic, main-group, and transition-metal electrophiles.