Redox-Switchable Tristable 1,3,2,4,5-Triboradiazoles

Abstract

Achieving multiple reversible redox states with distinct electronic structures and properties within a compact main-group molecular framework remains challenging. Here we report a 1,3,2,4,5-triboradiazole (2), an all-inorganic BN-heterocycle isoelectronic with Cp–, that undergoes clean and fully reversible 0/+1/+2 redox interconversion, enabling the isolation and structural characterization of three discrete redox states based on a single B3N2 ring. Stepwise oxidation progressively alters the aromatic character from weakly aromatic to nonaromatic and weakly antiaromatic states, accompanied by redox-dependent optical responses. The redox state dictates fundamentally different reaction pathways at the B–B unit, enabling π-bond functionalization in the neutral state but σ-bond insertion chemistry in the dication. These findings establish triboradiazoles as a compact BN platform that couples multistate redox chemistry with redox-dependent changes in aromatic character, optical properties, and chemical reactivity.