“Solvent-in-salt” (SIS) systems with a very high salt content have recently emerged as potent tools for solution of highly relevant chemical problems.

Significance: Strong electrophilicity usually goes hand in hand with positive charge. In contrast, most negative ions behave like nucleophiles. Here we challenge this conventional wisdom by introducing an apparently counterintuitive idea that anions can, under well-defined circumstances, behave as superelectrophiles and even show superior binding strength and kinetic product stabilization in comparison with typical superelectrophilic cations. Emanating from the most stable gas-phase dianion [B₁₂(CN)₁₂]²⁻, synthesized here, we generate its superelectrophilic fragment anion [B₁₂(CN)₁₁]⁻, which binds Ar covalently at room temperature. This opens up additional directions for activation of inert compounds and elements.