Vertex Differentiation Strategy for Tuning the Physical Properties of <i>closo</i>-Dodecaborate Weakly Coordinating Anions

Abstract

We report the synthesis and characterization of various compounds containing the 1,7,9-hydroxylated <i>closo</i>-dodecahydrododecaborate (B₁₂H₉(OH)₃^2-) cluster motif. Specifically, we show how the parent compound can be synthesized on the multigram scale and further perhalogenated, leading to a new class of vertex-differentiated weakly coordinating anions. We show that a postmodification of the hydroxyl groups by alkylation affords further opportunities for tailoring these anions' stability, steric bulk, and solubility properties. The resulting dodecaborate-based salts were subjected to a full thermal and electrochemical stability evaluation, showing that many of these anions maintain thermal stability up to 500 °C and feature no redox activity below ∼1 V vs Fc/Fc⁺. Mixed hydroxylated/halogenated clusters show enhanced solubility compared to their purely halogenated analogs and retain weakly coordinating properties in the solid state, as demonstrated by ionic conductivity measurements of their Li⁺ salts.