Nonclassical Applications of closo-Carborane Anions: From Main Group Chemistry and Catalysis to Energy Storage

Classically closo-carborane anions, particularly [HCB₁₁H₁₁]^- and [HCB₉H₉]^-, and their derivatives have primarily been used as weakly coordinating anions to isolate reactive intermediates, platforms for stoichiometric and catalytic functionalization, counteranions for simple Lewis acid catalysis, and components of materials like liquid crystals. The aim of this article is to educate the reader on the contemporary nonclassical applications of these anions. Specifically, this review will cover new directions in main group catalysis utilized to achieve some of the most challenging catalytic reactions such as C-F, C-H, and C-C functionalizations that are difficult or impossible to realize with transition metals. In addition, the review will cover the utilization of the clusters as dianionic C σ-bound ligands for coordination chemistry, ligand substituents for coordination chemistry and advanced catalyst design, and covalently bound spectator substituents to stabilize radicals. Furthermore, their applications as solution-based and solid-state electrolytes for Li, Na, and Mg batteries will be discussed.