Direct B-H Activation of Carborane Clusters via Synergistic LMCT and HAT Photocatalysis

The functionalization of B-H bonds in carboranes represents a significant goal in boron cluster chemistry, holding great potential for the construction of advanced functional materials and bioactive molecules. However, the inherent inertness of the B-H bond, characterized by a high bond dissociation energy (about 100 kcal/mol), presents a formidable challenge. Conventional strategies typically rely on transition-metal-mediated activation or prefunctionalization of the boron vertices, which may suffer from poor atom- and step-economy and frequently require harsh reaction conditions and noble catalysts. Herein, we report a photoinduced iron-catalyzed platform for the direct and redox-neutral B-H functionalization of carboranes via the merger of ligand-to-metal charge transfer (LMCT) and hydrogen atom transfer (HAT). This method leverages the LMCT excitation of commercially available and inexpensive iron(III) chloride to generate chlorine radicals under mild conditions, which subsequently mediate a B-H HAT process. This versatile protocol enables a diverse range of B-H derivatizations, including alkylation, hydrazination, thiolation, and heteroarylation. Its synthetic utility is demonstrated through scalable synthesis, facile post-modification of products, and the one-step construction of a carborane-based luminogen. Mechanistic studies provide evidence for the formation of a boron-centered carboranyl radical and a chlorine radical, corroborating the proposed synergistic LMCT/HAT pathway. This work establishes a new paradigm for the functionalization of inert B-H bonds, offering a practical strategy for the development of boron-cluster-based functional molecules.