A Pd-Catalyzed Route to Neutral and Anionic Aminated Carboranes

Functionalization of boron-rich clusters, such as icosahedral ortho-carborane, with nitrogen-containing groups is essential for advancing their use in medicinal research and materials science. A key challenge for the amination is that ortho-carborane readily undergoes deboronation under basic conditions, forming anionic nido-carborane species that deactivate metal catalysts. In this study, we developed a general protocol to achieve mono- and vicinal diamination of ortho-carborane under Pd-catalyzed cross-coupling conditions. Electron-rich triaryl phosphine ligands were found to significantly improve the reaction efficiency and minimize the uncontrolled deboronation. The resulting vicinally diaminated ortho-carboranes can undergo oxidative cyclization to form carborane-fused six-membered heterocycles. Furthermore, controlled deboronation of both the diamination products and the carborane-fused heterocycles afforded a range of anionic nido-carborane derivatives. Under anodic oxidation conditions, oxidative bond formation in the presence of pyridine derivatives, disulfide, and PPh3 was achieved efficiently, generating previously inaccessible trisubstituted nido-carboranes. The incorporation of a biological ligand in a diaminated nido-carborane demonstrates the potential applications of these new boron cluster scaffolds in medicinal chemistry.