Carboranes are a class of polyhedral boron hydride clusters in which one or more of the BH vertices are replaced by CH units,which can be viewed as three-dimensional relatives of benzene.They are finding many applications in medicine,supramolecular design,coordination/organometallic chemistry and optoelectronic functional materials.The unique 3D structure of o-carboranes makes their derivatization difficult especially at cage boron vertices,owing to the selectivity issue resulting from a total of ten B-H bonds in four different electronic environments.Thus it is eagerly desired to develop new methodologies for the selective functionalization of carboranes.In this connection,we installed a directing group-COOH into the cage carbon vertex to control the regioselective activation of the cage B-H bond(s).Subsequently,several transition metal catalyzed cage B(4)-alkenylation,B(4,5)-dialkenylation,B(4,5)-diarylation,B(4)-hydroxylation and B(4)-alkynylation of o-carboranes have been developed.These methods provide a toolbox for selective cage B-H functionalization,leading to the preparation of a large variety of functionalized carboranes for potential applications in various areas.