Unlike the hydrogens on the carbon vertices, the hydrogens on the boron vertices are not acidic and do not react with strong bases. This is because boron is not as electronegative as carbon and thus the polarity of the B—H bonds is relatively low. Substitution at the boron vertices is still possible using halogenating agents through electrophilic substitution or photochemical reactions. 
For example, the boron vertices at the 9 and 12 positions opposite to the carbon vertices can be iodinated using iodine and a catalytic amount of AlCl while in refluxing dichloromethane.  
Exohedral halogenation leads to an increase in the electron withdrawing effect of the carborane which increases the acidity of the C—H bonds especially when the halogens are located at the 9, and 12 positions. Per-halogenation is also possible and when increasing the number of halide atoms, the π backdonation ability of the halide decreases allowing for the formation of intramolecular halide-halide noncovalent bonds.
Iodinated derivatives of carborane can be further modified to access boron alkylated products via a cross coupling reaction. This can be done by treating the halogenated carborane with a Grignard reagent in the presence of a phosphine palladium complex. The bromo and chloro compounds do not react under the same conditions.