Rhodium-Catalyzed Regioselective Hydroxylation of Cage B-H Bonds of o-Carboranes with O2 or Air

A rhodium-catalyzed hydroxylation of a cage B4-H bond in o-carboranes with either O-2 or air as the oxygen source is described, and serves as a new methodology for the regioselective generation of a series of 4-OH-o-carboranes in a one-pot process. The use of either O-2 or air as both the oxidant and the oxygen source makes this protocol very environmentally friendly and practical.