NMR study of 1-aryl-1,2-dicarba-closo-dodecaboranes: intramolecular C–H⋯O hydrogen bonding in solution

Dicarba- closo -dodecaborane(12) (carborane) has recently received much attention as a building block for supramolecular assemblies and bioactive compounds. Among carborane isomers, 1,2-dicarba- closo -dodecaborane(12) ( o -carborane) has unique chemical properties, including the ability of the o -carborane C–H hydrogens to form hydrogen bonds. To evaluate intramolecular hydrogen bond formation between the o -carborane C–H hydrogen and various hydrogen bond acceptors in solution, we have designed and synthesized 1-aryl- o -carboranes 2 . Intramolecular hydrogen bonding ability was evaluated by means of 1 H NMR measurement of the o -carborane C–H hydrogen signal of 2 . The 1-(2-methoxyphenyl)- o -carborane derivative 2m appeared to form an intramolecular hydrogen bond between o -carborane C–H hydrogen and the oxygen atom acting as a hydrogen bonding acceptor. In this study, we present evidence for hydrogen bond formation in solution between the o -carborane C–H and hydrogen bond acceptors positioned with appropriate geometry.