A New Hydrogen Bonding Motif Based on 10-Hydroxy-10,9-Borazarophenanthrene

The rational design of a system which mimics the molecular recognition properties of carboxylic acids but displays markedly different reactivity is presented. 10-Hydroxy-10,9-borazarophenanthrene is predicted by both structural analogy with carboxylic acids and ab initio calculations to form cyclic hydrogen bonded homodimers and its crystal structure demonstrates that this expectation is fulfilled. In solution, however, the reactivity of 10-hydroxy-10,9-borazarophenanthrene is markedly different from that of carboxylic acids - reacting with itself under certain conditions by nucleophilic addition at boron followed by loss of water to form the corresponding anhydride. This reactivity is rationalised in terms of the electronic structure of the borazarophenanthrene system. (C) 1997 Elsevier Science Ltd.