Polyhedral monocarbaborane chemistry: The closo-[PhCB7H7]− and closo-[PhCB10H10]− anions: the two missing species in the closo-[PhCBnHn]− sequence

Reaction of the ten-vertex nido-[PhCB9H11]− anion with FeCl3 in aqueous acid results in cluster dismantling to give nine-vertex arachno-[PhCB8H13], which gives the eight-vertex closo-[PhCB7H7]− anion on treatment with NEt3. Reaction of the nido-[PhCB9H11]− anion with [BH3(THF)] results in cluster Aufbau to give the eleven-vertex nido-[PhCB10H12]− anion, which, on treatment with I2 in aqueous alkali solution, gives the eleven-vertex closo-[PhCB10H10]− anion. Both of the new closo anions, [PhCB7H7]− and [PhCB10H10]−, are characterised by NMR spectroscopy and by single-crystal X-ray diffraction analyses of their [NEt4]+ salts. The sequence of closo-[PhCBnHn]− anions, where n=7–11, is thereby completed.