Synthesis and crystal structure of an assembly of three ortho-carborane cages linked via para-phenylene units:: effect of aryl orientation on cage C-C bond lengths in C-aryl-ortho-carboranes

The synthesis and crystal and molecular structure are described Of (C2B10H11)C6H4(C2B10H10)C6H4 (C2B10H11) (4), an acyclic assembly of three ortho-carborane units connected through their carbon atoms by two para-phenylene units. For this compound, and published structures of other aryl-ortho-carboranes, correlations are noted between the orientations of aryl substituents and cage carbon-carbon distances (C1-C2). Ab initio RHF/6-31G* and MP2/6-31G* studies on 1-phenyl-ortho-carborane, PhC2B10H11, and other model systems have been used to explore the variations in their energies, C1-C2 bond lengths, and C2-C1-C-aryl bond angles with the orientation of their aryl groups, variations believed to reflect weak interactions between the aryl substituents' pi systems and the carborane cages. The synthesis of a pentafluorophenyl derivative of 4, (C2B10H11)C6H4(C2B10H10)C6H4(C2B10H10)C6F5, is also described. Copyright (C) 2003 John Wiley Sons, Ltd.