Synthesis and crystal structure of an assembly of threeortho-carborane cages linked viapara-phenylene units: effect of aryl orientation on cage C?C bond lengths inC-aryl-ortho-carboranes

The synthesis and crystal and molecular structure are described of (C 2 B 10 H 11 )C 6 H 4 (C 2 B 10 H 10 )C 6 H 4 (C 2 B 10 H 11 ) (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, PhC 2 B 10 H 11 , 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' π systems and the carborane cages. The synthesis of a pentafluorophenyl derivative of 4, (C 2 B 10 H 11 )C 6 H 4 (C 2 B 10 H 10 )C 6 H 4 (C 2 B 10 H 10 )C 6 F 5 , is also described.