Big macrocyclic assemblies of carboranes (big MACs): synthesis and crystal structure of a macrocyclic assembly of four carboranes containing alternate ortho- and meta-carborane icosahedra linked by para-phenylene units |
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Authors: | Mark A Fox Judith A K Howard J A Hugh MacBride Angus Mackinnon Kenneth Wade |
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Institution: | Chemistry Department, Durham University Science Laboratories, South Road, Durham DH1 3LE, UK |
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Abstract: | The macrocyclic compound, 1,2-C2B10H10-1,4-C6H4-1,7-C2B10H10-1,4-C6H4]2 (5)—a novel cyclooctaphane, was prepared by condensation of the C,C′-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)-ortho-carborane. The X-ray crystal structure of 5·C6H6·6C6H12 was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic Cs and local C2v symmetry; the macrocycle adopts a butterfly (dihedral angle 143°) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D2h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal mol?1 higher in energy than the C2v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful. |
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Keywords: | Macrocycle Carborane icosahedra Butterfly conformation |
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