Unprecedented Steric Deformation Of Ortho-carborane

摘要

The reduction and subsequent oxidation of meta-earboranes containing bulky groups attached to the cage C atoms affords sterically-crowded ortho-carboranes with unprecedentedly long C-C connectivities.rnAlthough it has been appreciated for more than 45 years that ortho-carborane, l,2-closo-C_2B_(10)H_(12), has a distorted icosahedral geometry, its accurate structure has been determined only relatively recently. In 1996 Davidson, Wade et al. used the acidic nature of the carborane CH units to form a supra-molecular dimer with hexamethylphosphoramide, locking the CH units in C-H…O hydrogen bonds and so overcoming the disorder that had frustrated previous attempts to obtain an accurate structure crystallographically; the two independent C-C distances measured at 150 K were 1.629(6) and 1.630(6) A. Later, Rankin and co-workers redetermined the gas phase structure of ortho-carborane by electron diffraction, improving on the accuracy of previous determinations and affording C1-C2 1.624(8) A, in excellent agreement with the results of a parallel computational study, 1.621 A.