COBALT BIS(1,2-DICARBOLLIDE) ION WITH A DISULFUR BRIDGE BETWEEN B(8) AND B(8'). X-RAY STRUCTURE, ABSOLUTE CONFIGURATION OF ONE ENANTIOMER, AND IMPLICATIONS

摘要

The structure and absolute configuration of one enantiomer of the [3-Co-(l,2-C_2B_2H_(10))_2-8,8'-mu-S_2][NEt_4] salt was established by X-ray diffraction. A spontaneous resolution took place during crystallization but attempts at resolution in solution via chiral HPLC and chiral capillary electrophoresis failed. The probable cause is discussed and successful resolution of less racemisable 8,8'-bridged metallacarboranes of this type is predicted. The criterion of re-solvability ought to be the observation of two C-H_(carborane) signals in ~1H NMR of the respective compound with a symmetric bridge. The geometry of the disulfur-bridged title compound is discussed in terms of accessibility of the central ion to external moieties. The central ion is apparently screened from the environment by terminal hydrogens at the rim of the pentagonal ligand planes in any kind of commo-bis-icosahedral sandwich complexes.