Methylsulfanyl-Stabilized Rotamers of Cobalt Bis(dicarbollide)

Methylsulfanyl derivatives of cobalt bis(dicarbollide), [8,8′-(MeS)2-3,3′-Co(1,2-C2B9H10)2]–, [4,4′-(MeS)2-3,3′-Co(1,2-C2B9H10)2]–, and [4,7′-(MeS)2-3,3′-Co(1,2-C2B9H10)2]–, were synthesized through the reactions of CoCl2with [10-MeS-7,8-C2B9H11]–and [9-MeS-7,8-C2B9H11]–in strong alkaline aqueous media. The 4,4′-(rac) and 4,7′-(meso) isomers were separated by column chromatography as the tetrabutylammonium salts. The structures of [Bu4N][8,8′-(MeS)2-3,3′-Co(1,2-C2B9H10)2], [Bu4N][4,4′-(MeS)2-3,3′-Co(1,2-C2B9H10)2], and [Bu4N][4,7′-(MeS)2-3,3′-Co(1,2-C2B9H10)2] were determined through single-crystal X-ray diffraction. In the solid state, the rotation of the two dicarbollide ligands with respect to each other is hampered by the formation of intramolecular CH···S(Me) hydrogen bonds between the ligands, and this results in the stabilization of definite rotamers, namely, the transoid conformation for the 8,8′ isomer and the gauche conformations for the 4,4′ and 4,7′ isomers. These data are in a good agreement with the results of quantum-chemical calculations.