MeS-Substituent-Stabilized Rotamers of Cobalt Bis(dicarbollide)

The methyl sulfide 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 by the reaction of CoCl2 with [10-MeS-7,8-C2B9H11]- and [9-MeS-7,8-C2B9H11]-, respectively, in strong alkaline aqueous media. The 4,4'-(rac)- and 4,7'-(meso)-isomers were separated by column chromatography on silica 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 by single crystal X-ray diffraction. In the solid state, the rotation of the two dicarbollide ligands with respect to each other is hampered due to formation of intramolecular CHcarb ***S(Me) hydrogen bonds between the ligands, that results in stabilization of definite rotamers - transoid- in the case of 8,8'-isomer, and gauche- in the case of 4,4'- and 4,7'-isomers. These data are in a good agreement with results of the quantum chemical calculations.