Synthesis and Structure of Methylsulfanyl Derivatives of Nickel Bis(Dicarbollide).

Symmetrically and unsymmetrically substituted methylsulfanyl derivatives of nickel(III) bis(dicarbollide) (Bu4N)[8,8'-(MeS)2-3,3'-Ni(1,2-C2B9H10)2], (Bu4N)[4,4'-(MeS)2-3,3'-Ni(1,2-C2B9H10)2], and (Bu4N)[4,7'-(MeS)2-3,3'-Ni(1,2-C2B9H10)2] were synthesized, starting from [Ni(acac)2]3 and the corresponding methylsulfanyl derivatives of nido-carborane (Bu4N)[10-MeS-7,8-C2B9H11] and (Bu4N)[10-MeS-7,8-C2B9H11]. Structures of the synthesized metallacarboranes were studied by single-crystal X-ray diffraction and quantum chemical calculations. The symmetrically substituted 8,8'-isomer adopts transoid conformation stabilized by two pairs of intramolecular C-H···S hydrogen bonds between the dicarbollide ligands. The unsymmetrically substituted 4,7'-isomer adopts gauche conformation, which is stabilized by two nonequivalent C-H···S hydrogen bonds and one short chalcogen B-H···S bond (2.53 Å, -1.4 kcal/mol). The gauche conformation was found to be also preferred for the 4,7'-isomer.