Synthetic, Spectroscopic, Computational And Structural Studies Of Some 13-Vertex Ruthenacarboranes

Reduction of 1,2-closo-C2B10H12 followed by treatment with [RuCl2(p-cymene)](2) (p- cymene = (C6H4MePr)-Pr-i-1,4) affords the 13-vertex ruthenacarborane 4-(p-cymene)-4,1,6-closo-RuC2B10H12, characterised both spectroscopically and, in two crystalline forms, crystallographically. Although asymmetric in the solid state, having a docosahedral cage architecture with cage C atoms at vertices 1 and 6, this species clearly has C-s symmetry on the NMR timescale at room temperature. However, the fluctional process in operation can be arrested at low temperature, and an activation energy of 43.1 kJ mol(-1) is estimated. A computational study of the related species 4-(eta-C6H6)-4,1,6-closo-RuC2B10H12 reveals that the fluctionality is due to a double diamond - square - diamond process, first suggested by Hawthorne et al for the analogous CpCo species. These calculations yield an activation energy of 40.4 kJ mol(-1), in excellent agreement with that derived from experiment. Reduction of 1,2-Ph-2-1,2-closo-C2B10H10 followed by treatment with [RuCl2(eta-C6H6)](2) or [RuCl2(p-cymene)](2) yields the analogous species 1,6-Ph-2-4-(eta-C6H6)-4,1,6-closo-RuC2B10H10 and 1,6-Ph-2-4-(p-cymene)-4,1,6- closo-RuC2B10H10, respectively. These C, C-diphenyl compounds were again studied spectroscopically and crystallographically, the p-cymene species again showing two crystalline modifications. In contrast to their CpCo and Cp*Co analogues all three ruthenacarboranes do not undergo isomerisation in refluxing toluene.