The first cyclic monothioether derivative of [C2B9H12]- has been synthesized from 1-(SH)-1,2-C2B10H11. Reaction of the latter with (BuLi)-Bu-n and 1,3-dibromopropane leads to 1,2-mu-(S(CH2)(3))-1,2-C2B(10)H(10) Partial degradation leads to [7,8-mu-(S(CH2)(3))-7,8-C2B9H10](-) Reaction of [7,8,-mu-(S(CH2)(3))-7,8-C2B9H10](-) With [PdCl2(PRR'(2))(2)] leads to different sets of compounds depending on the nature of R and R'. If R = R' = Bu-t, a close compound with one vertex occupied by "[Pd((PBu3)-Bu-t)(2)]" is obtained. When aryl groups are present in the starting phosphine complex, the zwitterionic non-metal-containing compounds are obtained. The crystal structure of one of them has been determined, and the compound has been proven to be 7,8-mu-(S(CH2)(3))-11-PPh3-7,8-C2B9H9. The reaction of [7,8-mu-(S(CH2)(3))-7,8-C2B9H10](-) with [RhCl(PPh3)(3)] leads to [Rh(7,8-mu-(S(CH2)(3))-7,8-C2B9H10)(PPh3)(2)]. An agostic B-H-->Rh interaction has been produced, identified by a H-1{B-11} NMR resonance at -4.78 ppm. In this instance the cluster is connected to "Rh" via the thioether and B(11)-H. The reaction of [7,8-mu-(S(CH2)(3))-7,8-C2B9H10](-) with [RuCl2(PPh3)(3)] leads to a compound with two B-H-->Ru interactions. Contrarily to its noncyclic analogues, it seems that only one isomer has been obtained.