Structure and electrochemical behavior of alkylidene-bridged metalladithiolene complexes (metals: cobalt and rhodium):: bond cleavage of alkylidene moieties by electrochemical redox reactions

We prepared thirteen alkylidene-bridged metalladithiolene complexes [(Cp)M(S2C2Y2)((CRR2)-R-1)] (M = Co and Rh) including two novel ones. We succeeded in X-ray structure analyses of six alkylidene-bridged dithiolene complexes together with three original dithiolene complexes. The Co-S bond distance of the dithiolene ring becomes long due to the formation of alkylidene-bridged complexes. Investigation of the redox process in a series of those alkylidene-bridged metalladithiolene complexes by cyclic voltammetry reveals a large dependence for the redox potentials on the nature of M, Y and R. In the reduction, the radical anion formed in the initial process eliminates the alkylidene moiety slowly to give the radical anion of the original dithiolene complexes. One-electron oxidation gives detectable cation radicals due to some structural change, but when these cation radicals are se-reduced, they rapidly eliminate the bridging moieties to give original dithiolene complexes. We could succeed in detecting the intermediary species in the elimination process. This is one of the very rare and important successes in the trapping of the intermediate in the elimination mechanism. We conclude that both reduction and oxidation weaken the M-C and S-C bonds in the M-S-C triangle ring to regenerate the original metalladithiolene complexes. (C) 1998 Elsevier Science S.A. All rights reserved.