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 dithi olene complexes together with three original dithiolene complexes. The Co-S bond distance of the dithiolene ring becomes long due to the for mation of alkylidene-bridged complexes. Investigation of the redox pro cess in a series of those alkylidene-bridged metalladithiolene complex es by cyclic voltammetry reveals a large dependence for the redox pote ntials on the nature of M, Y and R. In the reduction, the radical anio n formed in the initial process eliminates the alkylidene moiety slowl y to give the radical anion of the original dithiolene complexes. One- electron oxidation gives detectable cation radicals due to some struct ural change, but when these cation radicals are se-reduced, they rapid ly eliminate the bridging moieties to give original dithiolene complex es. We could succeed in detecting the intermediary species in the elim ination process. This is one of the very rare and important successes in the trapping of the intermediate in the elimination mechanism. We c onclude that both reduction and oxidation weaken the M-C and S-C bonds in the M-S-C triangle ring to regenerate the original metalladithiole ne complexes. (C) 1998 Elsevier Science S.A. All rights reserved.