Electrochemistry of dinuclear, thiolato-bridged transition-metal compounds. Part 4. Electrochemical activation of dinuclear thiolato-bridged molybdenum complexes [Mo2Cp2(CO)4(.mu.-SR)2]0/2+ (R = Me, Ph) toward carbonyl substitution reactions. Electrochemical and chemical syntheses of substituted derivatives. The x-ray crystal structure of [Mo2Cp2(CO)3(MeCN)(.mu.-SPh)2](BF4)2