OXIDATIVE METAL-METAL BOND-CLEAVAGE IN TP(2)RU(2)(CO)(4) (TP=HYDRIDOTRIS(PYRAZOLY)BORATE)

The Ru-Ru bonded dimer Tp(2)Ru(2)(CO)(4) (1) is oxidized at E degrees = 0.15 V vs Cp(2)Fe/Cp(2)Fe(+) in acetonitrile. The chemical or electr ochemical 2-electron oxidation of 1 results in the formation of the so lvent adducts TpRu(CO)(2)(Sol)(+) (Sol: MeCN, 2; THF, 3; Me(2)CO, 4; H 2O, 5). A derivative cyclic voltammetry investigation of the oxidation process has established that the metal-metal bond cleavage occurs fro m 1(.+) following the rate law -d[1(.+)]/dt = k[1(.+)][Sol] (Sol = MeC N, THF, Me(2)CO). An associative mechanism is furthermore implicated b y large and negative entropies of activation. The rate of Ru-Ru bond c leavage is strongly solvent dependent and decreases in the order Me(2) CO > MeCN > THF > CH2Cl2. The order of stabilities of the monomeric so lvent adducts was established by observation of ligand-exchange reacti ons by H-1 NMR spectroscopy in nitromethane-d(3), and the stabilities decrease in the order MeCN > H2O > THF > Me(2)CO.