SYNTHESIS AND REDOX PROPERTIES OF [(CPRU(L(2)))(2)-(MU-FUMARONITRILE)][OTF](2) AND [CPRU(L(2))(SIGMA-N-FUMARONITRILE)][OTF] WITH L(2) EQUALS N,N'-DIISOPROPYL-1,4-DIAZA-1,3-BUTADIENE (IPR-DAB) OR L=PPH(3)

The reaction of [CpRu(iPr-DAB)(OTf)] (iPr-DAB=N,N'-diisopropyl-1,4-dia za-1,3-butadiene with excess fumaronitrile yields [CpRu(iPr-DAB)(sigma N-fumaronitrile)][OTf] (1), which is in equilibrium with the binuclea r complex [{CpRu(iPr-DAB)}(2)(mu-fumaronitrile)][OTf](2) (2) and free fumaronitrile. Complex 2 could be prepared quantitatively by the react ion of [CpRu(iPr-DAB)][OTf] with 0.5 equiv. of fumaronitrile. The reac tion of [CpRu(PPh(3))(2)][OTf] with excess fumaronitrile led to the mo nomeric complex [CpRu(PPh(3))(2)(sigma N-fumaronitrile)][OTf] (3), whi le reaction with 0.5 equiv. of fumaronitrile gave [{CpRu(PPh(3))(2)}(2 )(mu-fumaronitrile)][OTf](2) (4) in 100% yield. Attempts to isolate th e asymmetric compound [CpRu(iPr-DAB)(mu-fumaronitrile) CpRu(PPh(3))(2) ][OTf](2) (5) failed since in all cases a mixture of 2, 4 and the desi red complex 5 was formed. The redox behavior of complexes 1 and 2 was investigated by cyclic voltammetry and UV-Vis/IR spectroelectrochemist ry. The chemically irreversible one-electron reduction of both complex es is localized on the fumaronitrile ligand, as was also found for the PPh(3)-substituted complexes 3 and 4. These results are in sharp cont rast with the chemically reversible, iPr-DAB-localized one-electron re duction of the mononuclear derivatives [CpRu(iPr-DAB) (X)](+) (X=CO, P Ph(3)). Oxidation of the Ru-II centers in 1 and 2 resulted in secondar y chemical reactions. The final oxidation product in the case of the b inuclear complex 2 has been unambiguously identified as the cation [Cp Ru(iPr-DAB)(OTf)](+). This result demonstrates that the Ru-III-(sigma N-fumaronitrile) bond in the studied complexes is rather weak and easi ly dissociates. The oxidation-induced reactivity of 2 hence rules out the spectroscopic characterization of the mixed-valence (RuRuIII)-Ru-I I intermediate 2(+).