ETA(2) COMPLEXES OF [RU-II(HEDTA)](-) - SENSITIVITY OF THE H-1-NMR CHEMICAL-SHIFTS OF THE OLEFINIC PROTONS TO ALPHA RING SUBSTITUENTS

The eta(2) coordination of olefinic units with Ru-II centers with amin e and oxygen donors has generally been associated with signature H-1 a nd C-13 NMR parameters. An upheld H-1 NMR shift of between +1.0 and +2 .0 ppm for protons of the eta(2) unit and an upheld C-13 NMR shift of +40 to +80 ppm for the eta(2) carbons has been noted previously. A ser ies of [Ru-II(hedta)L](-) complexes, hedta(3-)=N-hydroxyethylethyl-ene diaminetriacetate (L=3-cyclohexene-1-methanol (i), 2-cyclohexene-1-one (2), pyrithyldione (3), 1,3-dimethyluracil (4), 3-deazauracil (5), 3- methylcytosine (6)), have been examined by H-1 NMR, C-13 NMR and elect rochemical methods. The eta(2) complexes of [Ru-II(hedta)L](-) (L=1-6) exhibit the anticipated Ru-II/III wave in the range of 0.45 to 0.71 V versus NHE. Isolated olefinic cyclic units such as 1 exhibit a reduce d upheld H-1 NMR shift of between +0.39 and +0.80 ppm. Olefinic proton s of the eta(2) units with adjacent withdrawing carbonyl moieties exhi bit more positive upheld H-1 NMR shifts (>+0.80 ppm). The presence of an alpha NR(R') functionality of the ring promotes a downfield H-1 NMR shift in the range of -0.02 to -0.46 ppm for [Ru-II(hedta)L](-) compl exes that is not observed for [Ru-II(NH3)(5)L](2+) complexes. The H-1 NMR shifts of the eta(2)-coordinated olefinic units are both a functio n of chemical groups adjacent to the olefinic binding site and the sec ondary ligand system of the Ru(II) center. The C-13 NMR shifts of the eta(2) carbons of the [Ru-II(hedta)L](-) series remain in the range of +40 to +80 ppm upheld of the free ligand for complexes 1-6.