Reaction of [Ru(H20)6]2+ with [PWu039]7', followed by oxidation with 02 yields [PW11039Rum(H20)]4_ (1) isolated as the cesium salt. Cyclic voltammetry shows that 1 is reducible/oxidizable to the corresponding aquaruthenium(II) (2), oxoruthenium(IV), and oxoruthenium(V) derivatives. The pof 1 is 5.1, determined from a ca. 300 ppm shift of the 31P NMR line between pH 3 and 6. At pH 3.0 and 23 °C the rate of electron transfer between I and 2 was determined by 31P NMR line-broadening to be 1.2 X 106 M'1 s'1. 2 reacts with pyridine, sulfoxides, dialkyl sulfides, and active alkenes (maleic, fumaric, crotonic acids, l,4-dihydroxybut-2-ene) to form [PWn039Run(L)]5• species, which are oxidizable to the Ru111 stage only. At pH 3.0 and 20 ± 1 °C the half-life for substitution of DMSO for water on 2 is 3.5 h (kobs = 5.5 x 10'5 s'1 *) and this rate is some 3 orders of magnitude slower than that for water exchange on [Ru(H20)6]2+. The electronic spectra of the Ru11 derivatives show, in addition to the expected d-d bands, broad intense charge-transfer absorption attributed to Ru11 -* WVI. Tungsten-183 NMR spectra of 2 and the dimethyl sulfoxide and maleic acid derivatives show the expected six-line (2:2:2:1:2:2) pattern but with resonances for the W atoms adjacent to Ru deshielded by as much as ca. 360 ppm. This effect is greatest for 2 (L = H20) and least for L = maleic acid and is attributed to a partial delocalization of Ru 7r-electron density onto the polytungstate ligand. The anomalous redox potential for Ru111''11 in 2 (in comparison to other MIII/n couples in [PWu039M(H20)]5') is a further indicator of electron delocalization. In acidic solution, pH ~0, 1 is oxidized to the oxoruthenium(V) derivative in a single two-electron step, and this forms the basis of an electrocatalytic oxidation (40 turnovers) of dimethyl sulfoxide to the sulfone with >90% current efficiency. The tetrabutylammonium salt of 1 in acetonitrile solution catalyzes the epoxidation of /ww-stilbene by iodosylbenzene. Reduction of 2 to a heteropoly blue is not possible, due to catalytic hydrogen evolution, except in the presence of dimethyl sulfoxide which is catalytically reduced (30 turnovers) to dimethyl sulfide with ca. 50% current efficiency. Preliminary experiments show that the behavior of a2-[P2W17061Rum(H20)]7~parallels that of 1.3 456•7 and most of these have not been thoroughly characterized. We are in the process of exploring some of these species in more detail, with particular emphasis on those that might be expected to display significant redox and potential catalytic activity. For that reason we have chosen to investigate some ruthenium derivatives. Experimental SectionSynthesis. Potassium 11-tungstophosphate ( 7[ \ 39]•;<: 20) was prepared in a similar way to the 11-tungslosilicate8 and was identified by IR and 31P NMR spectroscopy. Hexaaquaruthenium(II) p-toluenesulfonate, [Ru(H20)6](C7H7S03)2, was prepared by the literature me•(2) (a) Hill, C.

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The adsorption of multiply charged, heteropoly tungstate anions on mercury electrodes is extraordinarily strong. For the chromium(III)-substituted anion, «2-[PzW 06 € (0 2)]7 *", the mercury surface is half-saturated at concentration of the heteropolyanion of only 5 X 10~9 M. In the presence of the adsorbed anions, the rate of reduction of the unadsorbed heteropolytungstates in solution is greatly diminished. The decreased reduction rates appear to result from increases in the negative diffuse layer potentials produced by the anion adsorption. The spontaneous adsorption of heteropolytungstates on mercury may prove useful in their electroanalysis at very low levels and in electrocatalytic applications.Electrochemical investigations of aqueous solutions of heteropolymetalates have been carried out by many previous authors using a variety of electrode surfaces.1-6 The deposition of certain of the heteropolymetalates at glassy carbon or graphite electrodes has been extensively exploited by Nadjo, Keita, and co-workers to obtain electrode surfaces with considerable catalytic activity toward the reduction of protons and some other substrates.5 In recent electrochemical studies from these laboratories in which transition metal-substituted heteropolytungstates were examined,6 measurements were restricted to glassy carbon or pyrolytic graphite electrodes because those obtained at mercury or gold electrodes were frequently less intense and more distorted than those obtained at graphite or glassy carbon electrodes. The present study was undertaken to try to identify the reasons for the poorer performance of mercury electrodes whose readily renewable, defect-free surfaces typically produce nearly ideal responses from simple electrode processes such as the reduction or oxidation of reactants like the heteropolytungstates in which bond-making or bond-breaking does not accompany the