Electrochemical studies on the cis and trans isomers of [ (bpy) 2Run(OH2)2]2+ (bpy is 2,2'-bipyridine) as a function of pH in aqueous solution have revealed the existence of a series of pH-dependent redox couples that interconvert oxidation states II -VI. The electrochemical data give insight into the relative stabilities of the cis and trans isomers as well the stabilities of individual oxidation states. In acidic solution, oxidation state VI for the cis complex is unstable with respect to ligand loss and the resulting Ru(VI) complexas unstable with respect to reduction to Ru(III). Comparisons with redox potentials for related couples allow a qualitative assessment to be made concerning the role of electronic structure in determining the magnitudes of redox potentials and of the possible use of monomeric aqua/hydroxo/oxo couples as four-electron oxidants for the catalytic oxidation of water to molecular oxygen.

The selective oxidation of sulfides to sulfoxides is an important reaction because of the synthetic versatility of sulfoxides.1 A variety of transition-metal complexes have been used to carry out this oxidation including the catalytic system based on Fe(TPP)Cl (TPP is 5,10,15,20-tetraphenylporphyrinato) with iodosylbenzene as cooxidant.2•3 With metal-oxo reagents such as chromic acid,4 permanganate,5 or Os045,6 however, selectivity is not observed because the sulfoxides are often more reactive than the corresponding sulfides. Riley and co-workers have investigated the oxidation of sulfides to sulfoxides by 02 catalyzed with dihaloruthenium(II) complexes,7•8 which give sulfoxide/sulfone ratios parallel to those observed in the H202 oxidation of sulfides,9 and have proposed a Ru(IV) intermediate.Here we report the results of a kinetic study on the oxidation of dimethyl sulfide to dimethyl sulfoxide and of dimethyl sulfoxide to dimethyl sulfone by the Ru(IV)-oxo complex [(bpy)2(py)-Ru(0)]2+. Our goals were to establish the mechanisms of oxidation in order to make comparisons with mechanistic results obtained for other substrates,10-15 to attempt to provide some insight into how sulfide oxidations based on RuC1316 and RuCl2(PPh3)317 occur, and to assess the possibility of developing an electrocatalytic procedure for the selective oxidation of sulfides to sulfoxides.18 Experimental SectionMaterials. Acetonitrile (Baker) was distilled immediately before use from P2Os under an argon atmosphere or used directly. Dimethyl sulfide (Aldrich) was distilled before use. Dimethyl sulfoxide (Burdick and Jackson) was distilled under vacuum before use.Preparations. The salts [(trpy)(bpy)Ru(0H2)](C104)2, [(trpy)-(bpy)Ru(O)] (C104)2, and [(bpy)2(py)Ru(0)](C104)2 were prepared by previously reported procedures.19,20

No abstract

No abstract

The work of Carruthers & Nieto on the harmonic oscillator coherent states is combined with Schwinger’s construction of angular momentum to produce the angular momentum coherent states. It is shown that these states become the vector representatives of angular momentum in the classical limit, and so are particularly useful for discussing the transition from quantum to classical angular momentum. The uncertainty relations for angle and angular momentum are described and are compatible with the classical limit. Under rotations the coherent states transform in a manner that in the classical limit is equivalent to the transformation of vectors, and in the same limit the root mean square variation of the expectation values of the components of angular momentum become negligible in comparison with the expectation values themselves. The coupling of two angular momenta in the classical limit is investigated: it is shown that although the product of two coherent states is not itself a coherent state, it does represent a packet similar to a true coherent state, and centred on the direction of the classical resultant of the two component vectors. The properties and implications of hyperbolic angular momentum space are discussed.