Reactivity of an adsorbed Ru(VI)-oxo complex: oxidation of benzyl alcohol.

The phosphonated ruthenium complex, [Ru(tpy-PO(3)H(2))(OH(2))(3)](2+) (1) (tpy-PO(3)H(2) = 4'-phosphonato-2,2':6',2' '-terpyridine), was synthesized and attached to glass|ITO or glass|ITO|TiO(2) electrodes. After attachment to the metal oxide surface through the phosphonate linkage, 1 can be oxidized (either chemically or electrochemically) to the reactive Ru(VI)-dioxo complex, glass|ITO|[((HO)(2)OP)tpy)RuVI(O)(2)(OH(2))](2+), which remains attached to the surface. The attached Ru(VI) complex reacts with benzyl alcohol through mechanisms similar to those proposed for the solution analog.

A test of the transition-metal nanocluster formation and stabilization ability of the most common polymeric stabilizer, poly(vinylpyrrolidone), as well as four other polymeric protectants.

Following an introduction to the nanocluster stabilization literature and DLVO (Derjaugin-Landau-Verwey-Overbeek) theory of colloidal stability, the most common steric stabilizer of transition-metal nanoclusters, poly(vinylpyrrolidone) (PVP), has been examined for its efficacy in the formation, stabilization, and subsequent catalytic activity of prototype, test case Ir(0)n nanoclusters. First, the five criteria established previously for ranking nanocluster protectants for their nanocluster formation and stabilization ability were evaluated for 1 monomer equiv of 10000 average molecular weight (MWav) PVP in the absence, and then presence, of the traditionally weakly coordinating anion BF4- as well as the absence and presence of the strongly coordinating, superior anionic stabilizer P2W15Nb3O62(9-), all in propylene carbonate solvent. It is found that neither 1 equiv of BF4- in propylene carbonate nor 1 monomer equiv of (undried) PVP alone allows for isolable and redissolvable nanoclusters without bulk Ir(0)n metal formation.

Synthesis and characterization of oligoproline-based molecular assemblies for light harvesting.

Helical oligoproline arrays provide a structurally well-defined environment for building photochemical energy conversion assemblies. The use of solid-phase peptide synthesis (SPPS) to prepare four such arrays, consisting of 16, 17, 18, and 19 amino acid residues, is described here. Each array contains the chromophore [Rub'(2)m](PF(6))(2) (b' = 4,4'-diethylamidocarbonyl-2,2'-bipyridine; m = 4-methyl-2,2'-dipyridine-4'-carboxylic acid) and the electron transfer donor PTZ (phenothiazine).

Photoelectrochemistry on Ru(II)-2,2'-bipyridine-phosphonate-derivatized TiO2 with the I3-/I- and quinone/hydroquinone relays. Design of photoelectrochemical synthesis cells.

Photocurrent measurements have been made on nanocrystalline TiO2 surfaces derivatized by adsorption of a catalyst precursor, [Ru(tpy)(bpy(PO3H2)2)(OH2)]2+, or chromophore, [Ru(bpy)2 (bpy(PO3H2)2)]2+ (tpy is 2,2':6',2' '-terpyridine, bpy is 2,2'-bipyridine, and bpy(PO3H2)2 is 2,2'-bipyridyl-4,4'-diphosphonic acid), and on surfaces containing both complexes. This is an extension of earlier work on an adsorbed assembly containing both catalyst and chromophore. The experiments were carried out with the I3-/I- or quinone/hydroquinone (Q/H2Q) relays in propylene carbonate, propylene carbonate-water mixtures, and acetonitrile-water mixtures.

The kinetics and mechanism of the ferrate(VI) oxidation of hydroxylamines.

Aqueous solutions of potassium ferrate(VI) cleanly and rapidly oxidize hydroxylamine to nitrous oxide, N-methylhydroxylamine to nitrosomethane, N-phenylhydroxylamine to nitrosobenzene, and O-methylhydroxylamine to methanol and nitrogen. The kinetics show first-order behavior with respect to each reactant and a two term component representing acid dependent and independent pathways. A general mechanism involving intermediate formation coupled with a two-electron oxidation is proposed.

The lacunary polyoxoanion synthon alpha-P(2)W(15)O(56)(12-): an investigation of the key variables in its synthesis plus multiple control reactions leading to a reliable synthesis.

A reliable way to determine the purity of the kinetically precipitated, noncrystalline lacunary polyoxoanion alpha-P(2)W(15)O(56)(12-) has been developed, namely, the conversion of alpha-P(2)W(15)O(56)(12-) into the tri-Nb(5+)- and V(5+)-containing polyoxoanions P(2)W(15)Nb(3)O(62)(9-) and P(2)W(15)V(3)O(62)(9-), respectively, followed by quantitative analysis of their purity by (31)P-NMR prior to recrystallization. With this previously unappreciated, straightforward alpha-P(2)W(15)O(56)(12-) purity-assessment methodology in hand, the five reported literature syntheses of alpha-P(2)W(15)O(56)(12-) are investigated with an emphasis on understanding the effects of the five differing variables within these syntheses (the amount of Na(2)CO(3) base, the rate of addition of the base, the reaction temperature, the reaction scale, and the product drying method). Two methods of Nb(5+) addition (Nb(6)O(19)(8-) and NbCl(5)) to yield P(2)W(15)Nb(3)O(62)(9-) are also evaluated, as is the issue of whether any purification is provided by the normally optimum strategy of first preparing a water-soluble salt and its crystallization from water (here the (CH(3))(4)N(+) salt of the Nb-O-Nb bridged anhydride, P(4)W(30)Nb(6)O(123)(16-)), followed by its conversion to the organic-solvent soluble, but noncrystalline, (n-C(4)H(9))(4)N(+) salt, [(n-C(4)H(9))(4)N](9)[P(2)W(15)Nb(3)O(62)].

Nanoclusters in catalysis: a comparison of CS(2) catalyst poisoning of polyoxoanion- and tetrabutylammonium-stabilized 40 +/- 6 A Rh(0) nanoclusters to 5 Rh/Al(2)O(3), including an analysis of the literature related to the CS(2) to metal stoichiometry issue.

It is crucial in metal particle catalysis to know the true number of catalytically active surface sites; without this knowledge it is impossible (i) to know the true turnover frequency (TOF, i.e., the moles of product/(moles of active metal atoms x time)); (ii) to know for certain whether a (quantitatively) better catalyst has been made-on a per-active-metal-atom basis; (iii) to know the amount of active sites remaining in a deactivated catalyst; and (iv) to know how many active sites have been regenerated in a reactivated catalyst.