Showing papers on "Polyoxometalate published in 1993"

Oxo transfer from high-valent totally inorganic oxometalloporphyrin analogs, [Xn+W11O39CrVO](9-n)- (Xn+ = P5+, Si4+), to hydrocarbons

Abstract: Chromium(III) heteropolytungstate complexes or their corresponding oxygenated forms, the oxo Cr(V) complexes [X n+ W 11 O 39 Cr V O] (9-1)- (X n+ =P 5+ and Si 4+ ), first reported by Katsoulis and Pope, can catalyze the oxidation of organic substrates (alkenes, alkanes, alcohols, and one phosphine, Ph 3 P) by a variety of oxidants (OCl - , H 2 O 2 , or iodosylbenzene). Many of the electronic, structural, chemical, and catalytic features of these transition metal-substituted polyoxometalate complexes parallel those in the versatile and thoroughly investigated metalloporphyrins, but the catalysts are thermodynamically resistant to oxidative degradation

Organosiloxane compounds containing polyoxometalate groups

Abstract: This invention provides organosiloxane compounds containing silicon-bonded polyoxometalate (POM) structures that are present as pendant groups. The invention also provides methods for preparing these reaction products.

Polyoxometalate compounds as antiviral agents

Abstract: Polyoxometalate compounds which exhibit anti-retroviral activity are disclosed. Compounds with anti-retroviral activity include those having the following general molecular formulas: M 7 PW 11 O 39 M 8 SiW 11 O 39 M 9 HSiW 9 O 34 M 8 HPW 9 O 34 M 10 (TM) 4 (PW 9 O 34 ) 2 M 16 (TM) 4 (P 2 W 15 O 56 ) 2 M 14 [NaP 5 W 30 O 110 ] M 12 (TM) 3 (PW 9 O 34 ) 2 M 6 P 2 W 18 O 62 wherein M is an alkali metal, NH 4 + or other common monocation or soluble dication, or any combination of the above provided adequate water solubility is exhibited, or histidinium ion, argininium ion, or lysinium ion or any dication of a dipeptide or oligopeptide with 2 protonated basic amino acid residues, or any combination of these monocations or dications with each other or with any common inorganic cation, and TM is a divalent transition metal ion, such as Mn, Fe, Co, Ni, Cu and Zn.

Catalytic Chemistry of Solid Polyoxometalates and Their Industrial Applications

Abstract: First, fundamental properties (structure, acid and redox properties) and advantages of solid polyoxometalate catalysts (catalyst design by acid and redox control, molecularity, unusual reaction field and unique basicity) are explained. Then, the mechanism of alcohol dehydration elucidated by direct observation of reaction intermediates by solid-state NMR and the very high activity of Cs2.5H0.5PW12O40 are described. Finally several industrial applications of polyoxometalate catalysts are briefly introduced placing stress on the role of unique chemical properties of polyoxometalates.

Oxidative bleaching of wood pulp by vanadium-substituted polyoxometalates

Abstract: A method for delignifying wood pulp is disclosed. The method comprises the steps of obtaining a wood pulp and exposing the wood pulp to a polyoxometalate of the formula: [VnMomW1NboTap(TM)q(MG)rOs]x- where n is 1-18, m is 0-40, l is 0-40, o is 0-10, p is 0-10, q « 6, r « 6, TM is a d-electron-containing transition metal ion, and MG is a main group ion, provided that n + m + o + 1 + p » 4 and s is sufficiently large that x > o. The exposure is under conditions wherein the polyoxometalate is reduced. In a preferable form of the invention, the method additionally comprises the step of reoxidizing the polyoxometalate.

Carbonylation reaction catalysts

Abstract: A process and novel catalyst for the carbonylation of one or more of alcohols, ethers and ether alcohols to esters and, optionally, to carboxylic acids. The reaction is effected in the vapor state over a solid catalyst comprising a polyoxometalate anion in which the metal is at least one taken from Group V and VI of the Periodic Chart of the Elements complexed with a cation from a member of Group VIIIA of the Periodic Chart of the Elements. Preferably, the catalyst is deposited on a support that is inert to the reaction. The preferred support is silica.

Photocatalytic Processes by Polyoxometalates. Splitting of Water. The Role of Dioxygen

Abstract: Photolysis of polyoxometalates at the oxygen to metal charge transfer bands, at the near visible and UV areas, in the presence of a great variety of organic compounds, results in multielectron reduction of polyoxometalates and concomitant oxidation of organic compounds. In the absence of dioxygen, photolysis accumulates electrons on polyoxometalates, moving the redox potential to more negative values, until the reduced catalyst is able to deliver its electrons to H+. At this point, a steady state is produced at which the rate of photoreduction of polyoxometalate is matched by its rate of reoxidation by H+ (H2-evolution). The presence of dioxygen has the following results: (a) It reoxidizes very fast and effectively and photoreduced polyoxometalate, accelerating the photo-catalytic cycle by an order of magnitude, and (b) its activation by the reduced catalyst provides, usually, an extra step in which further oxidations of a variety of organic compounds have been obtained.