Synthesis of 1,2,9-trisubstituted purin-6(9H)-ones catalyzed by heteropolyacids

1,2,9-Trisubstituted purin-6(9H)-ones have been synthesized in high yield by reaction of 5-amino-N,1-dimethyl-1H-imidazole-4-carboxamide with aromatic aldehydes in the presence of heteropolyacids, H₃PMo₁₂O₄₀ and H₅PV₂Mo₁₀O₄₀. The catalytic activity of H₃PMo₁₂O₄₀ is lower than that of H₅PV₂Mo₁₀O₄₀. This is an effective synthesis of l,2,9-trisubstituted guanine derivatives with the advantages of mild reaction conditions, simple operation, and good yields.     

Peroxide derivatives of heteropoly compounds with Keggin anions [PW<Subscript>12</Subscript>O<Subscript>40</Subscript>]<Superscript>3−</Superscript> and [SiW<Subscript>12</Subscript>O<Subscript>40</Subscript>]<Superscript>4−</Superscript>: Synthesis and structure

Peroxide derivatives of heteropoly compounds with Keggin anions [PW₁₂O₄₀]^3? and [SiW₁₂O₄₀]^4? are isolated in an individual state from concentrated hydrogen peroxide solutions and characterized by physicochemical methods. The structure of Ba₂[SiW₁₂O₄₀] · 4H₂O₂ · 11H₂O (I) is solved by X-ray crystallography. Crystals of compound I (H₃₀Ba₂O₅₉Si₁W₁₂, FW = 3483.21) are monoclinic, space group C2/c, a = 24.981(2) Å, b = 12.2103(11) Å, c = 18.7142(17) Å, β = 122.620(2)^o, V = 4808.0(8) ų, Z = 4. The structure contains Keggin anions [SiW₁₂O₄₀]^4?; all hydrogen peroxide molecules are coordinated to Ba²⁺ cations.     

Syntheses, structures and properties of 3D inorganic-organic hybrid frameworks constructed from lanthanide polymer and Keggin-type tungstosilicate

Inorganic-organic hybrid frameworks, namely [Ce(H₂O)₃(pdc)]₄[SiW₁₂O₄₀]·6H₂O 1, [M(H₂O)₄(pdc)]₄[SiW₁₂O₄₀]·2H₂O (M=Ce for 2a, La for 2b, Nd for 2c; H₂pdc=pyridine-2,6-dicarboxylic acid) were assembled through incorporation of Keggin-type heteropolyanion [SiW₁₂O₄₀]⁴⁻ within the voids of lanthanides-pdc network as pillars or guests under hydrothermal condition. Single-crystal X-ray analyses of these crystals reveal that compound 1 presents 3D pillar-layered framework with the [SiW₁₂O₄₀]⁴⁻ anions located on the square voids of the two-dimensional Ce-pdc bilayer. Compounds 2a-c are isostructural and constructed from 3D Ln-pdc-based metal-organic framework (MOF) incorporating noncoordinating guests Keggin structure [SiW₁₂O₄₀]⁴⁻. Solid-state properties of compounds 1 and 2a-c such as thermal stability and photoluminescence have been further investigated.     

A novel 1D organic-inorganic hybrid based on alternating heteropolyanions [GeMo12O40] and isopolyanions [Mo6O22]

A novel one-dimensional (1D) coordination polymer [{Cu(2,2′-bpy)}₆(Mo₆O₂₂)][GeMo₁₂O₄₀]·H₂O (2,2′-bpy=2,2′-bipyridine), which represents the first example of 1D organic-inorganic hybrid based on a Keggin-type heteropolyanion [GeMo₁₂O₄₀]⁴⁻ and an unprecedented isopolyanion [Mo₆O₂₂]⁸⁻, has been hydrothermally synthesized and characterized by single crystal X-ray diffraction. Crystal data: C₆₀H₅₀Cu₆GeMo₁₈N₁₂O₆₃, monoclinic, P2₁/c, a=13.9344(3), b=20.0329(3), c=17.2151(3) Å; β=94.0220(10)°, V=4793.70(15) Å³, T=293(2) K; Z=2.     

Acetylation of Alcohols Catalyzed by Dodeca-tungsto(molybdo)phosphoric acid

Summary. Acetylation of primary, secondary, and tertiary alcohols was carried out in some refluxing alkyl acetates and in two carboxylic acids with the participation of catalytic amounts of H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, and H₁₄P₅W₃₀O₁₁₀ with good yields and high stereo(regio)specificity under mild reaction condition. H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀ have also shown excellent reactivity in the formylation of 1-butanol with ethyl formate at room temperature and in short reaction times. Heteropolyacid catalysts could be separated after a simple work up and reused for several times.     

Synthesis,properties and photochromism of novel charge transfer compounds with Keggin anions and protonated 2,2′-biquinoline

Several novel compounds with protonated 2,2′-biquinoline (biqui) and Keggin polyoxoanions (α-isomers), having the general formula (Hbiqui)_m[XM₁₂O₄₀]·nsolv, X=P (m=3), Si (m=4); M=Mo, W; n=0, 3; solv=H₂O, N,N-dimethylformamide (dmf), were synthesized and characterized by analytical, spectroscopic and X-ray diffraction techniques. Electronic spectroscopy (visible/UV) indicated the presence of intermolecular charge transfer between the organic and inorganic moieties in the solid state. Evidence for the existence of intermolecular electronic interaction in solution was found for compounds with the [SiW₁₂O₄₀]⁴⁻ anion, a fact quite uncommon for charge transfer compounds based on Keggin anions. A single crystal X-ray diffraction study could be performed on (Hbiqui)₄[SiW₁₂O₄₀]·3dmf crystals, but the refinements revealed the presence of highly disordered 2,2′-biquinoline molecules and α-[SiW₁₂O₄₀]⁴⁻ anions. Photosensitivity to sunlight and to W-lamp visible light was assessed for all compounds. Photochromic properties were found for solids with [XMo₁₂O₄₀]^m− Keggin anions. Reduction of these anions upon irradiation was observed by diffuse reflectance and EPR spectroscopy. After a minimum of 5 h under sunlight, the extent of anion reduction followed the order (Hbiqui)₃[PMo₁₂O₄₀]·3dmf>(Hbiqui)₄[SiMo₁₂O₄₀]·3dmf>(Hbiqui)₃[PMo₁₂O₄₀]>(Hbiqui)₄[SiMo₁₂O₄₀]·4H₂O. The Kurtz powder test was used to evaluate the second-order non-linear optical properties of the prepared compounds. (Hbiqui)₄[SiW₁₂O₄₀]·3H₂O originated a second harmonic generation signal with intensity about 15% that of urea for 1064 nm radiation.     

A Study of the Acid Properties of Structurally and Compositionally Different Heteropoly Acids in Acetic Acid

The acid properties of heteropoly acids of the following three structure types were studied by conductometry in acetic acid: Keggin (H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, H₄SiW₁₂O₄₀, H₃PW₁₁ThO₃₉; and H₅PW₁₁XO₄₀, where X(IV) = Ti or Zr), Dawson (-H₆P₂W₁₈O₆₂and -H₆P₂Mo₁₈O₆₂), and H₆P₂W₂₁O₇₁(H₂O)₃. These compounds are electrolytes that dissociate in only the first step of this solvent. The thermodynamic dissociation constants of the heteropoly acids were calculated by the Fuoss–Kraus method. The Hammett acidity functions H ₀of the solutions of H₅PW₁₁XO₄₀, H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, and H₆P₂W₂₁O₇₁(H₂O)₃in 85% acetic acid at 25°C were determined by the indicator method. All of the test heteropoly acids were found to be strong acids.     

Synthesis of N-substituted amides by the Ritter reaction with heteropoly acids as catalysts

Reactions of a number of nitriles with camphene in the presence of the heteropoly acids H₃PW₁₂O₄₀, H₇PMo₁₂O₄₂, and H₄SiW₁₂O₄₀ as catalysts were studied. In all cases, N-substituted amides were obtained in sufficiently high yields. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 374–376, February, 2006.     

A novel hybrid material based on two symmetrically independent Keggin polyoxoanions: [NH3-CH(CH3)COOH][H3O]8[PMo12O40]3.4NH3CH(CH3)COO

Novel polyoxometalate-based organic-inorganic hybrid [NH₃-CH(CH₃)COOH][H₃O]₈[PMo₁₂O₄₀]₃.4NH₃CH(CH₃)COO was synthesized and characterized by ³¹P, ¹H, ¹³C NMR and IR spectroscopies, elemental analysis and single crystal X-ray determination. Two of the PMo₁₂O₄₀ ^3? anions in the title hybrid are symmetrically equivalent. They are crystallographically independent from the third PMo₁₂O₄₀ ^3? polyoxoanion, in the case of various interactions with neighboring components in the crystal network (i.e. ⁺NH_3-CH(CH₃)-COOH and H₃O⁺ cations, ₊NH₃CH(CH₃)COO^? zwitterions and polyoxoanions). The compound crystallizes in an orthorhombic C222 space group with a = 16.0392(16) Å, b = 34.480(4) Å, c = 12.8968(13) Å and Z = 2.     

Cationic polymerization of isobutyl vinyl ether coinitiated with heteropolyacid or its salts in aqueous medium

The suspension cationic polymerization of isobutyl vinyl ether (IBVE) in aqueous medium could be achieved by using H₃PW₁₂O₄₀, AlPW₁₂O₄₀, FePW₁₂O₄₀, K₃PW₁₂O₄₀, or Na₃PW₁₂O₄₀ as efficient water‐tolerant coinitiators in the presence of HCl. The addition reaction of IBVE with H₂O occurred to form IBVE–H₂O adduct and then subsequent decomposition immediately took place or turned to acetaldehyde diisobutyl acetal (A) in the presence of AlPW₁₂O₄₀, and ( A ) decomposed rapidly to form 2‐isobutanol ( B ) and acetaldehyde ( C ). Cationic polymerization of IBVE in aqueous medium was promoted greatly with increasing HCl concentration and proceeded extremely rapidly to get high polymer yield even at low concentration of AlPW₁₂O₄₀ of 0.3 mM. A sufficient amount of HCl was needed to decrease the hydrolysis of initiator IBVE–HCl and to accelerate the polymerization in aqueous medium simultaneously. The yield and molecular weight of poly(IBVE) increased with increasing concentrations of HCl and AlPW₁₂O₄₀ or with decreasing temperature. The isotactic‐rich poly(IBVE)s with m diad of around 60%, having M_n of 1200–4500 g mol^?1 and monomodal molecular weight distribution could be obtained via cationic polymerization of IBVE in aqueous medium. This is the first example of cationic polymerization of IBVE in aqueous medium coinitiated by heteropolyacid and its salts. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Hydrothermal syntheses and crystal structures of crystalline catalysts based on 3-D Ln3+–pdc2− frameworks and [BW12O40]5− and their heterogeneous photocatalytic oxidation of thiophene

Five [BW₁₂O₄₀]^{5 ?} -containing metal-organic frameworks (MOFs), {K[Ln(H₂O)₄(pdc)]₄}[BW₁₂O₄₀]·2H₂O (Ln=La 1 and Ce 2, H₂pdc = pyridine-2,6-dicarboxylate) and {K[Ln(H₂O)₃(pdc)]₄}[BW₁₂O₄₀]·6H₂O (Ln=Tb 3, Dy 4 and Er 5), are synthesized hydrothermally. Ln³⁺ and pdc^2? are built into 3-D MOF segments containing large channels and cavities which are occupied by [BW₁₂O₄₀]^{5 ?} . Herein, we report MOF-containing polyoxometalates (POMs) as photocatalysts to oxidize thiophene with O₂ as the oxidant. Photo-excited state species ([BW₁₂O₄₀]^5??) are generated under UV irradiation and then H₂O is oxidized into OH˙ radicals and O₂ is reduced into O₂ ^2?. The active oxygen species (O₂ ^2?, OH˙) oxidize thiophene in the presence of photocatalysts and SO₃, CO₂, and H₂O are obtained as photoproducts. ESR measurements provide evidence that OH˙ species are generated during photocatalysis.     

Hydrocarbon oxidation with an oxygen-hydrogen mixture: Catalytic systems based on the interaction of platinum or palladium with a heteropoly compound

A series of studies of hydrocarbon oxidation by the O₂ + H₂ mixture in the presence of catalytic systems based on Pt or Pd and a heteropoly compound (HPC) is reviewed. The catalytic systems were prepared from Pd(II) complexes with the heteropoly tungstate anions PW₁₁O ₂₉ ^7? and PW₉O ₃₄ ^9? , the complex salt [Pt(NH₃)₄][H₂Mo₁₂O₄₀]₂ · 7H₂O, mixtures of H₂PtCl₄ or H₂PtCl₆ with H_{3 + n} PMo_{12 ? n} V _n O₄₀ (n = 0–3) heteropoly acids, or supported platinum dispersed in HPC solutions. The interaction of metal ions and particles with HPCs in the initial state and after thermal and redox treatments was investigated by NMR, IR spectroscopy, XPS, EXAFS, HREM, and TPR. The catalytic systems were tested in the liquid-phase oxidation of alkanes, cyclohexane, cycloalkenes, benzene, toluene, and phenol with the O₂ + H₂ mixture at low temperatures. Effective supported catalysts based on platinum nanoparticles associated with the redox-active HPCs H₃PMo₁₂O₄₀ and H₄PMo₁₁VO₄₀ were prepared for gas-phase benzene oxidation into phenol. The oxidation mechanism includes the interaction between dioxygen and platinum (or palladium) and the participation of the HPC in the formation of active oxygen species of radical nature.     

Acidity of Solutions of Heteropoly Acids with Various Structures and Compositions

Hammett acidity functions H ₀ of solutions of heteropoly acids H₅PW₁₁XO₄₀ (X(IV) = Ti, Zr), H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₆P₂W₂₁O₇₁, and H₂₁B₃W₃₉O₁₃₂, as well as HClO₄ and CF₃SO₃H, in water and 90% aqueous acetone and acetonitrile, are measured at 20°C by the indicator method. In aqueous solutions all acids under study have the same strength, and in organic solvents their acidities differ. A correlation between the catalytic activity and acidity of the solution is found for the condensation of acetone to mesityl oxide.     

Synthesis, crystal structure and characterization of a 2-D network organic-inorganic hybrid polymer with [α-BW12O40]5− as building blocks

A two-dimensional network compound [Ce(DMF)₄(H₂O)][α-BW₁₂O₄₀]·H₂O·(HDMA)₂ (HDMA = protoned dimethylamine, DMF = N,N-dimethylformamide) was synthesized from α-H₅BW₁₂O₄₀·nH₂O, Ce(NO₃)₃·6H₂O and DMF and characterized by IR, UV spectra and TG-DTA. The result of the X-ray single crystal diffraction indicates that the crystal is monoclinic, space group P2₁/n, with unit cell dimensional: a = 1.1983(3), b = 2.4216(5), c = 1.9517(4) nm, β = 92.91(3)°, Z = 4, R ₁ = 0.07710, wR ₂ = 0.1416. Structural analysis indicates that every [Ce(DMF)₄(H₂O)]³⁺ building block is surrounded by three adjacent [α-BW₁₂O₄₀]^5? polyanions, meanwhile, every [α-BW₁₂O₄₀]^5? polyanion interconnects with three neighboring [Ce(DMF)₄(H₂O)]³⁺ subunits, by making use of which two-dimensional network structure can be constructed. The result of thermogravimetric analysis manifests that the title compound has two-stage weight loss and the decomposition temperature of the title polyanionic framework is 560°C. The electrochemical analysis shows the title polyanion has three-step redox processes in the pH = 4–7 media.     

Esterification of n-Butanol with Acetic Acid in the Presence of Heteropoly Acids with Different Structures and Compositions

The esterification reaction of n-butanol with acetic acid ([BuOH] : [HOAc] = 1 : 15 mol/mol; 55°C, 5% H₂O) was studied in the presence of tungsten heteropoly acids of the Keggin (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₅PW₁₁TiO₄₀, H₅PW₁₁ZrO₄₀, and H₃PW₁₁ThO₃₉) and Dawson structure (-H₆P₂W₁₈O₆₂, H₆P₂W₂₁O₇₁(H₂O)₃, H₆As₂W₂₁O₆₉(H₂O), and H₂₁B₃W₃₉O₁₃₂). The reaction orders with respect to H₆P₂W₂₁O₇₁(H₂O)₃, H₃PW₁₂O₄₀, and H₆P₂W₁₈O₆₉are equal to 0.78, 1.00, and 0.97, respectively. It was found that the reaction rate depends on the acidity, as well as on the structure and composition of heteropoly acids. The H₂₁B₃W₃₉O₁₃₂heteropoly acid is most active, whereas the Keggin-structure heteropoly acids exhibit the lowest activities. Of the Keggin structure heteropoly acids, H₅PW₁₁ZrO₄₀exhibits the highest activity because of the presence of a Lewis acid site in its structure.     

A study of complexation of chloral hydrate with heteropoly anions having various structures

¹H NMR was applied to study the interaction of chloral hydrate in deuterionitrobenzene solution with tetrabutylammonium salts of the heteropoly acids (HPA) belonging to five structural types: Keggin (H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, H₄SiW₁₂O₄₀), Dawson (-H₆P₂W₁₈O₆₂, -H₆P₂Mo₁₈O₆₂, -H₄S₂Mo₁₈O₆₂), H₆P₂W₂₁O₇₁(H₂O)₃, H₆As₂W₂₁O₆₉(H₂O), and H₂₁B₃W₃₉O₁₃₂. The surface of the HPA anions is nonuniform in acid-base properties. A general rule for all HPA was found, namely, that the HPA acidity increases with a decrease in the specific anion charge (per W or Mo atom).     

FT-IR and microbalance studies of diammonium ions formation in heteropolyacids

The sorption of gaseous ammonia into solid polyoxometalates such as the Keggin (H₄SiMo₁₂O₄₀, H₄SiW₁₂O₄₀ and H₃PW₁₂O₄₀) and Dawson type (H₆P₂W₁₈O₆₂) heteropolyacids was studied. The combination of microbalance measurements and FT-IR spectroscopy confirmed the formation of diammonium ion N₂H₇⁺ in the bulk of heteropolyacids of both types, which was found to depend on both the ammonia equilibrium pressure and sorption temperature. The diffusion coefficients of the ammonia molecules penetrating into the bulk of heteropolyacids were calculated.     

Synthesis and physicochemical properties of Zr-MCM-41 mesoporous molecular sieves and Pt/H3PW12O40/Zr-MCM-41 catalysts

For the first time, modifications of the surface and framework of Si-MCM-41 by depositing a heteropolyacid on the surface and by introducing foreign Zr⁴⁺ ions into the framework are investigated. The Zr-modified Si-MCM-41 mesoporous materials (hereafter referred as WSZn, n=Si/Zr=25, 15, 8, 4) were synthesized through a surfactant-templated preparation approach, using low-cost fumed silica as the Si precursor. After impregnation with 25 wt% of H₃PW₁₂O₄₀, the surface Brönsted acidity of the Pt/H₃PW₁₂O₄₀/WSZn catalysts was greatly enhanced by 2-10 times relative to the bare WSZn support. Two kinds of supported heteropolyacids were formed: (i) bulk-like heteropolyacid crystals with unchanged Keggin structures, and (ii) highly dispersed heteropolyacid with distorted Keggin units. The formation of various kinds of heteropolyacid structures is closely related to the interaction between the heteropolyanions and the hydroxyl groups in the host support.     

A Keggin heteropoly acid as an efficient catalyst for an expeditious, one-pot synthesis of 1-methyl-2-(hetero)arylbenzimidazoles

The Keggin heteropoly acid, silicotungstic acid, H₄SiW₁₂O₄₀, has been demonstrated to be highly efficient for an expeditious, one-pot synthesis of 1-methyl-2-(hetero)arylbenzimidazoles from N-methyl-1,2-phenylenediamine and (hetero)aryl aldehydes in ethyl acetate at room temperature. The catalyst works equally well for N-phenyl-1,2-phenylenediamine.     

Heteropolymolybdate–amino acid complexes: synthesis,characterization and biological activity

Three Keggin-type polyoxometalates functionalized by amino acids, (C₅H₁₃N₂O₂)₂(H₃O)PMo₁₂O₄₀·8H₂O 1, (C₅H₁₄N₂O₂)₂SiMo₁₂O₄₀·12H₂O 2 and (C₅H₁₄N₂O₂)₂GeMo₁₂O₄₀·12H₂O 3, were synthesized and characterized by elemental analysis, IR and ¹H?NMR spectra and single-crystal X-ray diffraction. The X-ray crystallographic study showed that the structures of the three compounds involved N–H···O and O–H···O hydrogen bonds among the protonated ornithine cations, water molecules and the heteropolyanion cluster, and thus represent a model interaction between polyoxometalates and proteins. These complexes display inhibitory actions to the human cancer cells Hela and PC-3?m in vitro.