36-Nuclearity Organophosphonate-Functionalized Polyoxomolybdates: Synthesis, Characterization and Selective Catalytic Oxidation of Sulfides

Two Tetra-Nuclear Ln-Substituted Prazine Dicarboxylic Acid-Functionalized Selenotungstates with Catalytic Oxidation of Thioether Properties

Two two-dimensional Ln-substituted prazine dicarboxylic acid-functionalized selenotungstates Na3H9[(H2N(CH3)2]2{(Se4W27O100)[Ln4(H2O)8(Hpzdc)2(pzdc)]}·26H2O [Ln = Nd (1) and Ce (2)]; H2pzdc = 2,3-pyrazine dicarboxylic acid) have been synthesized by one-pot self-assembly strategy, in which the basic polyanion [Se4W27O100]22-was composed of two [SeW8O31]10- fragments, a [SeW9O33]8- segment and an intriguing {SeO} group, simultaneously tetra-nuclear Ln3+ ions with H2pzdc pendants were embedded. Compounds 1 and 2 showed excellent catalytic oxidation of thioether properties within a short time (20 min) with high 100% conversion and 98.9% selectivity. In addition, the pioneering Ln-substituted selenotungstates were used as catalysts to degrade sulfur mustard simulant 2-chloroethyl ethyl sulfide at room temperature with 99% conversion and 100% selectivity. The chemical kinetic experiment studies revealed that the catalytic reaction was in compliance with the first-order reaction, and the kinetic half-life (t1/2) values were 3.814 and 3.849 min, respectively.

POM-based porous supramolecular framework for the efficient sulfide-sulfoxide transformation with low molar O/S ratio

The selective oxidation of organic sulfides is a pivotal avenue to prepare sulfoxides that can act as synthetic intermediates of fine chemicals, bioactive molecules, and asymmetric catalysis ligands. To construct...

Organo-Polyoxometalate-Based Hydrogen-Bond Catalysis

Several urea-inserted organo-polyoxometalates (POMs) derived from polyoxotungstovanadate [P₂ V₃ W₁₅ O₆₁ ]^9- were prepared. The insertion of the carbonyl into the polyoxometallic framework activates the urea toward Hydrogen-bond catalysis. This was shown on the Friedel-Crafts arylation of trans-β-nitrostyrene. Modelling shows that the most stable form of the organo-POMs features a cis-trans arrangement of the two N-H bonds, but that the likely catalytically active trans-trans form is accessible at room temperature. Finally, it is possible that the oxo substituents next to the vanadium atoms may help the approach of the nucleophile via H-bonding.

Flow Electrosynthesis of Sulfoxides, Sulfones, and Sulfoximines without Supporting Electrolytes

An efficient electrochemical flow process for the selective oxidation of sulfides to sulfoxides and sulfones and of sulfoxides to N-cyanosulfoximines has been developed. In total, 69 examples of sulfoxides, sulfones, and N-cyanosulfoximines have been synthesized in good to excellent yields and with high current efficiencies. The synthesis was assisted and facilitated through a supporting electrolyte-free, fully automated electrochemical protocol that highlights the advantages of flow electrolysis.

Assembly of a Hexameric Cluster of Polyoxomolybdotriphosphonate Builts from [Zn(H2O){TeMo6O21}{N(CH2PO3)3}]6- Subunits and Its Optical and Catalytic Properties

The crown-shaped organotriphosphonate-modified 36-molybdenum cluster (NH₄)₁₈Na₇H₁₁[Zn(H₂O)TeMo₆O₂₁{N(CH₂PO₃)₃}]₆·23H₂O (1) has been synthesized, which is the largest zinc-containing organophosphonate-based polyoxometalate to date. Compound 1 was prepared in buffer solution (pH 5.5) with heptamolybdate and amino trimethylene phosphonic acid (ATMP) as the organic ligand. The polyanion constructed from a hexmeric assembly of [Zn(H₂O){TeMo₆O₂₁}{N(CH₂PO₃)₃}]^6- subunits has been fully investigated by a few characterization methods. In this work, we discovered that 1 exhibited reversible photochromism and it changed from white to reddish brown upon UV irradiation. In addition, compound 1, as a catalyst, can oxidize sulfides to sulfoxides, showing a high yield/conversion and a good selectivity.

Organophosphonate-Functionalized Telluromolybdate Containing a [TeMo10O37]10- Building Block and Its Catalytic Efficiency for Knoevenagel Condensation

A novel organodiphosphonate-based telluromolybdate cluster, (NH₄)₆Na₃H₁₃[TeMo₁₀O₃₇(CoMo₂O₆L)₄]·11H₂O [1; L = (O₃P)₂C(O)(CH₂)₃NH₂], has been successfully synthesized by a simple one-pot aqueous reaction. Intriguingly, the [TeMo₁₀O₃₇]^10- subunit with tetrahedral geometry of TeO₄ is observed in the organophosphonate-functionalized polyoxometalates for the first time. Compound 1 was prepared in a buffer solution (pH = 5.5) with alendronic acid (Ale) and (NH₄)₆Mo₇O₂₄·4H₂O as raw materials. The polyanion [TeMo₁₀O₃₇(CoMo₂O₆L)₄]^22- was constructed from four {Mo₂O₆L} subunits encapsulating an interesting Te-Mo heterometal subunit [TeMo₁₀O₃₇]^10- through four CoO₆ octahedra and has been fully characterized by routine techniques. In addition, compound 1, as a heterogeneous catalyst, shows good conversion (92%) and high selectivity (99%) for Knoevenagel condensation reaction.

Regulating the catalytic activity of multi-Ru-bridged polyoxometalates based on differential active site environments with six-coordinate geometry and five-coordinate geometry transitions

Five-coordinate geometry around ruthenium with highly exposed active sites has attracted intensive scientific interest due to its superior properties and extensive applications. Herein, we report a series of structurally controllable multi-Ru-bridged polyoxometalates, K5NaH10[{Ru4(H2O)n}(WO2)4(AsW9O33)4]·mH2O {1, 1-dehyd-373K, 1-dehyd-473K, 1-dehyd-573K; n = 4, m = 36; n = 4, m = 6; n = 4, m = 0; n = 0, m = 0} fabricated through a feasible assembly strategy using arsenotungstate {2, KNa12H17Cl2(As4W40O140)·29H2O} as a structure-directing unit. Systematic characterization methods identified that the six-coordinate geometry can successfully transform into five-coordinate geometry about active sites (Ru) by removing aqua ligands under high reaction temperatures. All the multi-Ru-bridged polyoxometalates demonstrated strong stability and catalytic effectiveness in the transformation of 1-(4-chlorophenyl)ethanol to 4'-chloroacetophenone under very mild conditions. 1-dehyd-573K, specifically, achieves the best catalytic effectiveness with a turnover frequency (TOF) = 25 100·h-1 owing to its unique five-coordinate geometry on the Ru sites. To our knowledge, 1-dehyd-573K outperforms other POM-based catalysts in the oxidative catalysis of 1-(4-chlorophenyl)ethanol. The heterogeneous polyoxometalates were also proven to be strongly reusable, with their structural integrities well maintained after multiple-cycle catalytic reactions.