H Evolution at a Reduced Hybrid Polyoxometalate and Its Vanadium-Oxo Derivative Used as Molecular Models for Reducible Metal Oxides.

We herein report our investigations on the use of a tris-silanol-decorated polyoxotungstate, [SbWO(tBuSiOH)], as a molecular support model to describe the coordination of an isolated vanadium atom at metal oxides, focusing on the reactivity of the reduced derivatives in the presence of protons. Accumulation of electrons and protons at an active site is a main feature associated with heterogeneous catalysts able to conduct the (oxy)dehydrogenation of alkanes or alcohols. Our results indicate that two-electron reduced derivatives release H upon protonation, a reaction that probably takes place at the polyoxotungstic framework rather than at the vanadium center.

When Identification of the Reduction Sites in Mixed Molybdenum/Tungsten Keggin-Type Polyoxometalate Hybrids Turns Out Tricky.

The mixed molybdenum/tungsten Keggin-type polyoxometalate (POM) hybrid (TBA)[PWMoO{Sn(CHI)}] (TBA = -butylammonium) has been prepared by the reaction between [α-PWMoO] and [ClSn(CHI)] in dried acetonitrile, in the presence of tetra--butylammonium bromide. A further coupling reaction affords the ferrocenyl derivative (TBA)[PWMoO{Sn(CH)C≡C(CH)Fc}]. The POM hybrids have been thoroughly characterized by NMR and IR spectroscopies.

Supramolecular assemblies of organo-functionalised hybrid polyoxometalates: from functional building blocks to hierarchical nanomaterials.

This review provides a comprehensive overview of recent advances in the supramolecular organisation and hierarchical self-assembly of organo-functionalised hybrid polyoxometalates (hereafter referred to as hybrid POMs), and their emerging role as multi-functional building blocks in the construction of new nanomaterials. Polyoxometalates have long been studied as a fascinating outgrowth of traditional metal-oxide chemistry, where the unusual position they occupy between individual metal oxoanions and solid-state bulk oxides imbues them with a range of attractive properties ( solubility, high structural modularity and tuneable properties/reactivity). Specifically, the capacity for POMs to be covalently coupled to an effectively limitless range of organic moieties has opened exciting new avenues in their rational design, while the combination of distinct organic and inorganic components facilitates the formation of complex molecular architectures and the emergence of new, unique functionalities.

Modeling the Oxygen Vacancy at a Molecular Vanadium(III) Silica-Supported Catalyst.

Here we report on the use of a silanol-decorated polyoxotungstate, [SbWO( BuSiOH)] (1), as a molecular support to describe the coordination of a vanadium atom at a single-site on silica surfaces. By reacting [V(Mes)·thf] (Mes = 2,4,6-trimethylphenyl) with 1 in tetrahydrofuran, the vanadium(III) derivative [SbWO( BuSiO)V(thf)] (2) was obtained. Compound 2 displays the paramagnetic behavior expected for a d-V high spin complex (SQUID measurements) with a triplet electronic ground state (ca.

Functionalization and post-functionalization: a step towards polyoxometalate-based materials.

Polyoxometalates (POMs) have remarkable properties and a great deal of potential to meet contemporary societal demands regarding health, environment, energy and information technologies. However, implementation of POMs in various functional architectures, devices or materials requires a processing step. Most developments have considered the exchange of POM counterions in an electrostatically driven approach: immobilization of POMs on electrodes and other surfaces including oxides, embedding in polymers, incorporation into Layer-by-Layer assemblies or Langmuir-Blodgett films and hierarchical self-assembly of surfactant-encapsulated POMs have thus been thoroughly investigated.

Modifying the reactivity in the homologation of propane by introducing aryloxide ligands on a silica supported zirconium alkyl system.

Grafting the well-defined molecular complexes [(ArO)Zr(CH2tBu)3], , and [(ArO)2Zr(CH2tBu)2], , on SiO2-(700) (ArO=2,6-Ph2C6H3O) gives the corresponding monosiloxy surface complexes [([TRIPLE BOND]SiO)Zr(CH2tBu)2(OAr)] and [([TRIPLE BOND]SiO)Zr(CH2tBu)(OAr)2] as major surface species as evidenced by mass balance analysis, IR and NMR spectroscopies. In both cases, minor cyclometallated species (ca. 20%) are also probably formed during the grafting process.

Synthesis and metal complexes of chiral c(2)-symmetric diamino-bisoxazoline ligands.

A synthetic route to tetradentate chiral N(4) ligands has been developed with the aim to study the potential of corresponding iron and manganese complexes as catalysts for enantioselective epoxidation. These ligands, which contain two oxazoline rings and two trialkylamino groups as coordinating units, are readily prepared in enantiomerically pure form by the reaction of chiral 2-chloromethyloxazolines with achiral N,N'-dimethylethane-1,2-diamine or chiral (R,R)-N,N'-dimethylcyclohexane-1,2-diamine. The ligands derived from N,N'-dimethylethane-1,2-diamine reacted with anhydrous metal halides MnCl(2) and FeCl(2) in a stereoselective manner to give octahedral mononuclear complexes that have the general formula Delta-[(L)MCl(2)].

Use of calix[4]arenes in the redox chemistry of lanthanides: the reduction of dinitrogen by a calix[4]arene-samarium complex.

The synthesis and structural characterization of a samarium-dinitrogen complex supported by a calix[4]arene ligand in which the N-N bond distance has been stretched to 1.611(16) Angstrom are described. The central mu(3)-eta(2):eta(2):eta(2)-hydrazido tetraanion formed is bonded to three Sm(III) centers with an overall butterfly-type arrangement.

Alkali and alkaline-earth-metalated forms of calix[4]arenes: synthons in the synthesis of transition metal complexes.

This is the first coherent report on the metalation of calix[4]arene by alkali and alkaline-earth metals, thus providing a high-yield production of appropriate synthons for the synthesis of transition metal calix[4]arenes. In addition, various facets of the coordination chemistry by calix[4]arene anions of alkali and alkaline-earth metal ions have been singled out. Among them: 1) the exo and endo coordination of metal ions by the calix[4]arene skeleton; 2) the pi solvation of the ions by the phenyl rings; 3) the ion-carrier properties of metallacalix[4]arenes; 4) the simulation of the kinetically labile coordination sphere of alkali and alkaline-earth metal ions by a polyoxo rigid skeleton.