Palladium-Catalyzed Heck Reaction of Polyoxometalate-Functionalised Aryl Iodides and Bromides with Olefins

Bridge improvement work: maximising non-linear optical performance in polyoxometalate derivatives

New phenyl and stilbene-bridged polyoxometalate (POM) charge-transfer chromophores with diphenylamino donor groups produce, respectively, the highest intrinsic and absolute quadratic hyperpolarisabilities measured for such species. The β0,zzz obtained for the phenyl bridge - at 180 × 10-30 esu - is remarkable for a short conjugated system while changing to the stilbene (260 × 10-30 esu) produces a substantial increase in non-linearity for a minimal red-shift in the absorption profile. Together with TD-DFT calculations, the results show that maximising conjugation in the π-bridge is vital to high performance in such "POMophores".

Insights into organic-inorganic hybrid molecular materials: organoimido functionalized polyoxomolybdates

Polyoxometalates (POMs) are polyatomic anions that comprise transition metal group 5 (V, Nb, Ta) or group 6 (Mo, W) oxyanions connected together by shared oxygen atoms. POMs are fascinating because of their exclusive and remarkable characteristics. One of the most interesting features of POMs is their capability to function as an electron relay by performing stepwise multi-electron redox reactions while maintaining their structural integrity. Functionalization of POMs with amino organic compounds results in organoimido derivatives of polyoxometalates, which have aroused interest due to augmentation of their properties. Comprehensive study has shown that the synthesis methodologies to obtain desired organoimido derivatives of POMs by employing various imido-releasing reagents have progressed drastically in recent decades, particularly the innovative DCC-dehydrating technique. These organoimido functionalized POMs have been used as major building blocks to develop unique nanostructured organic-inorganic hybrid molecular materials. Many conventional organic synthesis processes such as Pd-catalyzed carbon-carbon coupling and esterification reactions have been performed with organoimido functionalized POMs where the presence of POM triggered the reaction process. Thus, investigation of the reactivity of organoimido derivatives of POMs foreshadows the intriguing future of POMs chemistry.

Hybrid polyoxometalates as post-functionalization platforms: from fundamentals to emerging applications

Polyoxometalates (POMs) represent an important group of metal-oxo nanoclusters, typically comprised of early transition metals in high oxidation states (mainly V, Mo and W). Many plenary POMs exhibit good pH, solvent, thermal and redox stability, which makes them attractive components for the design of covalently integrated hybrid organic-inorganic molecules, herein referred to as hybrid-POMs. Until now, thousands of organic hybrid-POMs have been reported; however, only a small fraction can be further functionalized using other organic molecules or metal cations. This emerging class of 'post-functionalizable' hybrid-POMs constitute a valuable modular platform that permits coupling of POM properties with different organic and metal cation functionalities, thereby expanding the key physicochemical properties that are relevant for application in (photo)catalysis, bioinorganic chemistry and materials science. The post-functionalizable hybrid-POM platforms offer an opportunity to covalently link multi-electron redox responsive POM cores with virtually any (bio)organic molecule or metal cation, generating a wide range of materials with tailored properties. Over the past few years, these materials have been showcased in the preparation of framework materials, functional surfaces, surfactants, homogeneous and heterogeneous catalysts and light harvesting materials, among others. This review article provides an overview on the state of the art in POM post-functionalization and highlights the key design and structural features that permit the discovery of new hybrid-POM platforms. In doing so, we aim to make the subject more comprehensible, both for chemists and for scientists with different materials science backgrounds interested in the applications of hybrid (POM) materials. The review article goes beyond the realms of polyoxometalate chemistry and encompasses emerging research domains such as reticular materials, surfactants, surface functionalization, light harvesting materials, non-linear optics, charge storing materials, and homogeneous acid-base catalysis among others.

Core–shell structured magnetic silica supported propylamine/molybdate complexes: an efficient and magnetically recoverable nanocatalyst

A novel core–shell structured magnetic silica supported propylamine/molybdate complex (Fe₃O₄@SiO₂/Pr-NMo[Mo₅O₁₈]) is prepared, characterized and applied as an effective and easily recoverable nanocatalyst in the synthesis of pyrano-pyrazole derivatives.

The Heck reaction as a tool to expand polyoxovanadates towards thiol-sensitive organic–inorganic hybrid fluorescent switches

Pd-catalysed Heck cross-coupling reactions between organically-tailored polyoxovanadates and a variety of olefins were realised. The synthesised organic–inorganic hybrids pave the way for the redox-driven luminescence switching, opening up great perspectives in tracing smart reducing agents such as e.g. toxic thiols.

Nucleophilic substitution reaction for rational post-functionalization of polyoxometalates

Substitution reactions of polyoxometalate–organic hybrid materials provide a post-functionalization protocol to bring in various additional functional groups.

New sterically encumbered arylimido hexamolybdates for organic oxidation reactions

Surface modification of the parent hexamolybdate by aryl amines results in useful catalysts for the oxidation of cyclohexene to cyclohexene epoxide and benzyl alcohol to benzaldehyde and benzoic acid.

A covalent polyoxomolybdate-based hybrid with remarkable electron reservoir properties

A new polyoxomolybdate-based hybrid platform TBA4[PMo11O39{Sn(p-C6H4I)}] is reported. The presence of a post-functionalisable iodo-aryl moiety allows the grafting of a ferrocenyl moiety onto the POM. The electrochemical characterisation shows the effect of molybdenum on the electron reservoir properties of POM-based hybrids, which are further enhanced upon the addition of an acid.

N-alkylation of organo-imido substituted polyoxometalates: an efficient and stoichiometric approach for the easy post-modification of polyoxometalates

A high-yield post-functionalization protocol developed here provides an easy inclusion of the desired organic groups on a POM's highly negative surface.

Postfunctionalization of polyoxometalates: an efficient strategy to construct organic–inorganic zwitterions

A class of monoorganoimido-substituted hexamolybdates containing a pyridine group have been firstly synthesized. Furthermore, a reaction protocol of alkylation based on the resulting pyridine-functionalized hexamolybdates has been developed, with which a type of zwitterionic clusters has been successfully obtained.

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. Meanwhile, the field of organic-inorganic POM hybrids has expanded and offers the opportunity to explore the covalent approach for the organization or immobilization of POMs. In this critical review, we focus on the use of POM hybrids in selected fields of applications such as catalysis, energy conversion and molecular nanosciences and we endeavor to discuss the impact of the covalent approach compared to the electrostatic one. The synthesis of organic-inorganic POM hybrids starting from bare POMs, that is the direct functionalization of POMs, is well documented and reliable and efficient synthetic procedures are available. However, as the complexity of the targeted functional system increases a multi-step strategy relying on the post-functionalization of preformed hybrid POM platforms could prove more appealing. In the second part of this review, we thus survey the synthetic methodologies of post-functionalization of POMs and critically discuss the opportunities it offers compared to direct functionalization.

Theoretical investigation of the mechanism of primary amines reacting with hexamolybdate: an insight into the organoimido functionalization and related reactions of polyoxometalates

The functionalization of polyoxometalates (POMs), especially with an amino group to yield organonitrogenous derivatives of POMs, is an efficient approach to the enrichment of their structures and the diversification of their properties for various applications. The mechanism for the formation of organonitrogenous-derivatized hexamolybdates was explored by investigating the monofunctionalization of the [Mo(6)O(19)](2-) ion with methylamine using the density functional theory (DFT) method. The calculations show that the direct imidoylization of hexamolybdate with methylamine is both kinetically and thermodynamically unfavorable. However, this imidoylization was found to take place readily in the presence of dimethylcarbodiimide (DMC), for which the free-energy barrier was calculated to be +32.5 kcal mol(-1) in acetonitrile. Moreover, various factors controlling the efficiency of the imidoylization were examined. The calculations show that [W(5)MoO(19)](2-) has a relatively lower reactivity than [Mo(6)O(19)](2-), and that the imidoylization of [W(6)O(19)](2-) is an unfavorable process. With respect to the effect of carbodiimides, it is found that the catalytic activity is directly proportional to the electron-withdrawing effects of the substituents. As to the reactivity of R-NH(2) , the computation results indicate that the free-energy barriers of the substitution reactions are linearly correlated with the basicity constants (pK(b)) of the amino groups. It is noteworthy that the introduction of the proton dramatically decreases the free-energy barrier of the imidoylization of [Mo(6)O(19)](2-) catalyzed by DMC to 24.3 kcal mol(-1) in acetonitrile.

Hybrid polyoxometalates: Keggin and Dawson silyl derivatives as versatile platforms

A new series of polyoxometalate-based hybrids has been synthesized. These covalently linked organic-inorganic materials represent valuable elementary building blocks ready for postfunctionalization, using classical organic reactions and couplings. This approach is exemplified by the grafting of an organic chromophore via a Sonogashira coupling.

DMAP-catalyzed esterification of pentaerythritol-derivatized POMs: a new route for the functionalization of polyoxometalates

A pentaerythritol-derived hexavanadate can be easily esterified with acid anhydrides using DMAP as a catalyst, providing a convenient way for the functionalization of polyoxometalates.

Preparation and characterization of Langmuir-Blodgett films of wheel-shaped Cu-20 tungstophosphate and DODA by two different strategies

A novel surfactant-encapsulated organic-inorganic hybrid compound (DODA)(24)Li[Cu(20)Cl(OH)(24)(P(8)W(48)O(184))] x 18 H(2)O (DODA-Cu20) has been prepared from the wheel-shaped tungstophosphate salt K(12)Li(13)[Cu(20)Cl(OH)(24)(H(2)O)(12)(P(8)W(48)O(184))] x 22 H(2)O (Cu20) and dimethyldioctadecylammonium bromide (DODA), and it has been characterized by elemental analysis (EA), thermogravimetric analysis (TGA), (1)H NMR, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) measurements. Monolayer and multilayer films of DODA-Cu20 were fabricated on different substrates by the Langmuir-Blodgett (LB) technique using H(2)O as the subphase. Another type of organic-inorganic hybrid film, DODA/Cu20, was also deposited on the same substrates as used for the film containing DODA-Cu20 under the same conditions by the LB technique using a Cu20 aqueous solution as the subphase and DODA as the cationic amphiphile for comparison. Both thus-prepared organic-inorganic hybrid films were characterized by UV-vis spectroscopy, XRD, transmission and polarized FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The results indicate that stable monolayers at the air-water interface for DODA-Cu20 and at the air-Cu20 solution interface for DODA can be formed and that two LB films containing DODA-Cu20 and DODA/Cu20 constructed by two different methods both exhibit well-ordered lamellar structures. It is proposed that Cu20 exhibits different packing modes in the two LB films depending on the deposition strategy used.