Controlled Assembly of Ru-Containing Polyoxometalates for Photocatalytic Activity of the Primary Amine Coupling Reaction

Three Ru-induced structural interconversion polyoxometalates (POMs), Na₁₃H₅[Ru₄(H₂O)₂(Cl)₂(WO₂)₄(AsW₉O₃₃)₄]·43H₂O (1), K₅Na₉H₈[Ru₂(WO₂)₄(AsW₉O₃₃)₄]·50H₂O (2), and KNa₁₃H₁₄[(WO₂)₄(AsW₉O₃₃)₄]·34H₂O (3), were successfully synthesized and thoroughly characterized. Interconversion of structures was accomplished by changing the number of active sites for compounds 1-3. All three compounds contain one {As₄W₄₀O₁₄₀} unit, showing similar structural characteristics except for the active center number (Ru). Interestingly, compound 1 [turnover number (TON)= 486; turnover frequency (TOF)= 20 h^-1] showed highly efficient photocatalysis in achieving oxidative coupling of primary amines. Compound 2 (TON = 406, TOF = 17 h^-1) was also found to promote the oxidative coupling with relatively poor efficiency; however, compound 3 (TON = 178; TOF = 7.4 h^-1) had no obvious contribution to the coupling reaction system, and a chain of evidence indicates that the catalytic performances are strongly dependent on element contents of active sites. Furthermore, the Ru-containing POM-based photocatalysts are conveniently recyclable and reusable during the photocatalytic processes. This study demonstrates the possibility of tuning the catalytic efficiency and stability of POM-based photocatalysts by well designing and controlling their structures. The possible reaction mechanism for the photocatalysis synthesis of imine product is also proposed based on experimental studies.

Polyoxometalate-supported metal carbonyl derivatives: from synthetic strategies to structural diversity and applications

This review aims to give an overview of the POM-supported metal carbonyl complexes obtained so far, focusing on their structural diversity and potential photochemical and catalytic properties.

Covalent hybrids based on Re(i) tricarbonyl complexes and polypyridine-functionalized polyoxometalate: synthesis, characterization and electronic properties

A series of [Re(CO)₃Br(N^N)] (N^N = substituted 2,2'-bipyridine ligand) complexes based on polypyridine-functionalized Dawson polyoxometalate (1-3) has been synthesized. The new hybrids (4-6) were characterized by various analytical techniques, including absorption, vibrational and luminescence spectroscopies as well as electrochemistry. Both units, the polyoxometalate and the transition metal complex, retain their intrinsic properties. Their combination in the newly prepared hybrids results in improved photosensitization in the high-energy visible region. However, a complete quenching of the emission for the [Re(CO)₃Br(N^N)] complexes is observed due to formation of a charge separated state, Re(ii) - POM^-, as shown by quenching experiments as well as theoretical modelling via DFT.

Immobilization of carbonyl rhenium tripods on the surface of a trinickel-substituted Dawson-type polyoxotungstate

A monomeric trinickel(ii)-substituted phosphotungstate [H₉P₂W₁₅O₆₂Ni₃]⁹⁻ ion is stabilized by grafting three {Re(CO)₃} organometallic groups on the surface of a trinickel cluster for the first time. The resulting polyanions [P₂W₁₅O₅₆Ni₃(H₂O)₃(μ₃-OH)₃(Re(CO)₃)₃]⁶⁻ stacked along the a-axis to form a wavy line.

Discovery and isolation of the trans-isomers of two 1 : 2-type lanthanide-containing monolacunary Dawson-type tungstophosphates: [LnIII(α2-P2W17O61)2]17− (Ln = La, Ce)

Two novel trans-isomers of 1 : 2-type lanthanide-containing monolacunary Dawson-type tungstophosphates [Ln(α₂-P₂W₁₇O₆₁)₂]¹⁷⁻ (Ln = La^III (1), Ce^III (2)) were successfully isolated and characterized.

Transition Metal Substitution Effects on Metal-to-Polyoxometalate Charge Transfer

A series of hetero-bimetallic transition metal-substituted polyoxometalates (TMSPs) were synthesized based on the Co(II)-centered ligand [Co(II)W11O39](10-). The eight complex series, [Co(II)(M(x)OHy)W11O39]((12-x-y)-) (M(x)OHy = V(IV)O, Cr(III)(OH2), Mn(II)(OH2), Fe(III)(OH2), Co(II)(OH2), Ni(II)(OH2), Cu(II)(OH2), Zn(II)(OH2)), of which six are reported for the first time, was synthesized starting from [Co(III)W11O39](9-) and studied using spectroscopic, electrochemical, and computational techniques to evaluate the influence of substituted transition metals on the photodynamics of the metal-to-polyoxometalate charge transfer (MPCT) transition. The bimetallic complexes all show higher visible light absorption than the plenary [Co(II)W12O40](6-) and demonstrate the same MPCT transition as the plenary complex, but they have shorter excited-state lifetimes (sub-300 ps in aqueous media). The decreased lifetimes are rationalized on the basis of nonradiative relaxation due to coordinating aqua ligands, increased interaction with cations due to increased negative charge, and the energy gap law, with the strongest single factor appearing to be the charge on the anion. The most promising results are from the Cr- and Fe-substituted systems, which retain excited-state lifetimes at least 50% of that of [Co(II)W12O40](6-) while more than tripling the absorbance at 400 nm.

Isopentatungstate-supported metal carbonyl derivative: synthesis, characterization, and catalytic properties for alkene epoxidation

An isopentatungstate-supported metal carbonyl derivative has been synthesized and characterized, and can efficiently catalyze alkene epoxidation with high activity.

Synthesis and characterization of a series of novel polyoxometalate-supported carbonyl manganese derivatives

A series of novel heteropolytungstates-supported carbonyl manganese derivatives have been synthesized, which are the first examples of grafting [Mn(CO)₃]⁺ moieties and Mn²⁺ on the tungsto-antimonates/bismutates.