Insights into the Coordination Chemistry of Phosphonate Derivatives of Heteropolytungstates
R. Villanneau, D. Racimor, E. Messner-henning, H. Rousselière, S. Picart, R. Thouvenot, A. Proust, Inorg. Chem., 2011, 50, 1164-1166.

The coordination properties of vacant bis-phosphonate derivatives of polyoxometalates, with easily tunable functions, have been explored. Preparation and crystallographic structure of their La³⁺ and Zr⁴⁺ complexes are described herein.

 Addition of N-Heterocyclic-Carbenes to Ruthenium(VI)-Nitrido Polyoxometalate : a new route to Cyclic Guanidines
C. Besson, J.-H. Mirebeau, S. Renaudineau, S. Roland, S. Blanchard, H. Vezin, C. Courillon, A. Proust, Inorg. Chem., 2011, 50, 2501-2506.

The scope of N-atom transfer from the electrophilic ruthenium(VI) nitrido containing polyoxometalate [PW₁₁O₃₉Ru^VIN]⁴− has been extended to the N-heterocyclic carbene {CH₂(Mes)N}₂C and the coupling product {CH₂(Mes)N}₂CNH₂⁺ characterized by ¹H NMR and high-resolution mass spectrometry. Because guanidines display many fields of applications ranging from biology to supramolecular chemistry, this could afford an original route to the synthesis of cyclic guanidines. This also enlarges the potential of nitrido complexes in the synthesis of heterocycles, mainly illustrated in the literature through the formation of aziridines through N-atom transfer to alkenes. In the course of the reaction, the ruthenium(III)-containing polyoxometallic intermediate [PW₁₁O₃₉Ru^III{NC{N(Mes)CH₂}₂}]⁵⁻ has been thoroughly characterized by continuous-wave and pulsed electron paramagnetic resonance, which nicely confirms the presence of the organic moiety on the polyoxometallic framework, Ru K-edge X-ray absorption near-edge structure, and electrochemistry.

 Polyoxometalates : Powerful Catalysts for Atom-Efficient Cyclopropanations I. Boldini, G. Guillemot, A. Caselli, A. Proust, E. Gallo, Adv. Synth. Catal. 2010, 352,2365-2370.

The polyoxometalate-based catalytic cyclopropanation of olefins by EDA (EDA = ethyldiazoacetate) is reported. The outstanding catalyst productivity (TON up to 100.000) and the use of equimolar EDA/olefin ratio confer to the methodology a high sustainability. Preliminary mechanistic investigations are also discussed.

 Cs₉[(γ-PW₁₀O₃₆)₂Ru₄O₅(OH)(H₂O)₄], a new all-inorganic, soluble catalyst for the efficient visible-light-driven oxidation of water Claire Besson, Zhuangqun Huang, Yurii V. Geletii, Sheri Lense, Kenneth I. Hardcastle, Djamaladdin G. Musaev, Tianquan Lian, Anna Proust and Craig L. Hill
Chem. Commun., 2010, 46, 2784-2786

The tetraruthenium-substituted polyoxometalate Cs₉[(γ-PW₁₀O₃₆)₂Ru₄O₅(OH)(H₂O)₄] was synthesized and structurally, spectroscopically and electrochemically characterized ; it was shown to be a catalyst for visible-light-induced water oxidation.

 Structural, Physicochemical, and Reactivity Properties of an All-Inorganic, Highly Active Tetraruthenium Homogeneous Catalyst for Water Oxidation
Y. V. Geletii, C. Besson, Y. H., Q. Yin, D. G. Musaev, D. Quinonero, R. Cao, K. I. Hardcastle, A. Proust, P. Kogerler, C. L. Hill,
J. Am. Chem. Soc., 2009, 131, 17360–17370

Several key properties of the water oxidation catalyst Rb₈K₂[{Ru^IV₄O₄(OH)₂(H₂O)₄}(γ-SiW₁₀O₃₆)₂] and its mechanism of water oxidation are given. The one-electron oxidized analogue [{Ru^VRu^IV₃O₆(OH₂)₄}(γ-SiW₁₀O₃₆)₂]¹¹⁻ has been prepared and thoroughly characterized. The voltammetric rest potentials, X-ray structures, elemental analysis, magnetism, and requirement of an oxidant (O₂) indicate these two complexes contain [Ru^IV₄O₆] and [Ru^VRu^IV₃O₆] cores, respectively. Voltammetry and potentiometric titrations establish the potentials of several couples of the catalyst in aqueous solution, and a speciation diagram (versus electrochemical potential) is calculated. The potentials depend on the nature and concentration of counterions. The catalyst exhibits four reversible couples spanning only ca. 0.5 V in the H₂O/O₂ potential region, keys to efficient water oxidation at low overpotential and consistent with DFT calculations showing very small energy differences between all adjacent frontier orbitals. The voltammetric potentials of the catalyst are evenly spaced (a Coulomb staircase), more consistent with bulk-like properties than molecular ones. Catalysis of water oxidation by [Ru(bpy)₃]³⁺ has been examined in detail. There is a hyperbolic dependence of O₂ yield on catalyst concentration in accord with competing water and ligand (bpy) oxidations. O₂ yields, turnover numbers, and extensive kinetics data reveal several features and lead to a mechanism involving rapid oxidation of the catalyst in four one-electron steps followed by rate-limiting H₂O oxidation/O₂ evolution. Six spectroscopic, scattering, and chemical experiments indicate that the catalyst is stable in solution and under catalytic turnover conditions. However, it decomposes slowly in acidic aqueous solutions (pH < 1.5).

 Palladium(II)-Phosphotungstate Derivatives : Synthesis and Characterization of the [Pd_x{WO(H₂O)}_3-x{A,α PW₉O₃₄}₂]^(6+2x)- Anions R. Villanneau, S. Renaudineau, P. Herson, K. Boubekeur, R. Thouvenot, A. Proust, Eur. J. Inorg. Chem., 2009, 479-488.

A series of Pd^II derivatives of the [P₂W₂₁O₇₁(H₂O)₃]^6- heteropolytungstate with general formula [Pd_x{WO(H₂O)}_3-x{A,α-PW₉O₃₄}2]^(6+2x)- (x = 1-3) have been obtained by reaction between palladium nitrate and [P₂W₂₀O₇₀(H₂O)₂]^10-, [P₂W₁₉O₆₉(H₂O)₂]^14- and [PW₉O₃₄]^9- respectively. The crystallographic structure of K₁₀[Pd₂{WO(H₂O)}{A,α -PW₉O₃₄}2]•30H₂O has been reported.

 Photochemical activation of an azido manganese-monosubstituted Keggin polyoxometalate : on the road to a Mn(V)-nitrido derivative G. Izzet, E. Ishow, J. Delaire, C. Afonso, J.-C. Tabet, A. Proust, Inorg. Chem., 2009, 48, 11865–11870.

The manganese(V)-nitrido polyoxometalate derivative [PW₁₁O₃₉{Mn^VN}]^5- has been synthesized by photochemical activation of the parent manganese(III)-azido derivative [PW₁₁O₃₉Mn^IIIN₃]^5-. The photoactivation proceeds through two competitive routes, yielding to the targeted product of photooxidation {Mn^VN} or the undesirable product of photoreduction {Mn^IIL} (L = H₂O, N₃) depending on the photolysis conditions. A simplified photolysis mechanism involving two different excited states was proposed to account for the temperature and wavelength dependence.

 Experimental and computational study of the framework fluxionality of organometallic derivatives of polyoxometalates : analysis of the effect of the metal and the solvent D. Laurencin, R. Thouvenot, K. Boubekeur, F. Villain, R. Villanneau, M.-M. Rohmer, M. Bénard, A. Proust, Organometallics, 2009, 28, 3140-3151.

Organometallic oxides of the general formula [Mo₄O₁₆{Ru(arene)}₄] display two isomeric forms, referred to as the “triple-cubane” and “windmill” structures. In a previous study (Laurencin et al. Chem.–Eur. J. 2004, 10, 208), we showed that the arene ligand plays an important role in the relative stability of the two isomers. In this work, new experiments and DFT calculations have been carried out to try to rationalize and further control the isomerization process in solution. The synthesis and spectroscopic study of [Mo₄O₁₆{Os(p-cymene)}₄] showed that, when ruthenium is replaced by osmium, the equilibria in CHCl₃ and CH₂Cl₂ can be altered. In the case of [Mo₄O₁₆{Ru(p-cymene)}₄], ¹H NMR experiments carried out in CD₂Cl₂/CD₃OD solutions revealed that the solvent, through its polarity and molecular form, has a strong impact on the isomerization. DFT calculations were performed on [Mo₄O₁₆{M(arene)}₄] (M = Ru, Os; arene = benzene, toluene, mesitylene, p-cymene, hexamethylbenzene). The change in relative energy of the computed structures upon switching from ruthenium to osmium was found to be in line with the experimental observations. Calculations also showed that the dielectric properties of the solvent, as well as the facility with which it can access the oxometallic core, directly influence the relative stabilities of the two isomers. This work should thus open the way to further studies of organometallic oxides, by allowing their rational preparation and a better understanding of their properties, through a precise analysis of their interaction with the solvation environment.

 Nitrogen-Atom Transfer from [PW₁₁O₃₉Ru_VIN]^4- to PPh3 C. Besson, Y. V. Geletii, F. Villain, R. Villanneau, C. L. Hill, A. Proust, Inorg. Chem., 2009, 48, 9436-9443

The nitrido derivative (n-Bu₄N)₄[PW₁₁O₃₉Ru_VIN] transfers its nitrogen atom to triphenylphosphine to give [Ph₃PNPPh₃]⁺. The reactivity of intermediate (n-Bu₄N)₃[PW₁₁O₃₉Ru^V{NPPh₃}] was investigated. By addition of one equivalent of hydroxide, [PW₁₁O₃₉Ru_III{N(OH)PPh₃}]^4- is obtained. The reaction can be reversed by the addition of a proton. The phosphinoxime [PW₁₁O₃₉Ru_III{N(OH)PPh₃}]^4- decomposes to yield quantitatively (n-Bu₄N)₄[PW₁₁O₃₉Ru^III{OPPh₃}]. All those species have been thoroughly characterized by mass spectrometry, paramagnetic ³¹P NMR, IR, Raman, UV-visible, XANES and EXAFS spectroscopies.

 Vicinal di-nitridoruthenium substituted polyoxometalates, γ [XW₁₀O₃₈RuN₂]^6- (X=Si or Ge) C. Besson, D. G. Musaev, V. Lahootun, R. Cao, L.-M. Chamoreau, R. Villanneau, Françoise Villain, R. Thouvenot, Y. V. Geletii, C. L. Hill, A. Proust, Chem. Eur. J., 2009, 10233–10243.

K₈[γ-XW₁₀O₃₆] (X = Si or Ge) reacts with two equivalents of Cs₂[Ru^VINCl₅] to form [γ XW₁₀O₃₈{RuN}₂]^6-, X = Si or Ge. Crystal structures of both show highly unusual vicinal terminal metal-nitrido units (d_RuN = 1.594(10) and 1.612(11) Å). The geometrical and electronic structures are established from EXAFS, XANES, NMR (²⁹Si and ¹⁸³W), CV, IR, Raman, reductive titrations, and DFT calculations. Reduction of Ru≡N groups by 4 electrons produces NH₃ in ca. 100% yield.

 A new synthetic route towards Ru(III) substituted heteropolytungstate anions C. Besson S.-W. Chen, G. Izzet, R. Villanneau, A. Proust, Inorg. Chem. Commun., 2009, 12, 1042-1044

Microwave irradiation of K₇[PW₁₁O₃₉]•14H₂O and [Ru(dmf)₆](CF₃SO₃)₃ allowed the synthesis of [PW₁₁O₃₉Ru^III(OH₂)]^4-. This study provides a complete set of spectroscopic and electrochemical references for Ru^III-incorporating heteropolytungstates.

 Hydrothermal Synthesis and Structural Characterization of the High-Valent Ruthenium-Containing Polyoxoanion [{PW₁₁O₃₉}₂{(HO)Ru^IV-O-Ru^IV(OH)}]^10- S. Chen, R. Villanneau, Y. Li, L.-M. Chamoreau, K. Boubekeur, R. Thouvenot, P. Gouzerh, A. Proust, Eur. J. Inorg. Chem., 2008, 2137-2142.

The hydrothermal synthesis and the characterization (X-ray diffraction, IR, multinuclear NMR spectroscopy, electrochemistry) of the high-valent ruthenium-containing heteropolytungstate [{PW₁₁O₃₉}₂{(HO)Ru-O-Ru(OH)}]^10- are reported. This complex is composed by the association of two [PW₁₁O₃₉]^7- subunits linked by a {RuIV-O-RuIV} diamagnetic core. Electrochemistry shows that it can be reversibly oxidized (1-electron process) or reduced (2-electron process).