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[Display omitted] • Two homoleptic clusters [{M 6 I 8 }(DMSO) 6 ](I 3) 4 (M = Mo, W) were obtained. • Addition of iodine in reaction media facilitates the terminal ligand substitution. • Composition of the compounds was confirmed by a set of physicochemical analyses. • The clusters possess broad absorption up to ∼ 800 nm with E g of 1.5–1.6 eV. • The absence of cluster emission was explained by the presence of triiodide anions. The family of octahedral iodide cluster complexes of molybdenum and tungsten – [{M 6 I 8 }L 6 ] n – exhibit a unique set of properties with significant practical potential. Due to the strong influence of terminal ligands L on these properties, the search for new simpler, more convenient and cheaper approaches for their substitution is an urgent task. This work demonstrates a new one-step method for terminal ligand substitution using well-known and readily available complexes [{M 6 I 8 }I 6 ]2–. The synthetic technique involves the addition of molecular iodine to the reaction mixture in order to bind the released I– ions, thereby facilitating the reaction process. As a result, two new cluster complexes with dimethyl sulfoxide ligands [{M 6 I 8 }(DMSO) 6 ](I 3) 4 (M = Mo (1), W (2)) have been obtained and structurally characterized. The optical properties of the obtained compounds have been studied both in solid state and in solution, and E g values have been calculated from the solid-state absorption spectra. The presence of I 3 – anions has been shown to quench the emission of the cluster complexes, explaining the absence of luminescence in the obtained compounds. [ABSTRACT FROM AUTHOR]

Phosphonium ylide complexes of Mo and W formulated as [M(η 3 -allyl){η 2 -(NPh) 2 CH}(CO) 2 (CH 2 PR 3 )] (M = Mo, R = Me: 2a-Mo ; M = Mo, R = Ph: 2b-Mo , and M = W, R = Me: 2a-W ) were prepared by the reaction of amidinato(pyridine) complex, [M(η 3 -allyl){η 2 -(NPh) 2 CH}(CO) 2 (NC 5 H 5 )] (M = Mo: 1-Mo and M = W: 1-W ), with a phosphonium ylide, CH 2 PR 3 (R = Me, Ph), which was generated in situ by the reaction of the corresponding phosphonium salt with n BuLi. These complexes were characterized spectroscopically, as well as by the X-ray diffraction. The phosphonium ylide ligand shows stronger electron donating ability toward the metal than N -heterocyclic carbene or phosphine ligands. This trend is supported by the comparison of the spectroscopic data and the DFT calculations. We also investigated the reactivity of the phosphonium ylide complexes 2-Mo with two-electron donors such as PEt 3 and NHC. In the case of the PPh 3 ylide complex ( 2b-Mo ), the substitution reaction of the ylide ligand for the two-electron donors took place cleanly to yield the corresponding complexes. On the other hand, in the PMe 3 ylide complex ( 2a-Mo ), the substituted complexes formed but the unreacted ylide complex 2a-Mo was also present in the reaction mixture. These results show that the bond strength of the M-C(phosphonium ylide) bond is affected by the substituents on the phosphorus atom. [ABSTRACT FROM AUTHOR]

[MI 2 (CO) 3 (pz*H) 2 ] complexes (M = Mo, W; pz*H = pzH, dmpzH, indzH) have been synthesized and characterized in solid state and in solution. These heptacoordinated complexes present a capped octahedron geometry in the solid state where the azole ligands are always coordinated pseudo- cis , and the iodido ligands are coordinated either pseudo- trans (pzH complexes and molybdenum complex with indzH) or pseudo- cis (tungsten complex with dmpzH). Both isomers are found in the crystal structure of [WI 2 (CO) 3 (indzH) 2 ]. The difference in energies between both isomers have been theoretically calculated and range between −2.9 and +1.0 kcal/mol. The complexes where the iodido ligands are coordinated pseudo- trans show unequivalent azoles in the NMR at low temperature while they undergo a dynamic process in solution which makes both heterocycles equivalent at room temperature. The other complexes display a dynamic behavior in solution where both heterocycles are equivalent both at room and at low temperatures. [ABSTRACT FROM AUTHOR]

The global energy demand and the present high dependence on fossil fuels have caused an unprecedented increase in the Earth’s atmosphere carbon dioxide concentration. Its exponential and uncontrollable rise is responsible for large and unpredictable impacts on the world climate and for ocean acidification, thus, being a major concern for the ecosystems and human’s daily life. On the other hand, the carbon dioxide abundance and low cost make it an interesting source for the production of chemical feedstocks and fuels. Yet, the thermodynamic and kinetic stability of the carbon dioxide molecule makes its utilization a laboratorial/industrially challenging task. In this Review, we propose to use the molybdenum and tungsten-containing formate dehydrogenase (FDH) enzymes as a model to understand the mechanistic strategies and key chemical features needed to reduce carbon dioxide to formate. We will highlight the present knowledge about the structure of FDHs, with particular emphasis on active site features, reaction mechanism and ability to reduce carbon dioxide to formate. The information gathered aims to inspire the development of new efficient (bio)catalysts for the atmospheric carbon dioxide utilization, to produce energy and chemical feedstocks, while reducing an important environmental pollutant. [ABSTRACT FROM AUTHOR]

Abstract: Novel molybdenum and tungsten complexes with tridentate bis(phenolate) ligands containing [O,X,O] donor atoms (X=S or Se), [MoO2LS] (1), [MoO2LSe] (2), [WO2LS] (3) and [WO2LSe] (4), were synthesized and characterized as functional models for molybdenum- and tungsten-dependent oxidoreductases. The catalytic oxo-transfer properties of 1–4 were investigated by oxo-transfer reactions from nitrate to PPh3 with a ratio of complex (1–4):PPh3:(Bu4N)(NO3 −)=1:10:20 and from DMSO to PPh3 with varied catalyst:PPh3 ratios. For the oxygen atom transfer reaction from nitrate to PPh3, the molybdenum compounds are catalytically more active than their tungsten analogues. Whereas for the oxygen atom transfer reaction from DMSO to PPh3, the tungsten compounds exhibit more efficient catalytic behavior than the molybdenum analogues. In all catalytic reactions, sulfur containing compounds have a higher catalytic ability than their selenium analogues. In comparison, all four compounds catalyze the oxygen atom transfer reaction from DMSO to PPh3 much more effectively than the oxidation of PPh3 with NO3 −. [Copyright &y& Elsevier]

Abstract: The dioxomolybdenum and dioxotungsten complexes [MoO2L1] (1-Mo) and [WO2L1] (2-W), supported by a diamine bis(phenolate) ligand (L1 =Me2NCH2CH2N(CH2-2-O-3,5-C6H2 tBu2)2) were prepared from MoO2Cl2 and WO2Cl2(dme) in good yields. The solid-state structures of both compounds obtained by single crystal X-ray diffraction reveal distorted octahedral geometries around the metals with cis terminal oxo ligands. Their performance in the catalytic epoxidation of cis-cyclooctene using H2O2 and TBHP as oxidants was evaluated. 2-W displays high activity with H2O2 as terminal oxidant, achieving 84% conversion in 6h (TOF=1400molsub molcat −1 h−1), while its molybdenum counterpart 1-Mo was inactive in the same conditions. Using TBHP as oxidant the opposite trend was observed and 1-Mo attained 93% conversion in 6h (TOF=1550molsub molcat −1 h−1). The Oxovanadium complexes [VOL1Cl] (3-V), [VOL2Cl] (4-V, L2 =Me2NCH2CH(CH3)N(CH2-2-O-3,5-C6H2 tBu2)2) and [(VOL1)2(μ-O)] (5-V) were also tested as catalysts in the epoxidation of cis-cyclooctene. The three compounds display high activity when the epoxidation reaction is performed using TBHP as oxidant. Using H2O2, 3-V and 4-V are moderately active while 5-V is inactive. [Copyright &y& Elsevier]

Abstract: Reactions of the molybdenum and tungsten precursors [MO2S2]2− with equimolar amounts of benzenedithiol in acetonitrile give the title compounds [M2O2(μ-S)2(bdt)2]2− with M=Mo, W and bdt=benzene-dithiolate. In case a tungsten to ligand ratio of 1:2 is used the dimer forms as well but only as a minor species whereas the monomer [WO(bdt)2]2− is the main product. In both dimeric compounds the syn-isomers are formed referring to the position of the apical oxo ligands with respect to the M2S2 plane. For the molybdenum compound this contrasts with a published crystal structure of the anti-isomer. Both complexes give highly symmetric isomorphous crystals but still show subtle differences in their bond lengths and angles around the central metal. The X-ray crystal structures of both are analyzed in detail and compared with each other and with the isomeric molybdenum compound. Differences and similarities between tungsten and both isomers of molybdenum complexes are shown to be more influenced by the conformation than by the central metal and a reason for the formation of syn- and anti-isomers based on the respective synthetic procedures is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of [Mo2O2(μ-S)2(H2O)6]2+ with Mo(CO)6 or metallic Mo under hydrothermal conditions (140°C, 4M HCl) gives oxido-sulfido cluster aqua complex [Mo3(μ3-S)(μ-O)2(μ-S)(H2O)9]4+ (1). Similarly, [W3(μ3-S)(μ-O)2(μ-S)(H2O)9]4+ (2) is obtained from [W2O2(μ-S)2(H2O)6]2+ and W(CO)6. While reaction of [Mo2O2(μ-S)2(H2O)6]2+ with W(CO)6 mainly proceeds as simple reduction to give 1, [W2O2(μ-S)2(H2O)6]2+ with Mo(CO)6 produces new mixed-metal cluster [W2Mo(μ3-S)(μ-O)2(μ-S)(H2O)9]4+ (3) as main product. From solutions of 1 in HCl supramolecular adduct with cucurbit[6]uril (CB[6]) {[Mo3O2S2(H2O)6Cl3]2CB[6]}Cl2⋅18H2O (4) was isolated and structurally characterized. The aqua complexes were converted into acetylacetonates [M3O2S2(acac)3(py)3]PF6 (M3 =Mo3, W3, W2Mo; 5a–c), which were characterized by X-ray single crystal analysis, electrospray ionization mass spectrometry and 1H NMR spectroscopy. Crystal structure of (H5O2)(Me4N)4[W3(μ3-S)(μ2-S)(μ2-O)2(NCS)9] (6), obtained from 2, is also reported. [ABSTRACT FROM AUTHOR]

Abstract: The syntheses and structures of homo- and heteronuclear biscarbene complexes with bithiophene spacers were investigated. The complexes were synthesized by lithiation of bithiophene followed by metallation using combinations of the metal precursors MnMeCp(CO)3, W(CO)6, Mo(CO)6 and Cr(CO)6, after which the reaction was quenched with triethyloxonium tetrafluoroborate. This classical Fischer method yielded monocarbene complexes, [ML n C(OEt)C4H2S–C4H3S], ([ML n ]=Cr(CO)5 1a, W(CO)5 2a or MnMeCp(CO)2 3a), homonuclear biscarbene complexes, [ML n C(OEt)C4H2S–C4H2SC(OEt)ML n ], ([ML n ]=Cr(CO)5 1b, W(CO)5 2b or MnMeCp(CO)2 3b) and heteronuclear biscarbene complexes, [ML n C(OEt)C4H2S–C4H2SC(OEt)M′L n ] (1d: [ML n ]=Cr(CO)5 and [M′L n ]=W(CO)5; 1e: [ML n ]=MnMeCp(CO)2 and [M′L n ]=Cr(CO)5; 1f: [ML n ]=Cr(CO)5 and [M′]=Mo(CO)5); 2d: [ML n ]=MnMeCp(CO)2 and [M′L n ]=W(CO)5; 3c: [ML n ]=MnMeCp(CO)2 and [M′L n ]=Mo(CO)5). Electron density calculations with the gaussian03 software package of 1e revealed a polar rod with the negative pole towards the chromium carbene side, whereas the biscarbenes 1d and 1b showed very little polarity. By-products resulting from activation of the carbene moieties in homonuclear biscarbene complexes included (i) ester-type complexes of the form [ML n C(OEt)C4H2S–C4H2SC(O)OEt], ([ML n ]=Cr(CO)5 1c or W(CO)5 2c), formed in situ in the reaction of 1b and 2b, (ii) the organic bis-ester compound [EtOC(O)C4H2S–C4H2SC(O)OEt] 4, where both metal moieties had been substituted by oxygen and (iii) the carbon–carbon coupled dimeric bithienyl compound [C4H3S–C4H2SC(O)C(O)C4H2S–C4H3S] 5. By-products obtained from heteronuclear biscarbene reactions contain the former diketo compound (or a derivative) as spacer between two metal carbonyl fragments and have the general formula [ML n C(OEt)C4H2S–C4H2SCR–CR′C4H2S–C4H2SC(OEt)ML n ] (5a: [M]=Cr(CO)5, R=OH, R′=OEt; 5b: [M]=W(CO)5, R=R′=O; 5c: [M]=Mo(CO)5, R=R′=O). Reaction of 1d, 1e and 1f with hex-3-yne resulted in the formation of benzannulated products 6a, 6b and 6c. All novel complexes were fully characterized using various spectroscopic techniques. The crystal structures of 1b, 2a and 5 are reported. [Copyright &y& Elsevier]

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO)5M＝C＝C＝CFc2] (1a–c, F=(C5H4)Fe(C5H5), M=Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc2＝CO with Me3Si–C≡CH, KF/MeOH, n-BuLi, and [(CO)5M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO)5Cr＝C＝C＝C(Fc)R] (R=Ph, NMe2), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HC≡CC(Fc)(Ph)OH with [(CO)5Cr(THF)] followed by desoxygenation with Cl2C＝O, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO)5Cr＝C(OR)CH＝C(NMe2)Fc], and (c) replacement of OMe in [(CO)5Cr＝C＝C＝C(OMe)NMe2] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO)5Cr＝C＝C＝C(Fc)NMe2] was treated first with Li[Fc] and the resulting adduct then with SiO2. The replacement route (c) was also applied to the synthesis of an allenylidene complex (7a) with a C≡C spacer in between the ferrocenyl unit and Cγ of the allenylidene ligand, [(CO)5Cr＝C＝C＝C(NMe2)-C≡CFc]. The related complex containing a CH＝CH spacer (9a) was prepared by condensation of [(CO)5Cr＝C＝C＝C(Me)NMe2] with formylferrocene in the presence of NEt3. The bis(ferrocenyl)-substituted allenylidene complexes 1a–c added HNMe2 across the Cα–Cβ bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the C≡C bond into the Cβ–Cγ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO)5M＝C＝C＝C(NEt2)CMe＝CFc2]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies. [Copyright &y& Elsevier]

Abstract: The reaction of MoO2(mes)2 with S-H2BINOL (mes=2,4,6-Me3C6H2; H2BINOL=1,1′-bi-2-naphthol) and (CF3)2MeCOH in THF yielded the novel dioxo-molybdenum(VI) complexes MoO2(S-BINOL)(THF)2 and MoO2[OCMe(CF3)2]2(THF), respectively. Similar tungsten derivatives WO2(S-BINOL)(THF) and WO2[OCMe(CF3)2]2(THF) have been prepared by the reaction of WO2Cl2(DME) with the corresponding lithium salts of BINOL and 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, respectively. Catalytic experiments have shown that MoO2(S-BINOL)(THF)2 is an active catalyst in the sulfoxidation of methyl phenyl sulfide and in the epoxidation of cis-cyclooctene with tert-butylhydroperoxide, under mild conditions. The BINOL complex was, however, not found to be enantioselective. In addition, the catalytic activity of the molybdenum species MoO2(S-BINOL)(THF)2 and MoO2[OCMe(CF3)2]2(THF) in the hydrosilylation of carbonyl groups has been explored. [Copyright &y& Elsevier]

Abstract: The reaction of the metal complexes MO2Cl2(mebipy) (M=Mo, W) with two equivalents thiophenol by the exact same procedure leads to two different products for molybdenum [Mo2O4(SPh)2(mebipy)2] and tungsten [WO2(SPh)2(mebipy)]. To understand why this is the case the redox potentials of the starting materials were measured showing that the redox potential for thiophenol is lower than the redox potentials (MV ↔MVI) for both of the metal precursors. A reduction of the metal and oxidation of the sulfur should be possible for both reactions but occurs only for the molybdenum compound. Theoretical calculations show that different metal–sulfur bond strengths are as well and equally responsible for the differing reaction behaviour as are the redox potentials. [Copyright &y& Elsevier]

Abstract: The syntheses of (PPh4)2[M(CN)3O(pic)]·nH2O (M=Mo, W; n=2.5, 4; pic=picolinate anion) as well as (PPh4)2[Mo(CN)4O(apic)]·3H2O (apic=2-pyridinecarboxaldehyde) are presented. The salts have been characterised by elemental analysis, IR and UV–Vis spectroscopy, cyclic voltammetry and X-ray crystal structure determination of (PPh4)2[Mo(CN)3O(pic)]·2.5H2O. The anion in the latter salt is approximately octahedral with O and N donor atoms of pic situated in the trans and cis position to the MoO bond, respectively. The picolinate complexes have the characteristic MLCT bands in the visible spectra with the absorption maxima linearly dependent on the Reichardt’s ET solvent parameter. These complexes are shown to exhibit the strongest solvatochromic effect of all studied tricyanooxo and hexacyano complexes of Mo(IV) and W(IV). The obtained values of E1/2 in these salts [0.333 V (Mo) and 0.018 V (W) in 1,2-C2H4Cl2] were found to be the highest of all [M(CN)3O(LL)]2− type complexes making these salts show reversibility in a remarkable variety of solvents. The oxidation of coordinated apic to pic has been demonstrated by means of electronic spectroscopy. The isolated salts were used to monitor the reaction of [M(CN)4O(H2O)]2− with 2,2′-pyridil in water–ethanol solution. It was found that 2,2′-pyridil disproportionate to Hpic and apic in the first step and the other decomposition products of 2,2′-pyridil postulated in the literature were not observed. [Copyright &y& Elsevier]

The reactions of [M(≡CC6H2Me3-2,4,6)X(CO)2(L)2] (M = Mo, W; X = Cl, Br; L = pyridine, 3,5-dimethylpyrazole) with Na[H2B(mt)2] (mt = methimazolyl) are metal dependent, providing either the alkylidyne complex [Mo(≡CC6H2Me3-2,4, 6)(CO)2{κ3-H,S,S′-H2B(mt)2}] or the bis(chelate) complex [W(CO){κ2-S,S′-H2B(mt)2}{κ3-H,S,S′-H2B(mt)2}], the latter featuring both bi and tridentate coordination modes for the H2B(mt)2 ligand. [Copyright &y& Elsevier]

The structure and bonding in MO4 n- (n=2, 3, 4; M=Cr, Mo, W) tetrahedral oxoanions have been investigated using density-functional methods. Good computational-experimental agreement for the geometrical parameters of the known species has been obtained which allowed the prediction of the cited parameters for those species that have not yet been isolated. The molecular-orbital analysis indicates that the chemical bonds mainly have d functions of the metal and p functions of oxygen. The electron affinities for the process MO4 n- + 1e → MO4 (n + 1)- have also been calculated and their importance in relation with the preparation of the oxoanions MO4 n- (M=Mo, W; n=3, 4) not reported in the bibliography is discussed. Comparative studies of the electronic structures of oxoanions allow to explain their reactivities against nucleophilic and electrophilic attacks. The vibrational frequencies have been calculated and compared with the experimental values and the different relationships between the symmetric-stretching and antisymmetric-bending frequencies allow to confirm the assignations of the calculated spectra. [Copyright &y& Elsevier]

The formation conditions of Keggin-type molybdotungstophosphate(V) (PWxMo12 − xO40 3− (PWxMo12 − x), x=0–12) and -arsenate(V) (AsWxMo12 − xO40 3− (AsWxMo12 − x)) complexes in aqueous-organic solvents were investigated with 31P NMR, Raman spectroscopy, and cyclic voltammetry. The conversion processes of the PMo12 and the PW12 anions into the PWxMo12 − x anions were also examined and compared with those of the AsMo12 and AsW12 anions into the AsWxMo12 − x anions. The mean vibration frequencies of the PWxMo12 − x and AsWxMo12 − x (x=1–11) complexes were calculated in IR and Raman spectra from those of the PMo12 and PW12, and AsMo12 and AsW12 complexes, respectively. The formation conditions and conversion processes of Keggin-type molybdotungstophosphates(V) (PWxMo12 − xO403−, x=0–12) and -arsenates(V) (AsWxMo12 − xO403−) complexes in aqueous-organic solvents were investigated with 31P NMR, Raman spectroscopy, and cyclic voltammetry. The mean vibration frequencies of the molybdotungstophosphates(V) and -arsenates(V) complexes were calculated. [Copyright &y& Elsevier]

The reaction of Me3SiSiMe2C6H5 with M(CO)6 under thermal conditions afforded (η6-Me3SiSiMe2C6H5)M(CO)3 [M=Cr (1), Mo (2) and W (3)] with retention of the silicon–silicon bond. UV absorption properties of 1–3 were recorded and discussed with emphasis on the σ–π conjugation between the Si&z.sbnd;Si bond and the phenyl group. [Copyright &y& Elsevier]

The isomers, Cp*Ir(η4-2,5-Me2T) (1) and Cp*Ir(C,S-2,5-Me2T) (2), where 2,5-Me2T is 2,5-dimethylthiophene, are observed to coordinate to metal carbonyl fragments in various ways when reacted with metal complexes W(CO)5(THF), Cr(CO)4(COD), Mo(CO)4(NBD) and Fe(CO)3(BDA), that contain readily displaceable ligands (COD=1,5-cyclooctadiene, NBD=norbornadiene, BDA=benzylidene acetone). In Cp*Ir(η4-2,5-Me2T·M(CO)5), the M(CO)5 unit (M=Cr, Mo, or W) is coordinated to the sulfur atom of 1. The iridathiabenzene ring of 2 coordinates to a M(CO)3 moiety through all six atoms in [η6-Cp*Ir(C,S-2,5-Me2T)]M(CO)3, where M=Cr or Mo. The iridathiabenzene ring in the CO adduct of 2, Cp*Ir(C,S-2,5-Me2T)(CO), coordinates through the sulfur to W(CO)5 in 6, Cp*Ir[C,S-2,5-Me2T·W(CO)5](CO), and through five atoms (not the Ir) to Cr(CO)3 in 14, Cp*Ir(C,S-2,5-Me2T·Cr(CO)5)(CO). Structures of 6 and 14 are reported. [Copyright &y& Elsevier]

Reactions of [M3Q4(H2O)9]4+ with acetylacetone (Hacac) and pyridine (py) in weakly alkaline solutions (pH 8–9) give mixed-ligand complexes [M3Q4(acac)3(py)3]+ (M=Mo, W; Q=S, Se), isolated as hexafluorophosphate salts. For M=Mo, Q=S and for M=W, Q=both S and Se, X-ray structural analysis has been carried out. The three compounds are isostructural and crystallize as [M3Q4(acac)3(py)3]PF6·CHCl3. Each M is attached to one capping (μ3) and two bridging (μ2) chalcogen atoms, one pyridine ligand and one chelating acetylacetonate ligand. The latter are coordinated symmetrically in positions trans to the μ2-Q bridges to give cluster cations with crystallographic threefold rotation symmetry (point group 3m or C3v). The structure is preserved in solution. CV experiments show two almost reversible waves due to consecutive one electron reductions with the ease of reduction decreasing in the order, Mo3S4>Mo3Se4>W3Se4>W3S4. FAB MS data are also discussed. [Copyright &y& Elsevier]

[Display omitted] • New [WX 2 (CO) 3 (L Y)] complexes with L Y = C 5 H 4 NCY = N(CH 2) 2 CH 3 with Y = H, Me, Ph were synthesized. • The W(II) and Mo(II) analogues were immobilized inside the pores of MCM-41. • The homogeneous and heterogeneous species were active in the catalytic oxidation of olefins. • The materials with Mo(II) were more active catalysts than the complexes. • DFT calculations gave insight on the mechanism of olefin epoxidation. New tungsten(II) and molybdenum(II) heptacoordinate complexes [MX 2 (CO) 3 (L Y)] (MXL y : M = W, Mo; X = Br, I; L Y = C 5 H 4 NCY = N(CH 2) 2 CH 3 with Y = H (L 1), Me (L 2), Ph (L 3)) were synthesized and characterized by spectroscopic techniques and elemental analysis. The two tungsten complexes WXL 1 (X = Br, I) were also structurally characterized by single crystal X-ray diffraction. The metal coordination environment is in both a distorted capped octahedron. The complexes with L 1 and L 2 ligands were grafted in MCM-41, after functionalization of the ligands with a Si(OEt) 3 group. The new materials were characterized by elemental analysis, N 2 adsorption isotherms, 29Si MAS and 13C MAS NMR. The tungsten(II) complexes and materials were the first examples of this type reported. All complexes and materials were tested as homogeneous and heterogeneous catalysts in the oxidation of multifunctional olefins (cis- hex-3-en-1-ol, trans -hex-3-en-1-ol, geraniol, S -limonene, and 1-octene), with tert -butyl hydroperoxide (TBHP) as oxidant. The molybdenum(II) catalyst precursors are in general very active, reaching 99% conversion and 100% selectivity in the epoxidation of trans -hex-3-en-1-ol. Their performance is comparable with that of the [Mo(η3-C 3 H 5)X(CO) 2 (L Y)] complexes, but it increases with immobilization. On the other hand, most of the W(II) complexes display an activity similar or inferior to that of the Mo(II) analogues and it decreases after they are supported in MCM-41. DFT calculations show that tungsten complexes and iodide ligands are more easily oxidized from M(II) to M(VI) than molybdenum ones, while the energies of relevant species in the catalytic cycle are very similar for all complexes, making the theoretical rationalization of experimental catalytic data difficult. [ABSTRACT FROM AUTHOR]

Abstract: Oxidative addition of 1-bromo-1H-indene to [Mo(CO)3(NCMe)3] and [W(CO)3(NCEt)3] is a suitable method for preparation of the indenyl compounds [IndMo(CO)3Br] and [IndW(CO)3Br], respectively. These products were fully characterised using spectroscopic methods. Structure of [IndW(CO)3Br] was determined by single crystal X-ray diffraction analysis. [Copyright &y& Elsevier]

In this paper, the application of hemilabile phosphino-thioethers to trinuclear {M 3 S 4 } (M = Mo, W) clusters has been demonstrated. • Novel {W 3 S 4 } complexes containing phosphino-thioether ligands have been synthesized. • Their hemilabily properties and catalytic activity in nitrobenzene reduction have been studied. Reactions of [W 3 S 4 (tu) 8 (H 2 O)]Cl 4 ⋅2H 2 O (tu = thiourea) with (PhCH 2 CH 2) 2 PCH 2 CH 2 SR (R = Ph (PS1) or n -pentyl (PS2), followed by chromatography on silica gel with a solution of KPF 6 in acetone as eluent, result in [W 3 S 4 Cl 3 (PS1) 3 PF 6 ([1]PF 6) and [W 3 S 4 Cl 3 (PS2) 3 PF 6 ([2]PF 6) in moderate yields. Crystal structures of [1]PF 6 and [2]PF 6 were determined by X-ray single crystal analysis. All three phosphine-thioether molecules are bidentately coordinated to tungsten atoms in such a way that the phosphorus atoms are in the trans position to the capping µ 3 -S atom. The compounds were characterized by 1H, 31P{1H} NMR, and UV–vis spectroscopies and electrospray-ionization mass spectrometry. Unlike similar molybdenum complexes, interaction of [1]PF 6 or [2]PF 6 with Bu 4 NCl does not lead to the formation of neutral complexes [W 3 S 4 Cl 4 (PS) 2 (PS*)] with the monodentate coordination of one of the PS ligands. This indicates weaker hemilabile properties of phosphino-thioether ligands in the tungsten complexes. Consequently, both [1]PF 6 and [2]PF 6 exhibit significantly lower catalytic activity than the molybdenum analogues in the benchmark reaction of nitrobenzene reduction into aniline with Ph 2 SiH 2. The DFT calculations were performed to determine the relative stability of possible isomers with the chelate, bridging and monodentate manner of coordination of the PS ligands to {M 3 S 4 } (M = Mo, W) clusters, taking (CH 3) 2 PCH 2 CH 2 SCH 3 as a model. [ABSTRACT FROM AUTHOR]

A series of new molybdenum and tungsten(0, II, IV, V, VI) complexes stabilized by 1,4,7-trimethyl-l,4,7-triazacyclononane were synthesized by nucleophilic substitution, oxidation, hydrolysis and sulfido substitution reactions of MoVIO 3 groups. • Molybdenum and tungsten complexes with triazacyclononane (Me 3 tacn) were synthesized. • Nucleophilic substitution, oxidation, and hydrolysis were studied on these complexes. • Molybdenum and tungsten (0–VI) complexes were characterized by X-ray crystallography. The reported complexes of [(Me 3 tacn)M0(CO) 3 ] (Me 3 tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane; M = W, 1a ; Mo, 1b), [(Me 3 tacn)MII(CO) 3 I](PF 6) (M = W, 2a ; Mo, 2b), [(Me 3 tacn)MVOCl 2 ](PF 6) (M = W, 3a ; Mo, 3b), and [(Me 3 tacn)MVIO 3 ]·4H 2 O (M = W, 4a ; Mo, 4b) were synthesized as tungsten and molybdenum precursors according to the works by Wieghardt [20,21,24]. Reaction of 2a with sodium dialkyl dithiocarbamate afforded complexes [(Me 3 tacn)WII(CO) 2 (S 2 CNR 2)]I (R = Me, 5a ; i Pr, 6a). Similar reaction using 2b gave rise to the isolations of complexes [(Me 3 tacn)MoII(CO) 2 (S 2 CNR 2)](PF 6) (R = Me, 5b ; i Pr, 6b ; n Pr, 7). Hydrolysis of 3b in acetonitrile gave a dimeric molybdenum complex [{(Me 3 tacn)MoVO(OH)} 2 (μ-O)](PF 6) 2 ·2MeCN (8). Treatment of 4b with sodium diisopropyl dithiocarbamate in the presence of HPF 6 yielded [(Me 3 tacn)MoVIO 2 S] (9), while the similar reaction with S 8 powder yielded the oxotetrasulfido complex [(Me 3 tacn)MoIVO(S 4)] (10). All complexes are well characterized by electronic, infrared, and NMR spectroscopies, and the solid-state structures of 1a/b , 2a , 3b , 4a/b , 5a/b , 6a/b , and 7 – 10 have been also established by single-crystal X-ray diffraction. The electrochemical properties of these molybdenum and tungsten complexes were also investigated in the paper. [ABSTRACT FROM AUTHOR]

• Mo, W and V form complexes with a highly hydroxyl- functionalized Schiff base ligand. • Molecular structures were characterized. • V complex shows catechol oxidase mimetic activity. • Catechol oxidase activity of V complex was mechanistically assessed. A series of bioinspired dioxidomolybdenum(vi), dioxidotungsten (vi) and oxidovanadium (v) complexes [MoO 2 (H 2 LSaltris)], [WO 2 (H 2 LSaltris)] and [VO(HLSaltris)] 2 were prepared by the reaction of a hydroxyl-rich Schiff base proligand N -(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-3,5-di- tert -butylsalicylaldimine (H 4 LSaltris) with metal precursors in methanol solutions. Molybdenum and tungsten complexes crystallize as mononuclear molecules, whereas the vanadium complex forms dinuclear units. From the complexes, [VO(HLSaltris)] 2 shows activity in the oxidation of 4- tert -butylcatechol and 3,5-di- tert- butylcatechol, mimicking the action of the dicopper enzyme catechol oxidase. [ABSTRACT FROM AUTHOR]