Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XXXVII. Zur Existenz von 1-Norbornylverbindungen des Wolframs und Molybdäns

Contributions to the Chemistry of Transition Metal Alkyl Compounds. XXXVII. About the Existence of 1-Norbornyl Compounds of Tungsten and Molybdenum Reactions of WCl₆, WCl₄, WO₂Cl₂, WOCl₄, MoCl₅, and MoO₂(acac)₂ with 1-Norbornyl lithium (1-NorLi¹)) are described. From WCl₆ and WCl₄ [(1-Nor)₂W]_n is formed, whereas in dependence of the solvent WO₂Cl₂ and WOCl₄ are transformed into the complexes Li₂[1-NorWOCl₄] · THF, Li[WOCl₄], Li[WO₂Cl₂], and Li₂[WO₂Cl₂]. MoCl₅ and MoO₂(acac)₂ are reduced with formation of Li[MoCl₅], Li[MoO₂(acac)₂] and Li₂[MoO₂(acac)₂]. — Stable (1-Nor)₄M-derivatives of molybdenum and tungsten, comparable those of 3d-metals (M = Ti? Co) seem not to exist.     

Dioxomolybdenum(VI) and dioxotungsten(VI) complexes: efficient catalytic activity for crosslinking reaction in ethylene‐vinyl acetate copolymer/alkoxysilane composites

The catalytic performances of several bis(acetylacetonato)metal complexes [Cu(acac)₂, Zn(acac)₂, TiO(acac)₂, VO(acac)₂, MoO₂(acac)₂, and WO₂(acac)₂] were investigated for the crosslinking reaction via transesterifications in the ethylene‐vinyl acetate copolymer/tetraethoxysilane (EVA/TEOS) composite system by means of dynamic attenuated total reflectance Fourier transform infrared, solvent swelling, and solid‐state ²⁹Si cross polarization/magic angle spinning nuclear magnetic resonance techniques. Results of the kinetic examination revealed that MoO₂(acac)₂ and WO₂(acac)₂ exhibited a higher catalytic activity than di‐n‐butyltin(IV) oxide, which is a catalyst most commonly used for the transesterification process in polymer system, but has a toxic effect on the environmental health. And furthermore, the crosslink density and final siloxane network structure of crosslinked EVA/TEOS composites are found to be greatly correlated with the catalyst used. On the basis of the S_N2‐Si pathway, a plausible catalytic mechanism of MoO₂(acac)₂ and WO₂(acac)₂ was proposed for the crosslinking reaction via transesterifications of the vinyl acetate moieties in EVA backbone with the ethoxysilane groups in one TEOS molecule. The findings in this study may fill the blank in the high performance and environmentally friendly catalyst in the field of the crosslinking reactions in polymer system and provide useful clue for other transesterifications. Copyright © 2015 John Wiley & Sons, Ltd.     

Dinuclear oxomolybdenum(VI) acetylacetonates: Crystal and molecular structure of Mo2O5(acac)2L2 (L = D2O,DMF)

The behavior of MoO₂(acac)₂ (acac = acetylacetonate) towards representative amines, amides, sulfoxides and phosphine oxides in common solvents has been examined. Compounds of the composition Mo₂O₅(acac)₂L₂ [L = H₂O, D₂O, dimethylformamide (DMF), dimethylacetamide (DMA), dimethylbenzamide (DMBA), tetramethylurea (TMU), dimethylsulfoxide (DMSO), dibutylsulfoxide (Bu₂SO), p-tolylsulfoxide (p-Tol₂SO), tributylphosphine oxide (OPBu₃), triphenylphosphine oxide (OPPh₃), hexamethylphosphoramide (HMPA)], derived from partial hydrolysis of MoO₂(acac)₂ followed by condensation and coordination of L, can readily be isolated. The crystal and molecular structures of Mo₂O₅(acac)₂L₂ (L = D₂O, DMF) have been established by X-ray diffraction analysis.     

A gentle and efficient route for the deoxygenation of sulfoxides using catecholborane (HBcat; cat = 1,2-O2C6H4)

The addition of catecholborane (HBcat; cat = 1,2-O₂C₆H₄) to a wide range of sulfoxides affords the corresponding sulfides, dihydrogen, and catBOBcat. The diboron compound catBOBcat acts like a Lewis acid and will coordinate one molecule of the starting sulfoxide. Although deoxygenations with bulky or electron withdrawing sulfoxides are slow, these reactions can be greatly accelerated with the use of excess HBcat or by employing a rhodium catalyst.     

Highly efficient and chemoselective reduction of sulfoxides using the system silane/oxo-rhenium complexes

This work reports a novel method for the reduction of sulfoxides with silanes catalyzed by high valent oxo-rhenium(V) and (VII) complexes. The catalytic system PhSiH₃/ReIO₂(PPh₃)₂ (1 mol %) proved to be highly efficient for the reduction of a wide range of sulfoxides in excellent yields under mild conditions. This novel methodology is also highly chemoselective, tolerating several functional groups such as –CHO, –CO₂R, –Cl, –NO₂, and double or triple bonds.     

Syntheses and single-crystal structures of CsTh(MoO4)2Cl and Na4Th(WO4)4

Colorless crystals of CsTh(MoO₄)₂Cl and Na₄Th(WO₄)₄ have been synthesized at 993 K by the solid-state reactions of ThO₂, MoO₃, CsCl, and ThCl₄ with Na₂WO₄. Both compounds have been characterized by the single-crystal X-ray diffraction. The structure of CsTh(MoO₄)₂Cl is orthorhombic, consisting of two adjacent [Th(MoO₄)₂] layers separated by an ionic CsCl sublattice. It can be considered as an insertion compound of Th(MoO₄)₂ and reformulated as Th(MoO₄)₂·CsCl. The Th atom coordinates to seven monodentate MoO₄ tetrahedra and one Cl atom in a highly distorted square antiprism. Na₄Th(WO₄)₄ adopts a scheelite superlattice structure. The three-dimensional framework of Na₄Th(WO₄)₄ is constructed from corner-sharing ThO₈ square antiprisms and WO₄ tetrahedra. The space within the channels is filled by six-coordinate Na ions. Crystal data: CsTh(MoO₄)₂Cl, monoclinic, P2₁/c, Z=4, a=10.170(1) Å, b=10.030(1) Å, c=9.649(1) Å, β=95.671(2)°, V=979.5(2) Å³, R(F)=2.65% for I>2σ(I); Na₄Th(WO₄)₄, tetragonal, I4₁/a, Z=4, a=11.437(1) Å, c=11.833(2) Å, V=1547.7(4) Å³, R(F)=3.02% for I>2σ(I).     

Molybdenum oxide/bipyridine hybrid material {[MoO3(bipy)][MoO3(H2O)]}n as catalyst for the oxidation of secondary amines to nitrones

The inorganic-organic hybrid material {[MoO₃(bipy)][MoO₃(H₂O)]}_n (bipy = 2,2′-bipyridine) can be used as a water-tolerant catalyst for the oxidation of secondary amines under mild conditions using either urea hydrogen peroxide (UHP) or tert-butylhydroperoxide (TBHP) as the oxidant. Under optimized reaction conditions (2 mol % catalyst, 3-4 equiv TBHP, CH₂Cl₂ as the solvent, 40 °C), the corresponding nitrones were obtained with different efficiency depending on the nature of the cyclic or acyclic amine used.     

MoO2Cl2 as a novel catalyst for Friedel-Crafts acylation and sulfonylation

The use of MoO₂Cl₂ as a novel catalyst for Friedel-Crafts acylation and sulfonylation is described. A series of aromatic ketones and sulfones were prepared in moderate to good yields using acyl chloride or sulfonyl chloride in the presence of MoO₂Cl₂ (20 mol %), under solvent-free conditions.     

Vanadium complexes with thiosemicarbazones: Synthesis,characterization, crystal structures and anti-Mycobacterium tuberculosis activity

The development of more efficient anti-tuberculosis drugs is of interest. Three oxovanadium(IV) and three cis-dioxovanadium(V) complexes with thiosemicarbazone derivatives bearing moieties with different lipophilicity have been prepared and had their inhibitory activity against Mycobacteriumtuberculosis H₃₇Rv ATCC 27294 evaluated. The analytical methods used by the complexes’ characterization included IR, EPR, ¹H, ¹³C and ⁵¹V NMR spectroscopies, elemental analysis, cyclic voltammetry, magnetic susceptibility measurement and single crystal X-ray diffractometry. [VO(acac)(aptsc)], [VO(acac)(apmtsc)] and [VO(acac)(apptsc)] (acac = acetylacetonate; Haptsc = 2-acetylpyridinethiosemicarbazone; Hapmtsc = 2-acetylpyridine-N(4)-methyl-thiosemicarbazone and Happtsc = 2-acetylpyridine-N(4)-phenyl-thiosemicarbazone) are paramagnetic and their EPR spectra are consistent with the monoanionic N,N,S-tridentate coordination of the thiosemicarbazone ligands, resulting in octahedral structures of rhombic symmetry and with the oxidation state +IV for the vanadium atom. As result of oxidation of the vanadium(IV) complexes above, the diamagnetic cis-dioxovanadium(V) complexes [VO₂(aptsc)], [VO₂(apmtsc)] and [VO₂(apptsc)] are formed. Their ¹H, ¹³C and ⁵¹V NMR spectra were acquired and support a distorted square pyramidal geometry for them, in accord with the solid state X-ray structures determined for [VO₂(aptsc)] and [VO₂(apmtsc)]. In general, the vanadium compounds show comparable or larger anti-M. tuberculosis activities than the free thiosemicarbazone ligands, with MIC values within 62.5–1.56 (μg/mL).     

Unusual formation reaction of 2′-(methyl)-3′-acetyl-1,9-dihydro(4′,5′-dihydrofurano) [60]fullerene in reaction of C<Subscript>60</Subscript> with complexes VO(acac)<Subscript>2</Subscript> and MoO<Subscript>2</Subscript>(acac)<Subscript>2</Subscript>

A preparation method was developed for 2′-(methyl)-3′-acetyl-1,9-dihydro(4′,5′-dihydrofurano) [60]fullerene based on the liquid phase oxidation of C₆₀ using VO(acac)₂ and MoO₂(acac)₂.     

A novel method for the reduction of imines using the system silane/MoO2Cl2

A novel catalytic system, silane/MoO₂Cl₂ (10 mol %), for the reduction of imines in excellent to moderate yields and chemoselectivity was designed. These results extend the scope of the use of MoO₂Cl₂ as an effective catalyst for reduction reactions.     

Dioxomolybdenum(VI) complexes containing N-heterocyclic carbenes

Compound MoO₂Cl₂(THF)₂ reacts with two equivalents of 1,3-dialkyl substituted 4,5-dimethylimidazol-2-ylidenes to give the dioxomolybdenum(VI) complexes MoO₂Cl₂(L^R)₂ [R = Me (1), i-Pr (2)]. Treatment of MoO₂Cl₂(THF)₂ with one equivalent of the N-heterocyclic carbenes L^Me, L^i-Pr and ^C1L^n-Bu (L^Me = 1,3,4,5-tetramethylimidazol-2-ylidene, L^i-Pr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, and ^C1L^n-Bu = 1,3-dibutyl-4,5-dichloroimidazol-2-ylidene) affords the monocarbene adducts MoO₂Cl₂(L^R) [R = Me (3), i-Pr (4)] and MoO₂Cl₂(^C1L^n-Bu) (5), respectively. Decomposition of complexes 1-5 affords a molybdenum oxychloride anion [Mo₂O₅Cl₄]²⁻ as an imidazolium salt.     

Binuclear oxomolybdenum(V) chlorides: Molecular structure of Mo2O4Cl2(DMF)4 and Mo2O4Cl2(bipy)2 · DMF

Reduction of MoO₂Cl₂(DMF)₂ (DMF = dimethylformamide) with PPh₃ in mild conditions afforded the dinuclear species Mo₂O₃Cl₄(DMF)₄. Related compounds could be prepared by substitution of DMF with stronger bases. While attempting to grow crystals of these compounds new complexes with the syn-[Mo₂O₄]²⁺ core were obtained. The molecular structures of Mo₂O₄Cl₂(DMF)₄, and Mo₂O₄Cl₂(bipy)₂ (bipy = 2,2′-bipyridine) have been established by X-ray diffraction analysis.     

Interaction of salts in ionic melts of the ternary reciprocal systems Na,K‖BO2,MoO4 and Na,K‖BO2,WO4

The phase diagrams of the ternary reciprocal systems Na,K‖BO₂,MoO₄ and Na,K‖BO₂,WO₄ were studied for the first time by a calculation-experimental method and differential thermal analysis. The coordinates were determined for binary eutectics of the diagonal stable sections NaBO₂-K₂MoO₄(K₂WO₄) and the ternary invariant points e(55 mol % NaBO₂, 45 mol % K₂MoO₄, 740°C), e(55 mol % NaBO₂, 45 mol % K₂WO₄, 730°C), E(4.5 mol % NaBO₂, 78 mol % Na₂MoO₄, 17.5 mol % K₂MoO₄, 652°C), E(4.5 mol % NaBO₂, 78 mol % Na₂WO₄, 17.5 mol % K₂WO₄, 643°C), P₂(5 mol % NaBO₂, 56 mol % Na₂MoO₄, 39 mol % K₂MoO₄, 673°C), P₂(5 mol % NaBO₂, 56 mol % Na₂WO₄, 39 mol % K₂WO₄, 671°C). Binary solid solutions based on sodium and potassium metaborates were shown to be stable. Analytical models of phase equilibrium states of the ternary reciprocal systems Na,K‖BO₂,MoO₄(WO₄) were obtained, which enable one to calculate melting (crystallization) points and construct isotherms at any given composition. The specific heats of melting of samples of invariant compositions were found by quantitative differential thermal analysis.     

Oxovanadium(IV) and (V) complexes of acetylpyridine-derived semicarbazones exhibit insulin-like activity

Reaction of 2-acetylpyridine semicarbazone (H2APS), 3-acetylpyridine semicarbazone (H3APS) and 4-acetylpyridine semicarbazone (H4APS) with [VO(acac)₂] (acac = acetylacetonate) gave [VO(H2APS)(acac)₂] (1), [VO(H3APS)(acac)₂] (2) and [VO(4APS)(acac)(H₂O)] · 1/2H₂O (3). Oxidation of complex 1 in acetonitrile gave [VO₂(2APS)] (4). The crystal structures of complexes 1 and 4 have been determined. Complexes 1–3 were able to enhance glucose uptake and to inhibit glycerol release from adipocytes, which indicate their potential to act as insulin-mimics.     

Synthesis,X-ray studies,and catalytic activity of tridentate Schiff base dioxo-molybdenum(VI)

The reaction of a solution of MoO₂(acac)₂ in CH₃OH and salicylidene 2-picoloyl hydrazone as a tridentate ONO donor Schiff base (ONO) afford a six-coordinated Mo(VI) complex [MoO₂(ONO)(CH₃OH)], with a distorted octahedral configuration. [MoO₂(ONO)(CH₃OH)] was isolated as an air-stable crystalline solid and fully characterized by single-crystal X-ray structure analysis. [MoO₂(ONO)(CH₃OH)] shows reactivity in the oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air.     

Thermodynamic representation of the NaCl + Na2SO4 + H2O system with electrolyte NRTL model

A comprehensive thermodynamic model based on the electrolyte NRTL (eNRTL) activity coefficient equation is developed for the NaCl + H₂O binary, the Na₂SO₄ + H₂O binary and the NaCl + Na₂SO₄ + H₂O ternary. The NRTL binary parameters for pairs H₂O-(Na⁺, Cl⁻) and H₂O-(Na⁺, SO₄²⁻), and the aqueous phase infinite dilution heat capacity parameters for ions Cl⁻ and SO₄²⁻ are regressed from fitting experimental data on mean ionic activity coefficient, heat capacity, liquid enthalpy and dissolution enthalpy for the NaCl + H₂O binary and the Na₂SO₄ + H₂O binary with electrolyte concentrations up to saturation and temperature up to 473.15 K. The Gibbs energy of formation, enthalpy of formation and heat capacity parameters for solids NaCl_(s), NaCl·2H₂O_(s), Na₂SO_4(s) and Na₂SO₄·10H₂O_(s) are obtained by fitting experimental data on solubilities of NaCl and Na₂SO₄ in water. The NRTL binary parameters for the (Na⁺, Cl⁻)-(Na⁺, SO₄²⁻) pair are regressed from fitting experimental data on dissolution enthalpies and solubilities for the NaCl + Na₂SO₄ + H₂O ternary.     

A Ditopic Catechol Phosphane as Building Block for Selective Construction of Heterometallic Complexes with Early and Late Transition Metal Centers

Base‐assisted reaction of catechol phosphane 2 (H₂L) with [M′Cl₂(cod)] (cod = 1, 5‐cyclooctadiene, M′ = Pd, Pt) yielded chelate complexes [M′(HL)₂] ( 7a, b ). Spectroscopic and single‐crystal X‐ray diffraction studies revealed that both complexes feature cis‐configuration of the P‐ and O‐donor atoms in solution and in the solid state. Reaction of 7a, b with acetylacetonato or alkoxide complexes [MO₂(acac)₂] (M = Mo, W), [VO(acac)₂], [{Ti(μ‐O)(acac)₂}₂], or Ti(OiPr)₄ gave good to excellent yields of early‐late heterometallic complexes [MO_n(μ‐L)₂M′] (MO_n = MoO₂, WO₂, VO; 8a, b – 10a, b ) or [Ti(RO‐1κO)₂(μ‐L ‐1κ²O, O'‐2κ²P, O)₂Pd] (R = Me, iPr; 11a, b ), which were inaccessible via other synthetic routes. Spectroscopic and single‐crystal X‐ray diffraction studies revealed that the early metal centres in 8a, b, 9b and in 11b feature distorted octahedral coordination spheres with rigid transoid alignment of the catechol ring planes. Vanadium complexes 10a, b exhibit a square‐pyramidal coordination sphere with cisoid alignment of the catechol ring planes and evidence for intermolecular pairing via weak VO ··· Pd contacts in the solid state; complexes 8 , 9 do not undergo conformational inversion on the NMR time‐scale. The molecular structure of Ti complex 11a is characterized by a different orientation of the catechol moieties, which can be envisaged to picture an intermediate state during a configuration inversion process, and a strong hydrogen bridge between a terminally coordinated catecholato‐oxygen atom and a solvent molecule (MeOH). Solution NMR studies indicate that the (MeO)₂Ti(μ‐L)₂M' framework is in this case conformationally labile and that the MeO ligands undergo intermolecular dynamic exchange with the solvent.     

Phase formation in the systems Li2MoO4-K2MoO4-Ln2(MoO4)3 (Ln=La, Nd, Dy, Er) and properties of triple molybdates LiKLn2(MoO4)4

Subsolidus phase relations in the systems Li₂MoO₄-K₂MoO₄-Ln₂(MoO₄)₃ (Ln=La, Nd, Dy, Er) were determined. Formation of LiKLn₂(MoO₄)₄ was confirmed in the systems with Ln=Nd, Dy, Er at the LiLn(MoO₄)₂-KLn(MoO₄)₂ joins. No intermediate phases of other compositions were found. No triple molybdates exist in the system Li₂MoO₄-K₂MoO₄-La₂(MoO₄)₃. The join LiLa(MoO₄)₂-KLa(MoO₄)₂ is characterized by formation of solid solutions.Triple molybdates LiKLn₂(MoO₄)₄ for Ln=Nd-Lu, Y were synthesized by solid state reactions (single phases with ytterbium and lutetium were not prepared). Crystal and thermal data for these molybdates were determined. Compounds LiKLn₂(MoO₄)₄ form isostructural series and crystallized in the monoclinic system with the unit cell parameters a=5.315-5.145 Å, b=12.857-12.437 Å, c=19.470-19.349 Å, β=92.26-92.98°. When heated, the compounds decompose in solid state to give corresponding double molybdates. The dome-shaped curve of the decomposition temperatures of LiMLn₂(MoO₄)₄ has the maximum in the Gd-Tb-Dy region.While studying the system Li₂MoO₄-K₂MoO₄-Dy₂(MoO₄)₃ we revealed a new low-temperature modification of KDy(MoO₄)₂ with the triclinic structure of α-KEu(MoO₄)₂¹ (a=11.177(2) Å, b=5.249(1) Å, c=6.859(1) Å, α=112.33(2)°, β=111.48(1)°, γ=91.30(2)°, space group , Z=2).     

The transition metal catalyzed hydroboration of enamines

The addition of catecholborane (HBcat, cat = 1,2-O₂C₆H₄) to 9-vinylcarbazole can give either the branched or linear hydroboration product depending upon the judicious choice of metal catalyst used in these reactions. Analogous reactions with pinacolborane (HBpin, pin = 1,2-O₂C₂Me₄) and HBBzpin (Bzpin = 1,2-O₂C₂Ph₄) using catalytic amounts (5 mol%) of either Rh(acac)(dppb) or [Cp^∗IrCl₂]₂ gave the linear hydroboration product selectively. Hydroborations of 1-pyrrolidino-1-cyclopentene and 1-pyrrolidino-1-cyclohexene were complicated by a competing dehydrogenative borylation pathway. The branched isomer was not observed to any significant extent in these reactions, suggesting that the directing effect of the nitrogen atom is negligible. Although catalyzed additions of HBcat to 1-vinyl-2-pyrrolidinone gave complicated product distributions arising from competing reactions, addition of HBpin effectively generated the corresponding linear hydroboration product in good yields.