Dioxomolybdenum Complexes Research Articles

Dioxomolybdenum(VI) Complexes with Salicylamide Ligands: Synthesis, Structure, and Catalysis in the Epoxidation of Olefins under Eco‐Friendly Conditions

Five salicylamides [R1R2SaAmH; R1, R2 = N‐substituents: nBu, H (1a); tBu, H (1b); nOc, H (1c); Bn, H (1d); and nBu, nBu (1e)] were successfully coordinated to the dioxomolybdic fragment, resulting in MoO2(R1R2SaAm)2 complexes 2a‐e, which were characterized through elemental analysis, IR, 1H‐ and 13C NMR, ESI‐HRMS, and XRD (for 2a,b,e). All complexes are active catalysts in the solvent‐free epoxidation of cis‐cyclooctene with tert‐butyl hydroperoxide in decane (TBHPdec), showing high turnover frequencies (TOF 1890 h–1 for 2b) at 1 % loading. Using aqueous TBHP (TBHPaq) or H2O2, selectivity to cyclooctene oxide is always 100 %, although reactions are more sluggish. The 2c/TBHPaq system, which displays the best TOF (1070 h–1) at 0.25 % loading and 75 °C, allowed for the quantitative conversion of trans‐2‐octene into its epoxide, while low epoxide selectivity was observed in the case of 1‐octene, styrene, and methyl oleate. In the latter case, 90 % epoxide selectivity at 92 % conversion was achieved with the 2b/TBHPdec system at 55 °C, under solvent‐free conditions. Compared to related MoO2X2(O‐amide)‐type complexes, 2a‐e exhibit increased catalytic performance under the greener conditions involving the use of aqueous oxidants.

Synthesis, Crystal Structures and Catalytic Property of Dioxomolybdenum(VI) Complexes Derived from Tridentate Schiff Bases

A pair of structurally similar new dioxomolybdenum(VI) complexes, [MoO2L1(EtOH)]·EtOH (1) and [MoO2L2(MeOH)] (2), where L1 and L2 are the dianionic form of 2-[(2-hydroxyphenylimino)methyl]-6-methoxyphenol (H2L1) and 2-ethoxy-6-[(2-hydroxyphenylimino)methyl]phenol (H2L2), respectively, were prepared and characterized by IR and UV-Vis spectroscopy, as well as single crystal X-ray diffraction. X-ray analyses indicate that the complexes are dioxomolybdenum(VI) species. Complex 1 contains ethanol as co-ligand, and complex 2 contains methanol as co-ligand. The coordination geometry around the Mo atoms can be described as distorted octahedron, with one imino-N and two phenolate-O of the Schiff base ligand, and one oxo group defining the equatorial plane, and with the other oxo group and one solvent-O occupying the axial positions. The catalytic oxidation property of the complexes with tert-butylhydroperoxide in CH2Cl2 was studied. Both complexes have excellent catalytic properties on cyclooctene and cyclohexene, and good properties on 1-hexene and 1-octene.

Dioxomolybdenum(VI) Complex with (1-Oxyethylidene)diphosphonic Acid in an Aqueous Medium: Synthesis and Crystal Structure

A new complex of hexaammonium bis(1-oxyethylidenediphosphonate)dioxomolybdenum tetrahydrate (NH4)6[MoO2(L)2] · 4H2O (I) (H4L is H2O3P–C(OH)(CH3)–PO3H2) is synthesized. Its molecular structure consisting of the complex anion [MoO2L2]6–, six out-of-sphere ammonium cations $${\text{NH}}_{{\text{4}}}^{ + }$$ , and four water molecules is determined by X-ray diffraction analysis (CIF file CCDC no. 813517). The solubility of complex I is studied. The changes in the IR absorption spectra upon complex formation are discussed.

Spectral and computational chemistry studies for the optimization of geometry of dioxomolybdenum(VI) complexes of some unsymmetrical Schiff bases as antimicrobial agent

This analysis highlights the design, spectroscopic characterization and quantum mechanical calculation of some new dioxomolybdenum(VI) complexes of some dibasic tetradentate Schiff bases. Ligands were derived from mono 5-bromosalicylaldehyde-orthophenylenediamine (BrSal-OPD) and different 2-hydroxyketone derivatives. The characterization was performed by elemental analysis, FTIR, electronic, 1H NMR and mass spectra, magnetic and molar conductance studies. Structure of the ligands and complexes were designed depending on experimental data and computational studies. According to all data, distorted octahedral geometry was proposed where oxygen atoms are in cis position. Prepared complexes exhibit moderate antimicrobial properties when evaluated against some pathogenic bacteria and fungi. Pharmacokinetic parameters were calculated to search their biological action, for example, absorption, distribution, metabolism, excretion, and toxicity.

Quinoline and pyrazolone functionalized cis-dioxomolybdenum(VI) complexes: synthesis, hyphenated experimental-DFT studies and bactericidal implications

ABSTRACTA new series of mixed-ligand complexes of dioxomolybdenum(VI) of the general composition [MoO2(L)(8-hq)(H2O)], where 8-hq=8-hydroxyquinoline and LH=4-acylpyrazolones viz., 3-methyl-1-phenyl-4-propionyl-2-pyrazolin-5-one (pmphpH), 4-butyryl-3-methyl-1-phenyl-2-pyrazolin-5-one (bumphpH), 4-iso-butyryl-3-methyl-1-phenyl-2-pyrazolin-5-one (iso-bumphpH) or 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (bmphpH) has been synthesized by the reaction of [MoO2(acac)2] and the target ligands in ethanol medium. The complexes have been characterized by elemental analyses, decomposition temperature, molar conductance, magnetic susceptibility, thermogravimetric studies, FT-IR, UV-vis, 1H NMR, 13C NMR, and FAB mass spectral studies. The thermal decomposition processes of one complex, cis-[MoO2(iso-bumphp)(8-hq)(H2O)] has been discussed with the evaluation of the order of reaction (n) and the activation energy (Ea) calculated from the thermogravimetric (TG) curve. Antibacterial study of one of the synthesized complexes at various dilutions has also been carried in comparison with the ligands and metal precursor using ampicillin as a standard drug. Gaussian09 software package was employed to carry out the theoretical study using density functional theory DFT/B3LYP level of theory under LANL2MB (for Mo)/6-311 + G (for non-metallic elements) basis set for one of the complexes, cis-[MoO2(bmphp)(8-hq)(H2O)]. Based on experimental and theoretical data, suitable pseudo pentagonal bipyramidal structures have been proposed for this class of metal complexes.

New mononuclear dioxidomolybdenum(VI) complexes with hydrazone ligands: Synthesis, crystal structures and catalytic performance

Three new dioxomolybdenum (VI) complexes, [MoO2L1(MeOH)] (1), [MoO2L2(MeOH)] (2) and [MoO2L3(H2O)]·EtOH (3), where L1, L2 and L3 are the dianionic form of N′-(2-hydroxybenzylidene)-3-methylbenzohydrazide, 4-bromo-N′-(2-hydroxybenzylidene)benzohydrazide and 2-bromo-N′-(2-hydroxy benzylidene)benzohydrazide, respectively, have been prepared and characterized by IR, UV–Vis and NMR spectra, as well as single crystal X-ray diffraction. The Mo atoms in the complexes are in octahedral coordination, with the ONO donor set of the hydrazone ligands, O atoms of the solvents, and two oxo groups. Crystals of the complexes are stabilized by hydrogen bonds of types OH⋯N and OH⋯O. Moreover, the catalytic properties of complexes 1–3 are compared in cyclohexane oxidation. It was found that sebacic acid and FeCl3 could promote the catalytic activities of the complexes.

Synthesis, characterization and antioxidant activities of dioxomolybdenum(VI) complexes of new Schiff bases derived from substituted benzophenones

Five novel ONS donor Schiff base ligands were synthesized by the reaction of 2-hydroxybenzophenone (L1), 2-hydroxy-4-methoxybenzophenone (L2), 2-hydroxy-4-octyloxybenzophenone (L3), 2-hydroxy-4-methoxy-4′-methylbenzophenone (L4), and 2-hydroxy-4-allyloxybenzophenone (L5) with thiocarbohydrazide. Neutral solvate dioxomolybdenum(VI) complexes with the general formula [MoO2L(ROH)], [C1–C5] (L = L1, L2, L3, L4, L5 and R = CH3, C2H5, or C4H9), were prepared from these Schiff bases. Characterization of all compounds was carried out by means of elemental analysis, conductivity measurements, 1H-NMR, FT-IR, UV-Vis spectroscopy and mass spectrometry (for L1, C2, and C4) techniques. The crystal structures of ligand (L5) and complex (C1) were determined by single-crystal X-ray crystallography. Spectroscopic data and X-ray diffraction studies confirmed that the ligand is coordinated to the cis-MoO22+ core through ONS, while the sixth coordination site is occupied by solvent (ROH). The ligands and complexes were tested for in vitro antioxidant capacities. The TEAC coefficients of the ligands and complexes were found higher than reference compound. DPPH radical scavenging activities of these compounds were also investigated.

Synthesis, Characterization, and Crystal Structures of Dioxomolybdenum(VI) Complexes Derived from Similar Tridentate Hydrazone Compounds with Catalytic Property

Two hydrazone compounds 2-chloro-N'-(2-hydroxy-4-methoxybenzylidene)benzohydrazide (H2L1) and N'-(2-hydroxy-4-methoxybenzylidene)-3-methylbenzohydrazide (H2L2) were prepared and characterized by IR, UV-Vis and 1H NMR spectra. Based on the hydrazone compounds, two new structurally similar dioxomolybdenum(VI) complexes, [MoO2L1(CH3OH)] (I) and [MoO2L2(CH3OH)] (II), were prepared and characterized by IR and UV-Vis spectra, and single crystal X-ray diffraction (CIF files nos. 1566491 (I) and 1566492 (II)). Complex I crystallizes as the triclinic space group P $$\bar {1}$$ with unit cell dimensions a = 8.0750(5), b = 10.5223(7), c = 10.8110(7) A, α = 96.975(2)°, β = 97.909(2)°, γ = 104.497(2)°, V = 869.2(1) A3, Z = 2, R1 = 0.0323, wR2 = 0.0620, GOOF = 1.089. Complex II crystallizes as the monoclinic space group P21/n with unit cell dimensions a = 11.680(1), b = 10.496(2), c = 14.879(2) A, β = 98.862(2)°, V = 1802.2(4) A3, Z = 4, R1 = 0.0270, wR2 = 0.0675, GOOF = 1.111. X-ray analysis indicates that the complexes are mononuclear dioxomolybdenum(VI) species with the Mo atoms in octahedral coordination. The complexes were studied for their catalytic oxidation property on some olefins with tert-butyl hydrogen peroxide as oxidant.

Synthesis, Crystal Structure, and Catalytic Property of a Dioxomolybdenum(VI) Complex Derived from N'-(3-Bromo-5-Chloro-2-Hydroxybenzylidene)-4-Nitrobenzohydrazide

New dioxomolybdenum(VI) complex [MoO2(L)(CH3OH)], where L is the dianionic form of N'- (3-bromo-5-chloro-2-hydroxybenzylidene)-4-nitrobenzohydrazide (H2L), was prepared and characterized by IR and UV-Vis spectra, as well as single crystal X-ray diffraction (CIF file ССDС no. 1567063). The complex crystallizes as the monoclinic space group P21/c with unit cell dimensions a = 13.8471(10), b = 7.5618(6), c = 17.9445(12) A, β = 90.107(2)°, V = 1878.9(2) A3, Z = 4, R1 = 0.0821, wR2 = 0.0907, GOOF = 1.024. X-ray analysis indicates that the complex is a dioxomolybdenum(VI) species with the Mo atom in octahedral coordination. The catalytic oxidation property of the complex with tert-butylhydroperoxide in CH2Cl2 was studied.

New magnetic supported hydrazone Schiff base dioxomolybdenum (VI) complex: An efficient nanocatalyst for epoxidation of cyclooctene and norbornene

A new dioxomolybdenum (VI) complex with tridentate hydrazone Schiff base ligand (H2L) derived from 2‐hydroxy‐5‐nitrobenzaldehyde and benzhydrazide was synthesized and designated as [MoO2L (DMF)]·2H2O. The Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) nanocatalyst was successfully prepared by grafting H2L ligand on modified Fe3O4 nanoparticles followed by reacting with MoO2 (acac)2. The complex and nanocatalyst were characterized by various techniques such as elemental analysis, mass, FT‐IR, UV–Vis, 1H NMR, 13C{1H}‐NMR, TGA, XRD, XPS, TEM, SEM and VSM. The catalytic activity of [MoO2L (DMF)]2H2O and Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) were evaluated for the oxidation of various alkenes (cyclooctene, norbornene, cyclohexene, styrene and α‐methyl styrene) in the presence of tert‐butylhydroperoxide as oxidant. The results revealed that the catalysts were especially efficient for oxidation of cyclooctene and norbornene with 100% selectivity towards corresponding epoxide product. Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) showed higher catalytic activity, shorter reaction time and higher turnover number (TON) compared with homogeneous complex [MoO2L (DMF)]·2H2O. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in activity were other advantages of the nanocatalyst.

DFT study on mechanism of carbonyl hydrosilylation catalyzed by high-valent molybdenum (IV) hydrides

Density functional theory (DFT) calculations have been employed to investigate hydrosilylation of carbonyl compounds catalyzed by three high-valent molybdenum (VI) hydrides: Mo(NAr)H(Cp)(PMe3) (1A), Mo(NAr)H(PMe3)3 (1B), and Mo(NAr)H (Tp)(PMe3) (Tp = tris(pyrazolyl) borate) (1C). Three independent mechanisms have been explored. The first mechanism is “carbonyl insertion pathway”, in which the carbonyls insert into Mo−H bond to give a metal alkoxide complex. The second mechanism is the “ionic hydrosilylation pathway”, in which the carbonyls nucleophilically attacks η1-silane molybdenum adduct. The third mechanism is [2 + 2] addition mechanism which was proposed to be favorable for the high-valent di-oxo molybdenum complex MoO2Cl2 catalyzing the hydrosilylation. Our studies have identified the “carbonyl insertion pathway” to be the preferable pathway for three molybdenum hydrides catalyzing hydrosilylation of carbonyls. For Mo(NAr)H (Tp)(PMe3) (Tp = tris(pyrazolyl) borate), the proposed nonhydride mechanism experimentally is calculated to be more than 32.6 kcal/mol higher than the “carbonyl insertion pathway”. Our calculation results have derived meaningful mechanistic insights for the high-valent transition metal complexes catalyzing the reduction reaction.

Cis-Dioxomolybdenum(VI) complex of N-o-hydroxyacetophenonene-isonicotinic acid hydrazide as nosocomial anti-infectious agent: experimental and theoretical study

Due to growing resistance and continuous colonization among microbes, researchers are eager to design and put forth antibiotic substances of effective anti-nosocomial infection activity. Under such...

Synthesis, characterization, density functional theory studies and antibacterial activity of a new Schiff base dioxomolybdenum(VI) complex with tryptophan as epoxidation catalyst

Synthesis, characterization, density functional theory studies and antibacterial activity of a new Schiff base dioxomolybdenum(VI) complex with tryptophan as epoxidation catalyst

A molybdenum(VI) Schiff base complex immobilized on functionalized Fe3O4 nanoparticles as a recoverable nanocatalyst for synthesis of 2-amino-4H-benzo[h]chromenes

A dioxomolybdenum(VI) complex of a Schiff base, immobilized on the surface of modified Fe3O4 with a silica coating, has been synthesized and characterized by spectroscopic and microscopic techniques including FTIR, TGA, ICP, SEM, EDX, VSM, and XRD analyses. The catalytic performance of this material has been evaluated for the preparation of 2-amino-4H-benzo[h]chromenes via the one-pot, three-component reaction of aldehydes, malononitrile, and 1-naphthol under solvent-free conditions. The benefits of this protocol are short reaction time, simple workup procedure, and high yields of products. Also, the synthesized nanocatalyst could be separated easily from the reaction mixture using an external magnet and reused for four consecutive times with only minor degradation of its catalytic performance.

Dioxomolybdenum(VI) Complexes with R1-Substituted Salicylidene Allylimines (Hl n ): Synthesis and Structure. Crystal Structure of [MoO2(L1)2] (R1 = H)

The synthesis and X-ray diffraction analysis of [MoO2(L1)2] has been performed. The molybdenum atom has a cis(Ooxo), cis(NL), trans(OL) octahedral coordination. The average bond lengths (A): Mo–O(oxo), 1.691; Mo–N(L1), 2.351; Mo–O(L1), 1.954.

Syntheses and Spectroscopic Studies on Macrocyclic Complexes of Dioxomolybdenum(VI) with Benzyl or Diketone as a Precursor

Syntheses and Spectroscopic Studies on Macrocyclic Complexes of Dioxomolybdenum(VI) with Benzyl or Diketone as a Precursor

Synthesis of dioxomolybdenum(VI) complexes with disubstituted salicylidene-2-furfurylimines: The crystal structure of binuclear complex [{MoO2(L5)}2(μ-O)], where L5 = 3-methoxy-5-bromosalicylidene-2-furfurylimine

Three mononuclear and one binuclear dioxomolybdenum(VI) complexes with disubstituted Z-salicylidene-2-furfurylimines (HL n ) have been prepared and characterized by IR spectroscopy, namely, MoO2Cl2 · 2HL n [Z = 3-MeO-5-Br (n = 5); 3,5-Cl2 (n = 7); 3,5-Br2 (n = 8)] and [{MoO2(L5)}2(μ-O)] (I). The structure of complex I has been determined by X-ray diffraction. Each of the atoms Мо1 and Мо2 has coordination number 5, which is unusual for binuclear complexes of [{MoO2(L)}2(μ-O)]. The coordination polyhedron of each of the atoms Мо(1) or Мо(2) may be described either as a heavily distorted trigonal bipyramid (TBP) with two oxo ligands and the atom О(L5) in the equatorial plane and the atoms Оbr, N(L5) in the axial sites, or as an intermediate between a TBP and a square pyramid (SP) (τ = 0.375 for Мо(1) and 0.470 for Мо(2)).

Dioxomolybdenum(VI) complexes of S-methyl-5-bromosalicylidene-N-alkyl substituted thiosemicarbazones: Synthesis, catalase inhibition and antioxidant activities

We synthesized a series of S-methyl-5-bromosalicylidene-N-alkyl substituted thiosemicarbazones and their cis-dioxomolybdenum(VI) complexes having long alkyl chains (propyl, butyl, pentyl, hexyl, and octyl) on thioamide nitrogen. The compounds were characterized by using analytical and spectroscopic methods. The structure of the complex with pentyl group (complex 3) as a representative molecule was determined by X-ray single-crystal diffraction method. The free ligand and their dioxomolybdenum(VI) complexes have been tested for in vitro antioxidant capacity by reduction of copper (II) neocuproine (Cu(II)-Nc) using the CUPRAC (CUPric Reducing Antioxidant Capacity) method. The ligands exhibited more potent in vitro antioxidant capacity than that of the complexes. The obtained trolox equivalent antioxidant capacity (TEAC) value of complex 1 (TEACCUPRAC=0.73) was higher than those of other complexes. Furthermore, the catalase activity and reactive oxygen species (ROS) scavenging ability of the free ligands and their complexes were determined, showing that complex 1 had significant scavenging activity for ROS.

Synthesis, crystal structures, and catalytic property of dioxomolybdenum(VI) complexes with hydrazone ligands derived from 3,5-Di-tert-butylsalicylaldehyde

Two new dioxomolybdenum(VI) complexes, [MoO2L1(MeOH)] (I) and [MoO2L2] (II), where L1 and L2 are the anionic forms of N'-(2-hydroxy-3,5-di-tert-butylbenzylidene)-4-methoxybenzohydrazide and 2-amino-N'-(2-hydroxy-3,5-di-tert-butylbenzylidene)benzohydrazide, respectively, have been synthesized and characterized by elemental analysis, FT-IR spectra, and single crystal X-ray determination (CF files CCDC nos. 1448089 (I), 1487063 (II)). The crystal of I is monoclinic: space group P21/n, a = 7.353(1), b = 24.758(3), c = 13.891(2) A, β = 101.013(2)°, V = 2482.3(6) A3, Z = 4, R 1 = 0.0848, wR 2 = 0.2050. The crystal of II is monoclinic: space group P21/c, a = 6.752(1), b = 16.947(1), c = 19.510(1) A, β = 96.891(2)°, V = 2216.5(4) A3, Z = 4, R 1 = 0.0670, wR 2 = 0.1638. The Mo atom in complex I is in octahedral coordination, with three donor atoms of the hydrazone ligand, two oxo groups, and one methanol O atom. The Mo atom in complex II is in square pyramidal coordination, with three donor atoms of the hydrazone ligand, and two oxo groups. The complexes have interesting catalytic properties for sulfoxidation reactions.

Synthesis, characterization, and crystal structures of dioxomolybdenum(VI) complexes with O,N,N type tridentate hydrazone ligands as catalyst for oxidation of olefins

The preparation of Mo(VI) hydrazone complexes, cis-[MoO2L1(CH3OH)] (I) and cis-[MoO2L2(CH3OH)] (II), derived from N'-(3-bromo-2-hydroxybenzylidene)-2-chlorobenzohydrazide (H2L1) and N'-(3-bromo-2-hydroxybenzylidene)-4-bromobenzohydrazide (H2L2), respectively, is reported. The complexes were characterized by elemental analyses, infrared and electronic spectroscopy, and single crystal structure analysis (CIF files ССDС nos. 1426875 (I), 1426871 (II)). The Mo atoms are coordinated by two cis terminal oxygen, ONO from the hydrazone ligand, and methanol oxygen. Even though the hydrazone ligands and the coordination sphere in both complexes are similar, the unit cell dimensions and the space groups are different. Complex I crystallized as orthorhombic space group Pca21 with unit cell dimensions a = 27.887(2), b = 8.0137(7), c = 15.544(1) A, V = 3473.8(5) A3, Z = 8, R 1 = 0.0450, wR 2 = 0.0539. Complex II crystallized as triclinic space group P1, with unit cell dimensions a = 8.2124(4), b = 8.5807(5), c = 12.9845(8) A, α = 83.366(2)°, β = 79.201(2)°, γ = 80.482(2)°, V = 883.03(9) A3, Z = 2, R 1 = 0.0278, wR 2 = 0.0569. The complexes were tested as catalyst for the oxidation of olefins, and showed effective activity.