Complex MoO Research Articles

Reaction Pathway for the Aerobic Oxidation of Phosphines Catalyzed by Oxomolybdenum Salen Complexes

AbstractCatalysis of O‐atom transfer (OAT) reactions is a characteristic of both natural (enzymatic) and synthetic molybdenum‐oxo and ‐peroxo complexes. These reactions can employ a variety of terminal oxidants, e. g. DMSO, N‐oxides, and peroxides, etc., but rarely molecular oxygen. Here we demonstrate the ability of a set of Schiff‐base‐MoO2 complexes (cy‐salen)MoO2 (cy‐salen=N,N’‐cyclohexyl‐1,2‐bis‐salicylimine) to catalyze the aerobic oxidation of PPh3. We also report the results of a DFT computational investigation of the catalytic pathway, including the identification of energetically accessible intermediates and transition states, for the aerobic oxidation of PMe3. Starting from the dioxo species, (cy‐salen)Mo(VI)O2 (1), key reaction steps include: 1) associative addition of PMe3 to an oxo‐O to give LMo(IV)(O)(OPMe3) (2); 2) OPMe3 dissociation from 2 to produce mono‐oxo complex (cy‐salen)Mo(IV)O (3); 3) stepwise O2 association with 3 via superoxo species (cy‐salen)Mo(V)(O)(η1‐O2) (4) to form the oxo‐peroxo intermediate (cy‐salen)Mo(VI)(O)(η2‐O2) (5); 4) the O‐transfer reaction of PMe3 with oxo‐peroxo species 5 at the oxo‐group, rather than the peroxo unit leading, after OPMe3 dissociation, to a monoperoxo species, (cy‐salen)Mo(IV)(η2‐O2) (7); and 5) regeneration of the dioxo complex (cy‐salen)Mo(VI)O2 (1) from the monoperoxo triplet 37 or singlet 17 by a concerted, asynchronous electronic isomerization. An alternative pathway for recycling of the oxo‐peroxo species 5 to the dioxo‐Mo 1 via a bimetallic peroxo complex LMo(O)‐O−O‐Mo(O)L 8 is determined to be energetically viable, but is unlikely to be competitive with the primary pathway for aerobic phosphine oxidation catalyzed by 1.

Chiral-at-Metal Racemization Unraveled for MX2 (a-chel)2 by Means of a Computational Analysis of MoO2 (acnac)2.

Invited for the cover of this issue are Koop Lammertsma and co-workers at the University of Johannesburg and Vrije Universiteit Amsterdam. The image of the kudu's antlers depicts the isomerization and racemization of the chiral-at-metal complex MoO2(acnac)2 (acnac=β-ketoiminate). Read the full text of the article at 10.1002/chem.202302516.

Multi Objective Optimization Design of Building Construction Period based on BIM and Genetic Algorithm

China’s construction industry market competition is becoming increasingly fierce, which requires construction enterprises to gradually enhance the core competitiveness. Therefore, the construction period must be multi objective optimization (hereinafter referred to as MOO), which will improve the level of project management in the construction process. Through the MOO of construction period, we can achieve the overall cost optimization of construction projects. Through the coordination of construction project scheduling, we can improve the overall efficiency and efficiency of project operation, which will improve the utilization of resources and save the project cost. Genetic algorithm (hereinafter referred to as GA) can solve the adaptive global optimization probability search, which is a method to optimize the model process. By integrating GA into BIM platform, we introduce methods such as virtual construction and collision check, which can reasonably deal with complex MOO problems. The construction schedule and cost can be determined more quickly and reliably through the construction schedule. Therefore, this paper puts forward the MOO design among construction period, quality, safety and cost.

Nanocomposite of ultra-small MoO2 embedded in nitrogen-doped carbon: In situ derivation from an organic molybdenum complex and its superior Li-Ion storage performance

MoO2 is a promising anode material for lithium-ion batteries, however, the lithiation of bulk MoO2 is usually limited to addition-type reaction at room temperature, and the conversion reaction is hindered because of the sluggish kinetics. Herein, a nanocomposite of MoO2 embedded in nitrogen-doped carbon (MoO2/NC) is synthesized through the in situ thermolysis of an organic molybdenum complex MoO2(acac)(phen) (acac = acetylacetone, phen = 1,10-Phenanthroline). Owing to the fact that [MoO2]2+ can be strongly chelated by phen, the molybdenum source in the MoO2(acac)(phen) precursor is highly dispersed, leading to the formation of ultra-small MoO2 nanoparticles in the nanocomposite, which can facilitate the conversion reaction. Moreover, the NC matrix can guarantee a high electrical conductivity and effectively accommodate the volume changes triggered by the conversion reaction. Consequently, the MoO2/NC nanocomposite exhibits outstanding electrochemical properties, including large reversible capacity of 950 mA h g−1 at 0.1 A g−1, high-rate capability of 605 mA h g−1 at 2 A g−1, and excellent cycling stability over 500 cycles as an anode material for lithium-ion batteries.

2,2′-Bipyridine or 1,10-phenanthroline chelated oxomolybdenum(V) complexes with glycolate, lactate and malate in acidic media

A series of dimeric oxomolybdenum(V) 2,2′-bipyridine or 1,10-phenanthroline α-hydroxycarboxylates trans-[(MoO)2O(glyc)2(bpy)2]·3H2O (1), trans-[(MoO)2O(lact)2(bpy)2]·3H2O (2), trans-[(MoO)2O(Hmal)2(bpy)2] (3), trans-[(MoO)2O(lact)2(phen)2]·4H2O (4) and trans-[(MoO)2O(Hmal)2(phen)2]·4H2O (5) have been synthesized in acidic media for comparisons, where glycolate, lactate and malate in 1–5 chelate to molybdenum(V) with bidentate α-alkoxy and α-carboxy groups respectively. Unlike the molybdenum(IV) lactate in low valence [1], no protonation was observed for α-alkoxy groups even under acidic condition. The two molybdenum atoms in 1 and 3 are paramagnetic independently as examples by EPR spectroscopies. Solid state 13C NMR spectra of 1 and 3 show large downfield shifts for the coordinated glycolate and malate (δα-alkoxy 75.4, 82.8 ppm, Δδ 13.4 ppm). Moreover, a monomeric mixed ligand oxomolybdenum(VI) complex MoO2(glyc)(bpy) (6) was isolated.

Selective hydroxylation of diamantane with 2,3,4,5,6-pentafluoroperbenzoic acid in the presence of molibdenum complexes

Oxidation of diamantane with 2,3,4,5,6-pentafluoroperbenzoic acid catalyzed with complexes MoO(O2)·2QOH, MoO(O2)(H2O)2 proceeds selectively affording diamantan-1-ol and diamantan-1-yl 2,3,4,5,6-pentafluorobenzoate.

Volatile Hexavalent Oxo-amidinate Complexes: Molybdenum and Tungsten Precursors for Atomic Layer Deposition

New complexes MoO2(tBuAMD)2 (1) and WO2(tBuAMD)2 (2) (AMD = acetamidinato) are synthesized and fully characterized as precursors for atomic layer deposition (ALD). They contain metal-oxo functionalities not previously utilized in ALD-type growth processes and are fully characterized by 1H and 13C NMR, X-ray diffraction (XRD), Fourier transform infrared, thermogravimetric analysis, single-crystal XRD, and elemental analysis. Guided by quartz-crystal microbalance studies, ALD growth methodologies for both complexes have been developed. Remarkably, these isostructural compounds exhibit dramatic differences in ALD properties. Using 1 and O3, amorphous, ultrathin molybdenum oxynitride (MoON) films are grown on Si(100) wafers. Using 2 and H2O yields amorphous WO3 films on Si(100) wafers that crystallize as WO3 nanowires upon annealing. Although 1/H2O and 2/O3 growth was attempted, effective ALD growth could only be obtained with 1/O3 and 2/H2O, underscoring reactivity differences in these precursors. Film thick...

Large Ligand Folding Distortion in an Oxomolybdenum Donor–Acceptor Complex

Interligand charge transfer is examined in the novel metallo-dithiolene complex MoO(SPh)2((i)Pr2Dt(0)) (where (i)Pr2Dt(0) = N,N'-isopropyl-piperazine-2,3-dithione). The title complex displays a remarkable 70° "envelope"-type fold of the five-membered dithiolene ring, which is bent upward toward the terminal oxo ligand. A combination of electronic absorption and resonance Raman spectroscopies have been used to probe the basic electronic structure responsible for the large fold-angle distortion. The intense charge transfer transition observed at ∼18 000 cm(-1) is assigned as a thiolate → dithione ligand-to-ligand charge transfer (LL'CT) transition that also possesses Mo(IV) → dithione charge transfer character. Strong orbital mixing between occupied and virtual orbitals with Mo(x(2)-y(2)) orbital character is derived from a strong pseudo Jahn-Teller effect, which drives the large fold-angle distortion to yield a double-well potential in the electronic ground state.

Thermodynamic and quantum-chemical study of the oxidative dehydrogenation of ethane to ethylene

The equilibrium product composition for the reaction of ethane dehydrogenation to ethylene with various quantities of oxygen fed to the reaction medium has been calculated using methods of chemical thermodynamics. Quantum-chemical calculation of the energy of interaction of ethane with molybdenum dioxide, used as an example, has shown that the absolute energy minimum in the energy profile of the potential energy surface along the ethane dehydrogenation reaction coordinate corresponds to the complex MoO2⋯H2⋯C2H4.

ChemInform Abstract: Dioxomolybdenum(VI) Complex Covalently Attached to Amino‐Modified Graphene Oxide: Heterogeneous Catalyst for the Epoxidation of Alkenes.

Transition metal salen complex MoO2–salen was successfully tethered onto amino-functionalized graphene oxide (designated as MoO2–salen–GO), which was tested in the epoxidation of various alkenes using tert-butylhydroperoxide or H2O2 as oxidant. Characterization results showed that dioxomolybdenum(VI) complex was successfully grafted onto the amino-functionalized graphene oxide and the structure of the graphene oxide was well preserved after several stepwise synthesis procedures. Catalytic tests showed that heterogeneous catalyst MoO2–salen–GO was more active than its homogeneous analogue MoO2–salen in the epoxidation of cyclooctene due to site isolation. In addition, the MoO2–salen–GO catalyst could be reused three times without significant loss of activity. Copyright © 2014 John Wiley & Sons, Ltd.

Dioxomolybdenum(VI) complex covalently attached to amino‐modified graphene oxide: heterogeneous catalyst for the epoxidation of alkenes

Transition metal salen complex MoO2–salen was successfully tethered onto amino‐functionalized graphene oxide (designated as MoO2–salen–GO), which was tested in the epoxidation of various alkenes using tert‐butylhydroperoxide or H2O2 as oxidant. Characterization results showed that dioxomolybdenum(VI) complex was successfully grafted onto the amino‐functionalized graphene oxide and the structure of the graphene oxide was well preserved after several stepwise synthesis procedures. Catalytic tests showed that heterogeneous catalyst MoO2–salen–GO was more active than its homogeneous analogue MoO2–salen in the epoxidation of cyclooctene due to site isolation. In addition, the MoO2–salen–GO catalyst could be reused three times without significant loss of activity. Copyright © 2014 John Wiley & Sons, Ltd.

Mechanistic insights into B–H bond activation with the high-valent oxo-molybdenum complex MoO2Cl2

The ionic mechanistic model involving the heterolytic cleavage of the B–H bond is slightly energetically favorable than the [2+2] addition mechanism for the high-valent oxo-molybdenum complex MoO2Cl2activating the B–H bond.

Dioxo and oxo-peroxo molybdenum(VI) complexes bearing salicylidene 2-picoloyl hydrazone: Structures and catalytic performances

Molybdenum complexes bearing a salicylidene 2-picoloyl hydrazone ligand have been synthesized and characterized. The salicylidene 2-picoloyl hydrazone ligand (H2sal-phz) was prepared by reaction of picoloyl hydrazine with salicylaldehyde. Reaction of H2sal-phz with MoO2(acac)2 generates the dioxo molybdenum complex MoO2(sal-phz)(CH3OH). Treatment of MoO3 in the presence of H2O2 with H2sal-phz produces the oxo-peroxo molybdenum(VI) complex MoO(O2)(sal-phz)(CH3OH). The new compounds were characterized by 1H NMR and IR spectroscopies, and elemental analysis. The complexes were also characterized by single crystal X-ray diffraction crystallography. The complexes were evaluated for epoxidation catalysis with tert-butyl hydroperoxide (tert-BuOOH). The MoO2(sal-phz)(CH3OH) complex exhibited high catalytic activity for the epoxidation of olefins, whereas the peroxo analogue is inert to reaction with olefins, thus ruling out the peroxide compound as the intermediate responsible in the [MoO2(sal-phz)(CH3OH)]-catalyzed epoxidation with tert-BuOOH.

Use of MoO2Cl2(DMF)2 as a precursor for molybdate promoted hydrolysis of phosphoester bonds

Phosphoester bond cleavage of para-nitrophenylphosphate (pNPP), a commonly used model substrate, is accelerated by using the complex MoO(2)Cl(2)(DMF)(2) (1) (DMF = dimethylformamide) as a hydrolysis promoting agent, even when catalytic amounts of 1 (10 mol% relative to pNPP) are used. The reactions were performed under mild conditions (37-75 °C) and followed by (1)H NMR spectroscopy. For assays performed with high amounts of 1 (1000 mol% relative to pNPP), a white solid (2) precipitates during the initial stages of the reaction, which subsequently dissolves, leading eventually to the precipitation of a less soluble yellow solid (3). Taken together, the characterization data for 2 (FT-IR spectroscopy, elemental analysis, (1)H and (13)C NMR, and electrospray ionization mass spectrometry) indicate that it is a polymeric material with the formula Mo(2)O(6)(DMF)(n) and a structure comprising infinite isopolyoxomolybdate chains built up from edge-shared {MoO(6)} octahedra. Compound 3 was identified as the Keggin-type phosphomolybdate [(CH(3))(2)NH(2)](3)PMo(12)O(40). The formation of 3 is explained by the reaction of inorganic phosphate ions with isopolymolybdate species derived from 2, with dimethylammonium ions arising from the degradation of DMF. Both 2 and 3 are active for phosphoester bond hydrolysis with conversion profiles comparable to the ones obtained with the precursor 1.

Dioxomolybdenum(VI) complexes with linear and tripodal tetradenate ligands: Synthesis, structures and their use as olefin epoxidation catalysts

A series of linear and tripodal tetradentate ligands containing an amine-bis(phenolate) core were synthesized by Mannich condensations. Treatment of these ligands with MoO2(acac)2 (acac=acetylacetonate) in dichloromethane and methanol at room temperature gave the corresponding cis-dioxomolybdenum(VI) complexes in good yields. All these complexes were characterized by a wide range of spectroscopic methods (NMR, IR, and UV–Vis) and elemental analysis. The molecular structures of complexes MoO2(Ln) (n=1–3, 5) were confirmed by single-crystal X-ray diffraction analysis. The catalytic activities of all complexes towards the epoxidation of styrene by tert-butyl hydroperoxide have also been investigated.

Molybdenum(VI) Complexes of a 2,2′-Biphenyl-bridged Bis(amidophenoxide): Competition between Metal–Ligand and Metal–Amidophenoxide π Bonding

The 2,2'-biphenyl-bridged bis(2-aminophenol) ligand 4,4'-di-tert-butyl-N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-2,2'-diaminobiphenyl ((t)BuClipH(4)) reacts with MoO(2)(acac)(2) to form ((t)BuClipH(2))MoO(2), where the diarylamines remain protonated and bind trans to the terminal oxo groups. This complex readily loses water on treatment with pyridine or 3,5-lutidine to form mono-oxo complexes ((t)BuClip)MoO(L), which exhibit predominantly a cis-β geometry with an aryloxide trans to the oxo group. Exchange of the pyridine ligands is rapid and takes place by a dissociative mechanism, which occurs with retention of stereochemistry at molybdenum. Oxo-free alkoxide complexes ((t)BuClip)Mo(OR)(2) are formed from ((t)BuClipH(2))MoO(2) and ROH. Treatment of NMo(O(t)Bu)(3) with (t)BuClipH(4) results in complete deprotonation of the bis(aminophenol) and formation of a dimolybdenum complex ((t)BuClip)Mo(μ-N)(μ-NH(2))Mo((t)BuClip) containing both a bridging nitride (Mo-N = 1.848 Å, Mo-N-Mo = 109.49°) and a bridging amide group. The strong π bonding of this bis(amidophenoxide) ligand allows the molybdenum center to interconvert readily among species forming three, two, one, or zero π bonds from multiply bonded ligands.

Molybdenum(vi) catalysts obtained from η3-allyl dicarbonyl precursors: Synthesis, characterization and catalytic performance in cyclooctene epoxidation

The oxidative decarbonylation of the η(3)-allyl dicarbonyl complexes [Mo(η(3)-C(3)H(5))Cl(CO)(2)(L)] (L = 2,2'-bipyridine (bipy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (di-tBu-bipy) (2)) by reaction with aqueous tert-butylhydroperoxide (TBHP) or H(2)O(2) gave the following compounds in good to excellent yields: the oxo-bridged dimers [MoO(2)Cl(L)](2)O (L = bipy (3), di-tBu-bipy (6)) using TBHP(10 equiv.)/CH(3)CN/r.t.; the molybdenum oxide/bipyridine hybrid material {[MoO(3)(bipy)][MoO(3)(H(2)O)]}(n) (4) and the octanuclear complex [Mo(8)O(24)(di-tBu-bipy)(4)] (7) using TBHP(50 equiv.)/H(2)O/70 °C; the oxodiperoxo complexes MoO(O(2))(2)(L) (L = bipy (5), di-tBu-bipy (8)) using H(2)O(2)(10 equiv.)/CH(3)CN/r.t. The structure of 7·x(solvent) (where solvent = CH(2)Cl(2) and/or diethyl ether) was determined by single crystal X-ray diffraction. Despite possessing the same windmill-type complex as that described previously for 7·10CH(2)Cl(2), the crystal structure of 7·x(solvent) is unique due to differences in the crystal packing. Compounds 1-8 were examined as catalysts or catalyst precursors for the epoxidation of cyclooctene using aqueous TBHP or H(2)O(2) as oxidant at 55 or 70 °C. Reactions were performed without co-solvent or with the addition of water, ethanol or acetonitrile. Cyclooctene oxide was always the only reaction product. Solids recovered after 24 h reaction at 70 °C were identified by FT-IR spectroscopy as the hybrid 4 from (1,3-5)/TBHP, complex 5 from (1,3-5)/H(2)O(2), and complex 8 from (2,6-8)/H(2)O(2). With TBHP as oxidant, the highest epoxide yields (for 24 h reaction at 70 °C) were obtained using excess H(2)O as solvent (28-38% for 1,3-5; 87-98% for 2,6-8), while with H(2)O(2) as oxidant, the highest epoxide yields were obtained using CH(3)CN as solvent (54-81% for 3-8).

A spectroscopic study of molybdenum extracts in organic solutions of dibutyl hydrogen phosphate in equilibrium with aqueous nitric acid solutions

The Mo extracts prepared by contacting dibutyl hydrogen phosphate (HDBP, HA) dissolved in xylene or CCl4 with HNO3 solutions of various concentrations in a wide range of Mo concentrations, and also the third phase formed in the analogous extraction system with tridecane as diluent were examined by IR and UV spectroscopy. The data obtained confirm the conclusion that, at the ratios HDBP: Mo ≥ 4 in the extract, molybdenum is extracted in the form of the acidic salt MoO2(HA2)2. The spectroscopic data obtained at higher extract loading were interpreted assuming the formation of binuclear complexes (HA2)MoO2A2MoO2(HA2) and, at HDBP: Mo < 3, of complexes of hydroxomolybdenyl and/or dimolybdenyl, and finally of polymeric complexes with bridging Mo-O-Mo bonds. In strongly acidic media, coextraction of outer-sphere molecular HNO3 and the presence of coordinated nitrate ion in the extract (probably in the form of molybdenyl nitrate complexes) are observed. A multistep extraction mechanism involving formation in the aqueous phase of an asymmetric monomeric complex MoO2(OH)(H2O)(HA2) was suggested.

A joint computational and experimental study of a novel dioxomolybdenum(VI) complex bearing chiral N,N-dimethyllactamide ligand

A new cis-dioxomolybdenum complex MoO2(DMLA)2 (DMLA=N,N-dimethyllactamide) has been synthesized and characterized by X-ray crystallography, H NMR and IR spectroscopies and electronic structure calculations at DFT/B3LYP level. This compound (chemical formula C10H20MoO6N2) crystallizes in the orthorhombic space group P212121 with Z=4, a=6.9357(2)Ǻ, b=11.8761(4)Ǻ, c=17.7251(5), V=1460.00(8)Ǻ3 and renders a slightly distorted octahedral structure with two long Mo–O bonds (2.253(3)Ǻ and 2.257(3)Ǻ) trans to each of the MoO groups and with two short Mo–O bonds of 1.942(3)4Ǻ cis to them. The MoO bond length are 1.715(3) and 1.704(3)Ǻ). Each lactamide ligand is bidentate; they are coordinated in their deprotonated form with the carbonyl oxygen occupying a position trans to the MoO moiety while the deprotonated hydroxyl oxygen is located cis to them. Structural characterization is complemented by DFT/B3LYP calculations.

Olefin Epoxidation by Molybdenum Peroxo Compound: Molecular Mechanism Characterized by the Electron Localization Function and Catastrophe Theory

The oxygen atom transfer reaction from the Mimoun-type complex MoO(η(2)-O(2))(2)OPH(3) to ethylene C(2)H(4) affording oxirane C(2)H(4)O has been investigated within the framework of the Bonding Evolution Theory in which the corresponding molecular mechanism is characterized by the topological analysis of the electron localization function (ELF) and Thom's catastrophe theory (CT). Topological analysis of ELF and electron density analysis reveals that all Mo-O bonds in MoO(η(2)-O(2))(2)OPH(3) and MoO(2)(η(2)-O(2))OPH(3) belong to closed-shell type interactions though negative values of total energy densities E(e)(r(BCP)) imply some covalent contribution. The peroxo O(i)-O(j) bonds are characterized as charge-shift or protocovalent species in which pairs of monosynaptic basins V(3)(O(i)), V(3)(O(j)) with a small electron population of ~0.25e each, are localized between core basins C(O(i)), C(O(j)). The oxygen transfer reaction from molybdenum diperoxo complex MoO(η(2)-O(2))(2)OPH(3) to C(2)H(4) system can be described by the following consecutive chemical events: (a) protocovalent peroxo O(2)-O(1) bond breaking, (b) reduction of the double C(1)=C(2) bond to single C(1)-C(2) bond in ethylene, (c) displacement of oxygen O(1) with two nonbonding basins, V(i=1,2)(O(1)), (d) increase of a number of the nonbonding basins to three (V(i=1,2,4)(O(1))); (e) reorganization and reduction in the number of nonbonding basis to two basins (V(i=1,4)(O(1))) resembling the ELF-topology of the nonbonding electron density in oxirane, (e) formation of the first O(1)-C(2) bond in oxirane, (f) C(2)-O(1)-C(2) ring closure, (g) formation of singular nonbonding basin V(O(2)) in new Mo=O(2) bond. The oxygen atom is transferred as an anionic moiety carrying a rather small electronic charge ranging from 0.5 to 0.7e.