Molybdenum Hexacarbonyl Research Articles

Density functional theory study on the mechanism of water gas shift reaction catalyzed by molybdenum hexacarbonyl in aqueous solvent

The mechanism of the water gas shift reaction (WGSR) catalyzed by Mo(CO)6 in both gaseous and aqueous phases were analyzed using the density functional theory (DFT) method. This study indicates that aqueous phase slightly increased every energy barrier for each step along the reaction path. The turnover frequency (TOF) of the reaction was determined using the energy span model (ESM). The TOF value in the aqueous phase (2.48 × 10−16 s−1) is slightly lower than in the gas phase (6.08 × 10−16 s−1). Actually, the advantages of aqueous phase may be attributed to high solubility and concentration of H2O, CO, OH−. The study of temperature (300–900 K) on energy profile shows that the reaction rate of WGSR can be increased with the increase of temperature. This research filled the gap in understanding the mechanism for the WGSR in aqueous phase, provides a reasonable theoretical foundation for molybdenum-based catalysts development.

Microwave-assisted synthesis and evaluation of chalcone-ligated molybdenum carbonyl complexes as cytotoxic agents and DNA binders

Microwave irradiation of a mixture of Mo(CO)6 and pyridinecarboxaldehyde (pyca), acetylpyridine (acpy) and pyridyl-anthryl chalcones with tetrahydrofuran solvent in a closed vessel afforded products in good yields without the need for an inert atmosphere. While the reaction with 3- and 4-pyridyl moieties gave the cis-disubstituted complexes Mo(CO)4(L)2, the reaction with 2-pyridyl entities yielded complexes with a range of structures such as Mo(CO)2(L)2, Mo(CO)4L and Mo2(CO)6(L)2. All the novel complexes have been characterised by IR and 1H NMR spectroscopy as well as elemental analysis. In addition, the solid-state structure of one of the chalcone-ligated compounds has been determined by single-crystal X-ray diffraction. The chalcone-ligated complexes were found to be cytotoxic through the brine shrimp lethality assay, and were able to bind to quadruplex DNA. On the other hand, the pyca- and acpy-ligated compounds did not display any lethality and were unable to interact with DNA. The results indicate that the inclusion of a chalcone ligand plays an important role in improving the cytotoxicity and DNA binding capabilities of molybdenum carbonyl compounds.

An organic-organometallic CO-releasing material comprising 4,4'-bipyridine and molybdenum subcarbonyl building blocks.

Over the past two decades, following the discovery of the important biological roles of carbon monoxide (CO), metal carbonyl complexes have been intensively studied as CO-releasing molecules (CORMs) for therapeutic applications. To improve the properties of "bare" low molecular weight CORMs, attention has been drawn to conjugating CORMs with macromolecular and inorganic scaffolds to produce CO-releasing materials (CORMAs) capable of storing and delivering large payloads of the gasotransmitter. A significant obstacle is to obtain CORMAs that retain the beneficial features of the parent CORMs. In the present work, a crystalline metal-organic framework (MOF) formulated as Mo(CO)3(4,4'-bipyridine)3/2 (Mobpy), with a structure based on Mo(CO)3 metallic nodes and bipyridine linkers, has been prepared in near quantitative yield by a straightforward reflux method, and found to exhibit CO-release properties that mimic those typically observed for molybdenum carbonyl CORMs. Mobpy was characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), FT-IR, FT-Raman and diffuse reflectance (DR) UV-vis spectroscopies, and 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR. The release of CO from Mobpy was studied by the deoxy-myoglobin (deoxy-Mb)/carbonmonoxy-myoglobin (MbCO) UV-vis assay. Mobpy liberates CO upon contact with a physiological buffer in the dark, leading to a maximum released amount of 1.3-1.5 mmol g-1, after 1.5 h at 37 °C, with half-lives of 0.5-1.0 h (time to transfer 0.5 equiv. of CO to Mb). In the solid-state and under open air, Mobpy undergoes complete decarbonylation over a period of 42 days, corresponding to a theoretical CO-release of 7.25 mmol g-1.

Optical Spectra of Composite Materials Based on Molybdenum- Containing Nanoparticles and High-Pressure Polyethylene

Molybdenum-containing composite nanomaterials are synthesized by the thermal decompositionof molybdenum hexacarbonyl in a solution-melt of polyethylene in mineral oil. The concentration of a metalcontainingfiller in the composite materials varied from 1 to 20 wt %. A technique for preparing film samplesfor spectroscopic studies is developed, and the samples obtained are studied by UVI, IR, and Raman spectroscopy.It is found that additional absorption bands appear in the IR range, whose intensity depends on theconcentration of molybdenum-containing nanoparticles in the composite materials. The spectral characteristicsof Raman scattering show that all samples are characterized by the stretching of the C–C bond. In thevisible light region, the spectrum of nanocomposites has a flat edge of its own absorption located in the regionof wave numbers (18–31) × 103 cm–1.

Two-Chamber Aminocarbonylation of Aryl Bromides and Triflates Using Amino Acids as Nucleophiles.

A palladium(0)-catalyzed aminocarbonylation reaction employing molybdenum hexacarbonyl as a carbon monoxide precursor for the production of N-capped amino acids using aryl and heteroaryl bromides and triflates is reported. The carbon monoxide is formed ex situ through the use of a two-chamber system, where carbon monoxide generated in one chamber is free to diffuse over and be consumed in the other palladium-catalyzed reaction chamber. Using this method, two series of aryl bromides and aryl triflates were utilized to synthesize 21 N-capped amino acids in isolated yields between 40 and 91%.

Stable Molybdenum(0) Carbonyl Complex for Upconversion and Photoredox Catalysis.

Photoactive complexes with earth-abundant metals have attracted increasing interest in the recent years fueled by the promise of sustainable photochemistry. However, sophisticated ligands with complicated syntheses are oftentimes required to enable photoactivity with nonprecious metals. Here, we combine a cheap metal with simple ligands to easily access a photoactive complex. Specifically, we synthesize the molybdenum(0) carbonyl complex Mo(CO)3(tpe) featuring the tripodal ligand 1,1,1-tris(pyrid-2-yl)ethane (tpe) in two steps with a high overall yield. The complex shows intense deep-red phosphorescence with excited state lifetimes of several hundred nanoseconds. Time-resolved infrared spectroscopy and laser flash photolysis reveal a triplet metal-to-ligand charge-transfer (3MLCT) state as the lowest excited state. Temperature-dependent luminescence complemented by density functional theory (DFT) calculations suggest thermal deactivation of the 3MLCT state via higher lying metal-centered states in analogy to the well-known photophysics of [Ru(bpy)3]2+. Importantly, we found that the title compound is very photostable due to the lack of labilized Mo-CO bonds (as caused by trans-coordinated CO) in the facial configuration of the ligands. Finally, we show the versatility of the molybdenum(0) complex in two applications: (1) green-to-blue photon upconversion via a triplet-triplet annihilation mechanism and (2) photoredox catalysis for a green-light-driven dehalogenation reaction. Overall, our results establish tripodal carbonyl complexes as a promising design strategy to access stable photoactive complexes of nonprecious metals avoiding tedious multistep syntheses.

The Mechanism of Growing MoS2 via Sulfuration of Molybdenum Hexacarbonyl: First principles study

AbstractTransition metal dichalcogenides (TMDCs) films are potential two‐dimensional materials for next‐generation optoelectronic and electronic devices. Chemical Vapor Deposition, Atomic Layer Deposition, and Metal‐Organic Chemical Vapor Deposition are usually used for the synthesis of the MoS2 films by taking Mo(CO)6 as precursors. However, the mechanism of adsorption and reaction of Mo(CO)6 on the substrate at the molecular level are hardly to know only by the experiments. In this study, the detailed reactions of Mo(CO)6 on α‐Al2O3(0001) are investigated by density functional theory to demonstrate the growth mechanism of MoS2. It is found that, Mo(CO)6 could form a stable chemical bond with the Al‐1 site on the surface, which has large adsorption energy and charge transfer. The decomposition of Mo(CO)6 into Mo(CO)3 exists in a clear order, with the top carbonyl composing firstly, follow by the two parallel carbonyls. In order to determine the stable model of Mo(CO)3, adsorption energy and DOS are analyzed. The Ead is −5.65 eV and the 4d5 s orbitals of Mo atom overlap with the 2 s2p orbitals of O atom, indicating the new chemical bond is forming in 3O‐Al‐2 model. Finally, the LST/QST (Linear Synchronous Transit/Quadratic Synchronous Transit) method is used to search for transition states of Mo(CO)3 sulfuration reactions with CH3S2CH3, H2S, and S2 respectively. This paper provides a theoretical basis for the experimental preparation of MoS2 and provides research ideas for the general synthesis of TMDCs.

Pyrazine-bridged molybdenum(0) carbonyl and molybdenum(VI) oxide network solids as catalysts for epoxidation and sulfoxidation

The horizons of epoxidation and sulfoxidation processes may be expanded by developing new, efficient, and versatile catalysts. In the present work, three pyrazine-bridged molybdenum(0/VI)-based coordination network solids have been investigated for the epoxidation of olefins and the oxidation of sulfides. The materials studied were the Mo0-based metal-organic framework (MOF) fac-Mo(CO)3(pyz)3/2·1/2pyz (1) with a structure consisting of stacked fac-Mo(CO)3(pyz)3/2 coordination layers, the cubic phase fac-Mo(CO)3(pyz)3/2 (2) with a dense framework consisting of two interpenetrating coordination networks, and the molybdenum oxide-pyrazine hybrid material [Mo2O6(pyz)] (3) with a structure consisting of perovskite-like MoO3 layers pillared by pyz molecules. In the model reaction of cis-cyclooctene with tert-butyl hydroperoxide (TBHP) at 70 °C, quantitative yields of the epoxide were obtained within 2 h for 1, 4 h for 2, and 24 h for 3. Catalysts 1-3 were further examined for the epoxidation of other olefins, including the bio-olefins dl-limonene, methyl oleate and methyl linoleate, and the reaction scope was expanded to include the oxidation of sulfides. In the reactions of the bio-olefins, 3 was highly selective, giving only diepoxide and/or monoepoxide products. While the tricarbonyl-pyrazine-molybdenum(0) compounds displayed higher activity, by-products were obtained in the reactions of dl-limonene and methyl linoleate, namely limonene-1,2-diol and hydroxytetrahydrofuran cyclization products, respectively. Catalysts 1-3 displayed high activity for the selective oxidation of sulfides (methyl phenyl sulfide and diphenyl sulfide) to sulfones under mild conditions (35 °C).

Densification and microstructure studies of Mo-30–40 wt% Cu nanocomposites prepared through chemical route

Mo-30–40 wt% Cu nanocomposites with average size lower than 50 nm were synthesized using molybdenum hexacarbonyl, Mo(CO)6 and copper acetonyl acetonate, [Cu(acac)2] as metal precursors. Compositional analysis of Mo-Cu nanocomposites was performed using X-ray fluorescence spectrometer (XRF). The Mo-Cu composites were sintered using spark plasma sintering. X-ray diffraction studies of as-prepared powders showed amorphous Mo-phase and FCC Cu-phase, while sintered Mo-Cu composites exhibited crystalline BCC Mo and FCC Cu-phase become sharper. The effect of sintering temperature on relative density and mechanical properties of Mo-Cu sintered compacts was investigated. Relative density in excess of 98% were achieved for Mo-30–40 wt% Cu composites on spark plasma sintering at 1000 °C for 30 min. Vickers hardness of 653 ± 10 and 587 ± 8 Hv were achieved for Mo-30 wt% Cu and Mo-40 wt% Cu composite compacts respectively. Mo-30 wt% Cu and Mo-40 wt% Cu composites exhibit thermal conductivity of 182.5 and 224.6 W.m−1. K−1, respectively. The friction coefficient of Mo-Cu composites decreased with an increase in Cu content.

Molybdenum carbonyl assisted reductive tetramerization of CO by activated magnesium(i) compounds: squarate dianion vs. metallo-ketene formation.

Reactions of a dimagnesium(i) compound, [{(DipNacnac)Mg}2] (DipNacnac = [HC(MeCNDip)2]-, Dip = 2,6-diisopropylphenyl), pre-activated by coordination with simple Lewis bases (4-dimethylaminopyridine, DMAP; or TMC, :C(MeNCMe)2), with 1 atmosphere of CO in the presence of one equivalent of Mo(CO)6 at room temperature, led to the reductive tetramerisation of the diatomic molecule. When the reactions were carried out at room temperature, there is an apparent competition between the formation of magnesium squarate, [{(DipNacnac)Mg}{cyclo-(κ4-C4O4)}{μ-Mg(DipNacnac)}]2, and magnesium metallo-ketene products, [{(DipNacnac)Mg}[μ-O[double bond, length as m-dash]CC{Mo(CO)5}C(O)CO2]{Mg(D)(DipNacnac)}], which are not inter-convertible. Repeating the reactions at 80 °C led to the selective formation of the magnesium squarate, implying that this is the thermodynamic product. In an analogous reaction, in which THF is the Lewis base, only the metallo-ketene complex, [{(DipNacnac)Mg}[μ-O[double bond, length as m-dash]CC{Mo(CO)5}C(O)CO2]{Mg(THF)(DipNacnac)}] is formed at room temperature, while a complex product mixture is obtained at elevated temperature. In contrast, treatment of a 1 : 1 mixture of the guanidinato magnesium(i) complex, [(Priso)Mg-Mg(Priso)] (Priso = [Pri2NC(NDip)2]-), and Mo(CO)6, with CO gas in a benzene/THF solution, gave a low yield of the squarate complex, [{(Priso)(THF)Mg}{cyclo-(κ4-C4O4)}{μ-Mg(THF)(Priso)}]2, at 80 °C. Computational analyses of the electronic structure of squarate and metallo-ketene product types corroborate the bonding proposed from experimental data, for the C4O4 fragments of these systems.

Gas-Phase Synthesis of PtMo Alloy Electrocatalysts with Enhanced Activity and Durability for Oxygen Reduction Reaction

The proton-exchange membrane fuel cell is a promising technology to effectively utilize hydrogen energy, which is the ideal alternative to fossil fuels. However, the high dependency on scarce Pt as an oxygen reduction reaction (ORR) electrocatalyst is still a severe barrier that hinders widespread commercialization. Herein, we propose a facile synthetic strategy facilitating mass production of Pt–Mo solid-solution alloy nanoparticles on a carbon support (PtMo/C) as a highly active ORR electrocatalyst. Without using organic surfactants or reducing agents, our synthesis process based on the gas-phase method in an inert atmosphere is cost-effective and does not require any post-treatment, unlike most reported solution-based reduction processes. Both molybdenum metal and carbon monoxide decomposed from molybdenum hexacarbonyl contribute to the reduction of the PtMo alloy during the annealing process. By elucidating the growth and synthesis mechanisms, we optimized the particle size of PtMo/C to approximately 3.1 nm, annealed at 800 °C (PtMo/C-800). Consequently, PtMo/C-800 shows high mass activity (146 mA mgPt–1), which is superior to that of commercial Pt/C, and excellent durability after accelerated degradation tests.

Front Cover: Mechanistic and Kinetic Investigations of ON/OFF (Photo)Switchable Binding of Carbon Monoxide by Chromium(0), Molybdenum(0) and Tungsten(0) Carbonyl Complexes with a Pyridyl‐Mesoionic Carbene Ligand (Chem. Eur. J. 51/2022)

Front Cover: Mechanistic and Kinetic Investigations of ON/OFF (Photo)Switchable Binding of Carbon Monoxide by Chromium(0), Molybdenum(0) and Tungsten(0) Carbonyl Complexes with a Pyridyl‐Mesoionic Carbene Ligand (Chem. Eur. J. 51/2022)

Mechanistic and Kinetic Investigations of ON/OFF (Photo)Switchable Binding of Carbon Monoxide by Chromium(0), Molybdenum(0) and Tungsten(0) Carbonyl Complexes with a Pyridyl-Mesoionic Carbene Ligand.

Invited for the cover of this issue are Gereon Niedner-Schatteburg, Biprajit Sarkar and co-worker at TU Kaiserslautern and the University of Stuttgart. The image depicts the selective dissociation of an axial CO from a metal complex. Read the full text of the article at 10.1002/chem.202201038.

A One-Stone-Two-Birds Strategy to Functionalized Carbon Nanocages.

Carbon nanocages (CNCs) have attracted tremendous interest in heterogeneous catalysis due to their promising properties of porous structure and improved mass transfer. Nevertheless, the controlled synthesis of CNCs remains a great challenge. Herein, we have shown the successful construction of functionalized N-doped CNCs (NCNCs) via a one-stone-two-birds strategy. The selective use of hexacarbonyl molybdenum (Mo(CO)6) can not only protect the profile of the ZIF-8 precursor from collapse during thermal treatment but also be sacrificed for the functionalization of NCNCs after pyrolysis. Detailed mechanism studies reveal that Mo(CO)6 evolves into MoO3 on the surface of ZIF-8 and then facilitates the rapid pyrolysis of ZIF-8, leading to the formation of NCNCs decorated with small-sized MoC nanoparticles (MoC/NCNCs). The versatility of this one-stone-two-birds strategy has been validated by the generations of Cr- and W-decorated NCNCs. Moreover, MoC/NCNCs can serve as a selective and stable catalyst for furfural hydrogenation. This work provides a facile and universal strategy for fabricating and functionalizing CNCs, which attracts research interest in the fields of chemistry, material science, catalysis, and beyond.

Assembly of trimetallic palladium-silver-copper nanosheets for efficient C2 alcohol electrooxidation

The synthesis of two-dimensional (2D) alloyed efficient electrocatalysts with several active sites has attracted considerable attention in recent years. In this work, trimetallic palladium-silver-copper (PdAgCu) nanosheet assemblies (NSAs) are synthesized in the presence of cetyltrimethylammonium bromide and molybdenum hexacarbonyl as the structure-directing agents. The morphologies and structures of the trimetallic PdAgCu NSAs are identified by high-angle annular dark-field scanning transmission electron microscopy, transmission electron microscopy, and X-ray diffraction. The trimetallic Pd6Ag3Cu2 NSA has high electrocatalytic performance with outstanding long-term stabilities for ethylene glycol oxidation reaction (EGOR = 5696 mA mgPd−1) and ethanol oxidation reaction (EOR = 4374 mA mgPd−1). The enhanced electrocatalytic activities can be attributed to the synergistic effects, including strain, ligand, and bifunctional effects. Furthermore, the electrocatalytic mechanisms of the trimetallic electrocatalysts toward C2 alcohols are determined, and high concentrations of OH− and C2 alcohols favor EGOR and EOR.

Mechanistic and Kinetic Investigations of ON/OFF (Photo)Switchable Binding of Carbon Monoxide by Chromium(0), Molybdenum(0) and Tungsten(0) Carbonyl Complexes with a Pyridyl‐Mesoionic Carbene Ligand

This work tackles the photochemistry of a series of mononuclear Cr0, Mo0 and W0 carbonyl complexes containing a bidentate mesoionic carbene ligand of the 1,2,3‐triazol‐5‐ylidene type. FTIR spectroscopy, combined with density functional theory calculations, revealed a clean photo‐induced reaction in organic solvents (acetonitrile, pyridine, valeronitrile) to give mainly one photoproduct with monosubstitution of a carbonyl ligand for a solvent molecule. The highest photodissociation quantum yields were reached for the Cr0 complex under UV irradiation (266 nm). Based on previous investigations, the kinetics of the dark reverse reactions have now been determined, with reaction times of up to several hours in pyridine. Photochemical studies in the solid state (KBr matrix, frozen solution) also showed light‐induced reactivity with stabilization of the metastable intermediate with a free coordination site at very low temperature. The identified reactive species emphasizes a mechanism without ligand–sphere reorganization.

Beneficial effect of V on stability of dispersed MoS2 catalysts in slurry phase hydrocracking of vacuum residue: XAFS studies

The structure and the catalytic activity of the dispersed VxMo(1−x)S2catalysts were investigated for hydrocracking (HCK) of vacuum residue (VR) with the same amount of catalyst loading of 0.113 mmol as a metal basis at 693 K and 9.5 MPa H2. The catalysts were prepared in situ in the reaction using vanadium acetylacetonate and molybdenum hexacarbonyl as V and Mo precursors, respectively. Structural properties of the dispersed catalysts were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy, which confirmed the formation of a well-dispersed V-MoS2phase in size range 6–8 nm. Furthermore, it was demonstrated that the V-MoS2catalysts feature higher stability in the catalyst recycle test for the VR HCK in terms of H2 consumption rate (TOF) and asphaltene conversion in comparison to monometallic sulfides of V2S3 or MoS2.

Plasma-enhanced atomic layer deposition of molybdenum oxides using molybdenum hexacarbonyl as the precursor

Molybdenum oxide (MoOx) thin films are fabricated by plasma-enhanced atomic layer deposition (PEALD) using molybdenum hexacarbonyl Mo(CO)6 as the precursor and oxygen as the reactant. The effect of plasma power for oxygen has been investigated on the evolution of film structure. Molybdenum oxide shows the orthorhombic α-MoO3 phase at low powers and gradually changes to the metastable monoclinic β-MoO3 phase as the power continually increases, which is confirmed by Raman spectroscopy. α-MoO3 is two-dimensional (2-D) phase with Pbnm space group, while β-MoO3 film belongs to three-dimensional phase with P21/c. From the observation of scanning electron microscopy (SEM), a rod-like structure has been detected, whereas a bulk-like grain corresponds to a high ratio of β-MoO3 to α-MoO3 phase at higher power of 150 W. Due to better coverage of 2-D layer preventing surface from oxidation, the interfacial layer of α-MoO3 checked from transmission electron microscopy (TEM) shows thinner at low powers when contacting with silicon substrate, which is consistent with the performance of leakage current. The changes in binding energies of Mo 3d and O 1s orbits at different milling depths are compared by different powers. Though the significant amount of Mo4+ oxidation state is shown from x-ray photoelectron spectroscopy (XPS), only α-MoO3 and β-MoO3 crystallites with +6 state of Mo are observed from x-ray diffraction (XRD) patterns. Above phenomenon is due to the structural change caused by the loss of oxygen atoms. Thus, according to the charge transformation and compensation, the defect reaction model can well explain that oxygen vacancies inside films are more prevalent in orthorhombic phase at low plasma power for oxygen of our reduced MoO3-x.

Photomodification of benzyl germanane with group 6 metal carbonyls

Successful postmodification of germanene-based materials opens new applications in the chemistry of monoelemental two-dimensional materials. Here, we demonstrate the successful synthesis of germanane bearing benzyl group and its coordination with carbonyl metal complexes from the group 6. The photochemical reaction was used for in situ formation of reactive intermediates based on chromium, molybdenum and tungsten carbonyls and led to the attachment of the metal-carbonyl group to the benzyl group on the germanane surface. Successful functionalization was proven by various spectroscopic methods including FTIR, Raman and x-ray photoelectron spectroscopy as well as TG-MS measurements showing the evolution of carbon monoxide at elevated temperature. The homogeneous distribution of metals and morphology was also approved by microscopy method SEM/EDS and AFM. This work shows new possibilities in the chemistry of two-dimensional monoelemental materials like germanane giving the opportunity to homogenously distribute metal atoms over the sheet surface by coordination to the benzyl group.

Low-energy electron interaction and focused electron beam-induced deposition of molybdenum hexacarbonyl (Mo(CO)6).

Motivated by the potential role of molybdenum in semiconductor materials, we present a combined theoretical and experimental gas-phase study on dissociative electron attachment (DEA) and dissociative ionization (DI) of Mo(CO)6 in comparison to focused electron beam-induced deposition (FEBID) of this precursor. The DEA and DI experiments are compared to previous work, differences are addressed, and the nature of the underlying resonances leading to the observed DEA processes are discussed in relation to an earlier electron transmission study. Relative contributions of individual ionic species obtained through DEA and DI of Mo(CO)6 and the average CO loss per incident are calculated and compared to the composition of the FEBID deposits produced. These are also compared to gas phase, surface science and deposition studies on W(CO)6 and we hypothesize that reductive ligand loss through electron attachment may promote metal–metal bond formation in the deposition process, leading to further ligand loss and the high metal content observed in FEBID for both these compounds.