Molybdenum Carbonyl Complexes Research Articles

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.

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.

Properties and cellular uptake of photo-triggered mixed metallosurfactant vesicles intended for controlled CO delivery in gas therapy

The scientific relevance of carbon monoxide has increased since it was discovered that it is a gasotransmitter involved in several biological processes. This fact stimulated research to find a secure and targeted delivery and lead to the synthesis of CO-releasing molecules. In this paper we present a vesicular CO delivery system triggered by light composed of a synthetized metallosurfactant (TCOL10) with two long carbon chains and a molybdenum-carbonyl complex. We studied the characteristics of mixed TCOL10/phosphatidylcholine metallosomes of different sizes. Vesicles from 80 to 800 nm in diameter are mainly unilamellar, do not disaggregate upon dilution, in the dark are physically and chemically stable at 4 °C for at least one month, and exhibit a lag phase of about 4 days before they show a spontaneous CO release at 37 °C. Internalization of metallosomes by cells was studied as function of the incubation time, and vesicle concentration and size. Results show that large vesicles are more efficiently internalized than the smaller ones in terms of the percentage of cells that show TCOL10 and the amount of drug that they take up. On balance, TCOL10 metallosomes constitute a promising and viable approach for efficient delivery of CO to biological systems.

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.

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.

Molybdenum Carbonyl Complexes with Benzimidazole Derivatives Against SARS-CoV-2 by Molecular Docking and DFT/TDDFT Methods

Benzimidazole derivative molecules attract attention of scientists due to their bioactivities. The dramatic changes in recorded activities according to the type and position of the substituents motivate synthesis and analysis of new molecules. Commercial benzimidazole-based molecules have been used in therapeutic procedures. It is known that the activities of metal complexes with benzimidazole derivative ligands have different activities when compared to the benzimidazole main structure. Nowadays, one of the most important health problems is COVID-19, which caused the pandemic that we are still experiencing. Although vaccine studies are important to overcome acute problems, regarding the possible post-vaccination adverse effects, the need for new drugs against the virus is obvious. Considering the urgency and the limited facilities during the pandemic, preliminary in silico studies of candidate molecules are essential. In this study, {[bis-(N-benzylbenzimidazole)] tetracarbonylmolybdenum}, {[bis-(N-4-chlorobenzylbenzimidazole)] tetracarbonylmolybdenum} and {[bis-(N-4-methoxybenzylbenzimidazole)] tetracarbonylmolybdenum} were synthesized and characterized. The optimization and the structural analysis of these molecules were performed by DFT/TDDFT methods. The molecules were docked into SARS coronavirus main peptidase (PDB ID: 2gtb), COVID-19 main protease in complex with Z219104216 (PDB ID: 5r82), COVID-19 main protease in complex with an inhibitor N3 (PDB ID: 6lu7) and Papain-like protease of SARS-CoV-2 (PDB ID: 6w9c) crystal structures for evaluation of their anti-viral activity.

Comparison and Synthesis of Molybdenum Carbonyl Complexes Substituted with Mono- and Bis-Triphenylphosphine Ligands for Hydrocracking of Vacuum Residue.

(PPh₃)Mo(CO)5 and (PPh₃)₂Mo(CO)₄ were synthesized by the reaction of molybdenum hexacar-bonyl with triphenylphosphine and applied as precursors to hydrocracking of vacuum residue under high-pressure and high-temperature conditions. (PPh₃)₂Mo(CO)₄ could also be synthesized by the reaction of (PPh₃)Mo(CO)5 with triphenyl phosphine. A commercial precursor (Mo-octoate) for hydrocracking of vacuum residue was used for comparison. The thermal decomposition behavior of (PPh₃)Mo(CO)5, (PPh₃)₂Mo(CO)₄, and Mo-octoate was also examined by the thermogravimetric analysis. The TGA curve of (PPh₃)Mo(CO)5 and (PPh₃)₂Mo(CO)₄ showed a similar weight-loss pattern. (PPh₃)Mo(CO)5 and (PPh₃)₂Mo(CO)₄ were decomposed into Mo metal and ligands rapidly in the range of 140 °C~270 °C. There were no ligands bound to a metal center of (PPh₃)Mo(CO)5 and (PPh₃)₂Mo(CO)₄ at the reaction temperature (430 °C) of hydrocracking. The amount of coke formed after hydrocracking over (PPh₃)Mo(CO)5 and (PPh₃)₂Mo(CO)₄ was 2.3% and 0.5%, respectively. Upgrading the qualities of heavy oils is an important issue in the energy industry. It is not easy to achieve the complete conversion of vacuum residue due to coke forming during hydrocracking of vacuum residue. This study showed that (PPh₃)₂Mo(CO)₄ was considerably effective in reducing coke formation.

Molybdenum carbonyl complexes as HER electrocatalysts

Four cyclopentadienyl and allylic molybdenum carbonyl complexes have been prepared and tested as proton reduction electrocatalysts using trifluoroacetic acid as the proton source in acetonitrile. Cyclic voltammetry studies showed that these complexes are able to function as moderate electrocatalysts with overpotentials of about 0.9 V and catalytic efficiency of up to 60%. The average turnover number and turnover frequency for each of the molybdenum catalyst measured over a five-hour period have been calcualted to be in the range of 16–24 and 3.2 h−1 to 5.4 h−1 respectively for 1 mM catalyst and 20 acid equivalent. A mechanism to account for the proton reduction process is also proposed based on the electrochemical and spectroscopic measurements.

Molybdenum and rhenium carbonyl complexes containing thiolato ligands

The reaction of fac-[M(OTf)(CO)3(N–N)](M = Mn, Re; N–N = 2,2′-bipyridine, 1,10-phenanthroline) complexes with in situ generated LiSEt afforded immediately, in THF at low temperature, the corresponding mononuclear terminal thiolato complexes fac-[M(SEt)(CO)3(N–N)](1-2a,b). Using an analogous synthetic strategy, tungsten and molybdenum (II) alkyl- and arylthiolatos of formula cis-[M(SR)(η3-allyl)(CO)2(N–N)] (3-6a,b) have been obtained. Preliminary reactions of the more reactive molybdenum thiolato complexes towards dimethylacetylenedicarboxylate led to Z-alkenyl products (7a,b), resulting from the insertion of the organic unsaturated electrophile into the Mo–S bond. For each new type of compound, one representative has been characterized in the solid state by X-ray diffraction.

Unexpected Multiple Coordination Modes in Silyl-Bridged Bis(phosphinine) Complexes

The bis(phosphinine) [bis{3-methyl-6-(trimethylsilyl)phosphinine-2-yl}dimethylsilane] (1) was synthesized and its coordination chemistry explored. Molybdenum and chromium carbonyl complexes were crystallographically characterized featuring 1 bound η6 through one phosphinine [Mo(CO)3(η6-1)] (2Mo), η6 through both phosphinines to two metal centers [{M(CO)3}2(μ-η6:η6-1)] (3M2, M = Cr, Mo), and chelating with η1 coordination through both phosphines [M(CO)4(κ:η1:η1-1)] (4M, M = Cr, Mo). However, only 3Mo2 could be isolated analytically pure. Heating species 3Mo2 in the presence of [Pd(COD)Cl2] removed one CO ligand and generated [{Mo(CO)2}(μ-κ:η1η6-η6-1){Mo(CO)3}] (5), which is the first crystallized example of a bis(phosphinine) featuring chelating η1 and η6 coordination, as well as a metal center bound to two phosphinines with different binding modes. In order to enforce a chelating bis-η1 binding mode, the Ru complex [Ru(Cp*)(Cl)(κ:η1:η1-1)] (6) was prepared, demonstrating that judicious choice of metal fra...

Synthesis, Spectral, Thermal and Magnetic Studies of Chromium and Molybdenum Carbonyl Complexes Containing N2O2 Donor Sites

Synthesis, Spectral, Thermal and Magnetic Studies of Chromium and Molybdenum Carbonyl Complexes Containing N2O2 Donor Sites

Theoretical analysis of frontier orbitals, electronic transitions, and global reactivity descriptors of M(CO)4L2 type metal carbonyl complexes: a DFT/TDDFT study

Metal carbonyl complexes, which have been known as effective catalysts since early days, find use in many fields both directly and indirectly. Although the use of metal carbonyl complexes as bio-probe and protein labeling agent due to their unique spectroscopic properties is known, metal carbonyls have recently been used as storage and transport carriers of carbon monoxide. These developments have motivated the synthesis of new metal carbonyl complexes. Despite the difficulties in obtaining prediction for the molecular properties of organometallic compounds, DFT-based calculation programs have been able to gain insight into the structural/electronic properties of inorganic and organic molecules. In this study, structural, electronic, and reactivity properties of characterized molybdenum and tungsten carbonyl complexes with benzimidazole and imidazoline derivative ligands were investigated using DFT-based calculation program ORCA.

Molybdenum Carbonyl Complexes with a Polymerizable Phosphorus/Nitrogen/Phosphorus Ligand and Corresponding Conducting Metallopolymers

AbstractThe design, synthesis, and characterization of the novel polymerizable ligand 3,5‐bis(3,4‐ethylenedioxythien‐2‐yl)‐N,N‐bis(2‐diphenylphosphinoethyl)‐phenylamine is achieved. The corresponding molybdenum complexes (EDOT)2PNP‐Mo(CO) n where n = 3,4 with carbonyls as ancillary ligands are also synthesized, and characterized by 1H NMR, 31P{1H} NMR, HRMS, FTIR (both the solution state spectrum between KBr discs and the solid‐state spectrum with attenuated total reflectance [ATR] apparatus). Single crystal X‐ray analysis of (EDOT)2PNP‐Mo(CO)3 complex is performed. The monomer complexes and the free ligand are electropolymerized to obtain the corresponding polymers that are studied electrochemically. The Mo/P and Mo/S ratios as well as the metal oxidations in the conducting metallopolymers are analyzed by X‐ray photoelectron spectroscopy.

Study of the interactions of bovine serum albumin with a molybdenum(II) carbonyl complex by spectroscopic and molecular simulation methods.

Therapy with inhaled carbon monoxide (CO) is being tested in human clinical trials, yet the alternative use of prodrugs, CO-Releasing Molecules (CORMs), is conceptually advantageous. These molecules are designed to release carbon monoxide in specific tissues, in response to some locally expressed stimulus, where CO can trigger a cytoprotective response. The design of such prodrugs, mostly metal carbonyl complexes, must consider their ADMET profiles, including their interaction with transport plasma proteins. However, the molecular details of this interaction remain elusive. To shed light into this matter, we focused on the CORM prototype [Mo(η5-Cp)(CH2COOH)(CO)3] (ALF414) and performed a detailed molecular characterization of its interaction with bovine serum albumin (BSA), using spectroscopic and computational methods. The experimental results show that ALF414 partially quenches the intrinsic fluorescence of BSA without changing its secondary structure. The interaction between BSA and ALF414 follows a dynamic quenching mechanism, indicating that no stable complex is formed between the protein Trp residues and ALF414. The molecular dynamics simulations are in good agreement with the experimental results and confirm the dynamic and unspecific character of the interaction between ALF414 and BSA. The simulations also provide important insights into the nature of the interactions of this CORM prototype with BSA, which are dominated by hydrophobic contacts, with a contribution from hydrogen bonding. This kind of information is useful for future CORM design.

Naphthophosphacyclophanes based on 1,6-dihydroxynaphthalene as bidentate ligands in the synthesis of molybdenum(0) carbonyl complexes

Binuclear molybdenum(0) carbonyl complexes were synthesized based on naphthophosphacyclophanes containing a 1,6-dihydroxynaphthalene fragment and diethylamide linkers. The physicochemical and spectral characteristics of the synthesized coordination systems were studied.

Synthesis and catalytic reactivity in Friedel–Crafts acylations of monobridged bis(cyclopentadienyl)molybdenum(I) carbonyl complexes

When the monobridged biscyclopentadienes (C5H5)R(C5H5) [R = C(CH3)2 (1), Si(CH3)2 (2), C(CH2)5 (3)] reacted with Mo(CO)6 in refluxing xylene, the corresponding complexes [(η5-C5H4)2R][Mo(CO)3]2 [R = C(CH3)2 (4), Si(CH3)2 (5), C(CH2)5 (6)] were obtained. These complexes were separated by chromatography and characterized by elemental analysis, IR, and 1H NMR spectroscopy. The molecular structures of 4 and 5 were determined by X-ray diffraction analysis. Friedel–Crafts acylation reactions of anisole derivatives with aromatic or aliphatic acyl chlorides catalyzed by complexes 4–6 showed that all of these monobridged bis(cyclopentadienyl)molybdenum carbonyl complexes have catalytic activity.

Syntheses, structures, and catalytic activity in Friedel–Crafts acylations of substituted tetramethylcyclopentadienyl molybdenum carbonyl complexes

Reactions of the substituted tetramethylcyclopentadienes [C5HMe4R] [R = t Bu, Ph, CH2CH2C(CH3)3] with Mo(CO)3(CH3CN)3 in refluxing xylene gave a series of dinuclear molybdenum carbonyl complexes [(η5-C5Me4R)Mo(CO)3]2 [R = t Bu (1), Ph (2), CH2CH2C(CH3)3 (3)], [(η5-C5Me t Bu)Mo(μ-CO)2]2 (4)], and [(η5-C5Me4) t Bu]2Mo2O4(μ-O) (5)], respectively. Complexes 1–5 were characterized by elemental analysis, IR, 1H NMR, and 13C NMR spectroscopy. In addition, their crystal structures were determined by X-ray crystal diffraction analysis. The catalytic activities of complexes 1–3 in Friedel–Crafts acylation in the presence of o-chloranil has also been investigated; the reactions were achieved under mild conditions to give the corresponding products in moderate yields.

Syntheses, structures and catalytic activities of molybdenum carbonyl complexes based on pyridine-imine ligands

Thermal treatment of pyridine imines [C5H4N-2-C(H)=N-C6H4-R] [R = H (1), CH3 (2), OMe (3), CF3 (4), Cl (5), Br (6)] with Mo(CO)6 in refluxing toluene provided six novel mononuclear molybdenum carbonyl complexes of the type [(η2-2-C5H4N)CH=N(C6H4-4-R)]Mo(CO)4 [R = H (7); CH3 (8); OMe (9); CF3 (10); Cl (11); Br (12)]. All of these complexes were separated by chromatography and fully characterized by elemental analysis, IR, and NMR spectroscopy. The crystal structures of complexes 7, 8 and 10 were determined by X-ray crystal diffraction analysis. In addition, the catalytic performance of these complexes was also tested, and it was found that these complexes had obvious catalytic activity on Friedel–Crafts reactions of aromatic compounds with a variety of acylation reagents.

Assessment of the electron donor properties of substituted phenanthroline ligands in molybdenum carbonyl complexes using molecular electrostatic potentials

Molecular electrostatic potential analysis of substituent effects in phenanthroline ligands clearly suggests that the coordination strength of the ligand to a metal complex is highly predictable solely from the quantification of substituent effects.