Molybdenum Hexacarbonyl Research Articles

Microwave assisted efficient aminocarbonylation of N-tosylhydrazones with molybdenum hexacarbonyl and amines

An efficient aminocarbonylation of N-tosylhydrazones derived from aromatic aldehydes and ketones mediated by molybdenum hexacarbonyl is reported. This method is palladium-free and provides a rapid access to the α-aryl acetamides in moderate to good yields.

Watching adsorption and electron beam induced decomposition on the model system Mo(CO)6/Cu(1 1 1) by X-ray absorption and photoemission spectroscopies

An in-depth study of the first steps of electron beam assisted growth of Mo from molybdenum hexacarbonyl on Cu(111) has been carried out exploiting the complementarity of X-ray photoemission and X-ray absorption spectroscopies. Frank van der Merwe (2D) growth mode has been observed for the completion of the two first monolayers of adsorbed molecules through a simple physisorption process. Irradiation of the Mo(CO)6 deposit by 1keV electron beam induces a modification of molybdenum coordination, the average number of C-neighbors decreasing from 6 to 3. Decomposed molecules remain on the surface after annealing at 520K and organize themselves, the molybdenum atoms moving in Cu(111) surface fcc hollow sites. After annealing at 670K, metallic molybdenum growth begins, if the total amount of adsorbed Mo atoms exceeds 1.2 monolayers.

Diarylated Ethanones from Mo(CO)6‐Mediated and Microwave‐Assisted Palladium‐Catalysed Carbonylative Negishi Cross‐Couplings

AbstractTwo protocols for palladium‐catalysed carbonylative Negishi cross‐couplings were developed for aryl iodides and aryl bromides. The two main breakthroughs were that molybdenum hexacarbonyl [Mo(CO)6] could be used as a solid in situ source of CO, and that controlled microwave irraditaion could be used for heating. Consequently, the reactions were safe (in contrast to when CO gas was used) and fast (in comparison to when conventional heating was used). The carbonylative cross‐coupling reactions were carried out using commercially available benzylzinc bromide in closed vials (90–120 °C for 0.5–1 h) to give a set of diarylated ethanones, a common pharmacophore found in several pharmaceuticals, in moderate to high isolated yields (47–84 %). The mild three‐component carbonylation protocol presented here is operationally simple, safe, and rapid, and the formation of the carbonylative Negishi cross‐coupling product is favoured over the product of Negishi cross‐coupling.

Polymer-supported diimine molybdenum carbonyl complexes as highly reusable and efficient pre-catalysts in epoxidation of alkenes

By reaction of aldehydic polystyrene and ethylene diamine, polystyrene–imine–amine reagent was produced. Reaction of this reagent with benzaldehyde and 4-nitrobenzaldehyde resulted in polystyrene-diimines (3a and 3b). These reagents were used for the immobilization of molybdenum hexacarbonyl. The functionalized polystyrene and supported-diimine molybdenum carbonyl catalysts were characterized by FT-IR spectrum and CHN analysis. The molybdenum content of catalysts was determined by neutron activation analysis. Supported-diimine molybdenum carbonyl pre-catalysts (3aM and 3bM) were used in epoxidation of cyclooctene, and the reaction parameters such as solvent and oxidant were optimized and the epoxidation of different alkenes was investigated in optimizing these conditions. The obtained results in the presence of polymer-supported diimine molybdenum carbonyl pre-catalysts (3aM and 3bM) showed that they were very active and selective in the epoxidation of a wide range of alkenes. The reusability of the supported pre-catalysts was also studied. The results showed that they were highly reusable in epoxidation of alkenes.

Small‐Molecule Activation with Molybdenum(0) Complexes Supported by Mixed Imidazol‐2‐Ylidene/Phosphanyl Hybrid Ligands – Electronic and Structural Consequences of Substituting a Phosphane by a Carbene Group

AbstractBy employing a series of mixed bi‐ and tridentate N‐heterocyclic carbene (NHC)/phosphane ligands, the new molybdenum(0) carbonyl complexes [Mo(CO)4(CP)] [1, CP = 3‐(2‐diphenylphosphanylethyl)‐1‐ethylimidazol‐2‐ylidene], fac‐[Mo(CO)3(PCP)] [2, PCP = 1,3‐bis(2‐diphenylphosphanylethyl)imidazol‐2‐ylidene], and fac‐[Mo(CO)3(CPC)] [3, CPC = bis(1‐ethyl‐3‐ethyleneimidazol‐2‐ylidene)phenylphosphane] have been synthesized. The compounds were investigated by X‐ray structure analysis and vibrational and NMR spectroscopy in conjunction with DFT calculations. For comparison, the complexes [Mo(CO)4(CC)] [4, CC = di(1‐ethylimidazol‐2‐ylidene)methane], fac‐[Mo(CO)3(dpepp)] [5, dpepp = bis(2‐diphenylphosphanylethyl)phenylphosphane], and [Mo(CO)4(dppp)] [6, dppp = 1,3‐bis(diphenylphosphanyl)propane] have also been prepared and investigated. In contrast to the phosphane donors, which exhibiting metal–ligand backbonding interactions, the π‐acceptor interactions of the carbene moieties are exactly cancelled by π‐donor interactions. The σ‐donor strengths of phosphane and carbene groups, on the other hand, are found to be comparable. The implications of this result with respect to the activation of small molecules (e.g., N2) are discussed.

Synthesis and Characterization of Hydrido Carbonyl Molybdenum and Tungsten PNP Pincer Complexes.

In the present study the Mo(0) and W(0) complexes [M(PNP)(CO)3] as well as seven-coordinate cationic hydridocarbonyl Mo(II) and W(II) complexes of the type [M(PNP)(CO)3H]+, featuring PNP pincer ligands based on 2,6-diaminopyridine, have been prepared and fully characterized. The synthesis of Mo(0) complexes [Mo(PNP)(CO)3] was accomplished by treatment of [Mo(CO)3(CH3CN)3] with the respective PNP ligands. The analogous W(0) complexes were prepared by reduction of the bromocarbonyl complexes [W(PNP)(CO)3Br]+ with NaHg. These intermediates were obtained from the known dinuclear complex [W(CO)4(μ-Br)Br]2, prepared in situ from W(CO)6 and stoichiometric amounts of Br2. Addition of HBF4 to [M(PNP)(CO)3] resulted in clean protonation at the molybdenum and tungsten centers to generate the Mo(II) and W(II) hydride complexes [M(PNP)(CO)3H]+. The protonation is fully reversible, and upon addition of NEt3 as base the Mo(0) and W(0) complexes [M(PNP)(CO)3] are regenerated quantitatively. All heptacoordinate complexes exhibit fluxional behavior in solution. The mechanism of the dynamic process of the hydrido carbonyl complexes was investigated by means of DFT calculations, revealing that it occurs in a single step. The structures of representative complexes were determined by X-ray single-crystal analyses.

Carbonyl complexes of transition metals with stabilized germylenes

Germylenes based on substituted diethylenetriamine (1), diethanolamines (2, 3) and pyridine-containing dialcohols (4, 5) were used as ligands in molybdenum and tungsten carbonyl complexes. Synthesis of new mono- and disubstituted (cis- or trans-) germanium(II) containing molybdenum (8, 9, 14, 15, 17) and tungsten (6, 7, 10–13, 16) carbonyl complexes were described. Composition of the complexes obtained was established by elemental analysis data and their structures were investigated by multinuclear NMR spectroscopy, IR and X-ray diffraction analysis (7, 13 and 17). The germylenes based on dialkanolamines and pyridine-containing dialcohols (O-ligands) give cis-digermanium complexes in contrast to the germylenes based on diethylenetriamines (N-ligands) which form trans-digermanium complexes.

Molybdenum hexacarbonyl-catalyzed condensation of malononitrile with ketones and aldehydes

Molybdenum hexacarbonyl activated with pyridine or morpholine catalyzes the condensation of malononitrile with ketones and aldehydes at 140 °C, which leads to alkylidenemalononitriles in 75–100% yield.

Reactions of substituted tetramethylcyclopentadienes with molybdenum hexacarbonyl

The reactions of the substituted tetramethylcyclopentadienes [C5Me4HR] [R=ethyl (1), n-propyl (2), i-propyl (3), cyclopentyl (4), cyclohexyl (5), 4-NMe2Ph (6)] with Mo(CO)6 in refluxing xylene gave the corresponding dinuclear metal carbonyl complexes [η5-C5Me4R]2Mo2(CO)6 (7–11), while similar treatment of [C5Me4H(4-NMe2Ph)] (6) with Mo(CO)6 afforded an unexpected product [(η5-C5Me4(4-NMe2Ph))MoO2]2(μ-O) (12). All the new complexes were fully characterized. The molecular structures of 7, 8, 11 and 12 have been determined by X-ray single crystal diffraction.

Intercalation of a molybdenum η3-allyl dicarbonyl complex in a layered double hydroxide and catalytic performance in olefinepoxidation

A Zn-Al layered double hydroxide (LDH) intercalated by [Mo(η(3)-C3H5)Cl(CO)2(bpdc)](2-) anions (bpdc = 2,2'-bipyridine-5,5'-dicarboxylate) has been prepared by coprecipitation from aqueous solution and characterised by various techniques. The one-pot method gives rise to a highly organised intercalate with an interlayer spacing of 18.3 Å and up to six (00l) basal reflections in the powder X-ray diffraction pattern. Spectroscopic studies (FT-IR, FT-Raman, (13)C CP MAS NMR and UV-Vis) confirm the presence of structurally intact [Mo(η(3)-C3H5)Cl(CO)2(bpdc)](2-) anions. The interlayer spacing of 18.3 Å indicates that the material contains a monolayer of guest anions positioned in such a way that the bpdc ligands are arranged with their longest dimension roughly perpendicular to the hydroxide layers of the host. Thermal properties were studied by thermogravimetric analysis and differential scanning calorimetry. The intracrystalline reactivity of intercalated dicarbonyl complexes was probed by using the hybrid nanocomposite as a precatalyst in the liquid phase epoxidation of cis-cyclooctene with tert-butylhydroperoxide as oxidant. Under the reaction conditions used, oxidative decarbonylation of the guest molecules takes place (with release of CO and CO2 as confirmed by on-line gas chromatography experiments) to give intercalated molybdenum oxide/bipyridine species that selectively catalyse the epoxidation reaction. The intracrystalline oxidative decarbonylation reaction is topotactic in nature.

Bis(pyrazolyl)methanetetracarbonyl-molybdenum(0) as precursor to a molybdenum(VI) catalyst for olefin epoxidation

Bis(pyrazolyl)methanetetracarbonyl-molybdenum(0), cis-[Mo(CO)4(BPM)] (1), was prepared from Mo(CO)6 and the ligand bis(pyrazolyl)methane (BPM), and examined as a catalyst precursor for the epoxidation of olefins using tert-butylhydroperoxide (TBHP) as oxidant. Catalytic activities followed the sequence 1-octene < trans-2-octene < α-pinene < (R)-(+)-limonene < cis-cyclooctene, and, with the exception of α-pinene and limonene, the corresponding epoxide was always the only reaction product. Turnover frequencies for the epoxidation of cyclooctene were 580 mol molMo−1 h−1 at 55 °C and 1175 mol molMo−1 h−1 at 75 °C, which compare favourably with those found for other molybdenum carbonyl complexes used as catalyst precursors for the same reaction under similar conditions. Catalytic activities were lower in the presence of organic co-solvents, decreasing in the sequence 1,2-dichloroethane > nitromethane > ethanol > hexane > acetonitrile. It is proposed that the oxodiperoxo complex [MoO(O2)2(BPM)] (2) may be the active catalyst formed in situ by oxidative decarbonylation of 1, since crystals of 2 suitable for structure determination by X-ray diffraction were obtained from the reaction solution recovered after a catalytic run at 55 °C with cis-cyclooctene as substrate. In support of this hypothesis, the catalytic performance of 2 for the epoxidation of cyclooctene at 55 °C is very similar to that for 1.

Atmospheric pressure plasma jet-synthesized electrochromic organomolybdenum oxide thin films for flexible electrochromic devices

An investigation is conducted into fast synthesis of electrochromic organomolybdenum oxide (MoOxCy) thin films onto 40Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates via atmospheric pressure plasma jet. A precursor [molybdenum carbonyl, Mo(CO)6] vapor, carried by argon gas, is injected into air plasma torch to synthesize MoOxCy films for offering extraordinary electrochromic performance. Only low driving voltages from −1V to 1V are needed to offer reversible Li+ ion intercalation and deintercalation in a 1M LiClO4-propylene carbonate electrolyte. Light modulation with transmittance variation of up to 61%, optical density change of 0.54 and coloration efficiency of 37.5cm2/C at a wavelength of 550nm after 200cycles of cyclic voltammetry switching measurements is achieved.

Molybdenum–Molybdenum Multiple Bonding in Homoleptic Molybdenum Carbonyls: Comparison with Their Chromium Analogues

The binuclear molybdenum carbonyls Mo(2)(CO)(n) (n = 11, 10, 9, 8) have been studied by density functional theory using the BP86 and MPW1PW91 functionals. The lowest energy Mo(2)(CO)(11) structure is a singly bridged singlet structure with a Mo-Mo single bond. This structure is essentially thermoneutral toward dissociation into Mo(CO)(6) + Mo(CO)(5), suggesting limited viability similar to the analogous Cr(2)(CO)(11). The lowest energy Mo(2)(CO)(10) structure is a doubly semibridged singlet structure with a Mo═Mo double bond. This structure is essentially thermoneutral toward disproportionation into Mo(2)(CO)(11) + Mo(2)(CO)(9), suggesting limited viability. The lowest energy Mo(2)(CO)(9) structure has three semibridging CO groups and a Mo≡Mo triple bond analogous to the lowest energy Cr(2)(CO)(9) structure. This structure appears to be viable toward CO dissociation, disproportionation into Mo(2)(CO)(10) + Mo(2)(CO)(8), and fragmentation into Mo(CO)(5) + Mo(CO)(4) and thus appears to be a possible synthetic objective. The lowest energy Mo(2)(CO)(8) structure has one semibridging CO group and a Mo≡Mo triple bond similar to that in the lowest energy Mo(2)(CO)(9) structure. This differs from the lowest energy Cr(2)(CO)(8) structure, which is a triply bridged structure. A higher energy unbridged D(2d) Mo(2)(CO)(8) structure was found with a very short Mo-Mo distance of 2.6 Å. This interesting structure has two degenerate imaginary vibrational frequencies. Following the corresponding normal modes leads to a Mo(2)(CO)(8) structure, lying ~5 kcal/mol above the global minimum, with two four-electron donor bridging CO groups and a Mo═Mo distance suggesting a formal double bond. All of the triplet Mo(2)(CO)(n) (n = 10, 9, 8) structures were found to be relatively high energy structures, lying at least 22 kcal/mol above the corresponding global minimum. The singlet-triplet splittings for the Mo(2)(CO)(n) (n = 10, 9, 8) structures are significantly higher than those of the Cr(2)(CO)(n) analogues. The Mo-Mo Wiberg bond indices confirm our assigned bond orders based on predicted bond distances.

Novel isatinoxime molybdenum and chromium complexes: Synthesis, spectroscopic, and thermal characterization

Reactions of molybdenum and chromium hexacarbonyls with isatin-3-oxime (H2L) in THF were carried out under sun light or according to the traditional thermal reflux synthetic routes. Di-μ-oxo bimolybdenum complex, [Mo(H2L)(THF)(O)2]2 was successfully synthesized under the reflux conditions. However, the dichromium oxo complex, [Cr(H2L)(O)2]2 was prepared using the sun light route. The prepared complexes were characterized using elemental analysis, IR, mass spectrometry, UV–Vis spectra, thermal analysis, and magnetic measurements.

Reactions of Doubly SiMe2-Bridged Bis(cyclopentadienyl) Complexes of Molybdenum and Iron Carbonyls: Competitive Ring-to-Metal Migrations of Hydrogen and SiMe2

Reaction of the doubly bridged bis(cyclopentadiene) (C5H4(SiMe2))2 (1) with Mo(CO)6 in refluxing xylene gave the corresponding dinuclear molybdenum carbonyl complex [(η5-C5H3)2(SiMe2)2]Mo2(CO)6 (3) and the desilylated product [(η5-C5H4)2(SiMe2)]Mo2(CO)6 (6), together with the singly SiMe2SiMe2-bridged dinuclear molybdenum product [(η5-C5H4)2(SiMe2SiMe2)]Mo2(CO)6 (5) and the novel complex [(SiMe2)(η5-C5H4)Mo(CO)3]2 (4) containing two Mo–Si bonds. This diversity of products is caused by similar ring-to-metal migrating abilities of the hydrogen and SiMe2 groups and their competitive migration during the reactions. Reaction of the dihydride cis-[(η5-C5H3)2(SiMe2)2]Mo2(CO)6(H)2 (7c) in refluxing xylene also afforded the above products except 4, which suggests that 7c might be intermediate precursor to 3, 5, and 6. Similar treatment of substituted doubly bridged bis(cyclopentadiene) (C5H3tBu(SiMe2))2 (2) with Mo(CO)6 provided the corresponding derivatives (8–10) of the above products and the product [(η5-C5H4tB...

Monolayer Formation of Molybdenum Carbonyl on Cu(111) Revealed by Scanning Tunneling Microscopy and Density Functional Theory

Molybdenum carbonyl Mo(CO)6 was adsorbed on the Cu(111) surface at 160 K in the monolayer coverage range and studied by scanning tunneling microscopy. A well-ordered monolayer of hexacarbonyl molecules was observed experimentally for the first time. The monolayer has a hexagonal structure compatible with a (√7 × √7)R19 superlattice on the copper (111) plane. The arrangement and orientation of the molecules on the surface were determined by density functional theory calculations, including van der Waals interactions. The comparison of adsorption and cohesive energies reveals that the molecule–substrate interaction is stronger than the intermolecular one, which explains the observed two-dimensional growth.

Molybdenum-Mediated Deconjugation of α,β-Unsaturated Fused-Cyclopentenone Phosphonates

The synthesis of diethyl (3-alkyl-5-oxo-4,5,6,6a-tetra­hydro-1H-cyclopenta[c]furan-4-yl)phosphonates from the corresponding 3-allyloxy-1-propynylphosphonates is described. The in situ reaction involves two steps: an intramolecular Pauson-Khand reaction followed by an unusual double bond deconjugation mediated by molybdenum hexacarbonyl in dimethyl sulfoxide.

Reactions of SnMe2-bridged biscyclopentadienes with molybdenum carbonyl to give compounds containing Mo–Sn–Mo units

In the reactions of double-bridged biscyclopentadienes (EMe2)(SnMe2)(RC5H3)2 (E=C (1), E=Si (2 or 4), E=Ge (3)), or single-bridged biscyclopentadiene (SnMe2)(tBuC5H4)2 (5) with Mo(CO)6 in refluxing xylene, the bridging SnMe2 group migrates from the ligand to the molybdenum atoms to give compounds (6–10) containing the Mo–Sn–Mo units; the bridging group EMe2 (E=C or Si in 1, 2, or 4) does not migrate. It is noteworthy that [(η5-C5H5)Mo(CO)3]2SnMe2 (8) obtained from the reaction of (GeMe2)(SnMe2)(C5H4)2 (3) with Mo(CO)6 is a degermylated and SnMe2 group migrated product, another outcome worth mentioning is that the complex 9 is afforded only in the rac-configuration. The stability of complexes (6, 7, and 10) containing the Mo–Sn–Mo unit toward heat and light was also studied. The molecular structures of 6, 9, and 10 were determined by X-ray diffraction.

Molybdenum Hexacarbonyl Mediated CO Gas-Free Carbonylative Reactions

This Account summarizes predominately our own experiences in developing microwave-heated palladium-catalyzed Mo(CO)6-mediated gas-free carbonylative reactions, although contributions from other groups, including non-palladium-catalyzed examples, have also been covered. Presented reactions include amino-, amido-, and alkoxycarbonylations as well as carbonylative cyclizations and carbonylative cross-couplings, using Mo(CO)6 as a solid source of CO. The methodology was developed mainly for rapid small-scale applications, avoiding the problematic use of gaseous CO in a standard laboratory. In most cases, the reported Mo(CO)6-mediated carbonylations were conducted in sealed vessels and with reaction times of less than 1 hour. The Account also highlights relevant applications in medicinal and high-speed chemistry.

Carbonyl Complexes of Molybdenum and their Catalytic Activity

This is a review of the published papers that focus on the reactivity of carbonyl complexes of molybdenum in low oxidation states (usually zero or two) and possible applications of molybdenum complexes as precursors of catalysts in different reactions of unsaturated organic substrates such as alkenes and alkynes. The following reactions are analyzed: metathesis, metathesis polymerization, free radical reactions of alkenes, hydrogenation, hydrosilylation, hydrogermylation, hydrostannation, hydroarylation, asymmetric allylic alkylation, and epoxidation. In addition to the interesting practical aspects of these catalytic reactions, they provide additional insights into molybdenum chemistry. Keywords: Metathesis, hydrogenation, hydrosilylation, hydrogermylation, hydrostannation, hydroarylation, asymmetric allylic alkylation, epoxidation, bidentate phosphine ligands, diphenylphosphinomethane (dppm), diphenylphosphinoethane (dppe), diphenylphosphinopropane (dppp), molybdenum carbonyl complexes, hydrostannation reaction