Molybdenum Hydride Complexes Research Articles

Assembly and Redox-Rich Hydride Chemistry of an Asymmetric Mo2S2 Platform.

Although molybdenum sulfide materials show promise as electrocatalysts for proton reduction, the hydrido species proposed as intermediates remain poorly characterized. We report herein the synthesis, reactions and spectroscopic properties of a molybdenum-hydride complex featuring an asymmetric Mo2S2 core. This molecule displays rich redox chemistry with electrochemical couples at E½ = −0.45, −0.78 and −1.99 V vs. Fc/Fc+. The corresponding hydrido-complexes for all three redox levels were isolated and characterized crystallographically. Through an analysis of solid-state bond metrics and DFT calculations, we show that the electron-transfer processes for the two more positive couples are centered predominantly on the pyridinediimine supporting ligand, whereas for the most negative couple electron-transfer is mostly Mo-localized.

A capped trigonal pyramidal molybdenum hydrido complex and an unusually mild sulfur-carbon bond cleavage reaction.

DFT calculations reveal that a reported molybdenum hydride complex has an unprecedented geometry with the molybdenum in the base of trigonal pyramid defined by three thiolate ligands with a phosphine ligand on the apex and a hydride capping a PS2 face. This complex reacts with methanol to produce a sulfido complex by a new reaction: the protonation of an ipso carbon of a thiolate ligand by coordinated methanol.

Synthesis, Characterization, and Reactivities of Molybdenum and Tungsten PONOP Pincer Complexes

A new series of molybdenum and tungsten tricarbonyl pincer complexes, bearing pyridine-based PONOP-type pincer ligands, have been synthesized and fully characterized. Addition of HBF4·Et2O to these tricarbonyl complexes generated seven-coordinate molybdenum and tungsten hydride complexes, and these compounds have been isolated in good yields. These metal hydrides show fluxional behavior in solution. The hydride ligands on these metal complexes are acidic in nature and are readily deprotonated by bases. The molybdenum hydride complex is shown to catalyze isomerization of 1-hexene to internal isomers under mild conditions.

Functionalization of Carbon Dioxide with Ethylene at Molybdenum Hydride Complexes

The molybdenum tetrahydride species (Triphos)MoH4PPh3 (Triphos = PhP(CH2CH2PPh2)2) generated from sodium triethylborohydride addition to (Triphos)MoCl3 was found to promote CO2 functionalization to afford acrylate, propionate, and formate species. The formation of (Triphos)MoH4PPh3 occurs via a (Triphos)Mo(H)Cl(PPh3) intermediate followed by dismutation of an unobserved six-coordinate molybdenum(II) dihydride complex. Addition of dihydrogen to the dismuation product mixture affords a nearly quantitative yield of (Triphos)MoH4PPh3. The molybdenum tetrahydride species facilitates CO2 insertion into a metal hydride to produce a formate complex, (Triphos)Mo(H)(κ2-CHO2)(PPh3), with an observed rate constant of [2.9(2)] × 10–4 s–1 (25 °C), which is independent of CO2 pressure. Selective formation of acrylate and propionate carbon dioxide–ethylene coupling products, (Triphos)Mo(H)(κ2-C3H3O2)(PPh3) and (Triphos)Mo(H)(κ2-C3H5O2)(PPh3), was achieved by sequential addition of olefin and heterocumulene to (Triphos)Mo...

Modeling aspects of hydrodesulfurization by molybdenum hydride compounds: Desulfurization of thiophene and benzothiophene and C–S bond cleavage of dibenzothiophene

The molybdenum hydride complexes Mo(PMe 3) 5H 2 and Mo(PMe 3) 4H 4 are capable of cleaving the C–S bonds of thiophene, benzothiophene and dibenzothiophene. For example, Mo(PMe 3) 5H 2 reacts with thiophene to give the η 5-thiophene and butadiene–thiolate complexes, (η 5-C 4H 4S)Mo(PMe 3) 3 and (η 5-C 4H 5S)Mo(PMe 3) 2(η 2-CH 2PMe 2). These complexes are also obtained from the reaction between Mo(PMe 3) 4H 4 and thiophene under photochemical conditions, whereas at elevated temperatures thiophene is desulfurized to liberate but-1-ene. Similarly, Mo(PMe 3) 4H 4 desulfurizes benzothiophene at elevated temperatures to liberate ethylbenzene, while the arylthiolate complex Mo(PMe 3) 4(SC 6H 4Et)H 3 is obtained photochemically. Furthermore, Mo(PMe 3) 4H 4 cleaves the C–S bond of dibenzothiophene to give [η 6,κ 1-C 6H 5C 6H 4S]Mo(PMe 3) 2H.

Formation and Structure of a Sterically Protected Molybdenum Hydride Complex with a 15-Electron Configuration: [(1,2,4-C5H2tBu3)Mo(PMe3)2H

Formation and Structure of a Sterically Protected Molybdenum Hydride Complex with a 15-Electron Configuration: [(1,2,4-C5H2tBu3)Mo(PMe3)2H

Formation and Structure of a Sterically Protected Molybdenum Hydride Complex with a 15‐Electron Configuration: [(1,2,4‐C5H2tBu3)Mo(PMe3)2H]+

Got to get up to get down: Oxidation of [(1,2,4-C5H2tBu3)Mo(PMe3)2H3] induces H2 reductive elimination and yields the first stable 15-electron molybdenum hydride complex, [(1,2,4-C5H2tBu3)Mo(PMe3)2H]+ (see picture). The stability of this complex can be attributed to steric protection, as no additional electron density is available on the ligands for a π-stabilization mechanism.

Synthesis and Structure of CpMo(CO)(dppe)H and Its Oxidation by Ph3C+

The reaction of CpMo(CO)(dppe)Cl (dppe = Ph2PCH2CH2PPh2) with Na+[AlH2(OCH2CH2OCH3)2]- gives the molybdenum hydride complex CpMo(CO)(dppe)H, the structure of which was determined by X-ray crystallography. Electrochemical oxidation of CpMo(CO)(dppe)H in CH3CN is quasi-reversible, with the peak potential at -0.15 V (vs Fc/Fc+). The reaction of CpMo(CO)(dppe)H with 1 equiv of Ph3C+BF4- in CD3CN gives [CpMo(CO)(dppe)(NCCD3)]+ as the organometallic product, along with dihydrogen and Gomberg's dimer (which is formed by dimerization of Ph3C.). The proposed mechanism involves one-electron oxidation of CpMo(CO)(dppe)H by Ph3C+ to give the radical-cation complex [CpMo(CO)(dppe)H].+. Proton transfer from [CpMo(CO)(dppe)H].+ to CpMo(CO)(dppe)H, loss of dihydrogen from [CpMo(CO)(dppe)(H)2]+, and oxidation of Cp(CO)(dppe)Mo. by Ph3C+ lead to the observed products. In the presence of an amine base, the stoichiometry changes, with 2 equiv of Ph3C+ being required for each 1 equiv of CpMo(CO)(dppe)H because of deprotonation of [CpMo(CO)(dppe)H].+ by the amine. Protonation of CpMo(CO)(dppe)H by HOTf provides the dihydride complex [CpMo(CO)(dppe)(H)2]+OTf-, which loses dihydrogen to generate CpMo(CO)(dppe)(OTf).

04/02253 Ethanol learning curve — the Brazilian experience: Goldemberg, J. et al. Biomass and Bioenergy, 2004, 26, (3), 301–304

The molybdenum hydride complexes Mo(PMe3)5H2 and Mo(PMe3)4H4 are capable of cleaving the C–S bonds of thiophene, benzothiophene and dibenzothiophene. For example, Mo(PMe3)5H2 reacts with thiophene to give the η5-thiophene and butadiene–thiolate complexes, (η5-C4H4S)Mo(PMe3)3 and (η5-C4H5S)Mo(PMe3)2(η2-CH2PMe2). These complexes are also obtained from the reaction between Mo(PMe3)4H4 and thiophene under photochemical conditions, whereas at elevated temperatures thiophene is desulfurized to liberate but-1-ene. Similarly, Mo(PMe3)4H4 desulfurizes benzothiophene at elevated temperatures to liberate ethylbenzene, while the arylthiolate complex Mo(PMe3)4(SC6H4Et)H3 is obtained photochemically. Furthermore, Mo(PMe3)4H4 cleaves the C–S bond of dibenzothiophene to give [η6,κ1-C6H5C6H4S]Mo(PMe3)2H.

Hydridic Character and Reactivity of Di[1,2-bis- (dimethylphosphino)ethane]hydridonitrosylmolybdenum(0)

The synthesis of the tetraphosphine-substituted molybdenum hydride complex trans-Mo(dmpe)2(H)(NO) (3) (dmpe = bis(dimethylphosphino)ethane) is described, which is obtained by starting from the know...

Synthesis of molybdenum hydride complexes via electron-transfer mechanism and carbonyl exchange by phosphine in the 17-electron intermediates

Synthesis of molybdenum hydride complexes via electron-transfer mechanism and carbonyl exchange by phosphine in the 17-electron intermediates