Oxomolybdenum Complexes Research Articles

Tungsten and molybdenum oxo complexes of tetrakis(phenyldiazenyl)calix[4]arene substituted derivatives: EHMO calculations, spectroscopic characterization, and perturbations of the photophysical properties by neutral guest molecules

Bowl-shaped chromophores fabricated with tungsten and molybdenum oxo complexes of calix[4]arenes substituted at the para positions with phenyldiazenyl (R2C6H3N2) derivatives are investigated. The nature of the lowest energy excited states has been addressed theoretically using Extended Hückel Molecular Orbital (EHMO) calculations and experimentally using UV-visible, luminescence, and polarized emission spectroscopy at 77 K. The lowest energy excited states are intraligand (azobenzene fragment) ππ* (S2 and T2) and ππ*states (S1, and T1). The compounds are weakly luminescent in the 600–630 nm range exhibiting emissions arising from the 1(ππ*) states [Formula: see text]. The region located above 900 nm was not investigated. Evidence for guest–host chemistry has been demonstrated by1H-NMR spectroscopy, and the binding constants for two of the compounds with pyridine in toluene as a solvent were obtained by UV–visible spectroscopy. The presence of a guest molecule inside the luminescent metal oxo complex of a calix[4]arene hosts decreases the emission lifetimes.Key words: host–guest, photophysics, calix[4]arene, EHMO, fluorescence

Activation of Bis(trimethylsilyl) Peroxide and tert‐Butyl Hydroperoxide with Oxo and Peroxo Complexes of Vanadium, Molybdenum, and Tungsten for the Sulfoxidation of Thianthrene 5‐Oxide

AbstractBis(trimethylsilyl) peroxide (BTSP) and tert‐butyl hydroperoxide (tBuOOH) were activated by various oxo and peroxo complexes of molybdenum, tungsten, and vanadium as catalysts for the sulfoxidation of thianthrene 5‐oxide (SSO). A screening of a number of phosphane oxide and amine oxide ligands revealed that BTSP was most efficiently activated by the [MoO5(OPtBu3)] complex. The best results for tBuOOH as oxygen source were achieved with the vanadates [VO(OR)3] (R = tBu, iPr). Comparative selectivity and rate data for the stoichiometric and catalytic sulfoxidations of SSO mediated by the MoO5L complex (L = OPtBu3, OPnOct3, ONnBu3, ONnOct3) suggest that the bisperoxo metal complex is the active oxygen transfer species.

Oxomolybdenum(V) complexes of 2-benzothiazolyl hydrazones

Oxomolybdenum(V) complexes of general formulae [Mo2O3L2Cl2]H2O and [Mo2O3L2(OH)2(H2O)2] (LH = hydrazones derived from 2-hydrazinobenzothiazole with salicyladehyde, 5-methyl-, 5-chloro-, 5-bromo-, 3-methoxysalicyldehyde and 2-hydroxy-1-naphthaldehyde) have been prepared and characterized by elemental analysis, conductivities, magnetic moments, thermal studies, and i.r., u.v.-vis. and e.p.r. spectra. The data suggest that the complexes are non-electrolytes, paramagnetic and have distorted octahedral structures with possible metal-metal interactions via oxo bridging.

Trimethylsilyloxo complexes of oxomolybdenum(V)

The complexes LMoVIO2X [L = hydrotris(3,5-dimethylpyrazol-1-yl)borate; X = Cl, Br, NCS, OPh, SPh, SCH2Ph] are converted to air-stable complexes LMoVO(OSiMe3)X by one-electron coupled electron-electrophile transfer (CEET) reactions involving cobaltocene and the electrophilic reagent Me3SiCl. These complexes may also be obtained from LMoVO(OH)X by reaction with Me3SiCl in the presence of base. LMoVO(OSiMe3)(SCH2Ph) crystallises in space group P21/n, with a = 8.526 (1) A, b = 23.141 (3) A, c = 16.499 (2) A, β = 103.75 (12)° and Z = 4. The complex exhibits a distorted octahedral structure with a facially tridentate L ligand and mutually cis oxo [Mo=O = 1.675 (4) A], silyloxo [Mo–O = 1.932 (4) A] and thiolato [Mo–S = 2.398 (2) A] ligands. The detailed redox properties of LMoVO(OR)X (R = SiMe3, alkyl, aryl) differ from those of LMoVO(OH)X. Centres [MoVO(OR)] are candidates for the stable "inhibited" forms of certain molybdenum enzymes formed under conditions which apparently disfavour the catalytically active [MoVO(OH)] centres. In the coordinating solvent pyridine (py), both LMoVIO2(SPh) and LMoVO(OSiMe3)(SPh) are reduced in one-electron steps to stable LMoIVO(py)(SPh). LMoIVO(py)(SR) complexes are also obtained from LMoVIO2(SR) (R = Ph, CH2Ph, CHMe2) via a two-electron oxygen atom transfer reaction with tertiary phosphines in pyridine. Consequently, the Mo(IV) product is accessible via a concerted two-electron step or via two one-electron steps.

Charge‐Transfer Complexes of Metal Dithiolenes, XXII. Bis(maleonitriledithiolato)oxomolybdate(IV) – Bipyridinium Ion Pairs

AbstractThe oxomolybdenum complex (NBu4)2[MoO(mnt)2] (mnt2− = maleonitriledithiolate) 2 was characterized by X‐ray structural analysis. By metathetic reaction with bipyridinium salts AX2 ion pair charge‐transfer complexes of composition {A2+[MoO(mnt)2]2−} were isolated. Although a plot of the energy of the ion pair charge‐transfer band vs. the driving force of electron transfer from the dianion to the dication afforded a straight line, the slope of 0.45 suggests significant deviations from the Hush‐Marcus model. When bis(2‐hy‐droxyethyl)viologen is the acceptor, in addition to the supra‐molecular charge‐transfer interaction, hydrogen bridges are introduced between the two components as indicated by IR and X‐ray diffraction analysis.

Synthesis and Properties of a Nitridomolybdenum(VI) Complex Having Benzenedithiolate Ligands. Effect of the Thiolate on the Activation of the Nitrido Ligand

Abstract A nitridomolybdenum(VI) complex having 1,2-benzenedithiolate (bdt2−) (NEt4)2[MoVIN(bdt)2Cl] was synthesized by the reaction of (NEt4)[MoVINCl4] with 2 equiv of Li2bdt in DMF/THF solution. This complex was characterized by measurements of the absorption, Raman, IR, and 14N NMR spectra. A lower Mo≡N band (1010 cm−1) in the Raman spectrum and the upfield shifted 14N NMR signal (−374 ppm) of the nitrido ligand compared to those of (NEt4)[MoVINCl4] (1055 cm−1 and −350 ppm) were observed, which strongly suggest the existence of a competitive π-electron donation from S (pπ) to Mo (dπ). The complex readily reacts with O2 or H2O to produce an oxomolybdenum(IV) complex [MoIVO(bdt)2]2−. This extremely air-sensitive complex shows a higher reactivity to O2 than that of (NEt4)[MoVINCl4]. It is concluded that the observed high reactivity is the result of a weakened Mo≡N bond by thiolate coordination.

Dinuclear Oxomolybdenum(V) Complexes Showing Strong Interactions across Diphenol Bridging Ligands: Syntheses, Structures, Electrochemical Properties, and EPR Spectroscopic Properties

We have prepared a series of dinuclear complexes [{MoV(O)(Tp*)Cl}(μ-OO)], where “OO” represents one of the series of diphenolate bridging ligands [1,4-O(C6H4)nO]2- (n = 1−4; complexes 1−4, respectively), [O(C6H3-2-Me)2O]2- (complex 5), or [1,3-OC6H4O]2- (complex 6) [Tp* = tris(3,5-dimethylpyrazolyl)hydroborate]. The complexes therefore contain two paramagnetic (d1), redox-active metal centers. For complexes 1−4 the metal−metal separation increases due to the increasing number of phenyl spacers in the bridge. Complex 5 is similar to 2 with the exception that for steric reasons there is a larger dihedral twist between the halves of the complex. Complex 6 is similar to 1, but with a meta substitution pattern at the bridging ligand instead of para. Complexes 1 and 6 were characterized by X-ray crystallography. For 1·2Et2O: C44H68B2Cl2Mo2N12O6; orthorhombic, Pnnm; a = 24.566(11), b = 8.085(4), c = 14.172(4) Å; Z = 2. For 6·3CH2Cl2: C39H54B2Cl8Mo2N12O4; monoclinic, P21/n; a = 15.984(3), b = 16.934(3), c = 20.931(3) Å, β = 105.33(1)°; Z = 4. Due to the cocrystallization of the two diastereoisomers of the complexes (the Mo centers are chiral), disorder is present in both cases between the oxo and chloride ligands which could be completely resolved for 6 but not for 1. Electrochemical measurements showed that each Mo(V) center undergoes a one-electron oxidation [to Mo(VI)] and a one-electron reduction [to Mo(IV)]. Electrochemical interactions across the bridge result in very large splittings between the two oxidations (e.g. 990 mV for 1) and smaller but still significant splittings between the reductions (e.g. 250 mV for 1). The much stronger interaction between the oxidation processes is due to the fact that they are partly delocalized onto the bridging ligand, whereas the reduction processes are almost completely metal-localized. EPR spectra of the complexes showed the presence of magnetic exchange between the paramagnetic centers, with several features characteristic of magnetic exchange: the hyperfine pattern, line broadening, and the presence of a half-field (Δms = 2) transition. The magnitudes of the electrochemical interactions and of the magnetic interactions could be related to the structures (length, substitution pattern, dihedral twist) of the bridging ligands.

Temperature and orientation dependence of electron spin relaxation in molybdenum(V) porphyrins

AbstractElectron spin lattice relaxation rates were measured by saturation recovery for three oxo(5,10,15,20‐tetratolylporphyrinato)molybdenum(V) complexes, OMo(TTP)X, X=Cl−, OH−, OEt−. For O=Mo(TTP)(OEt) in glassy solution between 15 and 130 K the temperature dependence of 1/T1 is consistent with a two‐photon Raman process. For each of the complexes at 100 K 1/T1 is faster when the magnetic field is in the molecular plane than when it is perpendicular to the molecular plane, which is attributed to orientation dependence of intramolecular vibrations. The orientation‐dependent values of 1/T1 are approximately the same for isotopes with I = 0 or I = 5/2, which indicates that molybdenum nuclear hyperfine interaction is not a major factor in the electron spin‐lattice relaxation rate. Phase memory relaxation rates were measured by electron spin echo. Below about 90 K 1/Tm is weakly temperature dependent and becomes more strongly temperature dependent at higher temperature as 1/T1 approaches 1/Tm and as the host lattice softens. For isotopes with I = 5/2 at 100 K 1/Tm is faster at molecular orientations for which the resonant field is more strongly dependent on small changes in molecular orientation.

Reactions of chlorosilanes with dioxomolybdenum(VI) complexes

Various trialkylchlorosilanes were reacted with a number of molybdenum-oxo complexes in order to establish the main factors which influence the process of addition of the SiCl function across the MoO bond. A novel intermolecular mode of hexaalkyldisiloxane formation was observed in one case.

Synthesis, characterization and reactivity of oxomolybdenum(V) complexes with ONS and NNS donors

The monomeric oxomolybdenum(V) complexes, [MoOLCl2]1a-1d [HL = S-benzyl/methyl 3-(2-pyridyl)methylenedithiocarbazate (1a and1b), or N-methyl-S-benzyl/methyl 3-(2-hydroxy phenyl)methylenedithiocarbazate (1c and1d) are synthesized by the reaction of MoOCl 5 2− with HL ligands. All these complexes show magnetic moment of about 1.7 B.M. The complexes,1a and1b, exhibit rhombicg-tensor anisotropy (like xanthine oxidase) whilst1c and1d show axial spectrum. The above complexes undergo irreversible electrochemical reduction furnishing Mo(IV) species and the potentials are dependent on the S-substituents. Reactions of MoOX 5 − (X = Cl or Br) with H2L1 [H2L1 = S-methyl 3-(5-R-2-hydroxyphenyl)methylenedithiocarbazate] (R = H, CH3, Cl, Br) produce complexes of thiolatobridged dimers, [Mo2O2L 2 1 X2], which show sub-normal magnetic moments at room temperature. The metal-centred irreversible oxidation and reduction of these complexes show expected dependence on the R-substituents of the salicyl phenyl ring of the ligands.

Oxomolybdenum Chemistry: An Experiment

Oxo complexes dominate the high-valent chemistry of the early and middle transition elements and oxygen atom transfer is important in industrial and biological processes. This undergraduate experiment focuses on the reactivity of oxomolybdenum complexes. A number of complexes, with a variety of coordination numbers, geometries and nuclearities, are prepared via nucleophilic or electrophilic attack on an oxo ligand of cis-MoO2(S2CNEt2)2: they are characterized by analysis, infrared and 1H NMR spectroscopy, and mass spectrometry. Finally, an examination is made of their oxygen atom and sulfur atom transfer reactions. The complexes synthesized and examined include: cis-MoO2(S2CNEt2)2, MoO(S2CNEt,))2, Mo2O2(micro-O)(S2CNEt2)4, MoOCl2(S2CNEt2)2 and MoO(S2)(S2CNEt2)2.

Crystal structure of [{Mo(=O)Cl 2(O = PPh 2C 10H 15 = NH)} 2O]. A binuclear oxygen-bridged oxomolybdenum(V) complex containing chelating imino-phosphine oxide ligands

Air oxidation of the tricarbonylmolybdenum(II) complex [ MoCl 2( CO 2( PPh 2 C 10 H 15 = NH)] ( 20) gave the oxygen oxomolybdenum(V) complex [{ MO (= O) Cl 2( O = PPh 2 C 10 H 15 = NH)} 2 O] ( 4) , containing bidentate imino-phosphine oxide ligands. Crystals of ( 4) are orthorhobic, space group P2 1 P2 12 12 1 with a = 13.885(2), b = 18.308(4), c = 18.439(5) A ̊ , Z = 4, R = 0.0395 for 3531 observed reflections with I > 2.0 σ( I). Each molybdenum atom is in a disorted octahedral coordination linked by a bent Mo-O-Mo bridge with an angle of 158.2(3)°, and Mo(=O) groups are cis to each other.

Synthesis and crystal structure of an encapsulated fragment of MoO2in the unique Mo8oxo-cluster compound [Mo8O8Cl6(µ3-O)4(OH)2(µ-OH)4(µ-OEt)4(HOEt)4] and its relevance to the sol–gel synthesis of molybdenum oxides

Reaction of the dimeric oxomolybdenum(V) complex [Cl2OMo(µ-OEt)2(µ-HOEt)MoOCl2]1 with SbF3 in toluene followed by overlaying with light petroleum followed an unexpected course to give crystals of the complex [Mo8O8Cl6(µ3-O)4(OH)2(µ-OH)4(µ-OEt)4(HOEt)4]2 in low yield. The crystal structure of 2[triclinic, space group P, a= 10.803(5), b= 11.159(6), c= 11.659(6)A, α= 69.66(3), β= 64.06(3), γ= 66.258(24)°, Z= 1, R= 0.058, wR2= 0.143] has been determined and reveals a new structural type for an M8 cluster which is closely related to the distorted rutile structure adopted by MoO2. Incorporating two Mo4 layers connected with each other by a layer of four bridging oxygen atoms in a centrosymmetric arrangement, it serves as a model for intermediates in the sol–gel synthesis of molybdenum oxides.

Preparation and Characterisation of some Oxomolybdenum(V) Complexes using 2-(2' -Pyridyl)benzthiazole

Preparation and Characterisation of some Oxomolybdenum(V) Complexes using 2-(2' -Pyridyl)benzthiazole

Synthesis and structural characterisation of dithiocarbamate-stabilised dimeric molybdenum(V) imido complexes via oxo substitution reactions with organic isocyanates

Thermolysis of molybdenum–oxo complexes [MoO2(S2CNEt2)2]1, [{MoO(S2CNEt2)(µ-O)}2]2 and [Mo2O2(S2CNEt2)2(µ-O)(µ-S)]3 with organic isocyanates afforded a range of imido-substituted binuclear molybdenum(V) complexes. Reaction of complex 1 with 1 equivalent of RNCO gave terminally substituted mono(imido) complexes [Mo2O(NR)(S2CNEt2)2(µ-S)2]4a–4c(R = But, 2,6-Me2C6H3 or adamant-1-yl) and bridging bis(imido) complexes [{MoO(S2CNEt2)(µ-NR)}2]5a and 5c(R = Ph or p-tolyl). Reaction of complex 2 with an excess of RNCO afforded the tetraimido complex [{Mo(NR)(S2CNEt2)(µ-NR)}2]6b(R =o-tolyl) and the bridging ureato complex [Mo2(NPh)2(S2CNEt2)2(µ-NPh){µ-PhNC(O)NPh}]7a, while with PhNCO and complex 3 a further ureato complex [Mo2(NPh)2(S2CNEt2)2(µ-S){µ-PhNC(O)NPh}]7b resulted. Thermolysis of complex 7a gave the tetraimido complex [{Mo(NPh)(S2CNEt2)(µ-NPh)}2]6a, a reaction which is reversed in the presence of PhNCO. Acid-catalysed hydrolysis of complex 6b afforded the bis(imido) complex [{MoO(NR)(S2CNEt2)}2](R =o-tolyl)5b which upon thermolysis with o-tolyl isocyanate regenerated 6b. Addition of HBF4 to 5a resulted in oxo substitution by dithiocarbamate to give [Mo2O(S2CNEt2)3(µ-NPh)2][BF4]8. Six of these complexes, namely 4a, 4b, 5b, 6b, 7a and 8, have been characterised by X-ray crystallography. All are dimeric and contain relatively short molybdenum–molybdenum contacts (2.625–2.822 A) indicative of metal–metal bonding, the longer distances being associated with bridging sulfido ligands. Terminal imido ligands are all linear and bridging imido ligands planar.

Doubly-bridged binuclear complexes of oxomolybdenum(V) and oxotungsten(V) containing sexadentate ligands

Binuclear oxomolybdenum(V) and oxotungsten(V) complexes of the type, [M 2(O)2(μ-X)(μ-X 1)]”, where M=Mo, W;X.X 1=O, S; L=edta, pdta (n=2-), tpen, tppn (n=2+) (edta4– =ethylenediaminetetraacetate(4–), pdta=R- orR,S-propylenediaminetetraacetate(4–), tpen=N,N,N 1,N1-tetrakis(2-pyridyhnethyl)-ethylenediamine, and tppn=R- orR,S-N,N,N 1,N1-tetrakis(2-pyridylmethyl)-propylenediami ne) are reviewed with respect to their preparation, structure, spectroscopic properties, reactivities, and in particular asymmetric distortion around the bicyclo [4.1.1 ] type core and stereoselectivity related to this distortion,

Bridging Disulfido Complexes of Molybdenum and Tungsten Formed by Reductive Sulfurization of Oxo-Molybdenum(VI) Complexes and Reductive Desulfurization of Thio(disulfido)-Tungsten(VI) Complexes

Bridging Disulfido Complexes of Molybdenum and Tungsten Formed by Reductive Sulfurization of Oxo-Molybdenum(VI) Complexes and Reductive Desulfurization of Thio(disulfido)-Tungsten(VI) Complexes

Oxo and Nitrido Complexes of Molybdenum, Tungsten, Rhenium, and Osmium. A Theoretical Study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOxo and Nitrido Complexes of Molybdenum, Tungsten, Rhenium, and Osmium. A Theoretical StudyArndt Neuhaus, Achim Veldkamp, and Gernot FrenkingCite this: Inorg. Chem. 1994, 33, 23, 5278–5286Publication Date (Print):November 1, 1994Publication History Published online1 May 2002Published inissue 1 November 1994https://doi.org/10.1021/ic00101a020RIGHTS & PERMISSIONSArticle Views338Altmetric-Citations59LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (840 KB) Get e-Alerts Get e-Alerts

Effect of substituting sulfur for oxygen on the heterogeneous electron transfer kinetics of oxomolybdenum(V) hydrotris (3,5-dimethyl-1-pyrazolyl)borate complexes

Heterogeneous electron transfer rate constants ( k s,h) and formal potentials ( E o′) are measured for the one-electron reduction of a series of oxomolybdenum(V) complexes, HB(Me 2pz) 3MoO(LL), where HB(Me 2pz) 3 −=hydrotis(3,5-dimethyl-l-pyrazolyl)borate and LL 2− is a bidentate 1,2-disubstituted ethane or benzene ligand whose donor atoms can be either O or S. E o′ shifts in the negative direction by about 1 V and k s,h decreases by about 1.5 orders of magnitude as S is replaced by O in the inner coordination sphere of these compounds. These observations are rationalized in terms of a hard acid-hard base interaction between the HB(Me 2pz) 3MoO 2+ fragment and LL 2− which stabilizes the metal-ligand bond and increases the energy of the metal-centered redox orbital as the hard base character of the bidentate ligand increases. Electron transfer rate differences are believed to arise primarily from larger inner-shell contributions to the activation energy barrier for MoO versus MoS complexes, but contributions from differences in outer-shell energies and adiabaticities cannot be eliminated at this time.

Structure and Properties of (NEt4)2[MoIVO(α,2-toluenedithiolato)2

Abstract A novel oxomolybdenum(IV) complex, (NEt4)2[MoIVO(α,2-toluenedithiolato)2], was synthesized and characterized by visible, Raman and 1H NMR spectroscopies. The complex crystallizes as (NEt4)2[MoIVO(α,2-toluenedithiolato)2]·Et2O in the space group Cc with a = 15.429(3), b = 16.618(2), c = 15.079(3) Å, β = 99.38(2)°, V = 3815(2) Å3, Z = 4, and Dcalcd = 1.315 g cm−3. The structure was solved and refinement based on 5975 reflections converged at R = 0.044and Rw = 0.052. The complex has an apical oxo and transbis(α,2-toluenedithiolato) structure with a tetragonal-pyramidal MoOS4 core. Inertness of the complex to trimethylamine-N-oxide is due to the narrow S(alkane)–Mo–S(alkane) angle preventing from its coordination to the trans position of Mo=O, and/or two strong Mo–S(alkane) bonds preventing a rearrangement from trans dioxo to cis dioxo structure.