- Aqueous chemistry of the metallocene [Cp2MoCl 2]BF4: Evidence of autocatalytic molybdenum(V) reduction in water
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The aqueous chemistry of the air-stable Mo(V) metallocene [Cp 2MoCl2]BF4 (1) yields an unexpected autocatalytic reduction when water is added to an acetonitrile solution of 1. While 1 yields the expected stable Cp-Mo ligation and rapid chloride hydrolysis in water, a Mo(V) → Mo(IV) reduction to the metallocene Cp 2MoCl2 (2) was evident. Under acidic conditions (pH ～2) or trace amounts of water this reduction was slow enough to be monitored spectroscopically, and it is shown to be autocatalytic in aqueous 2. No reaction occurs when 1 and 2 are in the dichloride form in acetonitrile (i.e., no water). It is hypothesized that the added water serves two roles. First it initially reduces a small population of 1 to 2, and then as the aquated Mo(IV) metallocene, it catalyzes the reduction of the remaining Mo(V) in water. This is the first aqueous investigation of the Mo(V) metallocene, and it shows a novel and unprecedented autocatalytic reduction that is mediated by water.
- Kuo, Louis Y.,Shari'Ati, Yusef A.,Valente, Edward J.
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p. 2902 - 2907
(2013/06/27)
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- Reactivity of coordinated carbon dioxide: Reactions of (C5H5)2Mo(η2-CO2) with electrophiles
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The title complex 1 reacts with a variety of electrophilic reagents to afford products derived from O-centered electrophilic attack on coordinated CO2. In the case of Me3SiCl, tBuMe2SiCl, and HCl complete oxygen transfer occurs, producing [(C5H5)2Mo(CO)Cl]Cl (2a) and R3SiOSiR3 or H2O. The reaction of 1 with Me3SiOSO2CF3 in THF affords the unusual dicationic complex [(C5H5)2Mo(CO)(THF)](OSO2CF 3)2 (3), whose structure has been established by X-ray diffraction.
- Tsai, Jing-Cherng,Khan, Masood,Nicholas, Kenneth M.
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p. 2967 - 2968
(2008/10/08)
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- New Molybdenocene Dihydrocarbyls
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The preparation and characterization of 5-C5H5)2R2)> (R = C2H5, n-C4H9, C6H5) and 5-C5H5)2R2>PF6 (R = C2H5, n-C4H9) are described.Cyclic voltammograms in CH3CN and CH2Cl2 show that the reversible 1-electron oxidation of Mo
- Dias, A. R.,Garcia, M. H.,Martins, A. M.,Pinheiro, C. I.,Romao, C. C.,Veiros, L. F.
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p. C59 - C62
(2007/10/02)
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- Energetics of transition-metal-sulfur and -oxygen bonds in M(η5-C5H5)2L2 complexes (M = Ti, Mo, W). Molecular structure of Mo(η5-C5H5)2(SO4)
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The energetics of transition-metal-sulfur bonds in bis(η5-cyclopentadienyl)bis(thiolato)metal complexes, M(η5-C5H5)2(SR)2 (M = Mo, W, Ti), has been reinvestigated and compared with reevaluated metal-oxygen data on the same type of molecules. Bond enthalpy terms, E(Mo-SR) (R = n-C3H7, i-C3H7, n-C4H9, t-C4H9, and n-C10H21), which were obtained by using calorimetric values for the standard enthalpies of formation of the complexes, confirm a strong steric effect in the case of t-C4H9S and indicate an increase in metal-sulfur bond strength with the length of the n-alkyl chain, E(Mo-SC10H21-n) ? E(Mo-SC4H9-n) ? E(Mo-SC3H7-n). The thermochemistry of the complex Mo(η5-C5H5)2(SO4) was also studied, leading to E(Mo-O) ≈ 338 ± 13 kJ mol-1. This value excludes noticeable strain on the metallacycle, since it compares with other molybdenum-oxygen bond enthalpy terms. The molecular structure of the sulfate complex, which was also determined in the present study, is compatible with the Mo-O bond enthalpy. The structural data were obtained by X-ray diffraction and show bidentate coordination of the sulfate ligand, with O-Mo-O = 66.1 (2)° and Mo-O = 211.3 (3) pm. The angle O-S-O = 98.3 (2)° (coordinated oxygen) shows a small distortion of this moiety, and extended Hu?ckel calculations show that the rigidity of the SO4 geometry is responsible for the small O-Mo-O angle. The sulfate complex crystallizes in the orthorhombic space group Cmcm with four molecules per unit cell; the lattice constants are a = 935.6 (5) pm, b = 854.7 (2) pm, and c = 1297.9 (4) pm.
- Calhorda, Maria J.,Carrondo, Maria A. A. F. De C. T.,Dias, Alberto R.,Domingos, ?ngela M. T. S.,Martinho Sim?es, José A.,Teixeira, Clementina
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p. 660 - 667
(2008/10/08)
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- NEW OBSERVATIONS ON DICYCLOPENTADIENYLMOLYBDENUM COMPLEXES DERIVED FROM DIMETHYL ACETYLENEDICARBOXYLATE. CRYSTAL STRUCTURE OF 5-C5H5)2MoOC(O)CH=CCO2CH3>
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Addition of chloroform to a solution of (η-C5H5)2MoH2 and dimethylacetylenedicarboxylate (CH3CO2CCCO2CH3) in THF at 0 deg C gives two new complexes: (i) chloro-?-alkenyl (η5-C5H5)2MoCl and (ii) metallacyclic 5-C5H5)2MoOC(O)CH=CCO2CH3>.An X-ray diffraction study of the latter product revealed the presence of one water molecule per one organometallic molecule in the unit cell: space group P21, a 12.111(9), b 7.374(2), c 7.830(5) Angstroem, β 93.43(4) deg, Z = 2.The Mo-C bond length is 2.180(6) Angstroem.A mechanism involving an intramolecular elimination of CH4 from the initially formed insertion product (η5-C5H5)2MoH is proposed for its formation.
- Cariou, M.,Kubicki, M. M.,Kergoat, R.,Guerchais, J. E.
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p. 127 - 136
(2007/10/02)
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- Photochemistry and electronic structure of the (η5-C5H5)2MoS2 complex
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The photochemistry of the Cp2MoS2 complex was studied in order to determine if d-d excited states gave different photochemistry than the S → Mo charge-transfer excited states. The various excited states were identified with the aid of a self-consistent field-Xα-scattered-wave molecular orbital calculation. No wavelength dependent photochemistry was found as irradiation of the Cp2MoS2 complex in inert solvents at all selected wavelengths led to Cp2MoS4. The mechanism of Cp2MoS4 formation was studied. Two pathways seemed likely: photochemical extrusion of either S2 or S22-. The formation of Cp2MoS4 does not necessarily imply the extrusion of S2 rather than S22- because the latter species can disproportionate: 2S22- → S2 + 2S2-. In order to differentiate between homolytic and heterolytic Mo-S bond cleavage pathways, the Cp2MoS2 complex was irradiated in CDCl3. The products in this solvent are Cp2MoCl2 and Cp2MoS4, at all wavelengths. Other unidentified minor products also formed in the photochemical reactions of the Cp2MoS2. Since the reaction of molybdenocene with CHCl3 produces Cp2MoCl2 and because attempts to trap Cp2Mo2+ failed, it is proposed that homolytic extrusion of S2 follows irradiation of the Cp2MoS2 complex. Reasons for the wavelength independent photochemistry and for the homolytic extrusion of S2, upon irradiation in either the 14a1 → 9b1 d-d band (490 nm) or the 6a2 → 9b1 S → Mo charge-transfer (420 nm) band, are discussed.
- Bruce, Alice E.,Bruce, Mitchell R. M.,Sclafani, Anthony,Tyler, David R.
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p. 1610 - 1614
(2008/10/08)
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- Preparation and Properties of Metallocyclopentane and Dineopentyl Derivatives of Molybdenocene and Tungstenocene. X-ray Crystal and Molecular Structure of Bis(η-cyclopentadienyl)molybdenacyclopentane
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The interaction of with the appropriate dilithium reagents yields the metallacyclopentane derivatives (1), (η-C5H5)2> (2), and (3).Structures for these compounds are proposed on the basis of elemental analysis, n.m.r. and mass spectrometry.The crystal structure of the molybdenum parent compound (1) has been determined from X-ray diffractometer data and refined by least squares.Crystals of (1) are Monoclinic, space group P21/c, with unit-cell parameters a = 11.352(2), b = 7.665(1), c = 16.111(3) Angstroem, β = 121.37(2) deg, and Z = 4; R = 0.047 based on 1272 observed reflections.The structural details are discussed also in terms of their chemical significance.Carbonylation of (1) yields cyclopentanone; compounds (1)-(3) give, by thermal decomposition, the corresponding olefins as the major products in addition to small amounts of olefins derived from metallacycle fragmentation.The dineopentyl derivatives (M = Mo or W) have been prepared and their thermal decomposition has been investigated.No isolable metallacyclobutane has been obtained.
- Diversi, Pietro,Ingrosso, Giovanni,Lucherini, Antonio,Porzio, William,Zocchi, Marcello
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p. 967 - 974
(2007/10/02)
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- NUCLEOPHILIC ATTACK ON BENT MOLYBDENUM AND TUNGSTEN METALLOCENE COMPLEXES
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Reactions of some 5-C5H5)2L2>n+ complexes (M = Mo, W; L = ligand; n = 0, 1, 2) with NaBH4 and LiAlH4 are reported.New neutral and cationic hydride derivatives of the type 5-C5H5)2HL>m+ (m = 0, 1) are des
- Dias, Alberto R.,Romao, Carlos C.
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p. 223 - 231
(2007/10/02)
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- Inter-relationships in Molybdenocene Dimer Chemistry: a Convenient Synthesis of Bis-η-cyclopentadienyldichloromolybdenum
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The dimers 1:η5-C5H4)>Mo(η-C5H5)> and5:η1-C5H4)Mo(CO)2(η-C5H5)> have been prepared from and characterised by crystal structure determination; the former dimer reacts readily with aqueous hydrochloric acid forming the dichloro-monomer .
- Green, Malcolm L. H.,Poveda, Manuel L.,Bashkin, Jim,Prout, Keith
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- Photochemical Studies on Binuclear Hydrido-molybdenocene Compounds
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Photolysis of 2(μ-η5-C5H4-η5-C5H4)> (3), gives first cis- and trans-2(μ-?:η5-C5H4)2> (4) and then 2(μ-?:η5-C5H4)2> (1).Previously it was thought that the formation of (1) did not proceed via the intermediacy of cis- and trans-2(μ-?:η5-C5H4)2>.A new mechanism for the photolysis of (3) to (1) is presented.
- Barral, Maria del Carmen,Green, Malcolm L.H.,Jimenez, Reyes
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p. 2495 - 2498
(2007/10/02)
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- Synthesis, Structure, and Reactions of a New Dimer of Molybdenocene, and Related Bi- and Tri-nuclear Compounds; Molecular Structures of 5-C5H5)2Mo(μ-?:η5-C5H4)Mo(η5-C5H5)>, 5-C5H5)(OC)Mo(μ-η5:?-C5H4)Mo(CO)2(η5-C5H5)>, and 5-C5H5)>2(μ-η5-C5H4-η>.
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Convenient syntheses of the black dimer 5-C5H5)2Mo(μ-?:η5-C5H4)Mo(η5-C5H5)> (2) and the compound 5-C5H5)(OC)Mo(μ-η5:?-C5H4)Mo(CO)2(η5-C5H5)> (5) are described.Compound (2) is a precursor for a number of new and known binuclear molybdenocene derivatives, including cis- or trans-5-C5H5)H>2(μ-?:η5-C5H4)2>, 5-C5H5)H>2(μ-η5-C5H4-η5-C5H4)>,5-C5H5)>2(μ-H)(μ-O)(μ-η5-C5H4-η5-C5H4)>PF6, and 5-C5H5)>2(μ-H)(μ-OH)(μ-η5-C5H4-η5-C5H4)>2.Due to the variety of structural isomers found in this series of dimers, (2) and (5) were characterised by X-ray diffraction methods.The crystal structure of the trihydride 5-C5H5)>2(μ-η5-C5H4-η5-C5H4)H3>PF6 (9) is also reported.Compound (2) is monoclinic, space group P21/c, with a=13.674(7), b=8.012(7), c=15.37(1) Angstroem, β=108.69(6) deg, and Z=4.Refinement converged at R=0.062,R'=0.090 for 2149 observed reflections 3?(I)>.The Mo-Mo distance is 3.189(1) Angstroem.The carbonyl dimer (5) is monoclinic, space group P21/n, with a=8.644(2), b=15.336(2), c=12.203(6) Angstroem, β=92.59(3) deg, and Z=4.The final R value was 0.033 (R'=0.045) for 3574 observed reflections.The Mo-Mo distance is 3.089(1) Angstroem.Both (2) and (5) contain a cyclopentadienediyl bridge.Crystals of (9) are orthorhombic, space group Pbcn, with a=13.030(1), b=13.302(3), c=11.446(2) Angstroem, and Z=4.Refinement with 1284 observed reflections resulted in R=0.034, R'=0.037.A fulvalene ligand bridges the two Mo atoms which are separated by 3.227(1) Angstroem.The black dimer (2) reacts with aqueous hydrochloric acid to give 5-C5H5)2Cl2>, providing a convenient laboratory-scale synthesis of this useful compound.The compound 5-C5H5)>2(μ-O-MoO3)(μ-η5-C5H4-η5-C5H4)>*2Me2SO, which contains a unique μ-O-MoO3 group, is also described.
- Bashkin, Jim,Green, Malcolm L.H.,Poveda, Manuel L.,Prout, Keith
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p. 2485 - 2494
(2007/10/02)
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