- Ligand substitution kinetics in M(CO)4 (η2:2-1,5-cyclooctadiene) complexes (M=Cr, Mo, W) - Substitution of 1,5-cyclooctadiene by bis(diphenylphosphino)alkanes
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The thermal substitution kinetics of 1,5-cyclooctadiene (COD) by bis(diphenylphosphino)alkanes (PP), (C6H5)2P(CH2)nP(C 6H5)2 (n = 1, 2, 3) in M(CO)4(η2:2-COD) complexes (M = Cr, Mo, W), were studied by quantitative FT-IR spectroscopy. The reaction rate exhibits first-order dependence on the concentration of the starting complex, and the observed rate constant depends on the concentration of the leaving COD ligand and on the concentration and the nature of the entering PP ligand. In the proposed mechanism, the rate determining step is the cleavage of one metal-olefin bond of the COD ligand. A rate-law is derived from the proposed mechanism. The evaluation of the kinetic data gives the activation parameters which support an associative mechanism in the transition states. Both the observed rate constant and the activation parameters show little variation with the chain length of the diphosphine ligand.
- Kayran, Ceyhan,Kozanoglu, Ferda,Oezkar, Saim,Saldamli, Saltuk,Tekkaya, Aysin,Kreiter, Cornelius G.
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- Rapid synthesis of Group VI carbonyl complexes by coupling borohydride catalysis and microwave heating
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Several Group VI tetracarbonyl phosphine and tertiary amine complexes [M(CO)4 L2, M = Cr, Mo, W, L2 = 2PPh 3, dppm, dppe, dppp, dppb, bpy, phen, dppf] were synthesized in minutes in the microwave at moderate temperature, atmospheric pressure, and utilizing NaBH4 as a catalyst. The reactions were optimized by careful solvent selection. The octahedral complexes were isolated in percent yields ranging from 17 to 95. The lower temperatures, shorter reaction times, benign solvents, and lower pressures as compared to the traditional thermal syntheses provide a rapid, eco-friendly synthetic route to these common Group VI complexes.
- Birdwhistell, Kurt R.,Schulz, Brian E.,Dizon, Paula M.
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- Ligand substitution kinetics in M(CO)4(η2:2-norbornadiene) complexes (M=Cr, Mo, W): Displacement of norbornadiene by bis(diphenylphosphino)alkanes
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The thermal substitution kinetics of norbornadiene (NBD) by bis(diphenylphosphino)alkanes (PP), (C6H5)2P(CH2)nP(C 6H5)2 (n=1, 2, 3) in M(CO)4(η2:2-NBD) complexes (M=Cr, Mo, W), were studied by quantitative FT-IR spectroscopy. The reaction rate exhibits first-order dependence on the concentration of the starting complex, and the observed rate constant depends on the concentration of the leaving NBD ligand and on the concentration and the nature of the entering PP ligand. In the proposed mechanism there are two competing initial steps: an associative reaction involving the attachment of the entering PP ligand to the transition metal center and a dissociative reaction involving the stepwise detachment of the diolefin ligand from the transition metal center. A rate law is derived from the proposed mechanism. The activation parameters are obtained from the evaluation of the kinetic data. It is found that at higher concentrations of the entering ligand, the associative path is dominant, while at lower concentrations the contribution of the dissociative path becomes significant. Both the observed rate constant and the activation parameters show noticeable variation with the chain length of the diphosphine ligand.
- Tekkaya, Aysin,Oezkar, Saim
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p. 208 - 216
(2007/10/03)
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- Reactions of (PPh3)3> with Group 6 Metal Carbonyls. Crystal Structure and Reactivity with Diphosphines of the Linear Heterotrinuclear Complex 2(CO)6(PPh3)2>
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The compound (PPh3)3> 1 reacts with the Group 6 metal carbonyls, , in hot aromatic solvents giving different reaction products according to the stability of the metal carbonyl: (CO)4(PPh3)2> 2 (M = Cr); and trans- (M = W) and the dark brown 2(CO)6(PPh3)2> 3 (M = Mo).The structure of 3 has been established from X-ray diffraction analysis.This compound reacts, in boiling toluene, with diphosphines (Ph2P)2X to form 2(CO)4 (diphosphine)2> (diphosphine = dppm 4 or dppb 5) and for X = C2H4 (dppe) or C3H6 (dppp) a mixture of and (CO)(diphosphine)> was obtained.The new trinuclear complexes have been characterised by elemental analysis and by spectroscopic (IR and NMR) methods.
- Anillo, Adela,Garcia-Granda, Santiago,Obeso-Rosete, Ricardo,Rubio-Gonzalez, Juan Manuel
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p. 3287 - 3292
(2007/10/02)
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- Effect of ring size on NMR parameters: Cyclic bisphosphine complexes of molybdenum, tungsten, and platinum. Bond angle dependence of metal shieldings, metal-phosphorus coupling constants, and the 31P chemical shift anisotropy in the solid state
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The 31P chemical shift tensors of bis(phosphine) complexes of the type [M] [Ph2P(CH2)nPPh2] ([M] = (OC)4Mo, (OC)4W, Cl2Pt; n = 1-5) and of fac-(OC)3Mo[PPh(CH2CH2PPh2) 2] were determined by solid-state NMR techniques and correlated with structural features of the compounds. δ(31P), 1JM-P, and δ(M) show a dependence on the ring size in the solution NMR spectra of the four- to six-membered chelates; for larger rings this dependence vanishes. A model for the orientation of the 31P shift tensor principal components within the molecular frame is proposed. Each tensor component displays a different dependence on the ring size; the isotropic shift is dominated by the component perpendicular to the ring plane. Changes in this component are explained in terms of variations of the M-P-C angles. Generally speaking, the behavior of each of the tensor components must be regarded as a complex interplay of all six bond angles at phosphorus. The crystal structure of (OC)4W[Ph2P(CH2)4PPh2] (2d) was determined by X-ray diffraction. Crystals of 2d are monoclinic, space group P21/n, a = 1202.8 (1) pm, b = 1531.8 (1) pm, c = 1654.1 (2) pm, β = 104.72 (1)°, and Z = 4.
- Lindner, Ekkehard,Fawzi, Riad,Mayer, Hermann August,Eichele, Klaus,Hiller, Wolfgang
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p. 1033 - 1043
(2008/10/08)
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- Heat of reaction of (norbornadiene)molybdenum tetracarbonyl with monodentate and bidentate ligands. Solution thermochemical study of ligand substitution in the complexes cis-L2Mo(CO)4
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The enthalpy of reaction of (NBD)Mo(CO)4 (NBD = norbornadiene) with a number of monodentate and bidentate ligands forming cis-L2Mo(CO)4 has been measured at 30°C in THF solution. The heats of reaction span a range of 33 kcal/mol. The order of stability for monodentate ligands is PCl3 6H5)3 6H5)3 3 6H5)3 6H5)2(CH3) 6H5)(CH3)2 3)3 3 6H11)NC 3 3. The series of chelating bidentate phosphines R2P-(CH2)nPR2 (n = 1-4, R = C6H5; n = 1, 2, R = CH3) and several related ligands were investigated. The chelating ring systems in the metallacycles show strain energies of about 8 kcal/mol for four-membered rings. The mixed ligand (C6H5)2PCH2CH2-As(C 6H5)2 shows a heat of binding midway between the heats of binding of (C6H5)2PCH2CH2P(C 6H5)2 and (C6H5)2AsCH2C-H2As(C 6H5)2, implying group additivity in this system. The complex (phen)Mo(CO)4 is some 5 kcal/mol more stable than (bpy)Mo(CO)4, presumably due to conformational effects in the free ligand. The ligand 1,5-cyclooctadiene forms a complex 2 kcal/mol less stable than that of norbornadiene. The influences of steric and electronic factors in determining the Mo-L bond strength are discussed.
- Mukerjee, Shakti L.,Nolan, Steven P.,Hoff, Carl D.,Lopez De La Vega, Ramon
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- Substituted metal carbonyls IV. Studies of the synthesis and decomposition of singly-bridging 1,3-bis(diphenylphosphino)propanedimetal decacarbonyls of chromium, molybdenum and tungsten
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Singly-bridging diphosphine complexes M2(CO)10(μ-dppp) (M=Cr, W; dppp=Ph2P(CH2)3PPh2 have been isolated in a facile synthesis via an oxidative decarbonylation of M(CO)6 using trimethylamine-N-oxide as the initiator.The thermal decomposition of these complexes, together with the molybdenum analogue, have been studied in refluxing acetonitrile, benzene or toluene under N2 or CO.The characterisations and thermal stabilities of these species are described and discussed.Conversion of the 1,3-bis(diphenylphosphino)propanedimetal decacarbonyl complexes of chromium, molybdenum and tungsten into the chelate M(CO)4(η2-dppp) is promoted by free dppp but inhibited by CO gas.
- Hor, Andy T. S.
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