104198-75-6Relevant academic research and scientific papers
Why does D2 bind better than H2? A theoretical and experimental study of the equilibrium isotope effect on H2 binding in a M(η2-H2) complex. Normal coordinate analysis of W(CO)3(PCy3)2(η2-H2)
Bender, Bruce R.,Kubas, Gregory J.,Jones, Llewellyn H.,Swanson, Basil I.,Eckert, Juergen,Capps, Kenneth B.,Hoff, Carl D.
, p. 9179 - 9190 (1997)
Vibrational data (IR, Raman and inelastic neutron scattering) and a supporting normal coordinate analysis for the complex trans-W(CO)3(PCy3)2(η2-H2) (1) and its HD and D2 isotopomers are reported. The vibrational data and force constants support the well-established η2-bonding mode for the H2 ligand and provide unambiguous assignments for all metal-hydrogen stretching and bending frequencies. The force constant for the HH stretch, 1.3 mdyn/A?, is less than one-fourth the value in free H2 and is similar to that for the WH stretch, indicating that weakening of the H-H bond and formation of W-H bonds are well along the reaction coordinate to oxidative addition. The equilibrium isotope effect (EIE) for the reversible binding of dihydrogen (H2) and dideuterium (D2) to 1 and 1-d2 has been calculated from measured vibrational frequencies for 1 and 1-d2. The calculated EIE is 'inverse' (1-d2 binds D2 better than 1 binds H2 With K(H)/K(D) = 0.78 at 300 K. The EIE calculated from vibrational frequencies may be resolved into a large normal mass and moment of inertia factor (MMI = 5.77), an inverse vibrational excitation factor (EXC = 0.67), and an inverse zero-point energy factor (ZPE = 0.20), where EIE = MMI x EXC x ZPE. An analysis of the zero-point energy components of the EIE shows that the large decrease in the HH stretching frequency (force constant) predicts a large normal EIE but that zero-point energies from five new vibrational modes (which originate from translational and rotational degrees of freedom from hydrogen) offset the change in zero-point energy from the H2(D2) stretch. The calculated EIE is compared to experimental data obtained for the binding of H2 or D2 to Cr(CO)3(PCy3)2 over the temperature range 12-36 °C in THF solution. For the binding of H2 ΔH = -6.8 ± 0.5 kcal mol-1 and ΔS = -24.7 ± 2.0 cal mol-1 deg-1; for (D)2 ΔH = -8.6 ± 0.5 kcal/mol and ΔS = -30.0 ± 2.0 cal/(mol deg). The EIE at 22 °C has a value of K(H)/K(D) = 0.65 ± 0.15. Comparison of the equilibrium constants for displacement of N2 by H2 or D2 in the complex W(CO)3(PCy3)2(N2) in THF yielded a value of K(H)/K(D) = 0.70 ± 0.15 at 22 °C.
Direct measurements of rate constants and activation volumes for the binding of H2, D2, N2, C2H 4, and CH3CN to W(CO)3(PCy3) 2: Theoretical and experimental studies with time-resolved step-scan FTIR and UV-Vis spectroscopy
Grills, David C.,Van Eldik, Rudi,Muckerman, James T.,Fujita, Etsuko
, p. 15728 - 15741 (2007/10/03)
Pulsed 355 nm laser excitation of toluene or hexane solutions containing W-L (W = mer,trans-W(CO)3(PCy3)2; PCy 3 = tricyclohexylphosphine; L = H2, D2, N 2, C2H4, or CH3CN) resulted in the photoejection of ligand L and the formation of W. A combination of nanosecond UV-vis flash photolysis and time-resolved step-scan FTIR (s2-FTIR) spectroscopy was used to spectroscopically characterize the photoproduct, W, and directly measure the rate constants for binding of the ligands L to W to reform W-L under pseudo-first-order conditions. From these data, equilibrium constants for the binding of L to W were estimated. The UV-vis flash photolysis experiments were also performed as a function of pressure in order to determine the activation volumes, ΔV?, for the reaction of W with L. Small activation volumes ranging from -7 to -3 cm3 mol-1 were obtained, suggesting that despite the crowded W center an interchange mechanism between L and the agostic W...H-C interaction of one of the PCy3 ligands (or a weak interaction with a solvent molecule) at the W center takes place in the transition state. Density functional theory (DFT) calculations were performed at the B3LYP level of theory on W with/without the agostic C-H interaction of the PCy3 ligand and also on the series of model complexes, mer,trans-W(CO)3(PH3)2L (W′-L, where L = H2, N2, C2H4, CO, or n-hexane) in an effort to confirm the infrared spectroscopic assignment of the W-L complexes, to simulate and assign the electronic transitions in the UV-vis spectra, to determine the nature of the HOMO and LUMO of W-L, and to understand the agostic C-H interaction of the ligand vs solvent interaction. Our DFT calculations indicate an entropy effect that favors agostic W...H-C interaction over a solvent σ C-H interaction by 8-10 kcal mol -1.
Stopped-Flow Kinetic Study of the Reaction of (P(C6H11)3)2W(CO)3(L) (L = H2, D2, and N2) with Pyridine. Kinetic Resolution of Reaction of Dihydride versus Molecular Hydrogen Complexes.
Zhang, Kai,Gonzalez, Alberto A.,Hoff, Carl D.
, p. 3627 - 3632 (2007/10/02)
The rates of reaction of (P(C6H11)3)2W(CO)3(L) (L = H2, D2, and N2) with pyridine have been studied by stopped-flow kinetics.The molecular nitrogen system shows simple first-order loss of N2 with a rate constant of 75 s-1 at 25 deg C and an activation energy of 17.8 +/- 0.7 kcal/mol.The rate of reaction of the intermediate (P(C6H11)3)2W(CO)3 with N2 gas is 5.0 +/- 1.0 x 1E5 M-1 s-1 at 25 deg C in toluene solution.Reactions of the hydrogen and deuterium complexes are complicated due to the presence of both molecular hydrogen (deuterium) and dihydride(dideuteride) complexes.These data are resolved and interpreted in terms of a rapid loss of molecular hydrogen (k = 469 s-1 for H2 and 267 s-1 for D2 at 25 deg C, ΔH(excit.) = 16.9 +/- 2.2 kcal/mol for H2 and 16.2 +/- 1.1 kcal/mol for D2).The hydride complex, which is present in ca. 30percent, reacts an order of magnitude slower than the molecular hydrogen complex (k = 37 s-1 for H2 and 33 s-1 for D2 at 25 deg C, ΔH(excit.) = 14.4 +/- 0.5 kcal/mol for H2 and 14.7 +/- 0.8 kcal/mol for D2).The rate of addition of H2 to (P(C6H11)3)2W(CO)3 is calculated to be 2.2 +/- 0.3 x 1E6 M-1 s-1 at 25 deg C.These data are combined with earlier thermodynamic measurements to generate a reaction profile for binding and oxidative addition of hydrogen to the complex (P(C6H11)3)2W(CO)3.
Thermodynamic and kinetic studies of the complexes W(CO)3(PCy3)2(L) (L = H2, N2, NCCH3, Pyridine, P(OMe)3, CO)
Gonzalez,Zhang,Nolan,Lopez de la Vega,Mukerjee,Hoff,Kubas
, p. 2429 - 2435 (2008/10/08)
The complexes W(CO)3(PCy3)2(L) have been studied by solution calorimetry. The enthalpies of binding (kcal/mol) of ligands to W(PCy3)2(CO)3 in toluene solution are as follows: H2, -9.9, N2, -13.5; NCCH3, -15.1; pyridine, -18.9; P(OMe)3, -26.5; CO, -30.4. Similar values are obtained in tetrahydrofuran solution. These data imply bond strengths much lower than expected from gas-phase studies. The origin of this discrepancy is attributed to the presence of the W...H-C 'agostic' interaction. This is estimated to be on the order of 10±6 kcal/mol. In order to investigate the role of the 'agostic' interaction in the energetics of this complex, the kinetics of reaction of W(CO)3[P(C6H11)3]2(py) and W(CO)3[P(C6D11)3]2(py) with P(OMe)3 in toluene were studied. A kinetic isotope effect, kH/kD=1.20±0.05, was observed, and verifies the importance of the 'agostic' bond in ligand substitution for this complex. A mechanism is proposed that involves concrete replacement of coordinated pyridine by the three-center W...H-C bond.
Molecular Hydrogen Complexes of the Transition Metals. 4. Preparation and Characterization of M(CO)3(PR3)2(η2-H2)(M = Mo, W) and Evidence for Equilibrium Dissociation of the H-H bond To Give MH2(CO)3(PR3)2
Kubas, Gregory J.,Unkefer, Clifford J.,Swanson, Basil I.,Fukushima, Eiichi
, p. 7000 - 7009 (2007/10/02)
The syntheses, properties, and spectral characterization of the first examples of molecular hydrogen complexes, M(CO)3(PR3)2(H2) (M = Mo, W; R3 = Cy3, i-Pr3, Cy2-i-Pr), are reported in full.All six of the expected fundamental vibrational modes for η2-H2 binding, including ν(HH) at 2690 cm-1, have been located.The hydrogen atoms of the H2 ligand, but not of the phosphines, undergo exchange with D2 to give HD, even in the solid state.Solid-state 2H NMR of W(CO)3(P-i-Pr3)2(D2) shows rapid rotation of the D2 about the metal-D2 axis.IR and variable-temperature 1H and 31P NMR of solutions of the H2 complexes reveal the presence of equilibrium amounts (10-30percent) of a species that the data indicate is a 7-coordinate dihydride, MH2(CO)3(PR3)2.The latter is presumably formed by dissociation of the H-H bond, thus completing oxidative addition of H2 to the metal.The dihydride is fluctional, but low-temperature NMR spectroscopy shows that both the hydride and phosphorus ligands are inequivalent.At -80 deg C the T1 value for the 1H NMR signal of the H2 ligand is 0.004 s, almost three orders of magnitude less than that of the hydride protons (1.7 s) in WH2(CO)3(P-i-Pr3)2.
Five-co-ordinate Molybdenum and Tungsten Complexes, , which Reversibly add Dinitrogen, Dihydrogen, and Other Small Molecules
Kubas, Gregory J.
, p. 61 - 62 (2007/10/02)
New complexes of molybdenum and tungsten with dinitrogen and other small molecules, trans- (L = N2, H2, C2H4, or SO2), have been synthesized by the reaction of with 2PCy3 in the presence of L; removal of L yield
