104198-75-6Relevant articles and documents
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.
Entropy of binding molecular hydrogen and nitrogen in the complexes (P(C6H11)3)2M(CO)3 (M = Cr, Mo, W)
Gonzalez, Alberto A.,Hoff, Carl D.
, p. 4295 - 4297 (2008/10/08)
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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.
