73690-57-0Relevant articles and documents
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.
