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

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Abstract

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.

Original languageEnglish
Pages (from-to)15728-15741
Number of pages14
JournalJournal of the American Chemical Society
Volume128
Issue number49
DOIs
Publication statusPublished - Dec 13 2006

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Fourier Transform Infrared Spectroscopy
Carbon Monoxide
Ultraviolet spectroscopy
Rate constants
Spectrum Analysis
Theoretical Models
Chemical activation
Ligands
Photolysis
Hexane
Density functional theory
Laser excitation
Equilibrium constants
Interchanges
Toluene
Entropy
Hexanes
Lasers
Spectroscopy
Infrared radiation

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{421477c383e1444ebb7d12a9ab5f576e,
title = "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",
abstract = "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.",
author = "David Grills and {Van Eldik}, Rudi and James Muckerman and Etsuko Fujita",
year = "2006",
month = "12",
day = "13",
doi = "10.1021/ja064627e",
language = "English",
volume = "128",
pages = "15728--15741",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "49",

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TY - JOUR

T1 - 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

T2 - Theoretical and experimental studies with time-resolved step-scan FTIR and UV-Vis spectroscopy

AU - Grills, David

AU - Van Eldik, Rudi

AU - Muckerman, James

AU - Fujita, Etsuko

PY - 2006/12/13

Y1 - 2006/12/13

N2 - 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.

AB - 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.

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