Solution calorimetric and stopped-flow kinetic studies of the reaction of •Cr(CO) 3C 5Me 5 with PhSe-SePh and PhTe-TePh. Experimental and theoretical estimates of the Se-Se, Te-Te, H-Se, and H-Te bond strengths

James E. McDonough, John J. Weir, Matthew J. Carlson, Carl Hoff, Olga P. Kryatova, Elena V. Rybak-Akimova, Christopher R. Clough, Christopher C. Cummins

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Abstract

The kinetics of the oxidative addition of PhSeSePh and PhTeTePh to the stable 17-electron complex •Cr(CO) 3C 5Me5̈ have been studied utilizing stopped-flow techniques. The rates of reaction are first-order in each reactant, and the enthalpy of activation decreases in going from Se (ΔH = 7.0 ± 0.5 kcal/mol, ΔS = -22 ± 3 eu) to Te (ΔH‡ = 4.0 ± 0.5 kcal/mol, ΔS = -26 ±3 eu). The kinetics of the oxidative addition of PhSeH and •Cr(CO) 3C 5Me 5 show a change in mechanism in going from low (overall third-order) to high (overall second-order) temperatures. The enthalpies of the oxidative addition of PhE-EPh to •Cr(CO) 3C 5Me 5 in toluene solution have been measured and found to be -29.6, -30.8, and -28.9 kcal/mol for S, Se, and Te, respectively. These data are combined with enthalpies of activation from kinetic studies to yield estimates for the solution-phase PhE-EPh bond strengths of 46, 41, and 33 kcal/mol for E = S, Se, and Te, respectively. The corresponding Cr-EPh bond strengths are 38, 36, and 31 kcal/mol. Two methods have been used to determine the enthalpy of hydrogenation of PhSeSePh in toluene on the basis of reactions of HSPh and HSePh with either •Cr(CO) 3C 5Me 5or 2-pyridine thione. These data lead to a thermochemical estimate of 72 kcal/mol for the PhSe-H bond strength in toluene solution, which is in good agreement with kinetic studies of H atom transfer from HSePh at higher temperatures. The reaction of H-Cr(CO) 3C5́Me 5 with PhSe-SePh is accelerated by the addition of a Cr radical and occurs via a rapid radical chain reaction. In contrast, the reaction of PhTe-TePh and H-Cr(CO) 3C 5Me 5 does not occur at any appreciable rate at room temperature, even in the presence of added Cr radicals. This is in keeping with a low PhTe-H bond strength blocking the chain and implies that H-TePh ≤ 63 kcal/mol. Structural data are reported for PhSe-Cr(CO) 3C 5Me 5 and PhS-Cr(CO) 3C 6Me 5. The two isostructural complexes do not show signs of an increase in steric strain in terms of metal-ligand bonds or angles as the Cr-EPh bond is shortened in going from Se to S. Bond strength estimates of the PhE-H and PhE-EPh derived from density functional theory calculations are in reasonable agreement with experimental data for E = Se but not for E = Te. The nature of the singly occupied molecular orbital of the •EPh radicals is calculated to show increasing localization on the chalcogenide atom in going from S to Se to Te.

Original languageEnglish
Pages (from-to)3127-3136
Number of pages10
JournalInorganic Chemistry
Volume44
Issue number9
DOIs
StatePublished - May 2 2005

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Carbon Monoxide
enthalpy
Kinetics
kinetics
toluene
estimates
Enthalpy
Toluene
activation
Chemical activation
hydrogenation
atoms
pyridines
molecular orbitals
Atoms
density functional theory
Molecular orbitals
ligands
Temperature
Hydrogenation

ASJC Scopus subject areas

  • Inorganic Chemistry

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Solution calorimetric and stopped-flow kinetic studies of the reaction of •Cr(CO) 3C 5Me 5 with PhSe-SePh and PhTe-TePh. Experimental and theoretical estimates of the Se-Se, Te-Te, H-Se, and H-Te bond strengths. / McDonough, James E.; Weir, John J.; Carlson, Matthew J.; Hoff, Carl; Kryatova, Olga P.; Rybak-Akimova, Elena V.; Clough, Christopher R.; Cummins, Christopher C.

In: Inorganic Chemistry, Vol. 44, No. 9, 02.05.2005, p. 3127-3136.

Research output: Contribution to journalArticle

McDonough, James E. ; Weir, John J. ; Carlson, Matthew J. ; Hoff, Carl ; Kryatova, Olga P. ; Rybak-Akimova, Elena V. ; Clough, Christopher R. ; Cummins, Christopher C. / Solution calorimetric and stopped-flow kinetic studies of the reaction of •Cr(CO) 3C 5Me 5 with PhSe-SePh and PhTe-TePh. Experimental and theoretical estimates of the Se-Se, Te-Te, H-Se, and H-Te bond strengths. In: Inorganic Chemistry. 2005 ; Vol. 44, No. 9. pp. 3127-3136.
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abstract = "The kinetics of the oxidative addition of PhSeSePh and PhTeTePh to the stable 17-electron complex •Cr(CO) 3C 5Me5̈ have been studied utilizing stopped-flow techniques. The rates of reaction are first-order in each reactant, and the enthalpy of activation decreases in going from Se (ΔH ‡ = 7.0 ± 0.5 kcal/mol, ΔS ‡ = -22 ± 3 eu) to Te (ΔH‡ = 4.0 ± 0.5 kcal/mol, ΔS ‡ = -26 ±3 eu). The kinetics of the oxidative addition of PhSeH and •Cr(CO) 3C 5Me 5 show a change in mechanism in going from low (overall third-order) to high (overall second-order) temperatures. The enthalpies of the oxidative addition of PhE-EPh to •Cr(CO) 3C 5Me 5 in toluene solution have been measured and found to be -29.6, -30.8, and -28.9 kcal/mol for S, Se, and Te, respectively. These data are combined with enthalpies of activation from kinetic studies to yield estimates for the solution-phase PhE-EPh bond strengths of 46, 41, and 33 kcal/mol for E = S, Se, and Te, respectively. The corresponding Cr-EPh bond strengths are 38, 36, and 31 kcal/mol. Two methods have been used to determine the enthalpy of hydrogenation of PhSeSePh in toluene on the basis of reactions of HSPh and HSePh with either •Cr(CO) 3C 5Me 5or 2-pyridine thione. These data lead to a thermochemical estimate of 72 kcal/mol for the PhSe-H bond strength in toluene solution, which is in good agreement with kinetic studies of H atom transfer from HSePh at higher temperatures. The reaction of H-Cr(CO) 3C5́Me 5 with PhSe-SePh is accelerated by the addition of a Cr radical and occurs via a rapid radical chain reaction. In contrast, the reaction of PhTe-TePh and H-Cr(CO) 3C 5Me 5 does not occur at any appreciable rate at room temperature, even in the presence of added Cr radicals. This is in keeping with a low PhTe-H bond strength blocking the chain and implies that H-TePh ≤ 63 kcal/mol. Structural data are reported for PhSe-Cr(CO) 3C 5Me 5 and PhS-Cr(CO) 3C 6Me 5. The two isostructural complexes do not show signs of an increase in steric strain in terms of metal-ligand bonds or angles as the Cr-EPh bond is shortened in going from Se to S. Bond strength estimates of the PhE-H and PhE-EPh derived from density functional theory calculations are in reasonable agreement with experimental data for E = Se but not for E = Te. The nature of the singly occupied molecular orbital of the •EPh radicals is calculated to show increasing localization on the chalcogenide atom in going from S to Se to Te.",
author = "McDonough, {James E.} and Weir, {John J.} and Carlson, {Matthew J.} and Carl Hoff and Kryatova, {Olga P.} and Rybak-Akimova, {Elena V.} and Clough, {Christopher R.} and Cummins, {Christopher C.}",
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TY - JOUR

T1 - Solution calorimetric and stopped-flow kinetic studies of the reaction of •Cr(CO) 3C 5Me 5 with PhSe-SePh and PhTe-TePh. Experimental and theoretical estimates of the Se-Se, Te-Te, H-Se, and H-Te bond strengths

AU - McDonough, James E.

AU - Weir, John J.

AU - Carlson, Matthew J.

AU - Hoff, Carl

AU - Kryatova, Olga P.

AU - Rybak-Akimova, Elena V.

AU - Clough, Christopher R.

AU - Cummins, Christopher C.

PY - 2005/5/2

Y1 - 2005/5/2

N2 - The kinetics of the oxidative addition of PhSeSePh and PhTeTePh to the stable 17-electron complex •Cr(CO) 3C 5Me5̈ have been studied utilizing stopped-flow techniques. The rates of reaction are first-order in each reactant, and the enthalpy of activation decreases in going from Se (ΔH ‡ = 7.0 ± 0.5 kcal/mol, ΔS ‡ = -22 ± 3 eu) to Te (ΔH‡ = 4.0 ± 0.5 kcal/mol, ΔS ‡ = -26 ±3 eu). The kinetics of the oxidative addition of PhSeH and •Cr(CO) 3C 5Me 5 show a change in mechanism in going from low (overall third-order) to high (overall second-order) temperatures. The enthalpies of the oxidative addition of PhE-EPh to •Cr(CO) 3C 5Me 5 in toluene solution have been measured and found to be -29.6, -30.8, and -28.9 kcal/mol for S, Se, and Te, respectively. These data are combined with enthalpies of activation from kinetic studies to yield estimates for the solution-phase PhE-EPh bond strengths of 46, 41, and 33 kcal/mol for E = S, Se, and Te, respectively. The corresponding Cr-EPh bond strengths are 38, 36, and 31 kcal/mol. Two methods have been used to determine the enthalpy of hydrogenation of PhSeSePh in toluene on the basis of reactions of HSPh and HSePh with either •Cr(CO) 3C 5Me 5or 2-pyridine thione. These data lead to a thermochemical estimate of 72 kcal/mol for the PhSe-H bond strength in toluene solution, which is in good agreement with kinetic studies of H atom transfer from HSePh at higher temperatures. The reaction of H-Cr(CO) 3C5́Me 5 with PhSe-SePh is accelerated by the addition of a Cr radical and occurs via a rapid radical chain reaction. In contrast, the reaction of PhTe-TePh and H-Cr(CO) 3C 5Me 5 does not occur at any appreciable rate at room temperature, even in the presence of added Cr radicals. This is in keeping with a low PhTe-H bond strength blocking the chain and implies that H-TePh ≤ 63 kcal/mol. Structural data are reported for PhSe-Cr(CO) 3C 5Me 5 and PhS-Cr(CO) 3C 6Me 5. The two isostructural complexes do not show signs of an increase in steric strain in terms of metal-ligand bonds or angles as the Cr-EPh bond is shortened in going from Se to S. Bond strength estimates of the PhE-H and PhE-EPh derived from density functional theory calculations are in reasonable agreement with experimental data for E = Se but not for E = Te. The nature of the singly occupied molecular orbital of the •EPh radicals is calculated to show increasing localization on the chalcogenide atom in going from S to Se to Te.

AB - The kinetics of the oxidative addition of PhSeSePh and PhTeTePh to the stable 17-electron complex •Cr(CO) 3C 5Me5̈ have been studied utilizing stopped-flow techniques. The rates of reaction are first-order in each reactant, and the enthalpy of activation decreases in going from Se (ΔH ‡ = 7.0 ± 0.5 kcal/mol, ΔS ‡ = -22 ± 3 eu) to Te (ΔH‡ = 4.0 ± 0.5 kcal/mol, ΔS ‡ = -26 ±3 eu). The kinetics of the oxidative addition of PhSeH and •Cr(CO) 3C 5Me 5 show a change in mechanism in going from low (overall third-order) to high (overall second-order) temperatures. The enthalpies of the oxidative addition of PhE-EPh to •Cr(CO) 3C 5Me 5 in toluene solution have been measured and found to be -29.6, -30.8, and -28.9 kcal/mol for S, Se, and Te, respectively. These data are combined with enthalpies of activation from kinetic studies to yield estimates for the solution-phase PhE-EPh bond strengths of 46, 41, and 33 kcal/mol for E = S, Se, and Te, respectively. The corresponding Cr-EPh bond strengths are 38, 36, and 31 kcal/mol. Two methods have been used to determine the enthalpy of hydrogenation of PhSeSePh in toluene on the basis of reactions of HSPh and HSePh with either •Cr(CO) 3C 5Me 5or 2-pyridine thione. These data lead to a thermochemical estimate of 72 kcal/mol for the PhSe-H bond strength in toluene solution, which is in good agreement with kinetic studies of H atom transfer from HSePh at higher temperatures. The reaction of H-Cr(CO) 3C5́Me 5 with PhSe-SePh is accelerated by the addition of a Cr radical and occurs via a rapid radical chain reaction. In contrast, the reaction of PhTe-TePh and H-Cr(CO) 3C 5Me 5 does not occur at any appreciable rate at room temperature, even in the presence of added Cr radicals. This is in keeping with a low PhTe-H bond strength blocking the chain and implies that H-TePh ≤ 63 kcal/mol. Structural data are reported for PhSe-Cr(CO) 3C 5Me 5 and PhS-Cr(CO) 3C 6Me 5. The two isostructural complexes do not show signs of an increase in steric strain in terms of metal-ligand bonds or angles as the Cr-EPh bond is shortened in going from Se to S. Bond strength estimates of the PhE-H and PhE-EPh derived from density functional theory calculations are in reasonable agreement with experimental data for E = Se but not for E = Te. The nature of the singly occupied molecular orbital of the •EPh radicals is calculated to show increasing localization on the chalcogenide atom in going from S to Se to Te.

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