Gas-phase ionization energetics, electron-transfer kinetics, and ion solvation thermochemistry of decamethylmetallocenes, chromocene, and cobaltocene

M. F. Ryan, D. E. Richardson, Dennis L Lichtenberger, N. E. Gruhn

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Abstract

The gas-phase free energies of ionization, ΔGi° for Cp*2Mn, Cp±2Fe, Cp*2Ni, Cp±2Os, Cp2Cr, and Cp2Co (Cp = η5-cyclopentadienyl, Cp* = η5-pentamethylcyclopentadienyl) have been determined by using the electron-transfer equilibrium (ETE) technique and Fourier transform ion cyclotron resonance mass spectrometry. The high-resolution valence photoelectron spectra of bis(benzene)chromium(0), Bz2Cr, Cp*Os, and Cp*2Ru have also been measured. Most of the ΔGi° values are referenced to the estimated ΔGi° value of Bz2Cr, for which the narrow first ionization band at 5.473 ± 0.005 eV is assigned as the adiabatic ionization potential. The ΔSi° for ionization of Bz2Cr is assumed to be equal to the electronic entropy change, ΔSelec° (= 1.4 cal mol-1 K-1), and the difference between the integrated heat capacities for Bz2Cr and Bz2Cr+ is also assumed to be negligible near room temperature (ΔHi,0° ≈ ΔHi,350°), leading to ΔGi° (Bz2-Cr) = 125.6 ± 1.0 kcal mol-1. Through the use of thermochemical cycles, estimates are given for the average heterolytic and homolytic M-Cp bond disruption enthalpies of Cp2Cr+/0 and Cp2Co+/0. Cyclic voltammetry experiments (CH3CN/0.1 M Bu4NPF6) for the decamethylmetallocenes, including Cp*2Ru, were performed in order to determine differential solvation energies, ΔΔGsolv°, for the +/0 redox couples. Generally, ΔΔGsolv° values for the decamethyl derivatives are in the range -21 to -29 (±4) kcal mol-1. Electron-transfer kinetics for several metallocene couples were measured from the approach to equilibrium in the ETE experiments, and couples that involved Cp±2M compounds were observed to have rate constants less than 10% of the Langevin collision frequency when the free energy change was in the range 0 to -6 kcal mol-1.

Original languageEnglish (US)
Pages (from-to)1190-1199
Number of pages10
JournalOrganometallics
Volume13
Issue number4
StatePublished - Apr 1994

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Thermochemistry
thermochemistry
Solvation
Ionization
solvation
electron transfer
Gases
Ions
vapor phases
ionization
Free energy
Kinetics
Electrons
kinetics
free energy
Cyclotron resonance
ions
Ionization potential
Chromium
cyclotron resonance

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

Gas-phase ionization energetics, electron-transfer kinetics, and ion solvation thermochemistry of decamethylmetallocenes, chromocene, and cobaltocene. / Ryan, M. F.; Richardson, D. E.; Lichtenberger, Dennis L; Gruhn, N. E.

In: Organometallics, Vol. 13, No. 4, 04.1994, p. 1190-1199.

Research output: Contribution to journalArticle

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abstract = "The gas-phase free energies of ionization, ΔGi° for Cp*2Mn, Cp±2Fe, Cp*2Ni, Cp±2Os, Cp2Cr, and Cp2Co (Cp = η5-cyclopentadienyl, Cp* = η5-pentamethylcyclopentadienyl) have been determined by using the electron-transfer equilibrium (ETE) technique and Fourier transform ion cyclotron resonance mass spectrometry. The high-resolution valence photoelectron spectra of bis(benzene)chromium(0), Bz2Cr, Cp*Os, and Cp*2Ru have also been measured. Most of the ΔGi° values are referenced to the estimated ΔGi° value of Bz2Cr, for which the narrow first ionization band at 5.473 ± 0.005 eV is assigned as the adiabatic ionization potential. The ΔSi° for ionization of Bz2Cr is assumed to be equal to the electronic entropy change, ΔSelec° (= 1.4 cal mol-1 K-1), and the difference between the integrated heat capacities for Bz2Cr and Bz2Cr+ is also assumed to be negligible near room temperature (ΔHi,0° ≈ ΔHi,350°), leading to ΔGi° (Bz2-Cr) = 125.6 ± 1.0 kcal mol-1. Through the use of thermochemical cycles, estimates are given for the average heterolytic and homolytic M-Cp bond disruption enthalpies of Cp2Cr+/0 and Cp2Co+/0. Cyclic voltammetry experiments (CH3CN/0.1 M Bu4NPF6) for the decamethylmetallocenes, including Cp*2Ru, were performed in order to determine differential solvation energies, ΔΔGsolv°, for the +/0 redox couples. Generally, ΔΔGsolv° values for the decamethyl derivatives are in the range -21 to -29 (±4) kcal mol-1. Electron-transfer kinetics for several metallocene couples were measured from the approach to equilibrium in the ETE experiments, and couples that involved Cp±2M compounds were observed to have rate constants less than 10{\%} of the Langevin collision frequency when the free energy change was in the range 0 to -6 kcal mol-1.",
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T1 - Gas-phase ionization energetics, electron-transfer kinetics, and ion solvation thermochemistry of decamethylmetallocenes, chromocene, and cobaltocene

AU - Ryan, M. F.

AU - Richardson, D. E.

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AU - Gruhn, N. E.

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N2 - The gas-phase free energies of ionization, ΔGi° for Cp*2Mn, Cp±2Fe, Cp*2Ni, Cp±2Os, Cp2Cr, and Cp2Co (Cp = η5-cyclopentadienyl, Cp* = η5-pentamethylcyclopentadienyl) have been determined by using the electron-transfer equilibrium (ETE) technique and Fourier transform ion cyclotron resonance mass spectrometry. The high-resolution valence photoelectron spectra of bis(benzene)chromium(0), Bz2Cr, Cp*Os, and Cp*2Ru have also been measured. Most of the ΔGi° values are referenced to the estimated ΔGi° value of Bz2Cr, for which the narrow first ionization band at 5.473 ± 0.005 eV is assigned as the adiabatic ionization potential. The ΔSi° for ionization of Bz2Cr is assumed to be equal to the electronic entropy change, ΔSelec° (= 1.4 cal mol-1 K-1), and the difference between the integrated heat capacities for Bz2Cr and Bz2Cr+ is also assumed to be negligible near room temperature (ΔHi,0° ≈ ΔHi,350°), leading to ΔGi° (Bz2-Cr) = 125.6 ± 1.0 kcal mol-1. Through the use of thermochemical cycles, estimates are given for the average heterolytic and homolytic M-Cp bond disruption enthalpies of Cp2Cr+/0 and Cp2Co+/0. Cyclic voltammetry experiments (CH3CN/0.1 M Bu4NPF6) for the decamethylmetallocenes, including Cp*2Ru, were performed in order to determine differential solvation energies, ΔΔGsolv°, for the +/0 redox couples. Generally, ΔΔGsolv° values for the decamethyl derivatives are in the range -21 to -29 (±4) kcal mol-1. Electron-transfer kinetics for several metallocene couples were measured from the approach to equilibrium in the ETE experiments, and couples that involved Cp±2M compounds were observed to have rate constants less than 10% of the Langevin collision frequency when the free energy change was in the range 0 to -6 kcal mol-1.

AB - The gas-phase free energies of ionization, ΔGi° for Cp*2Mn, Cp±2Fe, Cp*2Ni, Cp±2Os, Cp2Cr, and Cp2Co (Cp = η5-cyclopentadienyl, Cp* = η5-pentamethylcyclopentadienyl) have been determined by using the electron-transfer equilibrium (ETE) technique and Fourier transform ion cyclotron resonance mass spectrometry. The high-resolution valence photoelectron spectra of bis(benzene)chromium(0), Bz2Cr, Cp*Os, and Cp*2Ru have also been measured. Most of the ΔGi° values are referenced to the estimated ΔGi° value of Bz2Cr, for which the narrow first ionization band at 5.473 ± 0.005 eV is assigned as the adiabatic ionization potential. The ΔSi° for ionization of Bz2Cr is assumed to be equal to the electronic entropy change, ΔSelec° (= 1.4 cal mol-1 K-1), and the difference between the integrated heat capacities for Bz2Cr and Bz2Cr+ is also assumed to be negligible near room temperature (ΔHi,0° ≈ ΔHi,350°), leading to ΔGi° (Bz2-Cr) = 125.6 ± 1.0 kcal mol-1. Through the use of thermochemical cycles, estimates are given for the average heterolytic and homolytic M-Cp bond disruption enthalpies of Cp2Cr+/0 and Cp2Co+/0. Cyclic voltammetry experiments (CH3CN/0.1 M Bu4NPF6) for the decamethylmetallocenes, including Cp*2Ru, were performed in order to determine differential solvation energies, ΔΔGsolv°, for the +/0 redox couples. Generally, ΔΔGsolv° values for the decamethyl derivatives are in the range -21 to -29 (±4) kcal mol-1. Electron-transfer kinetics for several metallocene couples were measured from the approach to equilibrium in the ETE experiments, and couples that involved Cp±2M compounds were observed to have rate constants less than 10% of the Langevin collision frequency when the free energy change was in the range 0 to -6 kcal mol-1.

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