Charge-Transfer Structures of Aromatic EDA Complexes Leading to Electron Transfer with the Electrophilic Nitrosonium Cation

Eunkyoung Kim, J. K. Kochi

Research output: Contribution to journalArticle

106 Citations (Scopus)

Abstract

Benzene and hexamethylbenzene partake in the rapid formation of unique electron donor-acceptor (EDA) complexes with the nitrosonium cation, as reflected in the association constants that vary markedly from K = 0.5 to 31000 M−1, respectively. The 1:1 EDA complexes of electron-rich arene donors exhibit particularly high degrees of charge transfer that are established by X-ray crystallography coupled to the infrared spectroscopic analysis of the N-O stretching frequencies. Thus the N-O bond distance undergoes a dramatic lengthening from 0.95 ° in the simple salt NO+SbCl6 to 1.12 ° in the hexamethylbenzene (HMB) complex. Such a bond elongation of the nitrosonium acceptor is equivalent to that extant in nitric oxide (1.15 °), and it is accompanied by a corresponding change of the aromatic donor in the ground state of the EDA complex to that of the cation radical (HMB+), as deduced from the changes in the l3C NMR and the IR spectra. The same structural and spectroscopic analysis of the other NO+ complexes reveals a graded series of the EDA complexes in which the degree of charge transfer (Z) varies linearly with the donor strength as measured by the ionization potential of the arene (ArH). The increase of Z from benzene (0.52) to hexamethylbenzene (0.97) in the charge-transfer complex tracks their increasing proclivity to undergo electron transfer and afford arene cation radicals (ArH+) as reactive intermediates. A general mechanistic formulation based on electron transfer from the charge-transfer complex is developed, in which the facility of the followup reactions (such as fragmentation, cycloreversion, rearrangement, ion-pair annihilation, etc.) of the labile ArH+ is critical. When the electron transfer is reversible, this 1-electron mechanism is shown not to be readily distinguished from the more conventional electrophilic (2-electron) pathways.

Original languageEnglish
Pages (from-to)4962-4974
Number of pages13
JournalJournal of the American Chemical Society
Volume113
Issue number13
DOIs
Publication statusPublished - 1991 Jun 1

Fingerprint

Cations
Charge transfer
Positive ions
Electrons
Spectroscopic analysis
Benzene
Ionization potential
X ray crystallography
X Ray Crystallography
Nitric oxide
Structural analysis
Ground state
Stretching
Elongation
Nitric Oxide
Salts
Nuclear magnetic resonance
Association reactions
Ions
Infrared radiation

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

@article{d46e201c7ad84ebba76bcc3928e58edb,
title = "Charge-Transfer Structures of Aromatic EDA Complexes Leading to Electron Transfer with the Electrophilic Nitrosonium Cation",
abstract = "Benzene and hexamethylbenzene partake in the rapid formation of unique electron donor-acceptor (EDA) complexes with the nitrosonium cation, as reflected in the association constants that vary markedly from K = 0.5 to 31000 M−1, respectively. The 1:1 EDA complexes of electron-rich arene donors exhibit particularly high degrees of charge transfer that are established by X-ray crystallography coupled to the infrared spectroscopic analysis of the N-O stretching frequencies. Thus the N-O bond distance undergoes a dramatic lengthening from 0.95 ° in the simple salt NO+SbCl6− to 1.12 ° in the hexamethylbenzene (HMB) complex. Such a bond elongation of the nitrosonium acceptor is equivalent to that extant in nitric oxide (1.15 °), and it is accompanied by a corresponding change of the aromatic donor in the ground state of the EDA complex to that of the cation radical (HMB+), as deduced from the changes in the l3C NMR and the IR spectra. The same structural and spectroscopic analysis of the other NO+ complexes reveals a graded series of the EDA complexes in which the degree of charge transfer (Z) varies linearly with the donor strength as measured by the ionization potential of the arene (ArH). The increase of Z from benzene (0.52) to hexamethylbenzene (0.97) in the charge-transfer complex tracks their increasing proclivity to undergo electron transfer and afford arene cation radicals (ArH+) as reactive intermediates. A general mechanistic formulation based on electron transfer from the charge-transfer complex is developed, in which the facility of the followup reactions (such as fragmentation, cycloreversion, rearrangement, ion-pair annihilation, etc.) of the labile ArH+ is critical. When the electron transfer is reversible, this 1-electron mechanism is shown not to be readily distinguished from the more conventional electrophilic (2-electron) pathways.",
author = "Eunkyoung Kim and Kochi, {J. K.}",
year = "1991",
month = "6",
day = "1",
doi = "10.1021/ja00013a036",
language = "English",
volume = "113",
pages = "4962--4974",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "13",

}

Charge-Transfer Structures of Aromatic EDA Complexes Leading to Electron Transfer with the Electrophilic Nitrosonium Cation. / Kim, Eunkyoung; Kochi, J. K.

In: Journal of the American Chemical Society, Vol. 113, No. 13, 01.06.1991, p. 4962-4974.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Charge-Transfer Structures of Aromatic EDA Complexes Leading to Electron Transfer with the Electrophilic Nitrosonium Cation

AU - Kim, Eunkyoung

AU - Kochi, J. K.

PY - 1991/6/1

Y1 - 1991/6/1

N2 - Benzene and hexamethylbenzene partake in the rapid formation of unique electron donor-acceptor (EDA) complexes with the nitrosonium cation, as reflected in the association constants that vary markedly from K = 0.5 to 31000 M−1, respectively. The 1:1 EDA complexes of electron-rich arene donors exhibit particularly high degrees of charge transfer that are established by X-ray crystallography coupled to the infrared spectroscopic analysis of the N-O stretching frequencies. Thus the N-O bond distance undergoes a dramatic lengthening from 0.95 ° in the simple salt NO+SbCl6− to 1.12 ° in the hexamethylbenzene (HMB) complex. Such a bond elongation of the nitrosonium acceptor is equivalent to that extant in nitric oxide (1.15 °), and it is accompanied by a corresponding change of the aromatic donor in the ground state of the EDA complex to that of the cation radical (HMB+), as deduced from the changes in the l3C NMR and the IR spectra. The same structural and spectroscopic analysis of the other NO+ complexes reveals a graded series of the EDA complexes in which the degree of charge transfer (Z) varies linearly with the donor strength as measured by the ionization potential of the arene (ArH). The increase of Z from benzene (0.52) to hexamethylbenzene (0.97) in the charge-transfer complex tracks their increasing proclivity to undergo electron transfer and afford arene cation radicals (ArH+) as reactive intermediates. A general mechanistic formulation based on electron transfer from the charge-transfer complex is developed, in which the facility of the followup reactions (such as fragmentation, cycloreversion, rearrangement, ion-pair annihilation, etc.) of the labile ArH+ is critical. When the electron transfer is reversible, this 1-electron mechanism is shown not to be readily distinguished from the more conventional electrophilic (2-electron) pathways.

AB - Benzene and hexamethylbenzene partake in the rapid formation of unique electron donor-acceptor (EDA) complexes with the nitrosonium cation, as reflected in the association constants that vary markedly from K = 0.5 to 31000 M−1, respectively. The 1:1 EDA complexes of electron-rich arene donors exhibit particularly high degrees of charge transfer that are established by X-ray crystallography coupled to the infrared spectroscopic analysis of the N-O stretching frequencies. Thus the N-O bond distance undergoes a dramatic lengthening from 0.95 ° in the simple salt NO+SbCl6− to 1.12 ° in the hexamethylbenzene (HMB) complex. Such a bond elongation of the nitrosonium acceptor is equivalent to that extant in nitric oxide (1.15 °), and it is accompanied by a corresponding change of the aromatic donor in the ground state of the EDA complex to that of the cation radical (HMB+), as deduced from the changes in the l3C NMR and the IR spectra. The same structural and spectroscopic analysis of the other NO+ complexes reveals a graded series of the EDA complexes in which the degree of charge transfer (Z) varies linearly with the donor strength as measured by the ionization potential of the arene (ArH). The increase of Z from benzene (0.52) to hexamethylbenzene (0.97) in the charge-transfer complex tracks their increasing proclivity to undergo electron transfer and afford arene cation radicals (ArH+) as reactive intermediates. A general mechanistic formulation based on electron transfer from the charge-transfer complex is developed, in which the facility of the followup reactions (such as fragmentation, cycloreversion, rearrangement, ion-pair annihilation, etc.) of the labile ArH+ is critical. When the electron transfer is reversible, this 1-electron mechanism is shown not to be readily distinguished from the more conventional electrophilic (2-electron) pathways.

UR - http://www.scopus.com/inward/record.url?scp=0001111031&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0001111031&partnerID=8YFLogxK

U2 - 10.1021/ja00013a036

DO - 10.1021/ja00013a036

M3 - Article

AN - SCOPUS:0001111031

VL - 113

SP - 4962

EP - 4974

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 13

ER -