Mechanistic aspects of the oxidative and reductive fragmentation of n-nitrosoamines: a new method for generating nitrenium cations, amide anions, and aminyl radicals

Piech, Krzysztof; Bally, Thomas; Sikora, Adam; Marcinek, Andrzej

doi:10.1021/ja066855e

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Journal article

Mechanistic aspects of the oxidative and reductive fragmentation of n-nitrosoamines: a new method for generating nitrenium cations, amide anions, and aminyl radicals

Piech, Krzysztof Department of Chemistry, University of Fribourg, Switzerland
Bally, Thomas Department of Chemistry, University of Fribourg, Switzerland
Sikora, Adam Institute of Applied Radiation Chemistry, Technical University of Lodz, Poland
Marcinek, Andrzej Institute of Applied Radiation Chemistry, Technical University of Lodz, Poland

01.03.2007

Published in:

Journal of the American Chemical Society. - 2007, vol. 129, no. 11, p. 3211 -3217

English A new method for investigating the mechanisms of nitric oxide release from NO donors under oxidative and reductive conditions is presented. Based on the fragmentation of N-nitrosoamines, it allows generation and spectroscopic characterization of nitrenium cations, amide anions, and aminyl radicals. X-irradiation of N-nitroso-N,N-diphenylamine 1 in Ar matrices at 10 K is found to yield the corresponding radical ions, which apparently undergo spontaneous loss of NO^° under the conditions of this experiment (1^°⁺ seems to survive partially intact, but not 1^°⁻). One-electron reduction or oxidation of 1 is observed upon doping of the Ar matrix with DABCO, an efficient hole scavenger, or CH₂Cl₂, an electron scavenger, respectively. The resulting diphenylnitrenium cation, 2⁺, and the diphenylamide anion, 2⁻, were characterized by their full UV-vis and mid-IR spectra. The best spectra of 2⁺ and 2⁻ were obtained if 1 was homolytically photodissociated to diphenylaminyl radical 2^° and NO^° prior to ionization. 2⁺ and 2⁻ are bleached on irradiation at <340 nm to form 2^° or, in part, 1. DFT and CCSD quantum chemical calculations predict that the dissociation of 1^°⁺ and 1^°⁻ is slightly endothermic, a tendency which is partially reversed if one allows for complexation of the resulting 2⁺ (and, presumably, 2⁻) with NO^°. The method described in this work should prove generally applicable to the generation and study of nitrenium cations and amide anions R₂N^+/- under matrix and ambient conditions (i.e., in solution).

Faculty

Faculté des sciences et de médecine

Department

Département de Chimie

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