Faculté des sciences

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

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

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... Plus

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    Summary
    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).