Mechanistic aspects of the oxidative and reductive fragmentation of N-nitrosoamines: a new method for generating nitrenium cations, amide anions, and aminyl radicals.
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).
Piech
Krzysztof
K
Department of Chemistry, University of Fribourg, CH-1700 Fribourg, Switzerland.
Bally
Thomas
T
Sikora
Adam
A
Marcinek
Andrzej
A
D000577:Amides / Q000737:chemistry*; D000838:Anions; D002412:Cations; D005609:Free Radicals / Q000737:chemistry; D008958:Models, Molecular; D009569:Nitric Oxide / Q000737:chemistry*; D020030:Nitric Oxide Donors / Q000737:chemistry*; D009602:Nitrosamines / Q000737:chemistry*; D010084:Oxidation-Reduction; D010879:Piperazines / Q000737:chemistry; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared
D000577:Amides; D000838:Anions; D002412:Cations; D005609:Free Radicals; D020030:Nitric Oxide Donors; D009602:Nitrosamines; D010879:Piperazines; D009569:Nitric Oxide; C023649:N-nitrosodiphenylamine; C007306:triethylenediamine