AZODIOXIDE RADICAL CATIONS

This report provides the first examples of solution-stable azodioxide radical cations and describes their direct spectroscopic observation a nd, in one case, their thermal chemistry. The formal oxidation potenti als, Eo', for N,N-dioxo-2,3-diazabicyclo[2.2.2]oct-2-ene (3), N,N'-di oxo-2,3-diazabicyclo[2.2.1]hept-2-ene (4), and N,N-dioxo-1,1'-azobis(n orbornane) (5) are 1.65, 1.68, and 1.54 V vs SCE, respectively. ESR sp ectroscopy shows the intermediate cations to be pi radicals. Radical c ation 5(.+) (red, lambda(m), 510 nm) has a five-line ESR spectrum of a (2N) 1.1 G, while 3(.+) (bronze) has a nine-line ESR spectrum simulate d as a(4H) 0.86 and a(2N) 1.22 G. Both 3(.+) and 5(.+) decay in second s to minutes at room temperature. Thermal decomposition of 5(.+) resul ts in C,N and N,N bond cleavage, yielding 1-norbornyl cation (trapped by solvent) and NO+ (trapped in low yield by the oxidant under chemica l oxidation conditions). Two viable mechanisms are presented for 5(.+) 's thermal decay, both of which invoke nitrosoalkane monomer 5m as an intermediate. In a related study, oxidation of nitrosoalkane 2m is fou nd to mediate its facile denitrosation. This work affords the first ex amples of electron-transfer-mediated C,N band cleavage of azodioxides and of nitrosoalkanes. Substantial bond weakening is shown to accompan y electron loss from these substrates. For 5, pi oxidation leads ultim ately to a C,N bond activation.