36479-80-8Relevant articles and documents
Azodioxide radical cations
Greer, Melinda L.,Sarker, Haripada,Mendicino, Maria E.,Blackstock, Silas C.
, p. 10460 - 10467 (2007/10/03)
This report provides the first examples of solution-stable azodioxide radical cations and describes their direct spectroscopic observation and, in one case, their thermal chemistry. The formal oxidation potentials, Eo′, for N,N′-dioxo-2,3-diazabicyclo[2.2.2]oct-2-ene (3), N,N′-dioxo-2,3-diazabicyclo[2.2.1]hept-2-ene (4), and N,N′-dioxo-1,1′-azobis(norbornane) (5) are 1.65, 1.68, and 1.54 V vs SCE, respectively. ESR spectroscopy shows the intermediate cations to be π radicals. Radical cation 5?+ (red, λm 510 nm) has a five-line ESR spectrum of a(2N) 1.1 G, while 3?+ (bronze) has a nine-line ESR spectrum simulated as a(4H) 0.86 and a(2N) 1.22 G. Both 3?+ and 5?+ decay in seconds to minutes at room temperature. Thermal decomposition of 5?+ results 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 chemical 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 found to mediate its facile denitrosation. This work affords the first examples of electron-transfer-mediated C,N bond cleavage of azodioxides and of nitrosoalkanes. Substantial bond weakening is shown to accompany electron loss from these substrates. For 5, π oxidation leads ultimately to σ C,N bond activation.
