1,2-Dihydrotriazinyl-N-oxy free radicals.

Triazinyl-N-oxy free radicals, 2-methyl-2,4,6-triphenyl-1,2-dihydro-1,3,5-triazinyl-1-oxy (6a), 2,2,4,6-tetraphenyl-1,2-dihydro-1,3,5-triazinyl-1-oxy (6b), 2,2-dimethyl-4,6-diphenyl-1,2-dihydro-1,3,5-triazinyl-1-oxy (13), and 2,6-dimethyl-2,4-diphenyl-1,2-dihydro-1,3,5-triazinyl-1-oxy (14), in which the unpaired electron is delocalized over three nitrogen atoms, have been prepared and characterized. A method has been devised for introducing an N-oxide function into the triazinyl core. Then, by using a Grignard reagent, substitution α to the N-oxide group was achieved and the resulting 1,2-dihydrotriazine-N-oxide oxidized into the corresponding nitroxide. Solution EPR spectra exhibit hyperfine splitting that confirms spin delocalization over the three nitrogen atoms of the triazinyl ring. They also show that spin delocalization diminishes with increasing distance for the coupling and is largest for nitrogen N1 and weakest for N5. Free radicals 6a and 13 are stable in the solid state and have been characterized by X-ray diffraction, but they tend to gradually degrade in solution. In the solid state, these two free radicals are arranged into antiferromagnetically exchange-coupled pairs, J=-5.2(6) for 6a and -3.7(4) cm(-1) for 13 (H=-2JS(1)S(2)).