Evidence for a pi dimer in the electrochemical reduction of 1,3,5-trinitrobenzene: A reversible N-2-fixation system

(Figure Presented) Electrochemical reduction of 1,3,5-trinitrobenzene (1) forms π dimer 2, which evolves to a more stable ω complex. The crystal structure of the NEt4+ salt of 2 shows π-stacked chains of radical anions. Solid 2 or dimeric 2 in solution reacts with N2 to give a dianion in which an azo group links two 1,3,5-trinitrobenzene units (see picture). The azo derivative is reversibly electrochemically oxidized to 1. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.