Influence of Annulation on the Electron Spin within the 1,2,3-Triazole Ring in Annulenotriazole Anion Radicals.

Abstract

The low temperature (-100 °C) single electron reduction of N1-phenylbenzotriazole in liquid ammonia, and the room temperature reduction of N1-phenylcyclooctatetraenotriazole in hexamethylphosphoramide, yields stable solutions of both anion radicals, which were studied via EPR spectroscopy. The amount of electron spin localized within the triazole ring, and how spin is distributed within this ring, is greatly influenced by the size of the annulene ring attached. UB3LYP/6-31++G(d,p) geometry optimizations using DFT methods were carried out for both anion radicals, and the calculated coupling constants (and electron spin densities) are in good agreement with the EPR spectroscopic results. Both theory and experiment show that much of the unpaired electron spin in the N1-phenylbenzotriazole anion radical is delocalized over the entire π system of benzotriazole ring including the phenyl ring attached, but that a significant percentage of total spin is found to reside within triazole ring with much of it located on the second nitrogen (N2). With the N1-phenylcyclooctatetraenotriazole anion radical, the majority of spin is localized over the π system of the COT ring, however a relatively small amount of total spin, found within the triazole moiety, is largely concentrated on two of the nitrogens (N1 and N3) within the ring.