Dediazoniation of Arenediazonium Ions in Homogeneous Solution. Part IX. Spectral Evidence for a Homolytic Mechanism Involving Pyridine Complexes

The mechanism of dediazoniation of arenediazonium tetrafluoroborates in 2,2,2-trifluoroethanol (TFE) is strongly dependent on the concentration of added pyridine. The added base complexes with the diazonium ion and diverts it to a homolytic pathway. Complex formation is indicated by the disappearance of the documentclass{article}pagestyle{empty}begin{document}$raise1pthbox{---} mathop {rm N}limits^ oplus equiv {rm N}raise1pthbox{---}$end{document} stretching vibration and appearance of a new band at about 1640–1690 cm^?1 ascribed to the documentclass{article}pagestyle{empty}begin{document}$raise1pthbox{---} {rm N}raise1pthbox{=kern-3.45pt=} {rm N}raise1pthbox{---} mathop {rm N}limits^ oplus {rm C}_5 {rm H}_5$end{document} system. UV. and NMR. results support this conclusion. Chemically induced dynamic nuclear polarization (CIDNP) experiments clearly implicate a radical-pair as an important intermediate in the decomposition of these complexes.