Involvement of a Formally Copper(III) Nitrite Complex in Proton-Coupled Electron Transfer and Nitration of Phenols.

A unique high-valent copper nitrite species, LCuNO 2 , was accessed via the reversible one-electron oxidation of [M][LCuNO 2 ] (M = NBu 4 + or PPN + ). The complex LCuNO 2 reacts with 2,4,6-tri- tert -butylphenol via a typical proton-coupled electron transfer (PCET) to yield LCuTHF and the 2,4,6-tri- tert -butylphenoxyl radical. The reaction between LCuNO 2 and 2,4-di- tert -butylphenol was more complicated. It yielded two products: the coupled bisphenol product expected from a H-atom abstraction and 2,4-di- tert -butyl-6-nitrophenol, the product of an unusual anaerobic nitration. Various mechanisms for the latter transformation were considered.