Phenol Reduces Nitrite to NO at Copper(II): Role of a Proton-Responsive Outer Coordination Sphere in Phenol Oxidation

In the view of physiological significance, the transition-metal-mediated routes for nitrite (NO₂^–) to nitric oxide (NO) conversion and phenol oxidation are of prime importance. Probing the reactivity of substituted phenols toward the nitritocopper­(II) cryptate complex [mC]­Cu­(κ²-O₂N)­(ClO₄) (1a), this report illustrates NO release from nitrite at copper­(II) following a proton-coupled electron transfer (PCET) pathway. Moreover, a different protonated state of 1a with a proton hosted in the outer coordination sphere, [mCH]­Cu­(κ²-O₂N)­(ClO₄)₂ (3), also reacts with substituted phenols via primary electron transfer from the phenol. Intriguingly, the alternative mechanism operative because of the presence of a proton at the remote site in 3 facilitates an unusual anaerobic pathway for phenol nitration.