Mechanism of O-Atom Transfer from Nitrite: Nitric Oxide Release at Copper(II).

Nitric oxide (NO) is a key signaling molecule in health and disease. While nitrite acts as a reservoir of NO activity, mechanisms for NO release require further understanding. A series of electronically varied β-diketiminatocopper(II) nitrite complexes [CuII](κ2-O2N) react with a range of electronically tuned triarylphosphines PArZ3 that release NO with the formation of O═PArZ3. Second-order rate constants are largest for electron-poor copper(II) nitrite and electron-rich phosphine pairs. Computational analysis reveals a transition-state structure energetically matched with experimentally determined activation barriers. The production of NO follows a pathway that involves nitrite isomerization at CuII from κ2-O2N to κ1-NO2 followed by O-atom transfer (OAT) to form O═PArZ3 and [CuI]-NO that releases NO upon PArZ3 binding at CuI to form [CuI]-PArZ3. These findings illustrate important mechanistic considerations involved in NO formation from nitrite via OAT.