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

Abstract

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 [Cu II ](κ 2 -O 2 N) react with a range of electronically tuned triarylphosphines PAr Z 3 that release NO with the formation of OPAr Z 3 . 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 Cu II from κ 2 -O 2 N to κ 1 -NO 2 followed by O-atom transfer (OAT) to form OPAr Z 3 and [Cu I ]-NO that releases NO upon PAr Z 3 binding at Cu I to form [Cu I ]-PAr Z 3 . These findings illustrate important mechanistic considerations involved in NO formation from nitrite via OAT.

Photolytic or Oxidative Fragmentation of Trityl Diazeniumdiolate (O2N2CPh3–): Evidence for Both C–N and N–N Bond Cleavage

“…It is formed in 63% yield (calculated assuming a maximum of 3 equiv of N 2 O produced; Figure S33). However, we were unable to detect NO in the reaction mixture, according to a two-vial trapping experiment with [T(OMe)PP]Co. 60 Intriguingly, we see no evidence for products derived from N−N bond cleavage in the reaction mixture because both O(CPh 3 ) 2 and N 2 O are evidently derived from C−N bond cleavage. Their formation, along with the absence of NO, 3, and 9-PF, demonstrates that an entirely different mechanism of trityl hyponitrite fragmentation is operative.…”

A Copper(II)‐Nitrite Complex Hydrogen‐Bonded to a Protonated Amine in the Second‐Coordination‐Sphere

“…L‐ascorbic acid has been employed to reduce nitrite to NO and N 2 O at tripodal copper(II) sites [35] . [Cu II ]‐nitrite complexes have been shown to react with Ph 3 P forming NO and Ph 3 PO through oxygen‐atom‐transfer pathway [19,20,36,37] . Electron deficient diketiminato [Cu II ]( κ 2 ‐O 2 N) complexe undergoes facile nucleophilic attack by thiol, alcohol, and amine, thereby resulting in nitrosation of the nucleophiles and [Cu II ]−OH [38] .…”

“…[35] [Cu II ]-nitrite complexes have been shown to react with Ph 3 P forming NO and Ph 3 PO through oxygen-atom-transfer pathway. [19,20,36,37] Electron deficient diketiminato [Cu II ](k 2 -O 2 N) complexe undergoes facile nucleophilic attack by thiol, alcohol, and amine, thereby resulting in nitrosation of the nucleophiles and [Cu II ]À OH. [38] Tricopper(II) nitrite complexes also catalyze nitrite reduction by thiol to afford NO and disulfide.…”

An investigation on catalytic nitrite reduction reaction by bioinspired CuII complexes

“…Recently, a series of β-diketiminato Cu II -nitrito complexes reacted with thiol, and PPh 3 and CNAr also converted nitrite to NO (g) through an oxygen atom transfer reaction. [34][35][36][37] A Cu II complex bearing a proton-responsive outer coordination sphere ligand reported the phenol-mediated reduction which could convert nitrite to NO (g) . 38 These Cu I -nitro and Cu II -nitrito complexes are good bioinspired compounds and allow chemists to understand each step of the nitrite reduction mechanism; however, the catalytic aspects of copper-mediated nitrite reductions are rare, although there are a number of studies on bioinspired electro-catalysts used for nitrite reduction.…”

“…Recently, a series of β-diketiminato Cu II -nitrito complexes reacted with thiol, and PPh 3 and CNAr also converted nitrite to NO (g) through an oxygen atom transfer reaction. 34–37 A Cu II complex bearing a proton-responsive outer coordination sphere ligand reported the phenol-mediated reduction which could convert nitrite to NO (g) . 38…”