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Although copper‐catalyzed organic transformations are prevalent, insights into the interactions of phenols with simple copper(II) salts are not well understood. In contrast, inspired by the oxygenase‐type modifications of the phenolic substrates, the reactions of substituted phenols with metastable copper–oxygen intermediates are well documented. The present report sheds light on the reactions of substituted phenols with benchtop stable CuCl₂salt and the role of a common base like triethylamine. Moreover, the reactions of substituted phenols with CuCl₂in the presence of weakly coordinating tripodalN‐nitrosated ligandL^3NOhave been illustrated, while a closely related tripodal copper(II) complexL^3HCuCl₂(2) of the corresponding non‐nitrosated ligandL^3Hdoes not react with the phenolic substrates. Phenol reactions with CuCl₂in the presence of theL^3NOligand enable in depth mechanistic investigation, thereby illustrating a bimolecular rate law with ΔH^‡= 15.13 kcal mol⁻¹, ΔS^‡ = −9.6 eu, and kinetic isotope effectk₂(ArOH)/k₂(ArOD) in the range of 1.35–1.43. Thus, these findings suggest that simple copper(II) salts like CuCl₂are capable of facilitating a proton‐coupled electron transfer (PCET) pathway. 

Abstract Nitrous acid (HONO) plays pivotal roles in various metal‐free as well as metal‐mediated routes relevant to biogeochemistry, atmospheric chemistry, and mammalian physiology. While the metastable nature of HONO hinders the detailed investigations into its reactivity at a transition metal site, this report herein utilizes a heteroditopic copper(II) cryptate [oC]Cu^IIfeaturing a proton‐responsive second‐coordination‐sphere located at a suitable distance from a [Cu^II](ONO) core, thereby enabling isolation of a [Cu^II](κ¹‐ONO⋅⋅⋅H⁺) complex (2H‐NO₂). A set of complementary analytical studies (UV‐vis,¹⁴N/¹⁵N FTIR,¹⁵N NMR, HRMS, EPR, and CHN) on2H‐NO₂and its¹⁵N‐isotopomer (2H‐¹⁵NO₂) reveals the formulation of2H‐NO₂as {[oCH]Cu^II(κ¹‐ONO)}(ClO₄)₂. Non‐covalent interaction index (NCI) based on reduced density gradient (RDG) analysis on {[oCH]Cu^II(κ¹‐ONO)}²⁺discloses a H‐bonding interaction between the apical 3° ammonium site and the nitrite anion bound to the copper(II) site. The FTIR spectra of [Cu^II](κ¹‐ONO⋅⋅⋅H⁺) species (2H‐NO₂) shows a shift of ammonium NH vibrational feature to a lower wavenumber due to the H‐bonding interaction with nitrite. The reactivity profile of [Cu^II](κ¹‐ONO⋅⋅⋅H⁺) species (2H‐NO₂) towards anaerobic nitration of substituted phenol (2,4‐DTBP) is distinctly different relative to that of the closely related tripodal [Cu^II]‐nitrite complexes (1‐NO₂/3‐NO₂/4‐NO₂).