Investigation on the Reactivity of Copper(I) and Copper(II) Complexes Supported by Triethylenetetramine Ligands Toward Dioxygen and Peroxides

Abstract

Copper enzymes efficiently promote dioxygen reduction and catalyze the oxidation of small molecules. As a result, significant efforts have been directed toward the development of synthetic model systems that mimic the active sites of metalloproteins. Inspired by the efficiency of copper proteins and aiming to gain a deeper understanding of enzymatic processes involving copper-dioxygen adducts, this work focuses on the synthesis of bioinspired copper complexes featuring tetradentate tripodal ligands and on the investigation of the factors governing their stability and reactivity toward external substrates. The first part of this research focuses on the investigation of the unusual stability of a copper(II)−(end-on)superoxido (SE) complex observed under atom transfer radical polymerization (ATRP) conditions. A mechanistic study was performed to investigate the persistence of this species under ambient conditions, focusing on the roles of the ligand and the solvent. The detection of the SE species for several hours after oxygenation was attributed to the establishment of a catalytic cycle that enables the accumulation of both the SE intermediate and the dicopper(II)−(end-on)peroxido (PS) complex. The second part of this research investigates the formation of SE, copper(II)–hydroperoxido (PH), and copper(II)–alkylperoxido (PR) complexes supported by new tren-based ligand systems and explores their reactivity. First, the reaction of copper(I) and copper(II) species toward dioxygen, hydrogen peroxide, and cumene hydroperoxide was evaluated. The reaction between the copper(I) precursors and dioxygen was monitored using stopped-flow techniques, and the conversion from SE to PH species could be observed. The reactivity of PR and PH species toward various substrates was then examined, demonstrating their nucleophilic reactivity.