Copper(II) Hexaaza Macrocyclic Binuclear Complexes Obtained from the Reaction of Their Copper(I) Derivates and Molecular Dioxygen

Density functional theory (DFT) calculations have been carried out for a series of Cu<sup>I</sup> complexes bearing N-hexadentate macrocyclic dinucleating ligands and for their corresponding peroxo species (<b>1c</b>−<b>8c</b>) generated by their interaction with molecular O<sub>2</sub>. For complexes <b>1c</b>−<b>7c</b>, it has been found that the side-on peroxodicopper(II) is the favored structure with regard to the bis(μ-oxo)dicopper(III). For those complexes, the singlet state has also been shown to be more stable than the triplet state. In the case of <b>8c</b>, the most favored structure is the <i>trans-</i>1,2-peroxodicopper(II) because of the para substitution and the steric encumbrance produced by the methylation of the N atoms. Cu<sup>II</sup> complexes <b>4e</b>, <b>5e</b>, and <b>8e</b> have been obtained by O<sub>2</sub> oxidation of their corresponding Cu<sup>I</sup> complexes and structurally and magnetically characterized. X-ray single-crystal structures for those complexes have been solved, and they show three completely different types of Cu<sup>II</sup><sub>2</sub> structures:  (a) For <b>4e</b>, the Cu<sup>II</sup> centers are bridged by a phenolate group and an external hydroxide ligand. The phenolate group is generated from the evolution of <b>4c</b> via intramolecular arene hydroxylation. (b) For <b>5e</b>, the two Cu<sup>II</sup> centers are bridged by two hydroxide ligands. (c) For the <b>8e</b> case, the Cu<sup>II</sup> centers are ligated to terminally bound hydroxide ligands, rare because of its tendency to bridge. The evolution of complexes <b>1c</b>−<b>8c</b> toward their oxidized species has also been rationalized by DFT calculations based mainly on their structure and electrophilicity. The structural diversity of the oxidized species is also responsible for a variety of magnetic behavior:  (a) strong antiferromagnetic (AF) coupling with <i>J</i> = −482.0 cm<sup>-1</sup> (<i>g</i> = 2.30; ρ = 0.032; <i>R</i> = 5.6 × 10<sup>-3</sup>) for <b>4e</b>; (b) AF coupling with <i>J</i> = −286.3 cm<sup>-1</sup> (<i>g</i> = 2.07; ρ = 0.064; <i>R</i> = 2.6 × 10<sup>-3</sup>) for <b>5e</b>; (c) an uncoupled Cu<sup>II</sup><sub>2</sub> complex for <b>8e</b>.