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^I complexes bearing N-hexadentate macrocyclic dinucleating ligands and for their corresponding peroxo species (1c−8c) generated by their interaction with molecular O₂. For complexes 1c−7c, 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 8c, the most favored structure is the trans-1,2-peroxodicopper(II) because of the para substitution and the steric encumbrance produced by the methylation of the N atoms. Cu^II complexes 4e, 5e, and 8e have been obtained by O₂ oxidation of their corresponding Cu^I 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^II₂ structures:  (a) For 4e, the Cu^II centers are bridged by a phenolate group and an external hydroxide ligand. The phenolate group is generated from the evolution of 4c via intramolecular arene hydroxylation. (b) For 5e, the two Cu^II centers are bridged by two hydroxide ligands. (c) For the 8e case, the Cu^II centers are ligated to terminally bound hydroxide ligands, rare because of its tendency to bridge. The evolution of complexes 1c−8c 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 J = −482.0 cm^-1 (g = 2.30; ρ = 0.032; R = 5.6 × 10^-3) for 4e; (b) AF coupling with J = −286.3 cm^-1 (g = 2.07; ρ = 0.064; R = 2.6 × 10^-3) for 5e; (c) an uncoupled Cu^II₂ complex for 8e.