Mechanistic Studies of Second Coordination Sphere Interactions in the Dioxygen Activation of a Copper(I) Complex with a N-(2-Ethoxyethanol)-bis(2-picolyl)amine Ligand

While first coordination sphere interactions have been investigated in great detail for the reactivity of copper(I) model complexes with dioxygen, the interactions of the secondary coordination sphere with the bound dioxygen so far remain underexplored. A series of copper(I) complexes with ligands based on N-(2-ethoxyethanol)-bis(2-picolyl)amine (L(O)OH) were synthesized, and the reactivity towards dioxygen was monitored by low-temperature stopped-flow UV/vis spectroscopy. Various “oxygen adduct complexes” were observed, and the influence of the second coordination sphere interactions was analyzed. If the ether moiety or the hydroxy group in L(O)OH is removed/replaced, the formation of a trans-μ-1,2-peroxido dicopper(II) complex or a bis(μ-oxido) dicopper(III) complex is observed. Establishing stronger hydrogen bonding while maintaining the ether moiety leads to hydrogen bond stabilized trans-μ-1,2-peroxido dicopper(II) complexes. Based on these results, we deduced that the copper(I) complex with L(O)OH as ligand reacts with dioxygen first to a hydrogen bond stabilized trans-μ-1,2-peroxido dicopper(II) complex, which rapidly converts to a bis(μ-oxido) dicopper(III) complex.