Geometric Control of Nuclearity in Copper(I)/Dioxygen Chemistry

Copper­(I) complexes supported by a series of N₃-tridentate ligands bearing a rigid cyclic diamine framework such as 1,5-diazacyclooctane (L8, eight-membered ring), 1,4-diazacycloheptane (L7, seven-membered ring), or 1,4-diazacyclohexane (L6, six-membered ring) with a common 2-(2-pyridyl)­ethyl side arm were synthesized and their reactivity toward O₂ were compared. The copper­(I) complex of L8 preferentially provided a mononuclear copper­(II) end-on superoxide complex S as reported previously [Itoh, S., et al. J. Am. Chem. Soc. 2009, 131, 2788–2789], whereas a copper­(I) complex of L7 gave a bis­(μ-oxido)­dicopper­(III) complex O at a low temperature (−85 °C) in acetone. On the other hand, no such active-oxygen complex was detected in the oxygenation reaction of the copper­(I) complex of L6 under the same conditions. In addition, O₂-reactivity of the copper­(I) complex supported by an acyclic version of the tridentate ligand (LA, PyCH₂CH₂N­(CH₃)­CH₂CH₂CH₂N­(CH₃)₂; Py = 2-pyridyl) was examined to obtain a mixture of a (μ–η²:η²-peroxido)­dicopper­(II) complex ^SP and a bis­(μ-oxido)­dicopper­(III) complex O. Careful inspection of the crystal structures of copper­(I) and copper­(II) complexes and the redox potentials of copper­(I) complexes has revealed important geometric effects of the supporting ligands on controlling nuclearity of the generated copper active-oxygen complexes.