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.