Abstract
A macrocyclic
ligand (L
4–
) comprising two pyridine(dicarboxamide)
donors was used to target reactive copper species relevant to proposed
intermediates in catalytic hydrocarbon oxidations by particulate methane
monooxygenase and heterogeneous zeolite systems. Treatment of LH
4
with base and Cu(OAc)
2
·H
2
O yielded
(Me
4
N)
2
[L
2
Cu
4
(μ
4
-O)] (
1
) or (Me
4
N)[LCu
2
(μ-OH)] (
2
), depending on conditions. Complex
2
was found to undergo two reversible 1-electron oxidations
via cyclic voltammetry and low-temperature chemical reactions. On
the basis of spectroscopy and theory, the oxidation products were
identified as novel hydroxo-bridged mixed-valent Cu(II)Cu(III) and
symmetric Cu(III)
2
species, respectively, that provide
the first precedence for such moieties as oxidation catalysis intermediates.