Hydroxo-bridged dicopper(II,III) and -(III,III) complexes: Models for putative intermediates in oxidation catalysis

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. © 2014 American Chemical Society.