Synthesis and Characterization of Tricopper(II) Complexes with N6O2-Octadentate Ligands

There are considerable increasing interests of the interaction of redox-active transition metal ions, such as copper, and proradical ligands in metalloenzyme. As in methane oxidation (particulate methane monooxygenase, pMMO) of methanotrophs, it often requires copper for activation of molecular oxygen. The major reaction site has been ascribed to a trinuclear cluster. In order to model the enzyme, a series of tricopper(II) complexes with N6O2-octadentate ligand L which containing six member ring or seven member ring at A site and pyridineamine or imidazoleamine substituents at B site (abbreviated as 6-PyR or 7-PyR or 6-ImR or 7-ImR; see Chart I) from CuII(ClO4)2•6H2O and CuII(BF4)2 has been synthesised. These tricopper(II) complexes have been characterized by UV-Vis absorption spectroscopy, ESI mass spectra, conductivity measurement, electron paramagnetic resonance (ESR), IR spectrum, elemental analysis (EA) as well as Single-crystal X-ray diffractions.
Based on Single-crystal X-ray diffraction, the tricopper(II) complexes were combined with mononuclear and dinuclear copper cofactors in triangular geometry by the octadetate ligands. The mononuclear copper was bonded in a square pyramidal environment with a N2O3-donor and the dinuclear copper were bridged by hydroxide ion. The structure will be compared with the known species with similar configurations. There was a result of Single-crystal X-ray diffraction beyond our expectations, a solution of tricopper(II) complex with octadentate ligand containing six-membering at A site and ethyl pyridineamine substituents at B site was explored to air after a few days a octanuclear copper(II) carbonate species was formed. The Single-crystal X-ray structure of octanuclear copper(II) carbonate complex was established. The structure of the octanuclear copper(II) carbonate species containing two octadentate ligands which were chair form at A site and bridged by hydroxide and carbonate ions.