A Dinucleating Ligand System with Varying Terminal Donors to Mimic Diiron Active Sites

Abstract

To mimic dinuclear active sites of metalloproteins, we have developed a dinucleating ligand system consisting of two tetradentate tripodal ligand compartments with varying terminal donors (carboxylates, phenolates, and pyridines). These ligands provide access to a series of μ-oxo-bridged diferric complexes. The spectroscopic study allows to investigate the molecular structures even in solution, e. g. depending on protonation/deprotonation of coordinated OH− and H2O ligands or to observe a reversible pH-dependent carboxylate-shift between terminal and bridging binding mode. The electrochemical behavior is strongly influenced by the exogenous ligands, e. g. OH− facilitates oxidation to FeIV by 690 mV relative to Cl−. Using the terminal carboxylates and a {FeIII(μ-O)2FeIII} core even allows oxidation with O2 to a high-valent species with FeIV (S=2). The implications of this study for further generation of high-valent or peroxo species and their utilization in catalysis is discussed.