Synthesis, structural studies, and oxidation catalysis of the manganese(II), iron(II), and copper(II) complexes of a 2-pyridylmethyl pendant armed side-bridged cyclam

Abstract

The first 2-pyridylmethyl pendant armed structurally reinforced cyclam ligand has been synthesized and successfully complexed to Mn2+, Fe2+, and Cu2+ cations. X-ray crystal structures were obtained for the diprotonated ligand and its Cu2+ complex demonstrating pentadentate binding of the ligand with trans-II configuration of the side-bridged cyclam ring, leaving a potential labile binding site cis to the pyridine donor for interaction of the complex with oxidants and/or substrates. The electronic properties of these complexes were determined by means of solid state magnetic moment, with a low value of μ=3.10μB for the Fe2+ complex suggesting that it has a trigonal bipyramidal coordination geometry, matching the crystal structure of the Cu2+ complex, while the μ=5.52μB value for the Mn2+ complex suggests that it is high spin octahedral. Cyclic voltammetry in acetonitrile revealed reversible redox processes in all three complexes, suggesting that catalytic reactivity involving electron transfer processes are possible for these complexes. Screening for oxidation catalysis using hydrogen peroxide as the terminal oxidant identified the Fe2+ complex as the oxidation catalysts most worthy of continued development.