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

•The first 2-pyridylmethyl side-bridge cyclam ligand and its X-ray crystal structure•The first transition metal complex of a 2-pyridylmethyl side-bridge cyclam ligand and its X-ray crystal structure•Screening of Mn2+, Fe2+, and Cu2+ complexes of this new ligand showing promising hydrogen atom abstraction for the Fe2+ complex

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 = 3.10 μB for the Fe2 + complex suggesting that it has a trigonal bipyramidal coordination geometry, matching the crystal structure of the Cu2 + complex, while the μ = 5.52 μB 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.

Graphical abstract2-Pyridylmethyl pendant armed ethylene side-bridged cyclam complexes of copper(II), iron(II), and manganese(II) have been prepared, characterized, and screened for oxidation catalysis.Figure optionsDownload full-size imageDownload as PowerPoint slide