Synthesis, structural studies, kinetic stability, and oxidation catalysis of the late first row transition metal complexes of 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane†
Synthetic details for 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.5.2]pentadecane, the dimethyl ethylene cross-bridged homocyclen ligand are presented for the first time. Its novel Mn2+, Fe2+, Mn3+, and Fe3+ complexes have been synthesized and characterized. X-ray crystal structures were obtained for both manganese complexes, along with five additional Co3+, Cu2+, and Zn2+ structures, the first structural characterization of complexes of this ligand. Each complex has the cis-V configuration of the cross-bridged macrocycle ring, leaving cis labile binding sites for interaction of the complex with oxidants and/or substrates. The copper(II) complex kinetic stability in 5 M HCl and at elevated temperatures was determined and compared to related complexes in the literature. The electronic properties of the manganese and iron complexes were evaluated using solid state magnetic moment determination and acetonitrile solution electronic spectroscopy, revealing high spin metal complexes in all cases. Cyclic voltammetry in acetonitrile of the divalent iron and manganese complexes revealed reversible redox processes, suggesting catalytic reactivity involving electron transfer processes are possible for both complexes. Screening of the Mn2+ and Fe2+ complexes for oxidation catalysis using hydrogen peroxide as the terminal oxidant showed both complexes are worthy of continued development.
- This article is part of the themed collection: Earth Abundant Element Compounds in Homogeneous Catalysis