Synthesis and structural studies of two pyridine-armed reinforced cyclen chelators and their transition metal complexes

Abstract

Two novel pyridine pendant-armed macrocycles structurally reinforced by an ethyl bridge, either between adjacent nitrogens (for side-bridged) or non-adjacent nitrogens (for cross-bridged), have been synthesized and complexed with a range of transition metal ions (Co2+, Ni2+, Cu2+ and Zn2+). X-ray crystal structures of selected cross-bridged complexes were obtained which showed the characteristic cis-V configuration with potential labile cis binding sites. The complexes have been characterized by their electronic spectra and magnetic moments, which show the expected high spin divalent metal complex in most cases. Exceptions are the nickel side-bridged complex, which shows a mixture of high-spin and low spin, and the cobalt cross-bridged complex which has oxidized to cobalt(III). Cyclic voltammetry in acetonitrile was carried out to assess the potential future use of these complexes in oxidation catalysis. Selected complexes offer significant catalytic potential enhanced by the addition of the pyridyl arm to a reinforced cyclen backbone.

Bis-Argentivorous Molecules Bridged by Phenyl and 4,4′-Biphenyl Groups: Structural and Dynamic Behavior of Silver Complexes

“…The introduction of side-arm substituents on cyclen can increase the stability for complexation with various metal cations, lanthanide ions, and transition-metal ions through cooperation between cyclen and side arm. − Especially, the lanthanide complexes have been used in several areas such as contrast agents in magnetic resonance imaging (MRI), − the labeling of biomolecules, − and luminescence probes. − For example, the Gd­(III) complexes of tetra-armed cyclen, known as DOTA (dodecanetetraacetic acid), have been studied in detail because of their importance as MRI contrast agents . The key roles in MRI applications are played by the diastereoisomers of lanthanoid complexes.…”

Acetate as a model for aspartate-based CXCR4 chemokine receptor binding of cobalt and nickel complexes of cross-bridged tetraazamacrocycles

“…1) imparts rigidity and kinetic stability to their transition metal complexes. 1 For this reason, these complexes have been utilised in applications where complex stability is paramount, such as aqueous oxidation catalysis [2][3][4][5][6][7][8][9][10][11] and medical imaging. 12,13 Another important property of these ligands is that the short cross-bridge restricts the configuration of the complex to a folded, cis geometry where the macrocycle takes up axial and cis-equatorial positions of octahedral, 4 square-pyramidal, 14 or trigonal bipyramidal 15 coordination geometries (Fig.…”

Increase of Direct C–C Coupling Reaction Yield by Identifying Structural and Electronic Properties of High-Spin Iron Tetra-azamacrocyclic Complexes

“…Tetra-azamacrocycles used to produce high-spin iron catalysts described herein and comparison of structures. ,,− …”