Bis phenylene flattened 13-membered tetraamide macrocyclic ligand (TAML) for square planar cobalt(III)

Abstract

The preparation, characterization, and evaluation of a cobalt(III) complex with 13-membered tetraamide macrocyclic ligand (TAML) is described. This is a square-planar (X-ray) S = 1 paramagnetic (1H NMR) compound, which becomes an S = 0 diamagnetic octahedral species in excess d5-pyridine. Its one-electron oxidation at an electrode is fully reversible with the lowest E1/2 value (0.66 V vs SCE) among all investigated CoIII TAML complexes. The oxidation results in a neutral blue species which is consistent with a CoIII/radical-cation ligand. The ease of oxidation is likely due to the two benzene rings incorporated in the ligand structure (whereas there is just one in many other CoIII TAMLs). The oxidized neutral species are unexpectedly EPR silent, presumably due to the π-stacking aggregation. However, they display eight-line hyperfine patterns in the presence of excess of 4-tert-butylpyridine or 4-tert-butyl isonitrile. The EPR spectra are more consistent with the CoIII/radical-cation ligand formulation rather than with a CoIV complex. Attempts to synthesize a similar vanadium complex under the same conditions as for cobalt using [VVO(OCHMe2)3] were not successful. TAML-free decavanadate was isolated instead.

Synthesis, structural characterization, thermal analysis, DFT, biocidal evaluation and molecular docking studies of amide-based Co(II) complexes

“…S4, a broad signal at 9.07 ppm in the 1 H-NMR spectra of the tetraamide macrocyclic ligands was possibly attributed to the -NH protons (Shakir et al 2017 ; Rahaman and Mruthyunjayaswamy 2014 ). The aromatic ring protons are represented by the multiplets that appear in the range of 6.63–8.14 ppm (Ellis et al 2018 ). The carbons connected to the nitrogen atoms were responsible for the resonance signal at 169.05 ppm, which was suggestive of their possible coordination in the ligands.…”