Synthesis, structural characterization and binding ability of A2B cobalt(III) corroles with pyridine

Abstract

A series of five A2B type bis-pyridine ligated cobalt complexes Co[(p-NO2Ph)2RCor](py)2, has been synthesized where R belongs to different electron withdrawing or electron donating substituent at meso position for different complexes. The synthesized complexes were fully characterized through 1H NMR, HRMS, UV–Visible and single crystal X-ray Spectroscopy. The effect of meso substituents were studied through NMR spectroscopy. The single crystal X-ray structure was obtained for the p-trifluoromethylphenyl substituents (Co-2) located at C10-meso position and indicated that cobalt corroles exist in Co(III) form. In these compounds, the axial pyridines were observed to be labile, and the complexes were almost entirely dissociated in the five coordinated cobalt corrole monopyridine complexes in dilute solutions such as in dichloromethane. Mono- and bis- pyridine ligation behavior was studied by UV–Visible spectroscopy. These complexes were also examined in different non-aqueous media such as dichloromethane, benzonitrile, and pyridine. The effect of substituent behavior present at meso position was also tested through the Hill equation. This provided the fact that the lower the electron density on corrole macrocycle, more the tendency of the complex to bind the ligands axially as the highest binding constant was found for the Co-1 complex, with more electronegative groups on meso position.