Kinetics of the interaction of some cobalt(II) chelates with air oxygen: mutual equatorial—axial influence of ligands on oxygen activation

• Published in: Journal of molecular catalysis 1991-06, Vol.66 (2), p.239-249
• Main Authors: Strašák, Milan, Kaválek, Jaromír
• Format: Article
• Language: English
• Subjects: 2-diaminoethane; aa=amino acidate; Abbreviations used: EBAA=ethylenebis(amino acidate); an-=amine; BzIm=benzimidazole; dien=diethylenetriamine= N-(2′-aminoethyl)-1; EBA=ethylenebis(α-alaninate); EBABA=ethylenebis(α-aminobutyric acidate); EBG=ethylenebis (glycinate) (=EDDA=ethylenediamine- N; EBPhe=ethylenebis(α-phenylalaninate); Hm=histamine; Im=imidazole; MIL=mutual influence of ligands; N′-bis(2′-aminoethyl)-1; N′-diacetate; trien=triethylenetetramine= N
• ISSN: 0304-5102
• DOI: 10.1016/0304-5102(91)80017-W

Reactions of air oxygen with mixed ligand complexes of cobalt(II) containing a linear tetradentate amino acid derivative L=EBAA and a heterocyclic nitrogen base B are described. Enthalpies and entropies of activation have been determined from the temperature dependency of the rate constant k 1 for the oxygenation reaction CoL(B)+O 2→CoL(B)O 2. Polar and steric effects in the oxygenation have been separated by use of the linear free energy relationship; it was found that steric effects were decisive in the case of equatorial influence, while electronic effects are important in the case of mutual equatorial-axial influence. A degree of the dioxygen ligand activation is interrelated with the stereochemical conditions dictated by the actual equatorial-axial influence. The classic concept of the MIL is extended to intramolecular interligand interactions. A comparison is made of the cobalt(II)-O 2 interaction with the iron(II)- and copper(I)-O 2 systems occurring in the biologically important respiratory proteins.