A novel reactivity descriptor for MN4 molecular catalysts for the oxidation of 2-mercaptoethanol and of thioglycolic acid: The Electrochemical Hardness

This manuscript describes a novel reactivity descriptor for Fe phthalocyanines molecular catalysts confined on the surface of OPG electrodes. The descriptor Δ E °’cat. is the gap in potential between the E °Fe(III)/(II) and E °Fe(II)/(I) redox processes for each FeN4 catalyst. This descriptor, labeled as the electrochemical hardness Δ E °’ cat . Was examined using FeN4 macrocyclic complexes for the electrooxidation of 2-mercaptoethanol (2-ME) and thioglycolic acid TGA. Our findings reveal that the reactivity as log log( j /Γ) E , plotted versus E °Fe(III)/(II) or E °Fe(II)/(I) give two linear correlations. The activity log( j /Γ) E in both cases decreases with the redox potential of each FeN4 catalyst. In contrast log( j /Γ) E , or log ( TOF) E , increase with Δ E °’ cat.. The Fe S binding energy Δ E °’ cat. Correlates linearly with Δ E °’ cat. so the softer the system the greater the binding energy and the lower the catalytic activity. • The “ electrochemical hardness ” as a reactivity descriptor is a new concept only proposed by us. • It has not been tested for other reactions, except oxygen reduction (ORR). • This descriptor is probably universal and probably valid for other reactions. • Electrochemical Hardness correlates linearly with the binding energies of Fe S • This concept agrees with the Chemical Hardness concept proposed by Parr and Pearson • This concept opens new areas of research for many reactions promoted by metal phthalocyanines.