Synthesis and Characterization of a Series of Thiol‐Derivatized Porphyrins and Electrocatalytic Reduction of Dioxygen by Cobalt(II)‐tetra‐[p‐(mercaptoprophyloxy)‐phenyl] Porphyrin (CoTMPP) on a Gold Support, Self‐Assembled Monolayers (SAMs)

Abstract

A series of thiol‐derivatized porphyrins with one to four [p‐(3‐mercaptopropyloxy)‐phenyl] groups appended to the meso‐position of the porphyrins, have been synthesized and shown to form molecular monolayers via irreversible chemical adsorption on the surface of gold via S‐Au linkage to form a highly ordered surface with fewer defects and exhibit a high degree of orientation, molecular ordering, packing density and thus as new chemically modified electrodes to study their electrochemical properties. Electrochemical surface coverage determinations, although not conclusive, suggested near monolayer coverage with preferential binding of the porphyrin ring perpendicular or coplanar to the gold surface. With post‐assembly insertion of Cobalt(II) into tetra‐[p‐(mercaptoprophyloxy)‐phenyl] porphyrin (H2TMPP) monolayers on gold electrode, molecular films of CoTMPP reduce dioxygen at potentials consistent with two‐electron reduction to hydrogen peroxide and a lower limit to the rate constant (k) for the reaction of dioxygen is 4.03×104 M−l s−l.