Application of 3-Quinolinoyl Picket Porphyrins to the Electroreduction of Dioxygen to Water: Mimicking the Active Site of Cytochromec Oxidase

Abstract

Functional analogues of the so‐called Fea3–CuB active site of cytochrome c oxidase were synthesized to elucidate the mechanism of the reduction of O2 to H2O. The role of each individual structural component, especially the CuB center, for catalytic activity was investigated. These quinolinoyl picket iron porphyrins (see picture) were shown to be efficient catalysts for the 4 e− reduction of dioxygen to water with or without a Cu ion in their distal site, clearly demonstrating that the Cu center is not essential for the catalytic activity.

Oxygen Activation Chemistry of Pacman and Hangman Porphyrin Architectures Based on Xanthene and Dibenzofuran Spacers

“…Finally, the mechanistic cycle clarifies some perplexing observations of synthetic constructs. Several porphyrin templates bearing a distal metal-binding cap exhibit comparable selectivities for the four-proton, four-electron pathway with or without a second redox-active metal ion bound in the distal cap (121,(132)(133)(134) In addition, cofacial Pacman porphyrins containing two cobalt centers (45,123), one cobalt and one Lewis acidic metal (39), or one cobalt and one metal-free subunit (63,64) are all effective catalysts for the direct production of H 2 O from O 2 . The mechanism of Fig.…”

Tripodal and/or picket porphyrins to mimic the cytochrome c oxidase activity

“…From the comparison of the oxygen reduction waves at electrodes coated with 13Fe (Fig. 3, curve a) and its analogue with 1,2-dimethylimidazole as an exogenous base (not depicted) [12], it clearly appears that anchoring a N-base as a potential fifth ligand for the iron does not improve the catalysis of O 2 reduction. In curves a and b (Fig.…”

“…This is the reason why we synthesized a second group of molecules which differs significantly from the first TRENcapped compounds. Indeed, they have an intramolecular nitrogen base attached to the iron porphyrin, the coordination sphere of copper consisting of three quinolinoyl pickets [12]. Obviously, the three aromatic nitrogen pickets should also off-center the two metallic cations tethered at a fixed length; meanwhile the encumbered quinolines should protect the distal side of the porphyrin.…”

“…Three molecules have been synthesized which differ only by N-substitution of the TREN amino functions bearing either a tribenzyl, a tris(4-dimethylamino)benzyl, or a tris(4-nitrobenzyl) group. Since it has been previously demonstrated that a nitrogen base covalently bound to the porphyrin is not critical for the efficiency of the catalyst [12,18], 1,2-dimethylimidazole was simply added as an exogeneous base. The synthesis of the iron five-coordinate complexes and heterobimetallic iron-copper catalysts is depicted in Scheme 3.…”

A Versatile and Convenient Method for the Functionalization of Porphyrins

“…[15] We have reported the synthesis [16] and the electrocatalytic studies of tris-(2-aminoethylamine) (tren) capped porphyrins and quinolinoyl-picket porphyrins. [17] Surprisingly, and in contrast with the bimetallic approach, the iron-only complexes -without an intramolecular fifth ligand -were shown to be more efficient and selective catalysts than the iron-copper ones. [18] However, it seems important to verify that this behaviour can be applied to the iron-only complexes of imidazolyl-picket porphyrins as this crucial information has never been studied.…”