Molecular Catalysts for Multielectron Redox Reactions of Small Molecules: The “Cofacial Metallodiporphyrin” Approach

Abstract

Thc role o f metalloenzymes in important biological transformations has attracted incrcasing attention over the past sever-;II decades. Of the many chemical transformations mediated by enzymes, few are a s challenging ;is multielectron redox reactions. Kcccnt studies have revealed ;I partial structiirnl and mechanistic dcscription o f these redox-active metallocn/ymes. but thcrc is much still to be Icarned regarding the mechanisms of substrate transformation. Due to the complexity of the metalloenzyme systems, simplified model systems are employed to mimic structural or functional features of the enzyme. In multielectron redox enzymes, several metals are probably involved in both substrate binding and the subsequent redox reactions. Thus, functional mimics of multielectron redox enzymes might also need two or more metal centers to be efficacious. The roles of multiple metal centers are to 1) increase the substrate's affinity for the catalyst, 2) increase the rate of electron transfer to the bound substrate, 3 ) increase the reactivity of the bound substrate, and 4) inhibit deleterious side reactions. Determining the importance of each factor may help in the development of these catalysts. Cofacial metallodiporphyrins, because of the control they provide over the geometric and electronic properties of the synthetic reaction center, are ideal bimetallic model complexes. The knowledge gained from model studies will help in understanding the mechanisms of metalloenzymes and can be used to design new homogeneous catalysts to effect multielectron transformations.

RETRACTED ARTICLE: Reduction of carbon dioxide to oxalate by a binuclear copper complex

“…Other researchers have used multifunctional ligands to control the spatial position of two metal centres. Some of the best known examples are the cofacial diporphyrins, which are capable of catalyzing multielectron redox processes [22][23][24] . Several research groups have prepared complexes from dipyridyltriazoles (though they lead to relatively short metal-metal distances) 25 ; other binucleating ligands have also been employed 26 .…”

Self-Assembled Molecular Rafts at Liquid|Liquid Interfaces for Four-Electron Oxygen Reduction

“…1,5 The possibility of formation of a stable self-assembled complex [P 4+ /P 4− ] with an appropriate Co−Co distance to perform the four-electron reduction of oxygen was confirmed by DFT calculations. However, only the cofacial dimer geometries were considered, thus the existence of more stable minima with different geometrical arrangements or oligomeration cannot be excluded.…”

“…At this point, we can conclude that P 4+ adsorbs at the interface to carry out oxygen reduction with a selectivity of 50% for the four-electron pathway whereas [P ] toward the four-electron route, the three steps of the mechanism proposed for the four-electron reduction of oxygen by synthetic Pacman cofacial porphyrins must be considered: 1,5,8,50 (i) Oxygen is held in the cavity formed between the two porphyrins. 1,5,8,50 To determine whether in the complex [P 4+ /P…”

Oxygen reduction behavior of RuO2/Ti, IrO2/Ti and IrM (M: Ru, Mo, W, V) Ox/Ti binary oxide electrodes in a sulfuric acid solution

“…The development of catalysts to replace platinum, including oxides [1][2][3], carbides [4,5], and metal complexes [6,7], etc., has widely been examined by many research groups up to the present. Since iridium oxide is a typical material that resists corrosion in acidic solutions and is one of the outstanding electrocatalysts for oxygen evolution, IrO 2 -Ta 2 O 5 /Ti electrodes [8,9] have been used as oxygen-evolving anodes in the industrial electro-plating process, and the IrO 2 -RuO 2 -TiO 2 /Ti ternary oxide electrode is widely used as the Dimensionally Stable Anode (DSA ® ) catalyst-electrode in the electrolysis process for chlorine production in chlor-alkali industries [10].…”