Electron catalysis

The two main conditions (besides the stability of the a radical towards the solvent to observe such an electron catalysis are a sufficient high rate of addition of the nucleophile and the thermodynamic inequality E°ll >E°12 implying a fast displacement of the latter equilibrium to the direction of the formation of the anion radical of 71. 

The concepts of electron-transfer catalysis and so-called hole-catalysis [1] are closely related. It is now generally accepted that many organic reactions that are slow for the neutral reaction system proceed very much more easily in the radical cation. Although hole-catalysis is now well documented experimentally [2], there is surprisingly little mention of the corresponding reductive process, in which a reaction is accelerated by addition of an electron to the reacting system. Although the concept of electron-catalysis is not as well known as hole-catalysis, there are experimental examples of electrocyclic reactions that proceed rapidly in the radical anion, but slowly or not at all in the neutral system [3], For reasons that will be outlined below, we can expect that, in many cases, difficult or forbidden closed-shell reactions will be very much easier if an unpaired electron is introduced into the system by one-electron oxidation or reduction. Thus, if a neutral reaction A - B proceeds slowly or not at all, the radical cation (A" -> B" ) or radical anion (A" B" ) may be facile... 

Let us now extend the concept of hole or electron catalysis to a redox system consisting of the original reaction and an oxidant or reductant, M. We need not specify the nature of M at this stage. If we simplify the reaction system by suming that there is no direct interaction (i.e. complexation or ion-pairing) between the reaction system, A B, and M, we obtain the simple reaction profiles shown in Fig. 1. 

So far, the bonding and surface structure aspects of electrocatalysis have been presented in a somewhat abstract sort of way. In order to make electrocatalysis a little more real, it is helpful to go through an example—that of the catalysis of the evolution of oxygen from alkaline solutions onto substances called perovskites. Such materials are given by the general formula RT03, where R is a rare earth element such as lanthanum, and T is a transition metal such as nickel. In the electron catalysis studied, the lattice of the perovskite crystal was replicated with various transition metals, i.e., Ni, Co, Fe, Mn, and Cr, the R remaining always La. 

Rhodium catalysis is very well developed with respect to its two-electron catalysis [464]. Applications involving radicals are rather rare. Similar to the cobalt-catalyzed processes, the reductive cleavage of endoperoxides 424 proceeds with rhodium(I) catalysts. Hagenbuch and Vogel reported the formation of bicyclic hydroxymethyl enals 425 catalyzed by 3.8 mol% [Rh(CO)2Cl]2 (Fig. 100) [465, 466]. 

Polyoxoanions have a demonstrated utility in a diverse range of applications spanning electronics, catalysis, and biology. The authoritative monograph... 

Many organic polymers are used as active materials with useful applications in demanding fields of electronics, catalysis, biotechnology, and space. As a fundamental... 

The concept of electron catalysis permits new correlations in organic and in inorganic mechanisms. The application to inorganic chemistry is illustrated with reference to substitution at platinum(IV). " ... 

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When two or more kinds of metals are melted together to form a metal alloy, the physical, electronic, mechanical and chemical properties will change considerably. Therefore, nanoparticles of metal alloys are expected to have more fascinating properties in electronics, catalysis and magnetism [21, 22] compared to nanoparticles of single metals. As a result, metal alloy nanoparticles have been the focus of intensive research in recent years [23-25]. 

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