ETC catalysis

Other applications of PVA are in areas of water and wastewater treatment (extraction, ultra-filtration, ion-exchange materials, etc.), catalysis, separation, etc. 

We first studied group 4 metals (titanium, zirconium and hafnium) supported on a silica dehydroxylated especially at 700 °C (Table 3.8). Following the laboratory-developed strategy, surface-species have been well-characterized by classical techniques (IR, solid-state NMR gas evolvement, reactivity, etc.). Catalysis results show that titanium is the most active even if its activity is far less than that of homogeneous catalysts. In addition, an important amount of metal was lost by lixiviation even if this phenomenon seemed to stop after a certain time. 

All these mechanisms are non-redox in nature, as is easily found by consideration of the oxidation states of the carbon centers involved. They are furthermore chain reactions, initiated by electron transfer, and the term electron-transfer chain catalysis (ETC catalysis) is therefore appropriate (Alder, 1980). Another term is the DAISET (Double Activation Induced by Single Electron Transfer) concept, recently introduced by Chanon and Tobe (1981). The DAISET (ETC) concept is applicable to inorganic mechanisms too. 

The principle of ETC catalysis consists in carrying out the reaction at a kineti-cally labile redox state of the reactant when the ground state is not enough reactive. 

A rare redox reaction carried out by ETC catalysis is the disproportionation of bimetallic metal carbonyl complexes such as [MoCp(CO)3]2 containing a metal-metal bond, in the presence of a two-electron donor such as PMc3. In this typical example, the reaction leads to the ion pair [Mo Cp(CO)2(PMe3)2][Mo°Cp(CO)2]. The photolysis of the dimer gives the 17-electron iron radical [Mo Cp(CO)3] re-... 

Many phosphane-substituted transition-metal clusters have been synthesized from late transition-metal carbonyl clusters and the appropriate phosphane using reductive ETC catalysis with reductive initiation [318-333]. Indeed such an initiation provides an exergonic cross electron-transfer propagation step. Most syntheses were carried out using a cathodic initiation or sodium benzophenone radical anion. The method was successful because it turned out that the first substitution of a carbonyl by a phosphane proceeds with high yield and coulombic efficiency in homoleptic metal carbonyl clusters and some others. 

Figure 1. Yields of the ETC catalysis product [FeCp(CO)( / -dtc)] and stoichiometrically oxidized complex [FeCp(CO)( / -dtc)][PF6 l (circles) as a function of the amount (%) of [FeCp2][PFg ] added to the starting complex [FeCp(CO)2(7 -dtc)J (see Scheme 37).

Coupling oxidative ETC catalysis using ferrocenium cation with organometallic catalysis polymerization of terminal alkynes... 

Besides ETC catalysis, atom-transfer chain (ATC) catalysis has been reviewed [2]. The initiation involves radicals and the redox propagation step exchanges an... 

Electrocatalysis, also named lectron-7ransfer-(2hain (ETC) catalysis, whereby a reaction (mostly of non-redox type) is catalyzed by an electron (reduction) or by an electron hole (oxidation). Organotransition-metal complexes can carry an electron or an electron hole and, if they achieve this function without decomposition, they are electron-reservoir complexes [6]. 

Most other inorganic reactions have been carried out using ETC catalysis isomerization of octahedral complexes [39 1], disproportionation [42], metal-metal bond cleavage and formation [43, 44], CO extrusion in formyl complexes [11]. Although many studies involve electrochemical initiation, the use of a chemical oxidant is also often shown to work. It is possible to use a photoexcited state as the initiator given its enhanced redox power [45]. 

The mixed-ligand complexes [M(CO)x(PR3)7] with M = Cr, Mn, Mo, W were prepared by CO or ligand substitution by electron transfer chain catalysis (ETC catalysis),47- 9 such as ... 

For at least the first half of the 21st century the world will continue to rely heavily on petroleum and coal as fuels and as hydrocarbon sources for use in making polymers, etc. Improved versions of existing catalysts, as well as new catalysts/processes, will be vital in making an orderly transition from reliance on nonrenewable resources. Included in this will be the continued development of practicable fuel cell technology and processes for synthesizing clean fuels from coal, tar sands, etc. Catalysis will play a role in the shift toward increased use of renewable/recycled materials and in efforts to minimize air pollution. Catalysts that mimic... 

Here, we have only emphasized types of dendrimer catalysis involving electron transfer (redox catalysis and electron transfer chain (ETC) catalysis). Other types of dendrimer catalysis are reviewed elsewhere.6,7... 

Reviews on ETC catalysis in transition-metal chemistry D. Astruc, Angew. Chem. Int. Ed. Engl., 27, 643 (1988) D. Astruc, Electron Transfer and Radical Processes in Transition-metal Chemistry, VCH, New York, 1995, Chapter 6. 

Coupling ETC Catalysis with Organometallic Catalysis Carbenic Polymerization of Terminal Alkvnes. 

An early electrochemical study of the ETC catalysis of ligand substitution in metal carbonyls is still one of the most thorough. In this work, Kochi et al. studied the oxidative catalysis of ligand substitution in manganese cyclo-pentadienyl complexes. A typical reaction was the ETC reaction for triph-enylphosphine substitution ... 

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