Metal electrochemical synthesis

Krautler B (1999) B12 electrochemistry and organo-metallic electrochemical synthesis. Qiemistiy and biochemistry of B12. Wiley, New York, pp 315-339... 

Oxygen-Evolving Anode. Research efforts to iacorporate the coated metal anode for oxygen-evolving appHcations such as specialty electrochemical synthesis, electro winning, impressed current, electrodialysis, and metal recovery found only limited appHcations for many years. 

Concern for the conservation of energy and materials maintains high interest in catalytic and electrochemistry. Oxygen in the presence of metal catalysts is used in CUPROUS ION-CATALYZED OXIDATIVE CLEAVAGE OF AROMATIC o-DIAMINES BY OXYGEN (E,Z)-2,4-HEXADIENEDINITRILE and OXIDATION WITH BIS(SALI-CYLIDENE)ETHYLENEDIIMINOCOBALT(II) (SALCOMINE) 2,6-DI-important industrial method, is accomplished in a convenient lab-scale process in ALDEHYDES FROM OLEFINS CYCLOHEXANE-CARBOXALDEHYDE. An effective and useful electrochemical synthesis is illustrated in the procedure 3,3,6,6-TETRAMETHOXY-1,4-CYCLOHEX ADIENE. ... 

In the following, selected results will be presented on the conventional electrochemical synthesis of metal chalcogenide binary and ternary systems, conducted by employing variants of the methods outlined in the previous sections. A brief account of chemical bath deposition principles exemplified will be addressed at the end of this chapter, as being closely related to electrochemical deposition of thin films. 

Chemical and electrochemical techniques have been applied for the dimensionally controlled fabrication of a wide variety of materials, such as metals, semiconductors, and conductive polymers, within glass, oxide, and polymer matrices (e.g., [135-137]). Topologically complex structures like zeolites have been used also as 3D matrices [138, 139]. Quantum dots/wires of metals and semiconductors can be grown electrochemically in matrices bound on an electrode surface or being modified electrodes themselves. In these processes, the chemical stability of the template in the working environment, its electronic properties, the uniformity and minimal diameter of the pores, and the pore density are critical factors. Typical templates used in electrochemical synthesis are as follows ... 

M. Faraday was the first to observe an electrocatalytic process, in 1834, when he discovered that a new compound, ethane, is formed in the electrolysis of alkali metal acetates (this is probably the first example of electrochemical synthesis). This process was later named the Kolbe reaction, as Kolbe discovered in 1849 that this is a general phenomenon for fatty acids (except for formic acid) and their salts at higher concentrations. If these electrolytes are electrolysed with a platinum or irridium anode, oxygen evolution ceases in the potential interval between +2.1 and +2.2 V and a hydrocarbon is formed according to the equation... 

The microtubular electrode concept described here also offers another possible advantage. In these concentric tubular electrodes, each particle of the Li intercalation material (the outer tube) has its own current collector (the inner metal microtubule). This could be an important advantage for Li+ intercalation materials with low electrical conductivity. This advantage was not demonstrated here because TiS2 has relatively high electronic conductivity. We have recently shown that electrochemical synthesis can be used to coat the gold microtubular current collector with outer mbes of a... 

The electrochemical synthesis of cadmium and zinc thiolate complexes and their properties were reviewed in addition to other metal ion complexes [152]. 

As regards other coordination compounds of silver, electrochemical synthesis of metallic (e.g. Ag and Cu) complexes of bidentate thiolates containing nitrogen as an additional donor atom has been described by Garcia-Vasquez etal. [390]. Also Marquez and Anacona [391] have prepared and electrochemically studied sil-ver(I) complex of heptaaza quinquedentate macrocyclic ligand. It has been shown that the reversible one-electron oxidation wave at -1-0.75 V (versus Ag AgBF4) corresponds to the formation of a ligand-radical cation. Other applications of coordination silver compounds in electrochemistry include, for example, a reference electrode for aprotic media based on Ag(I) complex with cryptand 222, proposed by Lewandowski etal. [392]. Potential of this electrode was less sensitive to the impurities and the solvent than the conventional Ag/Ag+ electrode. 

Chromium(lII) bromide can be prepared directly by treating the metal with bromine in a sealed tube at temperatures variously reported1 -2 as being between 750 and 1000°. The direct electrochemical synthesis described below leads to... 

Electrochemical Synthesis of Bimetallic Particles. Most chemical methods for the preparation of metal nanoparticles are based at first on the reduction of the corresponding metal ions with chemical reagents to form metal atoms and then on the controlled aggregation of the obtained metal atoms. Instead of chemical reduction, an electrochemical process can be used to create metal atoms from bulk metal. Reetz and Hclbig proposed an electrochemical method including both oxidation of bulk... 

Metals can be used as sacrificial anodes in the electrochemical synthesis of anhydrous salt and complexes. This method frequently produces chromium(IH) complexes, but electrochemi cal oxidation of chromium in a mixture of concentrated aqueous HBF4 and acetonitrile yield [CKMeCN KBF,),.82... 

The solvolysis of hexaaquachromium(HI) in DMSO proceeds via the series of complexes [Cr(DMS0)n(H20)6 ]3+ (n = 1 to 6).945,946 The anation and solvolysis of several chromium(III) complexes in DMSO have been studied 947,948 in general the reactions proceed by /d mechanisms. A direct electrochemical synthesis of [Cr(DMSO)6][BF4]3 has been reported.949 A comprehensive review of metal ion complexation by DMSO contains an extensive section on chromium(III).950... 

Synthesis of Polysilanes. The most commonly utilized method is based on the Wurt/ type alkali metal coupling or dichlorosilanes. Other synthesis methods include dehydrogenative coupling, ring-opening polymerization, polymerization of masked disilenes. electrochemical synthesis, and polymer modification. 

The direct electrochemical synthesis of metal alkoxides by the anodic dissolution of metals into alcohols containing conducting electrolytes was initially demonstrated by Szilard in 1906 for the methoxides of copper and lead.19 More recently the method has received some attention particularly in the patent literature.29-25 The preparation of the ethoxides of silicon, titanium, germanium, zirconium and tantalum by electrolysis of ethanolic solutions of NH Cl has been patented, although the production of the ethoxides was found to cease after several hours.24,25... 

It should be mentioned that by changing the conditions of electrochemical synthesis — such as nature of the alcohol, the purity of the metal used as anode, the nature and concentration of the conductive additive, the voltage (usually 30 — 110 V DC is applied), the temperature, and even the construction of the cell — one can significantly effect the process of the anodic dissolution or even change its mechanism. As it has already been mentioned, the electrochemical dissolution of iron in alifatic alcohols gives insoluble iron (II) alkoxides [1005], while in 2-methoxyethanol a soluble iron (HI) complex is obtained [1514], Another example is provided by tantalum dissolution in isopropanol while high-purity metal is rapidly dissolved anodically [1639], the one containing impurities is passivated. Therefore, it is quite clear that each synthesis requires careful study, optimization of parameters of electrochemical synthesis, and isolation and purification of final products. 

Recently, Ce43 75+0(0Pr )i3( Pr0H) was obtained by irradiation of Ce(OPr )4 PrOH solutions in (-CH2OMe)2 and PrOH by the visible light [1803]. Partial reduction ofalkoxides occurs in the course of electrolysis of metal alkoxides (see above). Oxoalkoxoniobates NbO(OR)3 (R=Me, Et, Bu), the products of oxidation of the Nb(OR)4, were isolated in the course of electrolysis performed with Nb anode and Pt cathode [911]. Although the reduction products are highly unstable (they cannot be used for synthesis of oxides) their formation in electrochemical synthesis should be taken into consideration because their subsequent oxidation by 02 (or even its traces) leads to ox-oalkoxides. 

The metatheis of acetates with the alkali alkoxides (method 5) can be used for the preparation of the methoxides and ethoxides of all three elements and is the only reaction leading to Hg(OR)2 [1623]. The trans-esterification of Zn(OMe)2 (method 6), according to [1121], can be carried out only in the presence of LiOR (forming soluble bimetallic complexes). The direct electrochemical synthesis on the anodic oxidation of metals in alcohols has been described for Zn(OEt)2 and a series of cadmium derivatives (Cd(OR)2 — obtained in the presence of such donor ligands as Dipy, Phen, and Dmso [98]) (method 2). 

Polycarbosilanes have also attracted much interest as starting material for silicon carbide fiber production. Reactive metal such as Mg88, Cu86,89,90 and Al91 electrodes have been shown to be highly effective for electrochemical synthesis of polycarbosilanes, as shown in Table 21. 

Electric arcs, in metal vapor synthesis, 1, 224 Electric-field-induced second harmonic generation Group 8 metallocenes, 12, 109 for hyperpolarizability measurement, 12, 107 Electrochemical cell assembly, in cyclic voltammetry, 1, 283 Electrochemical irreversibility, in cyclic voltammetry, 1, 282 Electrochemical oxidation, arene chromium carbonyls, 5, 258 Electrochemical properties, polyferrocenylsilanes, 12, 332 Electrochemical reduction, bis-Cp Zr(III) and (IV) compounds, 4, 745 Electrochemical sensors biomolecule—ferrocene conjugates... 

Use of the electrosynthesis allows us to isolate, together with neutral complexes, cationic and anionic compounds [506,551,559]. The most widespread principle of electrochemical synthesis of cationic complexes is based on the anodic dissolution of a metal in an organic solvent (which frequently acts as a ligand), containing a mineral acid [551]. Such syntheses, in particular (3.239) [551,560], were carried out under dissolution of metals (Cd, Zn, In, Ti, V, Mn, Co, Cr, Fe) in CH3CN or DMSO (L), containing an equal volume of 48% solution of HBF4 ... 

Among the electrochemical syntheses related to the change of metal oxidation number, we emphasize obtaining acetylacetonates of divalent iron, cobalt, and nickel [551,623]. The method of alternating-current electrochemical synthesis was applied to isolate Ji-complexes of monovalent copper with allylamines, allylimines, and ally-lurea from the salts of divalent copper [624-628], We note that the same method was used for preparation of analogous ji-complexes with copper(II) halides (X = Cl, Br) [629a]. Other electrochemical syntheses with participation of metal salts and complexes are described in monographs [201,202] and literature cited therein. 

Regioselective syntheses are of high interest in a series of complexes of chelating ligands which, as is usually accepted, form exclusively ICC (Secs. 1.2.2.2, 1.3.2.2) [22,84]. It is well known that (3-diketones form (3-diketonates 849 (4.19) in reactions with metal oxides and salts in various solvents (Sec. 3.1.1.2), as well as under gas-phase conditions (Sec. 3.4.1) and electrochemical synthesis. (Sec. 3.4.2). 

The regioselective synthesis can be carried out in the limits of only electrochemical synthesis. In these transformations, the nature of metal complex-former (material of the anode) and of donor atom X (N, O) are the main regiocontrolling factors forming, for instance (4.38), the coordination sphere of the chelates 864 and 865 [119] ... 

Classic Chemical and Electrochemical Methods of Metal Phthalocyanine Synthesis... 

Di-iminoisoindoline was used as a precursor for Pc in different protic and aprotic systems, without catalysts or promoters, to study the solvent effect on the possibility of phthalocyanine formation [32], As can be observed (Example 13), it is possible to carry out the chemical and electrochemical synthesis of metal-free Pc in aprotic solvents, such as DMF or DMSO, in contrast to the results with PN. It is surprising that the yields of Pc in ROH are comparatively small. The N,N-dimethyletanolamine is characterized by the best yields, as in the case when PN was used as precursor. 

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