Nickel catalysts synthetic applications

Electrocatalysis with nickel-bpy complexes has been shown useful for synthetic applications,202,211 especially when used in combination with the sacrificial anode process in an undivided cell (Equation (45)).207,211 Under these very simple experimental conditions, efficient nickel catalysts can be also generated in the presence of the cheap pyridine ligand.212... 

Significant synthetic applications of the nickel-salen catalysts are the formation of cycloalkanes by reduction of <>, -a-dihaloalkanes255,256 and unsaturated halides,257,258 the conversion of benzal chloride (C6H5CHC12) into a variety of dimeric products 259 the synthesis of 1,4-butanediol from 2-bromo- and 2-iodoethanol260 or the reduction of acylhalides to aldehydes261 and carboxylic acids.262... 

Active Raney nickel induces desulfurization of thiazoles. The reaction apparently occurs by two competing mechanisms (57JCS1652). In the first, under alkaline conditions, ring cleavage occurs before desulfurization, whereas in the second, using a neutral catalyst, the initial desulfurization is followed by fission of the C—N bond and formation of carbonyl derivatives (Scheme 18). Because of the easy and versatile syntheses of thiazoles, this reaction could have interesting synthetic applications. 

The metal-catalyzed cross-coupling of aryl-, heteroaryl-, and alkenyhnagnesium derivatives is a broad-scope transformation that has found many synthetic applications C(sp )-C(sp ) couplings are by far the most common. Catalysts by nickel, palladium, and iron complexes is most widespread, but the emerging fields of cobalt and manganese catalysis can also provide useful alternatives. 

Jackson, G.D.F., and W.H.F. Sasse Synthetical Applications of Activated Metal Catalysts. XXI. The Formation of Carbazole from Aniline and Related Compounds in Presence of Degassed Raney Nickel. Austr. J. Chem. 17, 347 (1964). 

Partial reduction of alkynes to Z-alkenes is another important synthetic application of selective hydrogenation catalysts. The transformation can be carried out under heterogeneous or homogeneous conditions. Among heterogeneous catalysts, the one that is most successful is Lindlar s catalyst, which is a lead-modified palladium-CaCOa catalyst.A nickel-boride catalyst prepared by reduction of nickel salts with sodium borohydride is also useful.A homogeneous rhodium catalyst has also been reported to show good selectivity. 

Heterogeneous hydrogenation of the C=N bond is a very widely used synthetic process with application to small and large-scale reactions. Many of the catalysts described in other sections may also be employed, for example those based on supported rhodium, palladium etc, and Raney Nickel. This area has been reviewed extensively recently192. Hydrogenation of oximes and hydrazones results in formation of amines. Milder conditions can be used for oxime reduction if the ethylaminocarbonyl derivative is prepared in situ prior to reduction276. 

The catalyzed complete combustion of individual hydrocarbons has been investigated by Todes in an attempt to establish the combustion characteristics of these hydrocarbons (220), while other workers have attempted to improve the techniques of catalyzed combustion (457). At the Power Institute Ravich has been working on the development of catalysts promoting complete combustion of gaseous and solid fuels with the aid of naturally occurring and synthetic minerals containing oxides of iron, chromium, nickel, potassium, aluminum, and manganese (317,-318,319). Industrial application of this process has been mentioned. 

The semihydrogenation of the carbon-carbon triple bond is a particularly valuable and frequently used application of heterogeneous catalysis to synthetic chemistry, and is the subject of several recent re-views. > Catalysts prepared from palladium and nickel are most commonly used, but the form of the catalyst and the conditions of use affect the results (see Section 3.1.1.2). A polymer-bound palladium catalyst, PdCh with poly-4-diphenylphosphinomethylstyrene, is intended to combine the selective properties of mononuclear transition metal complexes with the ease of separating the product from a solid. Whether catalysts of this type will replace the more traditional heterogeneous catalysts remains to be seen. 

Before the discovery of the nickel-phosphine catalyst, the cross-coupUng of Grignard reagents with organic halides was seldom used in synthetic practice. This fact was mainly due to the formation of homocoupling products along with significant elimination side reactions. With the use of this new catalyst, the reaction now has wide application in the synthesis of unsymmetrical allca-nes and alkenes. 

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