Nickel complexes applications

However, with the application in the 19, iOs of crystal held theory to transition-metal ehemistry it was realized that CFSEs were unfavourable to the lormation of tetrahedral d complexes, and previous assignments were re-examined. A typical ca.se was Ni(acac)i. which had often been cited as an example of a tetrahedral nickel complex, but which was shown - in I9. I6 to be trimeric and octahedral. The over-zealous were then inclined to regard tetrahedral d" as non-existent until Hrst L.. M. Venanz.i and then N., S. Gill and R. S. Nyholm" demonstrated the existence of discrete tetrahedral species which in some cases were also rather easily prepared. 

Flowever, information concerning the characteristics of these systems under the conditions of a continuous process is still very limited. From a practical point of view, the concept of ionic liquid multiphasic catalysis can be applicable only if the resultant catalytic lifetimes and the elution losses of catalytic components into the organic or extractant layer containing products are within commercially acceptable ranges. To illustrate these points, two examples of applications mn on continuous pilot operation are described (i) biphasic dimerization of olefins catalyzed by nickel complexes in chloroaluminates, and (ii) biphasic alkylation of aromatic hydrocarbons with olefins and light olefin alkylation with isobutane, catalyzed by acidic chloroaluminates. 

Modem cross coupling chemistry is heavily dominated by the use of palladium and nickel complexes as the catalysts, which show an impressively wide scope and an excellent compatibility with many functional groups.2 This favorable application profile usually overcompensates the disadvantages resulting from the high price of the palladium precursors, the concerns about the toxicity of nickel salts, the need for ancillary ligands to render the complexes sufficiently active and stable, and the extended reaction times that are necessary in certain cases. 

A much smaller amount of work has been done with nickel complexes of dmt ligands since they are more difficult to crystallize. Some complexes have been assembled combining [Ni(dmf)2] with viologen-based cations for applications in electrical conductivity and dioxygen activation.10 3-1035... 

Nickel complexes with the dmid ligand are also less recognized in research. A conductivity as high as 10-2 Scm-1 was reached with (Et4N)o.i7[Ni(dmid)2].1036 (Bu4N)x[Ni(dmid)2] complexes have been studied by XPS and for applications in electrical switching and memory devices.1 7,1038... 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

Nickel halides and nickel complexes resulting from oxidative addition can also give rise to subsequent replacement and insertion reactions. Replacement reactions have been described mainly with arylnickel halide complexes (examples 23, 29, and 31, Table III). Carbanionic species replace halide ions and can undergo coupling or insertion reactions. An example of application of a carbanionic reaction to the synthesis of a natural product is the coupling step between an aromatic iodo-derivative and an active methylene group to form cephalotaxinone (example 23, Table III). 

In an effort to introduce C2 symmetry into nickel complexes for their application in catalysis of asymmetric epoxidation, a series of oxocyclam analogues derived from amino acids 34 were synthesized. They did not react in the presence of PhIO as oxidant. However, they showed enhanced reactivity with NaOCl as the terminal oxidant under phase-... 

Both the C—C bond lengths [(I) - 149.7 pm (2) = 147.6 pm] and the bending of the substituents out of the plane [(11 = 32.2° (2) = 38.4°] are nearly the same. Although we can draw an alternative resonance form for the nickel complex, the bonding model shown is the only one applicable to Ihe oxide. In view of the strong structural similarities, we can feel justified in using the cyclic structure us nn approximation for certain complexes as welL... 

The most important azo compounds employed in the manufacture of dyes of this type are those containing the < ,o -dihydroxyazo-, the o-hydroxy-o -carboxyazo- and the o-hydroxy-o -amino-diarylazo systems. It is well established3 33-0 that these form four-coordinate copper and nickel complexes (35) in which the coordination sphere of the metal can be completed by a variety of neutral ligands. In both cases the light-fastness of the parent azo compound is improved as a result of complex formation but the nickel complexes are insufficiently stable towards acid to be of commercial interest as dyestuffs. The history of copper complexes has already been discussed (Section 58.1) and will not be considered further here, although it is worthy of mention that currently the most important copper complex dyestuffs are those containing fibre-reactive systems, e.g. (36), for application on cellulosic fibres. 

N-containing, in cobalt(III) complexes, 7, 28 in nickel complexes, 8, 120 palladium complexes, 8, 276 synthetic applications corroles, 1, 70... 

With the nickel complex in an aprotic solvent, such as THF, cyclohexyl isocyanide was polymerized instantaneously, affording the corresponding polymer in a quantitative manner. Furthermore, the successful application of this new catalyst system was demonstrated by the quantitative polymerization of tert-butyl isocyanide (DP=ca. 27), which is one of the least reactive isocyanides. 

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