Nickel addition reactions

Additive inhibitors have been developed to reduce the contaminant coke produced through nickel-cataly2ed reactions. These inhibitors are injected into the feed stream going to the catalytic cracker. The additive forms a nickel complex that deposits the nickel on the catalyst in a less catalyticaHy active state. The first such additive was an antimony compound developed and first used in 1976 by Phillips Petroleum. The use of the antimony additive reportedly reduced coke yields by 15% in a commercial trial (17). 

Nickel additions reduce corrosion due to both caustic solutions and ammonia. Monel is resistant to attack in ammonia-containing waters and vapors. Reactions with ammonia are as follows ... 

With the success in Lewis acid-catalyzed thiol conjugate addition reactions mentioned above, we further tried to apply the J ,J -DBFOX/Ph-nickel(II) aqua complex catalyst to the catalyzed asymmetric conjugate addition reactions of hydroxyl-amines [88, 89]. However, after some preliminary examinations, we found that... 

As shown above, it was not so easy to optimize the Michael addition reactions of l-crotonoyl-3,5-dimethylpyrazole in the presence of the l ,J -DBFOX/ Ph-Ni(C104)2 3H20 catalyst because a simple tendency of influence to enantio-selectivity is lacking. Therefore, we changed the acceptor to 3-crotonoyl-2-oxazolidi-none in the reactions of malononitrile in dichloromethane in the presence of the nickel(II) aqua complex (10 mol%) (Scheme 7.49). For the Michael additions using the oxazolidinone acceptor, dichloromethane was better solvent than THF and the enantioselectivities were rather independent upon the reaction temperatures and Lewis base catalysts. Chemical yields were also satisfactory. 

Much of the information available on resistance of nickel-iron alloys to corrosion by mineral acids is summarised by Marsh. In general, corrosion rates decrease sharply as the nickel content is increased from 0 to 30-40%, with little further improvement above this level. The value of the nickel addition is most pronounced in conditions where hydrogen evolution is the major cathodic reaction, i.e. under conditions of low aeration and agitation. Results reported by Hatfield show that the rates of attack of Fe-25Ni alloy in sulphuric and hydrochloric acid solutions, although much lower than those of mild steel, are still appreciable (Tables 3.35 and 3.36). In solutions of nitric acid, nickel-iron alloys show very high rates of corrosion. 

In an addition reaction, a small molecule (e.g., H2, Cl2, HC1, H20) adds across a double or triple bond. A simple example is the addition of hydrogen gas to ethene in the presense of a nickel catalyst. 

Although, as has already been mentioned, under matrix conditions between 10 and 77 K, there is no oxidative addition of a chloroolefin to nickel or palladium atoms (141), it is evident that this is simply a function of reaction and processing conditions, as it has been shown (68) that oxidative addition to C-C or C-H bonds by nickel atoms leads to pseudocomplexes having Ni C H ratios of 2-5 1 2. Klabunde and co-workers investigated the oxidative addition-reactions of palladium atoms with alkyl halides (73) and benzyl chlorides (74). 

For the nickel carbonyl reaction, the addition is syn for both alkenes and alkynes. The following is the accepted mechanism ... 

Substantially more work has been done on reactions of square-planar nickel, palladium, and platinum alkyl and aryl complexes with isocyanides. A communication by Otsuka et al. (108) described the initial work in this area. These workers carried out oxidative addition reactions with Ni(CNBu )4 and with [Pd(CNBu )2] (. In a reaction of the latter compound with methyl iodide the complex, Pd(CNBu )2(CH3)I, stable as a solid but unstable in solution, was obtained. This complex when dissolved in toluene proceeds through an intermediate believed to be dimeric, which then reacts with an additional ligand L (CNBu or PPh3) to give PdL(CNBu )- C(CH3)=NBu I [Eq. (7)]. 

The nickel addition in chromium oxide decreased the formation of alkenes which was smaller than the one observed in the presence of just chromium oxide. It is to be remarked that the decrease of alkene formation was independent of the quantity of nickel in the catalyst. However, the catalytic activity for the fluorination reaction decreased when the nickel content increased. Thus the addition of nickel in small quantities allowed to increase the selectivity for the fluorination reaction. We could suggest that nickel substitute... 

The regiochemistry of Al-H addition to unsymmetrically substituted alkynes can be significantly altered by the presence of a catalyst. This was first shown by Eisch and Foxton in the nickel-catalyzed hydroalumination of several disubstituted acetylenes [26, 32]. For example, the product of the uncatalyzed reaction of 1-phenyl-propyne (75) with BujAlH was exclusively ds-[3-methylstyrene (76). Quenching the intermediate organoaluminum compounds with DjO revealed a regioselectivity of 82 18. In the nickel-catalyzed reaction, cis-P-methylstyrene was also the major product (66%), but it was accompanied by 22% of n-propylbenzene (78) and 6% of (E,E)-2,3-dimethyl-l,4-diphenyl-l,3-butadiene (77). The selectivity of Al-H addition was again studied by deuterolytic workup a ratio of 76a 76b = 56 44 was found in this case. Hydroalumination of other unsymmetrical alkynes also showed a decrease in the regioselectivity in the presence of a nickel catalyst (Scheme 2-22). 

Nickel catalysts can be used instead of copper catalysts to promote the conjugate addition reaction, providing, in some cases, better results than the corresponding copper catalysts. In 2000, Yang et al. discovered a series of (li ,25, 3i )-3-mercaptocamphan-2-ol derivatives, which proved to be efficient ligands in the conjugate addition of ZnEt2 to chalcone upon catalysis with Ni(acac)2 (Scheme 2.29). 

A few further general examples of zinc catalytic activity or reactivity include the following. Other zinc-containing systems include a zinc phenoxide/nickel(0) catalytic system that can be used to carry out the chemo- and regioselective cyclotrimerization of monoynes.934 Zinc homoenolates have been used as novel nucleophiles in acylation and addition reactions and shown to have general utility.935,936 Iron/zinc species have been used in the oxidation of hydrocarbons, and the selectivity and conditions examined.362 There are implications for the mechanism of metal-catalyzed iodosylbenzene reactions with olefins from the observation that zinc triflate and a dizinc complex catalyze these reactions.937... 

Anderson and Kemball (35) examined the reaction between gaseous deuterium and benzene catalyzed by evaporated films of iron, nickel, palladium, silver, tungsten, and platinum. The order of reactivity (estimated from the temperature at which the addition reaction achieved an initial rate of 1% per minute for a 10 mg film at certain specified reactant... 

However, when the reductions were carried out with lithium and a catalytic amount of naphthalene as an electron carrier, far different results were obtained(36-39, 43-48). Using this approach a highly reactive form of finely divided nickel resulted. It should be pointed out that with the electron carrier approach the reductions can be conveniently monitored, for when the reductions are complete the solutions turn green from the buildup of lithium naphthalide. It was determined that 2.2 to 2.3 equivalents of lithium were required to reach complete reduction of Ni(+2) salts. It is also significant to point out that ESCA studies on the nickel powders produced from reductions using 2.0 equivalents of potassium showed considerable amounts of Ni(+2) on the metal surface. In contrast, little Ni(+2) was observed on the surface of the nickel powders generated by reductions using 2.3 equivalents of lithium. While it is only speculation, our interpretation of these results is that the absorption of the Ni(+2) ions on the nickel surface in effect raised the work function of the nickel and rendered it ineffective towards oxidative addition reactions. An alternative explanation is that the Ni(+2) ions were simply adsorbed on the active sites of the nickel surface. 

Klabunde has reported limited reactivity toward oxidative addition reactions of carbon halogen bonds with nickel slurries prepared by the metal vaporization technique(65). 

The second pathway is represented by Eqs. (8)—(11). These reactions involve reduction of the Nin halide to a Ni° complex in a manner similar to the generation of Wilke s bare nickel (37, 38) which can form a C8 bis-77-alkyl nickel (17) in the presence of butadiene [Eq. (9)]. It is reasonable to assume that in the presence of excess alkyaluminum chloride, an exchange reaction [Eq. (10)] can take place between the Cl" on the aluminum and one of the chelating 7r-allyls to form a mono-77-allylic species 18. Complex 18 is functionally the same as 16 under the catalytic reaction condition and should be able to undergo additional reaction with a coordinated ethylene to begin a catalytic cycle similar to Scheme 4 of the Rh system. The result is the formation of a 1,4-diene derivative similar to 13 and the generation of a nickel hydride which then interacts with a butadiene to form the ever-important 7r-crotyl complex [Eq. (11)]. 

Reactions a and b in Scheme 8 represent different ways of coordination of butadiene on the nickel atom to form the transoid complex 27a or the cisoid complex 27b. The hydride addition reaction resulted in the formation of either the syn-7r-crotyl intermediate (28a), which eventually forms the trans isomer, or the anti-7r-crotyl intermediate (28b), which will lead to the formation of the cis isomer. Because 28a is thermodynamically more favorable than 28b according to Tolman (40) (equilibrium anti/syn ratio = 1 19), isomerization of the latter to the former can take place (reaction c). Thus, the trans/cis ratio of 1,4-hexadiene formed is determined by (i) the ratio of 28a to 28b and (ii) the extent of isomerization c before addition of ethylene to 28b, i.e., reaction d. The isomerization reaction can affect the trans/cis ratio only when the insertion reaction d is slower than the isomerization reaction c. 

In the course of investigation into new C-C bond formation processes, Hiyama has developed an efficient nickel-catalyzed arylcyanation of alkynes.67 The addition reaction of an aryl-CN bond to alkyne affords aryl-substituted alkene nitrile in good yield. Good regioselectivity is reported in the case of unsymmetrical alkynes with two sterically different substituents. 

The starting material is an 18 electron nickel zero complex which is protonated forming a divalent nickel hydride. This can react further with alkenes to give alkyl groups, but it also reacts as an acid with hard bases to regenerate the nickel zero complex. Similar oxidative addition reactions have been recorded for phenols, water, amines, carboxylic acids, mineral acids (HCN), etc. 

In examples 2.22 a and b the metals increase their valence by two, and this is not just a formalism as indeed the titanium(II) and the nickel(O) are very electron rich metal centres. During the reaction a flow of electrons takes place from the metal to the organic fragments, which end up as anions. In these two reactions the metal provides two electrons for the process as in oxidative addition reactions. The difference between cycloaddition and oxidative addition is that during oxidative addition a bond in the adding molecule is being broken, whereas in cycloaddition reactions fragments are combined. 

Two types of intermediates, i.e., radicals or carbanions or their organometallic equivalents, can be used to perform addition reactions to Michael acceptors. The free-radical route has already been investigated with nickel or cobalt complexes as catalysts [62-64]. These studies have been reinvestigated recently with the aim of improving the turn-over of the catalyst and/or using easily prepared cheap complexes. 

Carbon-carbon bond-forming reactions are one of the most basic, but important, transformations in organic chemistry. In addition to conventional organic reactions, the use of transition metal-catalyzed reactions to construct new carbon-carbon bonds has also been a topic of great interest. Such transformations to create chiral molecules enantioselectively is therefore very valuable. While various carbon-carbon bond-forming asymmetric catalyses have been described in the literature, this chapter focuses mainly on the asymmetric 1,4-addition reactions under copper or rhodium catalysis and on the asymmetric cross-coupling reactions catalyzed by nickel or palladium complexes. 

Fhe electrochemical generation of alkyl radicals catalysed by square planar nickel complexes has been used to achieve radical-alkene addition reactions. Complex 64 was the catalyst of choice. Intramolecular cyclizations to give five raem-... 

Stereoselective) additions of nucleophiles to 5-alkylidene Meldmm s acid as displayed in Scheme 17 (Section 8.11.6.1.3) <2006TA2957, 2007AGE4964> and to the carbonyl group of 2,2-dimethyl-l,3-dioxan-5-one (Scheme 47, Section 8.11.6.3.3) either in a three component transformation <2006OL3689> or in a nickel-catalyzed reaction... 

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