Chlorobenzene, reaction with nickel

Nitro compounds in presence of carbonyl group are selectively reduced to amines in the presence of Raney nickel catalyst. Hydrazine reduces nitrdes yielding hydrazones. Under controlled reaction conditions other functional groups, including nitroso and oxime, may be reduced. Many partially hydrogenated derivatives, such as azo-, hydrazo-, and azoxy compounds may be obtained by partial reduction with hydrazine. Reaction with chlorobenzene yields benzene. 

Aryl chlorides Aryl chlorides will substitute alkenes only under very special conditions, and then catalyst turnover numbers are generally not very high. Palladium on charcoal in the presence of triethylphos-phine catalyzes the reaction of chlorobenzene with styrene,58 but the catalyst becomes inactive after one use.59 Examples employing an activated aryl chloride and highly reactive alkenes, such as acrylonitrile, with a palladium acetate-triphenylphosphine catalyst in DMF solution at ISO C with sodium acetate as base react to the extent of only 51% or less.60 Similar results have been reported for the combination of chlorobenzene with styrene in DMF-water at 130 C, using sodium acetate as the base and palladium acetate-diphos as a catalyst.61 Most recently, a method for reacting chlorobenzene with activated alkenes has been claimed where, in addition to the usual palladium dibenzilideneacetone-tri-o-tolylphosphine catalyst, nickel bromide and sodium iodide are added. It is proposed that an equilibrium concentration of iodobenzene is formed from the chlorobenzene-sodium iodide-nickel bromide catalyst and the iodoben-zene then reacts in the palladium-catalyzed alkene substitution. Moderate to good yields were reported from reactions carried out in DMF solution at 140 C 62... 

In the presence of a nickel (0) complex such as Ni(PPh3)4 the arylation of allylamine occurs in a very low yield (5%). With nickel (II) salts or complexes, the yields are higher and the best results are obtained for bipy2NiBr2 (50%) or to a less extent for phen2NiBr2 (30%). It is noteworthy that Cramer and coll. (ref. 7) pointed out, on the contrary, that "diamines which coordinate strongly to nickel (II) interfered in the reaction of dimethylamine with chlorobenzene and reduced by a factor of ten (ethylenediamine) or even inhibit (o-phenantroline) the arylation". 

Table 7.12 summarizes the results of the reaction of bromobenzenes with activated nickel. Although the reactivity of bromobenzenes toward nickel was relatively lower than that of iodobenzenes, they reacted at 85°C to give biphenyls in moderate to good yields, together with the corresponding reduction products. The reaction of 4-bromochlorobenzene with nickel powder from nickel bromide in glyme afforded chlorobenzene as the major product. Dimethyl sulfoxide and dimethylformamide were tried these solvents did... 

An obvious method to investigate the formation and the nature of the catalytically active nickel species is to study the nature of products formed in the reaction of complexes such as 3 or 4 with substrate olefins. This has been investigated in some detail in the case of the catalytic dimerization of cyclooctene to 1-cyclooctylcyclooctene (17) and dicy-clooctylidene (18) [Eq. (4)] using as catalyst 7r-allylnickel acetylacetonate (11) or 7r-allylnickel bromide (1) activated by ethylaluminum sesquihalide or aluminum bromide (4). In a typical experiment, 11 in chlorobenzene was activated with excess ethylaluminum sesquichloride cyclooctene was then added at 0°C and the catalytic reaction followed by removing... 

It is believed that such reactions proceed through aryne intermediates. These aryne intermediates have been confirmed by reactions of an isotopically labeled chlorobenzene with potassium amide in liquid ammonia1011. Additionally, aryne intermediates have been observed in flash-photolysis experiments and in mass spectrometry12 and trapped as a stable nickel complex (Figure 1), which was characterized by 111 NMR spectroscopy13. 

Bimetallic Pd/Ni [121] andPd/Co [122] systems have exhibited considerable catalytic activity in the Heck reaction of nonactivated chloroarenes with ethyl acrylate, acrylonitrile, and acrylic acid. For instance, ethyl acrylate and acrylonitrile reacted smoothly with chlorobenzene in the presence of Nal and catalytic amounts of NiBr2, Pd2(dba)3, and o-Tol3P in DMF to give E-isomers of ethyl cinnamate and cinnamonitrile, respectively [121]. The reaction occurred via the nickel-catalyzed halogen exchange between ArCl and Nal, followed by the conventional palladium-catalyzed olefination of the iodoarene generated in situ. 

TBAF can promote hiaryl formation from triaflyl(aryl)silanes and a wide variety of aryl halide suhstrates. For example, chlorobenzenes undergo smooth cross-couphng with triallyl(aryl)silanes to give biaryls in good to excellent yields (eq 31). Surprisingly, an appreciable amount of added water is required to achieve high yields however, the role of added water is not yet clear.In a recent variant of the Hiyama reaction, TBAF and palladium-coated nickel nanoclusters were employed to prepare biaryl compounds from aryl bromides and phenyltrimethoxysilane. ... 

Palladium- (and nickel-) catalysed coupling reactions proceed normally on halo-diazines, the most significant feature, as with pyridines, being the enhanced reactivity, relative to chlorobenzene, of chlorine at positions a and y to a nitrogen, but it is important to recognise that this activation does not overcome the higher intrinsic reactivity of bromine and iodine at any position." ... 

There are reports [592-594] on the dimerization of propylene catalyzed by heterogenized (ir-allyDnickel halides. Polymer-anchored -ir-allylic nickel complexes similar to nonsupported complexes are found to be effective catalysts for propylene dimerization after activation with a Lewis acid such as EtAlCL (molar ratio of Al/Ni = 15 5). Using a crosslinked resin as a support, the dimerization can be performed continuously, since the catalytic centers remain active for a long time without any further addition of aluminum cocatalyst. The release of metals during this reaction is low. The reactions are carried out either in bulk propylene or in chlorobenzene solution. The conversion reaches 95% at room temperature. The product has the composition of 2% dimethylbutenes, 67% methylpentenes, and 31% hexenes. Hexene content obtained with polymer-anchored nickel catalyst... 

A polystyrylnickel complex prepared by oxidative addition [490] of bromi-nated polystyrene to Ni(PPh3)4 and activated with BF3-OEt2 and a catalytic amount of water acts as an efficient catalyst for the dimerization of propylene at room temperature and atmospheric pressure. Solvents like n-hexane, toluene, benzene, methylene chloride, and chlorobenzene increase the rate of reaction. One role of the solvent is to swell the matrix pol)mier to allow access of the substrate olefin to the interior of the polymer gel. Some dipole—dipole interaction between the nickel site, the olefin, and the solvent molecule may be prevailing, so that competitive coordination of the olefin and the solvent to the nickel site may be possible. The effect of temperature shows that the rate of the dimerization reaction decreases with an increase in temperature, while selective formation of methyl-pentanes increases up to 90% at 40°C. 2-Methyl-2-pentane is the major Cg olefinic product. 

Different cocatalysts such as RjATCU or R4A12C12 produce a comparable catalyst with a somewhat decreased activity. The high rates of reaction in nonpolar solvents make the presence of ionic intermediates unlikely. Use of other solvents such as benzene or chlorobenzene do not produce any major change in the product composition. The following active species are formed by the reaction of the monomer with a coordinated nickel hydride ... 

The d phosphine and phosphite complexes of zerovalent nickel, palladium and platinum possess long-lived emissive excited states in both fluid solution and in the solid state.The lifetimes of the Ni and Pd complexes are in the 1.39-5.38 ps range, with the platinum complex Pt(PPh3)4 having the shorter excited state lifetime of 0.07 //s because of spin-orbit coupling. These long lifetimes allow for bimolecular reactions to occur, and under photochemical conditions chlorobenzene will add to the complex Pd(PPh3)3 (Ref. 75) ... 

Figure 7 Decomposition of CHP (1 x 10 M) in chlorobenzene at 110°C in the presence of nickel dithiolates (2 X lO"" M). Inset shows product yields after complete reaction of NiDBP with CHP at 110 °C in chlorobenzene at various...

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