4-chlorobenzene-, nickel

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... 

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. 

BIS(t 6-CHLOROBENZENE)MOLYBDENUM, BIS(776-iV,Ar-DIMETHYLANILINE)MOLYBDENUM, AND (1-3 6-7 10-12-rj-2,6,10-DODECATRIENE-1,12-DIYL)NICKEL... 

The addition and dissociation of pyridine and substituted pyridine molecules to a planar nickel(II) complex with a quadridentate N202 ligand have been studied by the microwave temperature-jump technique in chlorobenzene solvent (38). The data were interpreted with the assumption of mechanism C (Fig. 7), i.e., that k65 is the smallest rate constant. Subsequently, however, 14N NMR was used to measure the rate of pyridine exchange from the octahedral complex (138). The rates are the same for the two different experiments within a factor of two. This observation excludes mechanism B and is consistent with either mechanism A or C. The rate constants have consequently been presented in Table VI as k64. 

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... 

The catalytic activity of nickel and palladium films was studied in hydrogenation of nonene-1 and chlorobenzene [41] ... 

In this case it is possible for butadiene to coordinate to nickel by one double bond it is unprobable that a weak base like butadiene would be able to convert a 7r-allyl group into a cr-group. The 5th coordinate is not realized in this case no catalytic activity is observed if two phosphine molecules are bonded to the nickel. Our results are confirmed by Wilke s et al. work (20, 21) on butadiene polymerization in the presence of [C3H5NiP(C6Hn)3] [A1C14] in chlorobenzene. 

The nature of the cathode has been found to have major effect on the efficiency of electrochemical HDH of halogenated compounds. For instance, the HDH of 12 mM chlorobenzene at carbon cloth or lead cathodes gave conversions up to 95% with a current efficiency of 20%, lower conversion and efficiency (<5%) were observed using platinum, titanium or nickel cathodes (Zanaveskin et al. 1996). A 100% electrochemical HDH of 153 ppm 4-chlorophenol to phenol was achieved using a palladium-coated carbon cloth cathode (Balko et al. 1993). Unfortunately, several environmentally unacceptable materials, such as Hg and Pb, have also been used as cathodes (Bonfatti et al. 1999 Kulikov et al. 1996). 

Transfer the solution obtained in Sec. A after reduction with sodium tetrahy-droborate (but before addition of perchloric acid) to a 1-1. single-necked flask with 29 g (0.6 mole) of sodium cyanide. Fit the flask with a condenser and reflux the solution for 2 hr. Cool the solution to room temperature, add 15 g of sodium hydroxide, and evaporate on a rotary evaporator until a semisolid remains. Chloroform, 100 ml, is added to the flask, and the mixture is transferred to a large frit. The liquid is drawn off, and the solid is washed twice with 100-ml portions of chloroform. The aqueous layer is then separated from the filtrate and washed five to seven times with 50-ml portions of chloroform. All the chloroform extracts are dried over sodium sulfate and then evaporated to dryness. The yellowish solid is recrystallized from 800 ml of chlorobenzene to yield white needles which are collected by suction and washed with 50 ml of ethyl ether. The product is then air-dried. A second crop obtained by evaporating the filtrate is treated similarly. Yield 19 g or 63%. Anal. Calcd. for CioH24N4 C, 59.99 H, 12.09 N, 28.01. Found C, 60.1 H, 11.8 N, 28.2. Alternatively, the free base may be recovered from the isolated nickel complex by the above procedure. 

Because of the different rates of hydrogenolysis, aryl halides containing different halogens can be reduced selectively. 1 -Bromo-2-chlorobenzene is reduced to chlorobenzene in 96% yield on treatment for 2 h at room temperature with a complex reducing agent prepared from nickel(II) chloride, sodium hydride and t-pentyl alcohol. l-Bromo-4-chlorobenzene is converted to chlorobenzene on treatment with... 

Zinc dust in the presence of nickel chloride, triphenylphosphine and sodium iodide as a catalyst reduces chlorobenzene in methanol after 20 h at 60 C to benzene in 99% yield, and p-chloroanisole to ani-sole in dimethylformamide/water in 88-97% yields. The yields are considerably lower without sodium iodide (equation 52). ... 

A similar effect on aryl halides is produced by using a suspension of zinc dust, nickel chloride and sodium iodide in moist hexamethylphosphoramide at 60 C under ultrasound sonication. Chlorobenzene is thus converted to benzene in 64—93% yields. ... 

A strongly reducing mixture is prepared by treatment of nickel(II) chloride and f-pentyl alcohol with sodium hydride. In dimethoxyethane, o-bromochlorobenzene is selectively reduced to chlorobenzene in 96% yield after 2 h at 20 °C. ... 

The dimerization reaction has been carried out under two different conditions. In laboratory experiments, the reaction is conveniently carried out under 1 or less than 1 atmosphere and at a temperature of —20° to — 10°C. These relatively low temperatures are necessary to obtain a sufficient concentration of ethylene or propylene in the catalyst solution. The dimerization catalyst for laboratory experiments is usually prepared by mixing, for example, chlorobenzene solutions of a 7r-allylnickel halide and an aluminum halide (or alkylhalide) in molar ratio of at least 1 1. The phosphine-modified catalyst is obtained by simply adding 1 mole of a phosphine per mole of nickel to the solution of the catalyst. When ethylene or propylene is introduced into the catalyst solution, reaction starts immediately, as evidenced by a sudden rise in temperature. Dimerization is exothermic to the extent of about 28 kcal./mole propylene dimer. Hence, the mixture must be stirred and cooled intensively during the reaction. Under these conditions (Table V), reaction rates of about 6 kg. 

Anhydrous nickel chloride in chlorobenzene suspension is reduced in the presence of excess butadiene with aluminum triethyl. The product is the previously mentioned intermediate, I, of the cyclododecatriene synthesis. 

There are only a few systems, where the two components are closely similar in nature, in which the liquidus and solidus curves are given by the simple equations (23.3). As examples we may mention the systems chlorobenzene+ bromobenzene, silvers gold, copper + nickel, and certain pairs of optical isomers. The data for the system copper +nickel ... 

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. 

The Kumada coupling of aryl halides with phenylmagnesium bromide, in the presence of palladium or nickel, showed high catalyst activity. TON up to 800 was observed for the conversion of chlorobenzene into biphenyl (Table 14.5) [182]. 

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". 

Another approach is based on cyclization between a two-atom and a four-atom fragment. This involves treating alkynes (171) with nickel bisdiphenyldithiolene (172) in refluxing chlorobenzene in the presence of pyridine. Pyridine appears to be essential in order to avoid further transformation of 1,4-dithiins (173) to thiophenes <87SC1683>. 

G Tavoularis, MA Keane. Gas phase catalytic hydrodechlorination of chlorobenzene over nickel/silica. J. Chem. Technol. Biotechnol. 74 60-70,1999. 

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