Nickel-catalyzed

Iron, cobalt, and nickel catalyze this reaction. The rate depends on temperature and sodium concentration. At —33.5°C, 0.251 kg sodium is soluble in 1 kg ammonia. Concentrated solutions of sodium in ammonia separate into two Hquid phases when cooled below the consolute temperature of —41.6°C. The compositions of the phases depend on the temperature. At the peak of the conjugate solutions curve, the composition is 4.15 atom % sodium. The density decreases with increasing concentration of sodium. Thus, in the two-phase region the dilute bottom phase, low in sodium concentration, has a deep-blue color the light top phase, high in sodium concentration, has a metallic bronze appearance (9—13). 

The synthesis involves the nickel-catalyzed coupling of the mono-Grignard reagent derived from 3-alkyl-2,5-diiodothiophene (82,83). Also in that year, transition-metal hahdes, ie, FeCl, MoCl, and RuCl, were used for the chemical oxidative polymerization of 3-substituted thiophenes (84). Substantial decreases in conductivity were noted when branched side chains were present in the polymer stmcture (85). 

Both regio- and stereospecificiiy may be influenced by the catalyst and by alkali. Raney nickel opens ce>2,3-diphenylbul-2-ene epoxide with retention of configuration to give cr3 f/iro-2,3-diphenylbutan-2-ol, whereas palladium-on-carbon gives the inverted threo isomer. If a small amount of alkali is added to nickel-catalyzed reductions, nickel too gives the threo isomer (d5). 

As early as 1990, Chauvin and his co-workers from IFP published their first results on the biphasic, Ni-catalyzed dimerization of propene in ionic liquids of the [BMIM]Cl/AlCl3/AlEtCl2 type [4]. In the following years the nickel-catalyzed oligomerization of short-chain alkenes in chloroaluminate melts became one of the most intensively investigated applications of transition metal catalysts in ionic liquids to date. 

To be applied industrially, performances must be superior to those of existing catalytic systems (activity, regioselectivity, and recyclability). The use of ionic liquid biphasic technology for nickel-catalyzed olefin dimerization proved to be successful. 

An unprecedented nickel-catalyzed reductive coupling between an epoxide and an alkyne to give synthetically useful homoallylic alcohols has been developed by Jamison [55a], and was recently used in a short enantioselective synthesis of am-... 

Scheme 8.30 Nickel-catalyzed reductive coupling of alkynes with epoxides.

A disadvantage of the nickel-catalyzed reaction is that the alkylation is primarily limited to methylation and that it often gives products with low stereo- and regioselectivity. 

Stable enolates such as diethyl malonate anions react with allyl sulfones (or acetates) in the presence of nickel complexes to give a mixture of the a- and /-product83. The regioselectivity is generally poor in the nickel-catalyzed reaction, but the molybdenum-catalyzed reaction is selective for alkylation at the more substituted allylic site, thereby creating a quaternary carbon center84. 

Colquhoun at ICI first reported the synthesis of macrocyclic monomers containing ether and ketone linkages through nickel-catalyzed coupling of... 

Nickel-catalyzed [27t + 27t + 27r] (homo-Diels-Alder) and [27r-i-27r] cycloadditions of bicyclo[2.2.1 ]hepta-2,5-dienes [96]... 

Last, the nickel catalyzed halogen exchange for haloarenes, actually the arylation of halide anions, has been investigated. The equilibrated exchange between the phenyl bromide (60 %) and the phenyliodide (40 %) allows with some... 

Fig. 11. Influence of the base on the Nickel catalyzed arylation of alcohols...

Based on these observations the authors propose the following mechanism for the nickel-catalyzed hydroalumination (Scheme 2-4) During the catalysis process... 

Nickel-catalyzed hydroalumination has found some specific applications in organic synthesis (see below). 

The asymmetric nickel-catalyzed hydroalumination of prochiral terminal alkenes using adducts of BujAl and chiral amines was reported in 1981 [74], Among the different amines investigated, (-)-N,N-dimethylmenthylamine (DMMA) gave the best enantioselectivities. For example, reaction of 2,3,3-trimethyl-l-butene (39) at room temperature with 0.33 equiv. of the DMMA/iBu3Al adduct in the presence of 0.6 mol% of Ni(mesal)2 gave, after oxidation of the intermediate organoaluminum compounds, 2,3,3-trimethyl-l-butanol 40 in 76% yield and 27% ee (Scheme 2-19). 

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). 

Recent discoveries have expanded the utility of nickel-catalyzed coupling reactions. Inclusion of butadiene greatly improves the efficiency of the reactions.268... 

Aryl carbamates are also reactive toward nickel-catalyzed coupling.270 Since the carbamates can be readily prepared from phenols, they are convenient starting materials. 

Nickel-catalyzed carbonylation of a-haloalkynes with carbon monoxide under phase-transfer conditions gave either allenic monoacids or unsaturated diacids.93 The carbonylation initially afforded monoacids, which reacted further to give diacids with high stereoselectivity (Eq. 4.52). 

Nickel-catalyzed carbonylation of a-ketoalkynes has also been reported by Arzoumanian et al. under phase-transfer conditions.94 The carbonylation gave either furanone or unsaturated carboxylic acids depending on the substituents of substrates (Eq. 4.53). A similar reaction, nickel-catalyzed cyanation of a-ketoalkynes with KCN in water, was also reported to afford unsaturated hydroxylactams (Eq. 4.54).95... 

Later, a nickel-catalyzed cascade conversion of propargyl halides and propargyl alcohol into a pyrone in water was reported. The reaction involved a carbonylation by CO and a cyanation by KCN (Eq. 4.55).96 Recently, Gabriele et al. explored a facile synthesis of maleic acids by palladium catalyzed-oxidative carbonylation of terminal alkynes in aqueous DME (1,2-dimethoxyethane) (Eq. 4.56).97... 

It has been reported that nickel catalyzed the reactions of 6-amino-1,3-dimethyluracil with substituted alkynylketones in water to give substituted 2,4-dioxopyrido[2,3-f/ pyrimidine derivatives in quantitative yields at room temperature (Eq. 4.70).134 The products have potential pharmacological and biological activities. The reaction may have proceeded through an ionic process. 

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