Propene, nickel-catalyzed reactions

Formation of n-alkylnickels by addiction of Ni hydride to an alkene is important in many nickel-catalyzed reactions such as alkene dimerization and isomerization. However, stoichiometric formation of alkylnickels from alkenes and Ni hydrides is not synthetically useful because of the reactivity of alkylnickels. The regiochemistry of the addition of HNiX(PR3)2 to propene is affected by the nature of the trialkylphosphine group used in the Ni hydride complex. The observed ratios of n-propyl- to isopropyl-nickel found after the insertion step vary from 82 18 to 82 20 to 19 81 as the phosphine is changed from P(OC6Hs)3 to P(c-C6Hu) to P(t-C4H9)2(i-C3H7). ... 

They confirmed the reaction mechanism and underlined the effect of tertiaiy phosphanes on the regioselectivity of the linking of propene molecules. This complex is soluble only in chlorinated hydrocarbons. Many other systems based on nickel catalyze the dimerization reaction and have been described in many publications and patents. 

Nickel-catalyzed hydrocyanation of a-olefins t)q)ically produces the terminal nitrile as the more abundant, but not exclusive isomeric product. In contrast, nickel-catalyzed hydrocyanation of vinylarenes typically generates the branched product. This branched selectivity arises fijom the stability of -phenethyl complexes, as is shown in more detail in Section 16.2.5 on as)unmetric hydrocyanation. The relative rates for hydrocyanation follow the trend ethylene > styrene > propene 1-hexene > disubstituted olefins. Examples of these reactions and selectivities for formation of the linear and branched products are shown in Scheme 16.1. ... 

It was shown that room-temperature molten salts derived from the combination of 1,3-dialkylimidazolium chloride and A1C13 can be used as solvents in two-phase catalytic dimerization of propene to give hexenes catalyzed by Ni(II) compounds (125). The effects of phosphane ligands coordinated to nickel and operating variables were also investigated (126). The dimerization products separate as an organic layer above the molten salt. This reaction has been carried out with n-butenes as the reactant and cationic nickel complex catalysts dissolved in organochloroaluminate liquids (127). 

The applied nickel catalyst, promoted by copper halides, required rather severe reaction conditions T = 220 °C, F = 10 MPa), but gave good AA yields up to 90% based on acetylene. This so-called catalytic Reppe process was commercially operated in Germany, the USA, and Japan. Due to the limited availability of cheap acetylene as feedstock and the severe reaction conditions involved in the carbonylation process, this process has lost the competition with (heterogeneously catalyzed) oxidation of readily available propene, even though a perfect selectivity to AA is not achieved in the latter process. 

Indeed, methyl rw-6,6-dimethyl-2-(triphenylphosphanyl)-2-nickelabicyclo[3.1.0]hexane-3-carboxylate (13) [and the corresponding ethenebis(dimethylphosphane) complex] was isolated in 65% yield from the conversion of (/7 -methylacrylate)bis(triphenylphosphane)nickel and 3,3-dimethylcyclopropene. The former complex catalyzes the cotrimerization of dimethylcyclo-propene with methyl acrylate with almost identical activity as earlier observed with an in situ catalyst obtained by mixing bis(cycloocta-l,5-diene)nickel and triphenylphosphane (1 1). Thus, this metallacyclic system can be regarded as an intermediate in the co-cyclotrimerization reaction. ... 

HF reaction with 3-chloro-pentafluoro-l-propene (CF2=CF-CF2C1) at 200°C, catalyzed by activated carbon, yields HFP. l Hexafluoropropylene can be prepared from the catalytic degradation of fluoroform (CHF3) at 800-1000°C in a platinum-lined nickel re-actor.l l Another method is copyrolysis of fluoroform and chlorotrifluoroethylene (CF2=CFCl),f l or chlorodifluoromethane and l-chloro-1,2,2,2-tetrafluoroethane (CHClFCFg), giving good yields of HFP. 

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