Chlorobenzene, reaction with nickel complexes

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. 

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". 

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... 

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... 

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. 

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) ... 

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