Coupling reactions nickel chloride

The Ni(ii)/Cr(n)-mediated coupling reaction employs an excess of chromium(ii) chloride and a catalytic amount of nickel(n) chloride (0.1 %). The preferred solvent for this reaction is usually DMF, although THF, DMF/THF, or DMF/Me2S may also be used. The ability to activate the vinyl iodide (or related) substrate at ambient... 

However, the Buchwald-Hartwig reaction with NHCs as hgands is not limited to palladium. Nickel has also been successfully employed in this catalytic amination. In situ procedures have been described for the coupling of aryl chlorides [163] and tosylates [164] and, more interestingly, anisoles [165]. The use of well-defined Ni(0) catalysts has also been studied [166] (Scheme 6.49). 

Activated aryl chlorides, which are close in reactivity to unactivated aryl bromides, underwent reaction with the original P(o-tol)3-ligated catalyst.58 Nickel complexes, which catalyze classic C—C bond-forming cross-couplings of aryl chlorides, 9-64 also catalyzed aminations of aryl chlorides under mild conditions.65,66 However, the nickel-catalyzed chemistry generally occurred with lower turnover numbers and with a narrower substrate scope than the most efficient palladium-catalyzed reactions. 

An intermediate acylnickel halide is first formed by oxidative addition of acyl halides to zero-valent nickel. This intermediate can attack unsaturated ligands with subsequent proton attack from water. It can give rise to benzyl- or benzoin-type coupling products, partially decarbonylate to give ketones, or react with organic halides to give ketones as well. Protonation of certain complexes can give aldehydes. Nickel chloride also acts as catalyst for Friedel-Crafts-type reactions. 

In the late 1970s and early 1980s, Kumada described nickel-catalyzed asymmetric cross-coupling reactions of 1-arylethylmagnesium chlorides with vinyl bromide in... 

Figure 3.49. Chiral ligands that exhibit high enantioselectivity in the nickel-catalyzed Grignard cross-coupling reaction of vinyl bromide (or chloride) with 1-phenylethylmagne-sium chloride.

Carbon-nitrogen bonds can be made using similar coupling reactions. With nickel complexes of chelating phosphines such as l,l -bis(diphenylphosphino)ferro-cene, even the generally unreactive aryl chlorides can be converted to anilines.94... 

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