Nickel-catalysed coupling reactions

Palladium- (and nickel-) -catalysed coupling reactions proceed normally on halodiazines and the equivalent triflates, the most significant feature being the enhanced reactivity relative to chlorobenzenes of chlorine at position a and 7 to a nitrogen, just as in pyridine chemistry. In some particularly activated caes, this extra activation is sufficient to overcome the normally higher reactivity of bromine, but not... 

Palladium- (and nickel-) catalysed coupling reactions proceed normally on halo-diazines, the most significant feature, as with pyridines, being the enhanced reactivity, relative to chlorobenzene, of chlorine at positions a and y to a nitrogen, but it is important to recognise that this activation does not overcome the higher intrinsic reactivity of bromine and iodine at any position." ... 

During nickel-catalysed coupling reactions of aryl halides, following side-reactions were observed ... 

Organozinc reagents, including the Reformatsky reagents, are extensively used in transition metal catalysed coupling reactions with aryl halides or triflates, vinyl halides, and allylic halides or acetates, as reviewed by Erdik156. Nickel and palladium complexes are... 

Nickel-catalysed coupling of enynes (46) with allyl chlorides has been reported to occur in the presence of zinc the reaction gives rise to the cyclic products (47) in good yields.71... 

Tetrazolyl ethers can be used in two ways to activate phenols for nickel- or palladium-catalysed coupling reactions, as illustrated above or to allow catalytic hydrogenolysis of the C-O bond of the phenol. 

Organozinc, organomagnesium or other organometallic species can be effective partners in palladium-catalysed coupling reactions. Metals other than palladium(O), such as nickel(0) or copper(I) (see Section 1.2.1), can alternatively be used to promote cross-coupling of unsaturated halides and organometallic species. ... 

A nickel-catalysed coupling of alcohols and allgmes to form allylic alcohols was also reported (Scheme 14.64). The combination of Ni(COD)2 and IPr is an effective catalyst and no additives are needed. Both aliphatic and benzylic alcohols are suitable for this transformation. The reaction proceeds smoothly under mild conditions, generating allylic alcohols in good )delds. 

Similar process takes place during palladium- and nickel-catalysed couplings of aryl halides via various diarylnickel(ll, III or IV)- or diarylpalladium(lV) intermediates. In the case of the related Heck reaction [19], palladium(IV) intermediate has been isolated and characterized [20]. 

Transmetallation of the organic group from zirconium to another metal opens up possibilities. The palladium-catalysed coupling reactions can be found in Section 2.4. Addition of dimethyl cuprate results In transmetallation to copper. The resulting cuprate then displays typical cuprate reactivity, such as addition to enones. More economically, small amounts of copper can catalytically activate the zirconium complex towards this kind of chemistry, although the precise mechanism is unclear. Additions to enones can also be achieved directly using nickel catalysis (Scheme 5.64). Transmetallation to zinc has also been demonstrated. ... 

Pyridine compounds 45 can also be produced by the NHC-Ni catalysed cycloaddition between nitriles 43 and diynes 44 (Scheme 5.13) [16]. The SIPr carbene was found to be the best ligand for the nickel complex in this reaction. The reaction required mild reaction conditions and low catalyst loadings, as in the case of cycloaddition of carbon dioxide. In addition to tethered aUcynes (i.e. diynes), pyridines were prepared from a 3-component coupling reaction with 43 and 3-hexyne 23 (Scheme 5.13). The reaction of diynes 44 and nitriles 43 was also catalysed by a combination of [Ni(COD)J, NHC salts and "BuLi, which generates the NHC-Ni catalyst in situ. The pyridines 45 were obtained with comparable... 

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