Reactions Involving Organonickel Compounds

Procedures for synthesis of ketones based on coupling of organostannanes with acyl chlorides have also been developed.The catalytic cycle is similar to that involved in the coupling with alkyl or aryl halides. The scope of compounds to which the procedure can be applied is wide and includes successful results with tetra- -butylstannane. This example implies that the reductive elimination step in the mechanism can compete successfully with j5-elimination. 

Carbonylation can also be carried out via in situ generation of other types of electrophiles. For example, good yields of A/-acyl a-amino acids are obtained in a process in which an amide and aldehyde combine to generate a carbinolamide and, presumably, an acyliminium ion. The organopalladium intermediate is then carbonylated.  

The original synthetic processes using organonickel compoimds involved the coupling of halides. Allylic halides react with nickel carbonyl, Ni(CO)4, to give 7r-allyl 

These coupling reactions are believed to involve Ni(I) and Ni(III) intermediates in a chain process which is initiated by formation of a small amount of a Ni(I) species. 

Nickel carbonyl effects coupling of allylic halides when the reaction is carried out in very polar solvents such as DMF or DMSO. This coupling reaction has been used intramolecularly to bring about cyclization of bis-allylic halides and was found useful in the preparation of large rings. 

The most useful synthetic processes which have been developed around the chemistry of nickel involve the coupling of halides. Allyl halides react with nickel carbonyl, Ni(CO)4, to give 7r-allyl complexes. These compounds can react with a variety of halides to replace the halogen with an allyl group.These reactions 

Another nickel complex, bis-(l,5-cyclooctadiene)nickel(0), (COD)2Ni, has been found to bring about coupling of other halides, in addition to the allylic types that are reactive toward nickel carbonyl  

SECTION 6.4. SYNTHETIC APPLICATIONS OF OTHER TRANSITION METALS 

This reaction can be made catalytic in nickel by use of zinc as an in situ reductant to regenerate the active nickel(O) species. 

---