Nickel leaving groups

Where the nucleophile is the conjugate base of a primary amine, NH2 can be a leaving group. The method has been used to prepare secondary amines.827 In another process, primary amines are converted to secondary amines in which both R groups are the same (2RNH2 — R2NH + NH3)828 by refluxing in xylene in the presence of Raney nickel.829 Quaternary salts can be dealkylated with ethanolamine.830... 

Neither the palladium nor nickel catalyst described will promote the carbonylation of saturated aliphatic halides as noted above. However, this reaction can be catalyzed with cobalt (17) or iron (77) and probably with manganese (18) carbonyl anion salts. These carbonyl anions are strongly nucleophilic species and readily displace halide or other good leaving groups from primary or secondary positions giving alkyl metal carbonyl complexes. 

Cross-coupling is the reaction of an organometallic reagent R-M with an organic compound R -X (X is a leaving group) to give a product R-R and is often catalyzed by a complex of a transition metal such as nickel or palladium fEq.(l)] [1],... 

Trost and Martin have used the dimethylsulfoxonium ion to provide a leaving group. Thus, a cis addition of DMTSF to alkenes flrst led to adducts of the type (15), which then reacted with lithium alkynides in the presence of diethylaluminum chloride to give the trans adduct (Scheme 28). The reaction is presum to involve the episulfonium ion, which then ensures the observed stereospecificity. The reaction is also regiospecific, the anti-Markovnikov addition being illustrated by the second example in Scheme 28. The adducts can be converted to alkanes with Raney nickel and to alkenes by sulfoxide formation and elimination. 

The synthesis of such eight-membered rings by the nickel-catalysed dimerisation of butadienes, is used here with 2-methylbutadiene. The regio-selectivity and stereo-specificity of the hydro-boration of symmetrical 124 are as expected for a trisubstituted alkene. Conversion of the alcohol 125 into a good leaving group 126 made it reactive enough to carry out electrophilic addition on the other alkene. In aqueous solution, the final nucleophile was water and the product a mixture of diastereoisomers of the tertiary alcohol 127. 

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