Activation of a Substrate toward Nucleophilic Attack

In Fig. 4.35 the nucleophile depicted is anionic, but Nu may also be a neutral nucleophile, such as an amine or H2O. There are many alkene complexes of middle and late transition elements which undergo this type of reaction, e.g. M = Pd2+, Pt2, Hg2+, Zn2+, FeCp(CO)2+. The addition reaction of this type is the key step in the Wacker-type processes catalyzed by palladium. 

Alkynes show the same reaction, and again the product obtained is the trans isomer. After a suitable elimination from the metal the alkene obtained is the product of the trans-addition. Earlier we have seen that insertion into a metal-hydride bond and subsequent hydrogenolysis of the M-C bond will afford the c/s-alkene product. Thus, with the borohydride methodology and the hydrogenation route, both isomers can be prepared selectively. 

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