Active Nickel-Mediated Dehalogenative Coupling of Aryl and Benzylic Halides

8 Active Nickel-Mediated Dehalogenative Coupling of Aryl and Benzylic Halides 

Considerable interest has centered on the use of zerovalent transition metals and their complexes as selective and mild reagents in organic synthesis [74]. However, some of the useful complexes coordinated with ligands such as phosphine or carbon monoxide are unstable and not easy to prepare or are toxic. Other studies using the metal atom vaporization techniques have also been successful in employing transition metals in synthesis [119]. In many cases, however, this approach does not lend itself to being completely general. 

There are few reports of oxidative addition of metallic transition metals under mild conditions [120] two reports involving group 8 elements have appeared. Fischer and Burger reported the preparation of the n -allylpalladium complex by the reaction of a palladium sponge with allyl bromide [121]. The Grignard-type reaction addition of allyl haUdes to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy thiourea [122]. 

---

Active Nickel-Mediated Dehalogenative Coupling of Aryl and Benzylic Halides 287 Table 7.12 Reaction of bromobenzenes with activated nickel powder. 

---