Reactions Involving Organopalladium Intermediates

A second type of organopalladium intermediates are 7r-allyl complexes. These complexes can be obtained from Pd(II) salts and allylic acetates and other compounds with potential leaving groups in an allylic position.79 The same type of 7i-allyl complexes can be prepared from alkenes by reaction with PdCl2 or Pd(02CCF3)2.80 The reaction occurs by electrophilic attack on the n electrons followed by loss of a proton. The proton loss probably proceeds via an unstable species in which the hydrogen is bound to 

The re-allyl complexes can be isolated as halide-bridged dimers. 

These rc-allyl complexes are electrophilic in character and undergo reaction with a variety of nucleophiles. After nucleophilic addition occurs, the resulting organopalladium intermediate usually breaks down by elimination of Pd(0) and H+. 

Specific examples of these reactions will be discussed below. 

These vr-allyl complexes are electrophilic in character and undergo reaction with a variety of nucleophiles. 

After nucleophilic addition occurs, the resulting organopalladium intermediate usually breaks down by elimination of Pd(0) and 

The third general type of reactivity involves the reaction of Pd(0) species with halides by oxidative addition, generating reactive intermediates having the organic 

The o--bonded species formed by oxidative addition can react with alkenes and other unsaturated compounds to form new carbon-carbon bonds. Specific examples of this type of reaction will be discussed below. 

Another general process involves the reaction of Pd(0) species with halides or sulfonates by oxidative addition, generating reactive intermediates having the organic group attached to Pd(II) by a ct bond. The oxidative addition reaction is very useful for aryl and alkenyl halides, but the products from saturated alkyl halides often decompose by (3-elimination. The a-bonded species formed by oxidative addition can react with alkenes and other unsaturated compounds to form new carbon-carbon bonds. The 

These are called cross-coupling reactions and usually involve three basic steps oxidative addition, transmetallation, and reductive elimination. In the transmetallation step an organic group is transferred from the organometallic reagent to palladium. 

Organopalladium intermediates are also involved in the synthesis of ketones and other carbonyl compounds. These reactions involve acylpalladium intermediates, which can be made from acyl halides or by reaction of an organopalladium species with carbon monoxide. A second organic group, usually arising from any organometallic reagent, can then form a ketone. Alternatively, the acylpalladium intermediate may react with nucleophilic solvents such as alcohols to form esters. 

In considering the mechanisms involved in organopalladium chemistry, several general points should be kept in mind. Frequently, reactions involving organopalladium 

---

One of the most synthetically useful reactions involving organopalladium intermediates is that between rr-allyl complexes and relatively stable carbanions such as those derived from malonate esters and jS-ketoesters. The tt- allyl complexes can be synthesized separately and used in stoichiometric amount or they can be generated in situ by reaction of allylic acetates with a catalytic amount of tetrakis (triphenylphosphine)palladium. In the catalytic version of the reaction, the tt-allyl complex is formed by reaction of the allylic acetate and the Pd(0) species which is regenerated in the elimination step. 

---