Catalytic hydrogenation hydridopalladium complexes

The broad reactivity pattern displayed by transition metal hydrides is of special relevance in catalytic reactions " and has led to a great deal of theoretical studies. " The organometallic chemistry of hydridopalladium complexes has been reviewed. The involvement of hydridopalladium species is prevalent in Pd-catalyzed reactions. Then-precise roles in catalytic hydrogenation (Sect. VII), Tsuji-Trost (Sect. V.2.1), and other related reactions are covered in detail in later sections. Only a brief introduction to their general reactivity of mechanistic relevance will be presented here. 

Olefinic compounds will often insert into carbon-transition metal bonds as CO does, and this reaction is an important step in many catalytic syntheses. When this step is combined with an oxidative addition of an organic halide to a palladium(O) complex in the presence of a base, a very useful, catalytic olefinic substitution reaction results (26-29). The oxidative addition produces an organopalladium(II) halide, which then adds 1,2 to the olefinic reactant (insertion reaction). The adduct is unstable if there are hydrogens beta to the palladium group and elimination of a hydridopalladium salt occurs, forming a substituted olefinic product. The hydridopalladium salt then reforms the... 

A variety of palladium-catalyzed organic reactions involve the oxidative addition process. A typical example is seen in the catalytic arylation and alkenylation of olefins (eq (60)) [85]. Aryl- and alkenylpalladium(ll) complexes (9) formed by oxidative addition undergo olefin insertion into the palladium-carbon bond to give an alkylpal-ladium species (10), which provides arylated and alkenylated olefins via p-hydrogen elimination. The hydridopalladium species 11 thus generated is reduced to a Pd(0) species upon its interaction with a base and carries the sequence of reactions... 

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