Palladium-Catalyzed Organic Reactions

Malleron, J.-L. Fiaud, J.-C. Legros, J.-Y. Handbook of Palladium-catalyzed Organic Reactions Academic Press, 1997. 

The initial step of the catalytic cycle is oxidative addition of aryl triflate to a BINAP-coordinated Pd(0) species. Since, in the actual catalytic system, Pd(OAc)2 and (/ )-BINAP are used as the precursors of the Pd(0) species, reduction of Pd(OAc)2 into the BINAP-coordinated Pd(0) species should be operative prior to the catalytic reaction. Although Pd(OAc)2 is the most commonly used precursor of a Pd(0) species in many palladium-catalyzed organic reactions, no direct information has been reported so far on its reduction process. In this study, we confirmed for the first time that the reduction proceeds according to the process involving a combination of tertiary phosphine (BINAP) and water as the reducing reagent (Scheme 8) (Ozawa, F. Kubo, A. Hayashi, T., submitted for publication). 

The numerous palladium-catalyzed organic reactions have a relatively small number of elementary steps. Oxidative Addition, Reductive Elimination, ligand coordination, and addition to coordinated ligands (either intramolecular or intermolecu-lar) are the most important classes of transformations in most palladium catalytic cycles. The exact nature of the species within the coordination sphere of palladium and the order in which the steps take place are responsible for the variety of the organic products produced. Four representative and important palladium-catalyzed reactions are briefly discussed here to illustrate the range of organopalladium reactions. 

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... 

The Wacker oxidation is one of the longest known palladium-catalyzed organic reactions. It is the industrial process where ethylene is oxidized to acetaldehyde with oxygen in the presence of a catalytic amount of palladium and copper salt as the redox co-catalyst.1 There are plants that produce thousands of tons of acetaldehyde per year. Many reviews exist on this topic.2-6... 

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