Mechanistic Aspects of Transition Metal-Catalyzed Direct Arylation Reactions

Mechanistic Aspects of Transition Metal-Catalyzed Direct Arylation Reactions 

The vast majority of methods are based on the use of palladium complexes as catalysts, although copper, ruthenium, rhodium and iridium catalysts have also been used. Progress in the understanding of the mechanisms of these reactions has only been made during the past few years. As comprehensive reviews have been recently published on aryl-aryl bond-formation reactions, covering both mechanistic and synthetic aspects of these reactions [3-7], in this chapter we wiU summarize only those mechanishc studies on metal-catalyzed arylation reactions that have been carried out in detail. 

Modem Arylation Methods. Edited by Lutz Ackermann 

Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim 

Although the results of these experiments suggest that the palladation proceeds by an electrophilic aromatic substitution, the transformations are probably more complex than the above results suggest. Indeed, the reaction of alkyl palladium complex 6a with KOPh in MeCN was almost completely inhibited by the addition of lequiv. of PPhs [29], which indicates that ligand substitution, presumably by an associative mechanism, occurs during the C—H bond-activation process. Biden- 

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I 7 7 Mechanistic Aspects of Transition Metal-Catalyzed Direct Arylation Reactions... 

Although the direct arylation reactions catalyzed by transition metal complexes (other than palladium) are discussed in this chapter, the corresponding palladium-catalyzed transformations are summarized in Chapter 10. A detailed overview of the mechanistic aspects of metaldirect arylations is provided in Chapter 11. 

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