Metal-Catalyzed Direct Arylations excluding Palladium

Metal-Catalyzed Direct Arylations (excluding Palladium) 

The regioselechvihes of direct arylations can be controlled when the electrordc properhes of a given arene dominate its reachvity. This holds true for a variety of heteroarenes, and has enabled highly regioselechve palladium-catalyzed direct funchonahzahons of electron-rich, as well as electron-deficient arenes (these are 

Modem Arjlation Methods. Edited by Lutz Ackermann 

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

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 metal atalyzed direct arylations is provided in Chapter 11. 

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I 9 Metal-Catalyzed Direct Arylations (excluding Palladium)... 

I 9 Metal-Catalyzed Direct Arylations (excluding Palladium) [RuCl2(p-cymene)]2 (2.5 mol%)... 

Mechanistic studies performed with Freeh s pincer catalyst in the Heck reaction excluded catalytic cycles with the involvement of homogeneous palladium(O) species, as indicated by the results obtained from the (recently developed) dibenzyl-test, which is directly applicable under the reactions conditions applied [24aj. Dibenzyl formation was - in contrast to Heck reactions catalyzed by palladium(O) complexes of type [Pd(PR3)2, where Pd /Pd" cycles are operative - not detectable by gas chromatography-mass spectrometry (GC/MS) when reaction mixtures of aryl bromide, olefin, benzyl chloride ( 10 mol% relative to aryl bromide), catalyst, and base were thermally treated. On the other hand, experimental observations, such as quantitative poisoning experiments with metallic mercury and CS2, which were shown to eflfidently inhibit catalysis, as well as analysis of the reaction profiles showed sigmoidal-shaped kinetics with induction periods and hence indicated that palladium nanoparticles are the catalytically active form... 

With the electTOTi-poor allenic esters, palladium(0) is able to catalyze the reaction without gold. The reactiOTi then is initiated at the other end, after oxidative addition of the aryl halide to the electrophilic palladium(II) species cycloisomerizes the allenic ester and then forms the product by reductive elimination. With o-alkynylbenzoates, the intermediate vinylgold species contains an enol ether substructure and is able to directly intercept the activated allyl donors, even in the absence of palladium. In both cases, by careful trace analysis (ICP), the presence of the other metal was excluded [78]. 

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