Buchwald palladacycles

Application of Buchwald palladacycles and imidazole-derived monophosphines... 

A plausible mechanism for the one-pot synthesis ofcarbazoles is shown in Scheme 5. It consists of two interlinked catalytic cycles. In the first cycle a classical Buchwald-Hartwig amination reaction occurs to generate an intermediate 5 which then enters the second cycle by oxidative addition to Pd(0). The resulting Pd(II) complex then undergoes intramolecular C-H activation to give a six-membered palladacycle which subsequently yields the carbazole by reductive elimination. 

Ar = 2,6-diisopropylphenyl Scheme 16 A palladacycle-mediated Buchwald-Hartwig reaction... 

Zim and Buchwald synthesized the palladacyclic phosphine complex 44 based on their ligand P(Bu-f)2(o-biphenyl) 13 (equation 46)157. This air- and moisture-stable palladium complex is a convenient one-component precatalyst for animation of aryl chlorides when combined with sodium tert-butoxide or sodium methoxide. For coupling of anilines, the addition of NEt3, which is possibly acting as the reducing agent to produce Pd(0), is necessary. 

Bedford used a palladacycle complex [130], while Vilar investigated a variety of homobimetallic palladium complexes [131]. These species are based on Buchwald s biphenyl-type ligands and were found to be excellent precatalysts for aminations of aryl chlorides. 

Bedford RB (2008) PaUadacyclic pre-catalysts for Suzuki coupling, Buchwald-Hartwig ami-nation and related reactions. In Dupont J, Pfeifer M (eds) Palladacycles. Synthesis, characterization and applications. Wiley-VCH, Weinheim, p 209... 

In 2008, Application of CyclopaUadated Compounds as Catalysts for Heck and Sonogashira Reactions, by Najera and Alonso [110], Palladacyclic Precatalysts for Suzuki Coupling, Buchwald-Hartwig Amination and Related Reactions Bedford [111]... 

Scheme 8.59 Monoarylation of methyl esters using the palladacycle developed by Biscoe and Buchwald [107].

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