Phospha-palladacycles

A range of different palladium compounds immobilised in [(C NJBr have been screened in the coupling between styrene and chlorobenzene, with or without additional co-ligands. Apart from various simple palladium(II) salts these compounds included the carbene complexes 16-18 and the phospha-palladacycles 19 and 20, shown in Figure 6.1.[61,621... 

Herrmann, W. A., Ofele, K., von Preysing, D., Schneider, S. K. Phospha-palladacycles and N-heterocyclic carbene palladium complexes efficient catalysts for CC-coupling reactions. J. Organomet. Chem. 2003, 687, 229-248. 

Bohm, V.P.W. and Herrmann, W.A. (2001) Mechanism of the Heck reaction using a phospha-palladacycle as the catalyst classical versus palladium(IV) intermediates. Chem. Eur. J., 7, 4191-7. 

Herrmann, W.A. and Bohm, V.P.W. (1999) Heck reaction catalyzed by phospha-palladacycles in non-aqueous ionic Uquids. J. Organomet. Chem., 572, 141-5. 

Figure 15.1 Benzimidazolylidene palladium complex 2 and phospha-palladacycle 3 as...

Phospha-palladacycles are also powerful palladium catalysts for the Mizoroki-Heck reaction. Complexes like 3 (Figure 15.1) were successfully tested in Bu4NBr as solvent for the coupling of styrene (4) and chloroarenes (e.g. 5, X = Cl) in the presence of sodium acetate and [AsPh4]Cl, leading to 96% yield i(E)-6 (Z)-6 7 = 95 1 4) (Scheme 15.2)... 

Related Pd-catalyzed C-C coupling processes have also been described using 4-(2-bromophenoxy)coumarins 77, readily accessible from commercially available 4-bromocotmiarin and 2-bromophenols, as substrates (Scheme 35) [132], The reachons, performed in 1,4-dioxane with catalytic amotmts of the phospha-palladacycle complex 78 and three equivalents of K2CO3, afforded the corresponding cotunestan derivatives in excellent yields after 24 h of heating at 140 °C in 1,4-dioxane. 

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