Suzuki coupling palladium carbene complexes

A silver(i) complex having the heterosubstituted 3-methyl-l-(2-pyridylmethyl)imidazol-2-ylidene ligand, [Ag(carbene)2] [I/Agl2] 37, was reported, which was further reacted to give a series of palladium(n) carbene complexes that were demonstrated to be active catalysts toward Heck, Suzuki, and Sonogashira coupling reactions.87... 

Other palladium acetylacetonate complexes have also been developed for cross-coupling reactions. Indeed, an acac paUadacycle complex has recently been observed to effectively catalyze both the Suzuki-Miyaura and Heck reactions. Likewise, the A-heterocyclic carbene complex Pd(acac)Cl(ipr) (96) is an excellent catalyst for the formation of C—N and C—C bonds (equation 27) These catalysts were effective for coupling of ketones... 

On the nature of the active species in palladium catalyzed Mizoroki-Heck and Suzuki-Miyaura couplings (particularly, Pd complexes with imi-nopyridine and N-heterocyclic carbenes as ligands) 06ASC609. 

Ozdemir, L, Yigit, M., Cetinkaya, E. and Cetinkaya, B. (2006) Synthesis of novel palladium IV-heterocyclic-carbene complexes as catalysts for Heck and Suzuki cross-coupling reactions. 

Imidazolium-linked ortbo-cyclophane reacts with nickel(II) and palladium(II) salts in the presence of acetate base to afford complexes where a metal centre is bound by a pair of heterocyclic carbenes, which themselves are part of a cyclophane skeleton. These cyclophane-metal complexes have been characterized by NMR spectroscopy and X-ray diffraction studies. They are highly active as promoters of Suzuki couplings [69]. 

The performance of complex 10 bearing a quinolinylidene as a remote car-bene ligand (Figure 5.5) was compared to that of simple imidazol-2-ylidene and phosphine-containing palladium catalysts in the Heck coupling of activated and non-activated aryl bromides with butyl acrylate. " The remote carbene complex showed much higher activity in these reactions as well as in the Suzuki coupling of a deactivated aryl bromide with phenylboronic acid. Since the complexes tested were structurally very different, purely electronic comparisons... 

Through the direct coupling of 2-bromo-4,4-dimethyloxazoline 189 and 1-mesityl imidazole (188) the corresponding imidazolium salt 190 was obtained and used for the preparation of a mono-carbene-palladium complex 191 active as a catalyst in Heck and Suzuki C-C coupling reactions <020M5204>. 

Apart from palladacycles, a number of catalyst systems are currently known that show productivities up to 100,000 for Heck and Suzuki reactions of all kinds of aryl bromides. It is important to note that coupling reactions of electron-deficient aryl bromides (e.g., 4-bromoacetophenone), which are often used in academic laboratories, are not suitable as test reactions to judge the productivity of a new catalyst, because simple palladium salts without any Ugand give turnover numbers up to 100,000 with these substrates. Recently, palladium complexes in combination with sterically congested basic phosphines (e.g., tri-tcrt-butylphosphine), carbenes, and also phosphites led to productive palladium catalysts for the activation of various aryl chlorides. 

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