Suzuki-type reactions palladium catalyst

An efficient aqueous phase Suzuki-Miyaura reaction of activated aryl chlorides with aryl boronic acids has been reported. The method uses a new D-glucosamine-based dicyclohexylarylphosphine ligand for the palladium catalyst and works well with nitro-and cyano-activated chlorides.32 The aryl fluoride bond has been considered inert to palladium-catalysed substitution reactions. However, a computational study, backed up by experiment, shows that the presence of a carboxylate group ortho to fluorine will allow reaction both with phenylboronic acids in a Suzuki-type reaction and with organotin reagents in a Stille-type reaction the presence of the adjacent oxyanion stabilizes the transition state.33... 

The rather classic catalyst palladium on activated carbon has been applied by Sun and Sowa et al. [183] and Heidenreich et al. [158] without additional ligands. This simple system was able to convert (mainly activated) aryl chlorides in mixtures of water and an organic solvent (DMA and NMP, respectively). Lysen et al. were able to convert aryl chlorides in pure water and without addition of any ligand [184,185]. Suzuki reactions using Pd/C in an aqueous medium were also reported by Arcadi et al. (in the presence of surfactants) [186] and the group of Leadbeater, who applied microwave techniques [187]. Microwave (as weU as ultrasound) conditions were also employed by Cravotto and Palmisano et al. [188] The substrate scope of Suzuki-type reactions in the presence of Pd/C was extended to halopyri-dines and haloquinoUnes by Tagata and Nishida [189]. 

Alternative sulfonate leaving groups besides triflate have not been reported to be active in Pd catalyzed Suzuki-type reactions. Aryl mesylates, benzenesulfonates and tosylates are much less expensive than triflates and are usually unreactive towards palladium catalysts. However, in the first example of the use of a Ni-catalyst in the Suzuki reaction, aryl mesylates participated in cross-coupling reactions with arylboronic acids in good yields (equation 48) (745). 

Yamada, and Suzuki laid the base for one of the most important and useful transformations for the construction of C-C bonds in the modem day organic chemistry. The Suzuki reaction becomes popular because of the ready availability of a wide range of functionally substituted boron derivatives and the mildness of the coupling reaction itself Suzuki reactions generally employ organic solvents such as tetra-hydrofliran and ethers as well as complex palladium catalysts, which are soluble in these solvents (Miyaura and Suzuki, 1995). The use of microwave heating is a convenient way to facilitate the Suzuki-type reactions in water (Leadbeater and Marco, 2002). 

Other successful examples of catalysts containing NHC ligands are found in palladium- and nickel-catalyzed carbon-carbon bond formations. The catalyst development with these metals has focused in particular on Heck-type reactions, especially the Mizoroki-Heck reaction itself [Eq. (42)] and various cross coupling reactions [Eq. (43)], e.g., the Suzuki-Miyaura reaction ([M] = and the Kumada-Corriu reaction ([M] = MgBr). " Related reactions like the Sonogashira coupling [Eq. (44)]326-329 Buchwald-... 

The examples reported to date do not allow a clear ranking of palladium catalysts with regard to their ability to catalyze the Suzuki reaction. It should also be kept in mind that palladium(O) complexes are air-sensitive, and the quality of commercially available catalysts of this type can vary substantially. Some successful Suzuki couplings are listed in Table 5.12. Further examples have been reported [184,186-196],... 

One of the challenges in the Suzuki-type cross-coupling is to extend this reaction from electron-rich aryl iodides, bromides, and triflates to less reactive aryl sulfonates and aryl chlorides, which show poor reactivity in terms of oxidative addition in the catalytic cycle. Aryl mesylates, benzenesulfonates, and tosylates are much less expensive than triflates, and are unreactive toward palladium catalysts. The Ni(0)-catalyzed Suzuki-type cross-coupling reaction of aryl sulfonates, including mesylates, with arylboronic acids in the presence of K3P04 has been reported [123]. 

Aryl diazonium salts can be used coupled with alkenes in a Heck-Uke reaction (12-15)7 Other reactive aryl species also couple with aryldiazonium salts in the presence of a palladium catalyst7 A Suzuki type coupling (13-9) has also been reported using arylboronic acids, aryldiazonium salts and a palladium catalyst/ ... 

The cationic palladium(II) complex [Pd(24a)3Cl]+ of the para-isomer of 24a (M = Na) catalyzes the carbonylation of benzyl chloride in basic medium to give phenyl-acetic acid in high yields. The Pd(0) complex [Pd(24a)3], formed by reduction of [Pd(24a)3Cl]+ with CO, is asumed to be the catalytic species [93] (see Scheme 1). Palladium complexes of ligands related to 24a (M = Na) have also been employed in aqueous ethylene glycol phases as catalysts for Suzuki-type C—C cross-coupling reactions for the syntheses of substituted biphenyls (cf. Section 6.6) [97]. 

Suzuki-type C-C coupling reactions with palladium-phosphine complexes as catalysts can also be promoted by surfactants [21] in a toluene/water biphasic system. 

---