Suzuki catalysts

Figure 13.31. IMes and IPr carbene ligands for Suzuki catalysts Application of the Suzuki cross-coupling reaction...

Yin, J. Rainka, M. P. Zhang, X.-X. Buchwald, S. L. A highly active Suzuki catalyst for the synthesis of sterically hindered biaryls novel ligand coordination. J. Am. Chem. Soc. 2002, 124, 1162-1163. 

Similarly, Pd-mediated sp2-sp2 C—C (Suzuki-Miyaura) coupling has been enabled in biology through the development of an aqueous biologically compatible Suzuki catalyst system [152], This has now allowed the synthetic glycosylation of whole cell surfaces to create bacterial strains with a synthetic glycocalyx [153],... 

In an earlier investigation by the author [1] an emulsion polymerization was used to prepare the products of the current invention using dichlorobis(triphe-nylphosphine) palladium(II) as the Suzuki catalyst. 

The standard Suzuki catalysts are complexes of zerovalent Pd of which Structures 1 and 2 are most frequently used. 

Rocaboy, C. and Gladysz, J.A. (2003) Thermomorphic fluorous imine and thioether pallada-cycles as precursors for highly active Heck and Suzuki catalysts evidence for palladium nanoparticle pathways. NewJ. Chem., 27, 39 9. 

The Suzuki coupling reaction, also called the Suzuki-Miyaura reaction, couples an aryl, or vinyl halide to an aryl or vinyl boronic acid in which the Suzuki catalyst—a palladium catalyst with four triphenylphosphine ligands—plays the central bond forming role. 

The Suzuki catalyst has the rather forbidding name tetrakis(triphenylphosphine)paUadi-um(0). This looks a bit less complex when we write its condensed formula Pd[P(C6H5)3l4. Since Ph is a common abbreviation for the phenyl group, C Hg, we can condense the formula even more as Pd(PPh3)4. The palladium atom sits at the center of a tetrahedron and has an oxidation number of zero (Figure 17.4). The phosphorus atom of the triphenylphosphine donates an electron pair to a vacant 4d orbital of Pd(0) without altering its oxidation state. 

Palladium-catalyzed carbon-carbon bond forming reactions like the Suzuki reac-tion as well as the Heck reaction and the Stille reaction, have in recent years gained increased importance in synthetic organic chemistry. In case of the Suzuki reaction, an organoboron compound—usually a boronic acid—is reacted with an aryl (or alkenyl, or alkynyl) halide in the presence of a palladium catalyst. 

The postulated steps that constitute the Suzuki coupling process are shown in Scheme 25. After oxidative addition of the organic halide to the palladium(o) catalyst, it is presumed that a metathetical displacement of the halide substituent in the palladium(ii) complex A by ethoxide ion (or hydroxide ion) takes place to give an alkoxo-palladium(ff) complex B. The latter complex then reacts with the alkenylborane, generating the diorganopalladium complex C. Finally, reductive elimination of C furnishes the cross-coupling product (D) and regenerates the palladium(o) catalyst. 

The Suzuki reaction97 allows tire coupling of two aromatic rings by reaction of an arylboronic compound with a iodo or bromo aryl derivative. The tetrakis (U iphenylphosphine) Pd is the catalyst working in the basic medium. This reaction was recently used98 in aqueous media for the preparation of different isomers of diphenyldicarboxylic acids (Fig. 5.21) but also for the synthesis of soluble rodlike polyimides99 by coupling the 3,6-diphenyl- V, V,-bis(4-bromo-... 

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... 

The Suzuki reaction has been successfully used to introduce new C - C bonds into 2-pyridones [75,83,84]. The use of microwave irradiation in transition-metal-catalyzed transformations is reported to decrease reaction times [52]. Still, there is, to our knowledge, only one example where a microwave-assisted Suzuki reaction has been performed on a quinolin-2(lH)-one or any other 2-pyridone containing heterocycle. Glasnov et al. described a Suzuki reaction of 4-chloro-quinolin-2(lff)-one with phenylboronic acid in presence of a palladium-catalyst under microwave irradiation (Scheme 13) [53]. After screening different conditions to improve the conversion and isolated yield of the desired aryl substituted quinolin-2( lff)-one 47, they found that a combination of palladium acetate and triphenylphosphine as catalyst (0.5 mol %), a 3 1 mixture of 1,2-dimethoxyethane (DME) and water as solvent, triethyl-amine as base, and irradiation for 30 min at 150 °C gave the best result. Crucial for the reaction was the temperature and the amount of water in the... 

Alternatively, 3-phenyl pyrazinone was prepared via Suzuki reaction, when a polymer-bound pyrazinone was irradiated with 4 equiv of phenylboronic acid, 5 equiv of Na2C03 and 20 mol % of Pd[P(Ph)3]4 as the catalyst in DMF as the solvent (Scheme 36). Contrary to the results obtained in solution phase [29], all attempts to drive the reaction toward the formation of disub-stituted compound, using higher equivalents of reagents or longer reaction times, were unsuccessful. Apphcation of aqueous conditions afforded mixtures of 3-mono and 3,5-disubstituted pyrazinones. 

ArSnRs, and with arylmercury compounds. Aryl triflates react with arylbo-ronic acids ArB(OH)2, or with organoboranes, in the presence of a palladium catalyst, to give the arene in what is called Suzuki couplingCyclopropyl groups can be attached to aromatic rings by this reaction. Even hindered boronic acids give good yields of the coupled product. 

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