Suzuki biphasic

Today, the Suzuki cross coupling of aryl halides and arylboronic acids is also carried out in aqueous-biphasic operation starting from chlorinated derivatives instead of their more costly bromo or iodo equivalents (Equation 5.6, [39]). 

Palladium nanoparticles coated with a fluorous-derivatized surfactant (or stabilizer) have been used to catalyse Heck and Suzuki reactions in a C8F17Br-benzene biphase [11], The reaction between phenylboronic acid and cinnamyl bromide was investigated and the reaction is illustrated in Scheme 10.10. 

The palladium nanoparticle is prepared from the reaction of the stabilizer, 4,4 -bis(perfluorooctyl)dibenzylideneacetone with palladium(II) chloride. The average size of the nanoparticle varied according the ratio of PdCF to the stabilizer, but was typically around 4 or 5 nm. The initial yield observed in the Suzuki coupling reaction was 90%, but decreased to 78% after five consecutive runs. Fluorous boronates (alternative precursors in Suzuki reactions), have also been developed for use in fluorous biphasic processes [12], A generic structure of a fluorous boronate is shown in Figure 10.2. 

Figure 10.2 General structure of fluorous boronates used in fluorous biphase Suzuki reactions...

These critical aspects of the classical fluorous biphasic catalysis led in recent works to the development of protocols for the conversions with modified catalyst systems in non-fluorinated hydrocarbons as solvents. As part of the BMBE lighthouse project, Gladyzs and coworkers appHed this concept to C - C coupHng reactions (Suzuki reaction) and other metal-catalyzed addition reactions (hydrosilylation, selective alcoholysis of alkynes), which have direct relevance for the synthesis of fine chemicals and specialties [74]. 

An der Heiden, M. and Plenio, H. (2004) Homogeneous catalysts supported on soluble polymers biphasic Suzuki— Miyaura coupling of aryl chlorides using phase-tagged palladium—phosphine catalysts. Chem. Ear. ]., 10, 1789. 

Many other C-C bond forming reactions involving organometallic catalysis have been successfully performed in an aqueous biphasic system. Examples are shown in Fig. 7.13 and include Heck [47, 48] and Suzuki couplings [48] and the Rhone-Poulenc process for the synthesis of geranylacetone, a key intermediate in the manufacture of vitamin E, in which the key step is Rh/tppts catalyzed ad-... 

The successful demonstration of the fluorous biphasic concept for performing organometallic catalysis sparked extensive interest in the methodology and it has subsequently been applied to a wide variety of catalytic reactions, including hydrogenation [59], Heck and Suzuki couplings [60, 61] and polymerizations [62]. The publication of a special Symposium in print devoted to the subject [63] attests to the broad interest in this area. 

Tzschucke, C.C., Marker , C., Glatz, H., and Bannwarth, W. 2002. Fluorous biphasic catalysis without perfluorinated solvents Application to Pd-mediated Suzuki and Sonogashira couplings. Angewandte Chemie International Edition, 41 4500-03. 

Figure 10.3 Aqueous biphasic Suzuki coupling to yield substituted biphenyls.

The biphasic Suzuki coupling is commercialized by Clariant AG (the former Hoechst AG) [260]. Despite interesting proposals (e. g., [271]), no other industrial realizations of aqueous biphasic processes emerged. 

Suzuki-type C-C-coupling reactions (cf. Section 2.11) with Pd phosphine complexes as catalysts can also be promoted by amphiphiles in an aqueous biphasic system (toluene/water). The amphiphile should have a phase-transfer function, with the best effect being observed with micelle-forming amphiphiles [27]. 

The use of Suzuki couphng for the synthesis of polyphenylene polymers was introduced by Rehahn, Schlueter and Wegner [Eq. (9)] [230]. Poly(p-2,5-di-n-hexylphe-nylene) was prepared in a biphasic mixture of benzene and water as a reaction medium, using sodium carbonate as a water-soluble base. This AB-type polymerizahon afforded polymers containing, e.g., an average of about 28 phenylene units. 

Scheme 7.12 Synthesis of functionalized poly(p-phenylene) via AA/BB Suzuki coupling in an aqueous biphasic system.

Hereby, poly(p-phenylene) polymers containing ether and carbonyl linkages in the polymer backbone are accessible. By polymerization of the AB2 monomer 3,5-dibromobenzene boronic acid in a biphasic aqueous/organic medium, Kim and Webster obtained hyperbranched polyphenylenes [233]. Suzuki polycondensation in aqueous systems has proven to be a versatile method, which has been applied to the synthesis of various polymer types ]234]. 

Heck and Stille coupling reactions, also allowing reactions to be conducted under solvent-free conditions. The synergic effect of polymer 96 and TSIL not only reflected an increased stability during storage but also an enhanced activity during catalysis. Scheme 1.62 shows a typical Suzuki reaction occurring in an aqueous biphasic medium. 

A somewhat similar technique was discovered by Bergbreiter etal. [123]. He found that biphasic solvent systems exhibit an increase in phase miscibility at elevated temperature if special soluble polymers are added (cf. also Section 7.6). An elegant option is to fix the catalyst on this soluble polymer. For example, he used poly(N-isopropylacryl amide) derivatives which are able to bound phosphine ligands coordinated to a Pd catalyst. High yields in Heck- and Suzuki-couplings can be obtained and the catalyst can be recycled (cf. also Section 6.6). 

Other biphasic C—C bonding reactions were carried out with fluorous solvents, for instance Suzuki- and Sonogashira-couplings [124] or ethene or propene oligomerizations [125, 126], Further new solvent systems use ionic liquids for the linear dimerisation of 1-butene to octenes [127] or the hydrovinylation of styrene with a combination ionic liquid/supercritical carbon dioxide [128] (cf. Section 7.4). 

Nonpolar biphasic catalysis Suzuki- and Sonogashira coupling reactions... 

Nonpolar biphasic Suzuki reaction for the synthesis of 1-biphenyl-... 

NONPOLAR BIPHASIC CATALYSIS SUZUKI- AND SONOGASHIRA COUPLING REACTIONS... 

NONPOLAR BIPHASIC SUZUKI REACTION FOR THE SYNTHESIS OF 1-BIPHENYL-4-YL-ETHANONE... 

Palladium catalyst supported on poly(4-methylstyrene) can be used for biphasic nonpolar Suzuki and Sonogashira coupling of aryl bromides and chlorides with good product yields. The catalyst can be recycled five times with negligible decrease in the activity. 

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