Aryl cross-coupling

The authors used a synthesis of 9,9-spirobitluorenes 32 which was developed by Clarksen and Gomberg [60] and which includes the addition of biphenyl-2-yl-magnesium iodide to fluorenone and subsequent cyclization with protic acids. To obtain 2,2,, 7,7 -arylated 9,9-spirobifluorenes 33, 9,9-spirobifluorene (32) was tetrabrominated [58] to yield 34 followed by a Suzuki-type aryl-aryl cross-coupling with various oligoaryl and oligoheteroaryl boronic acids to obtain the 2,2, 7,7 -tetraarylated derivatives 33. 

The Suzuki aryl-aryl cross-coupling method, adapted to polymers by Schliiter, Wegner and co-workers, made it possible to synthesize solubilized PPPs 6 with a dramatically increased molecular weight (number average up to 100 1,4-phen-ylene units) [17]. 

In 1996, Wegner et al. published the synthesis of poly(oligophenylenevinyle-ne)s (96), consisting of biphenylene-, terphenylene- and quinquephenylene moieties as aromatic building blocks, via Suzuki-type aryl-aryl cross coupling of AA/BB-type monomers [121]. By judicious choice of the arylene moieties, the optical properties of the resulting polymers can be tailored within a wide range. 

Organomercuric compounds require nucleophilic assistance by soft iodide anions (cf. Section 9.6.3.2.2) for participation in cross-coupling reactions.158 The reaction is useful for aryl-aryl cross-coupling in those cases in which the organomercury species are obtained by direct mercuration of aromatic compounds (38).159... 

Marquais, S. Arlt, M. Aryl-Aryl Cross Coupling on a Solid Support using Zinc Organic Reagents and Palladium Catalysis, Tetrahedron Lett. 1996,37, 5491-5494. 

Scheme5.11 Iron-catalyzed aryl-aryl cross-coupling reaction with Ar-MgX developed by Hatakayama and Nakamura.

Aryl-aryl cross-coupling reactions have been exploited extensively, particularly by Snieckus and coworkers, in the synthesis of polyaryls and other aromatic nuclei243. 

DoM-transition metal catalyzed aryl-aryl cross coupling symbiosis ... 

The DoM-Transition Metal Catalyzed Aryl-Aryl Cross-Coupling Symbiosis... 

Sterically demanding substrates are tolerated well and Suzuki coupling has been used in a wide range of aryl-aryl cross-couplings. This example has three ortho substituents around the newly formed bond (marked in black) and still goes in excellent yield. It also shows that borate esters can be used instead of boronic acids. 

The synthetic sequence to methylene-bridged poly(phenylene)s 71 represents the first successful employment of the stepwise process to ladder-type macromolecules involving backbone formation and subsequent polymer-analogous cyclization. As shown, however, such a procedure needs carefully tailored monomers and reaction conditions in order to obtain structurally defined materials. The following examples demonstrate that the synthesis of structurally defined double-stranded poly(phenylene)s 71 (LPPP) via a non-concerted process is not just a single achievement, but a versatile new synthetic route to ladder polymers. By replacing the dialkyl-phenylenediboronic acid monomer 68 by an iV-protected diamino-phenylenediboronic acid 83, the open-chain intermediates 84 formed after the initial aryl-aryl cross-coupling can te cyclized to an almost planar ladder-type polymer of structure 85, as shown recently by Tour and coworkers [107]. 

Equation 12.80 shows a vinyl-aryl cross-coupling, which is apparently tolerant of the vinyl carbamate group on compound 59. The organozinc reagent (60)... 

By means of a repetitive Suzuki aryl-aryl cross-coupling method, developed by Schliiter, Wegner and co-workers, the synthesis of solubilized PPP s 6 with a dramatically increased molecular weight (number average up to 100 1,4-pheny-lene units) was possible [12]. 2,5-Dialkyl-substituted PPPs 6 were intensively studied as prototypes of so-called hairy-rod macromolecules, composed of a linear, rigid PPP main-chain and flexible, hairy alkyl side-chains. The individual, shape-persistent macromolecules can be imaged by transition electron microscopy within monolayers [16]. Poly(2,5-di-n-dodecyl-l,4-phenylene) 6 (R -C12H25) revealed a sandwich-type structure with layers of aliphatic side-chains perpendicular and layers of the PPP main-chain parallel to the substrate surface. 

With the success of transition-metal-catalyzed aryl-aryl cross-coupling reactions through C-H activation of one of the coupling partners, obviously, a more economic and attractive alternative is the coupling reaction via double C-H activation of two arenes, neither of which needs to be preactivated (Scheme 5). However, the development of such a process is very challenging because many difficulties remain to be solved. For instance, the control of selectivity when two coupling partners have more than one type of aromatic C-H bond is a challenge. 

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