Aryl cross-coupling reactions

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. 

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. 

Conjugated polymers remain prime candidates for use as semiconductors in the emergent field of organic electronics [40-43]. Such materials are typically synthesized via polycondensation reactions, using a variety of aryl cross-coupling reactions. These methods are subject to problems that relate to, for example, the elimination of precursor functional groups. Unfortunately, the polymers produced via these methods often contain defects and unwanted branching, that may have deleterious effects on the conductive properties of the resultant material. 

Scheme 10.137 Rhodium-catalyzed arylation/cross-coupling reaction initiated by an inter-molecular carborhodation step [114].

Scheme 11. Aryl-aryl cross-coupling reactions with polymer-bound aryl bromides. " ...

It is also possible to synthesize chiral PPPs as Scherf et al. reported [72]. They are composed of chiral cyclophane subunits, made by a Suzuki-type aryl aryl cross-coupling reaction of the corresponding diboronic acid and dibromo derivatives. The monomers containing cyclic -O-C10H20-O- loops were separated into the pure enantiomers and used to generate the corresponding stereoregular iso- and syndiotactic PPP-derivatives (Scheme 26). The isotactic derivative possesses a chirality of its main chain. 

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