Aryldiboronic acids

Poly p-phenylene (104) was expected to have good thermal and oxidative stability as well as electrical conductivity in the oxidized or reduced states. Rehahn et al. reported the first cross-coupling reaction of dihaloarenes 100 and aryldiboronic acids (101) to provide poly (p-phenylenes) (104) [160]. Homologation was achieved via repeating the following sequence of reactions lithiation, boration, and Suzuki coupling [160]. 

PPVs are accessible by polycondensation methods based on transition metal-catalyzed cross-coupling processes. Several individual reactions are known. For example, using palladium catalysts, divinylbenzene yields with diiodobenzene derivates directly from PPV derivates. Another reaction, the Suzuki coupling, uses 1,4-aryldiboron acids and 1,2-dibromo-ethene with palladium catalysts to arrive at PPV. 

Aromatic rigid-rod polymers play an important role in a number of diverse technologies including high-performance engineering materials, conducting polymers, and nonhnear optical materials. The cross-coupling reaction of aryldiboronic acids and dihaloarenes for the synthesis of poly(p-phenylenes) was first reported by Rehahn et al. The method has been extensively applied to water-soluble poly(p-phenylene), planar poly(p-phenylenes) fixed with the ketoimine bonds, poly(phenylenes) fused with polycyclic aromatics,and nonlinear optical materials (Scheme 14). 

Suzuki Coupling. PPV can also be synthesized by Pd-catalyzed coupling of alkyl-substituted aryldiboron acids with dibromo aromatic compounds (Fig. 67). Several derivatives have been synthesized in this way, among which poly(trisphenylene vinylene) [272, 705,878-880]. 

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