Synthesis of Conjugated Polymers via Transition Metal Catalysed C?H Bond Activation

Transition metal catalysed C?H bond activation chemistry has emerged as an exciting and promising approach in organic synthesis. This allows us to synthesize a wider range of functional molecules and conjugated polymers in a more convenient and more atom economical way. The formation of C?C bonds in the construction of pi-conjugated systems, particularly for conjugated polymers, has benefited much from the advances in C?H bond activation chemistry. Compared to conventional transition-metal catalysed cross-coupling polymerization such as Suzuki and Stille cross-coupling, pre-functionalization of aromatic monomers, such as halogenation, borylation and stannylation, is no longer required for direct arylation polymerization (DArP), which involve C?H/C?X cross-coupling, and oxidative direct arylation polymerization (Ox-DArP), which involves C?H/C?H cross-coupling protocols driven by the activation of monomers’ C(sp²)?H bonds. Furthermore, poly(annulation) via C?H bond activation chemistry leads to the formation of unique pi-conjugated moieties as part of the polymeric backbone. This review thus summarises advances to date in the synthesis of conjugated polymers utilizing transition metal catalysed C?H bond activation chemistry. A variety of conjugated polymers via DArP including poly(thiophene), thieno3,4-c]pyrrole-4,6-dione)-containing, fluorenyl-containing, benzothiadiazole-containing and diketopyrrolopyrrole-containing copolymers, were summarized. Conjugated polymers obtained through Ox-DArP were outlined and compared. Furthermore, poly(annulation) using transition metal catalysed C?H bond activation chemistry was also reviewed. In the last part of this review, difficulties and perspective to make use of transition metal catalysed C?H activation polymerization to prepare conjugated polymers were discussed and commented.