Nonstoichiometric Suzuki‐Miyaura Polycondensation of Donor and Acceptor Monomers for the Synthesis of Cyclic D‐A Polymers

In the previous work, nonstoichiometric Suzuki‐Miyaura polycondensation of excess dibromo monomer with more donor diboronate monomer in the presence of Pd catalyst, which undergoes intramolecular transfer on the π‐face of aromatics, afforded lower‐molecular‐weight polymer, in contrast to the case of polymerization of the reverse combination. In the present work, we investigated the nonstoichiometric Suzuki‐Miyaura polycondensation of acceptor dibromobenzotriazole with strong donor carbazolediboronate in the presence of the same Pd catalyst. The model reaction of two equivalents of acceptor dibromobenzotriazole with 1.0 equivalent of donor carbazoleboronate in the presence of t Bu 3 PPd precatalyst afforded exclusively the disubstituted product, confirming that the Pd catalyst undergoes intramolecular catalyst transfer. However, the polycondensation of dibromobenzotriazole with 2,7‐carbazolediboronate did not afford high‐molecular‐weight polymer, and only oligomers ( M n = 1240–1700) with boronate at both ends were obtained. In contrast, the polycondensation of dibromobenzotriazole with 3,6‐carbazolediboronate selectively afforded cyclic polymers ( M n = 4420–6440) even when excess dibromo monomer was used. These results suggest that the formation of oligomers in the former polycondensation is due to the strong affinity of the extended donor‐acceptor conjugated polymer backbone for the Pd catalyst, resulting in sluggish intermolecular catalyst transfer.