Dibenzobarrelene-derived Pd-NHCs: efficient precatalysts for the Suzuki–Miyaura polycondensations of dichloroarene monomers†

Pd-catalyzed Suzuki–Miyaura polycondensations (SMPs) have emerged as a powerful method for synthesizing conjugated polymers (CPs). While numerous reports have utilized dibromoarene and diiodoarene derivatives as monomers, there has been less research on the use of the deactive dichloroarenes due to harsh conditions and low efficiency. In this study, aiming to overcome these challenges and develop robust palladium precatalysts, a series of dibenzobarrelene-derived palladium N-heterocyclic carbenes (Pd-NHCs) were designed and synthesized. It was observed that the “large-but-flexible” nature of these Pd-IPr^DBB complexes as well as the “throw-away” ligands facilitated the stability of Pd(0) species and the polymerization process. Additionally, optimization of polycondensation conditions such as choice of base, solvent, and temperature was conducted. This work presents an efficient protocol for synthesizing conjugated polymers with high yields and high molecular weights, demonstrating a broad monomer scope and outperforming conventional palladium phosphine-based catalytic systems.