Direct Arylation Polymerization of Electron-Rich Arenes with Polar-Group Tolerance Enabled by Ligand-Coordination Tuning

Abstract

Electron-rich arenes are crucial building blocks in conjugated polymers due to their strong electron-donating properties and tunable electronic structures, underpinning diverse applications in organic electronics, biointerfaces, and energy technologies. However, the pronounced π-delocalization of electron-rich arenes can increase the arene distortion and reorganization energy required at the transition state, making efficient C-H activation under typical phosphine conditions challenging, particularly when polar substituents simultaneously compete for Pd coordination. The absence of a comprehensive mechanistic understanding of interactions among ligands, catalysts, arenes, and polar substituents has forced researchers to rely on empirical condition screening, significantly limiting synthetic efficiency and the scope of functional polymers. Using 3,4-ethylenedioxythiophene (EDOT) and its derivatives as representative electron-rich monomers, we demonstrate that the phosphine ligand coordination strength, quantified by electron-donating strength (EDS), critically governs both the C-H activation efficiency and the catalyst's tolerance toward polar groups. Weak-donating ligands facilitate Pd-C formation and disrupt localized π-delocalization, significantly enhancing C-H activation. Conversely, the more donating ligands within the weak-donating series, strengthen Pd-phosphine interaction relative to Pd-polar-group coordination, shifting the coordination balance away from inhibitory polar-group-bound Pd states and thereby mitigating catalyst poisoning. This mechanistic insight provides a predictive framework for rational condition selection in DArP, replacing empirical screening with a design-driven strategy. The resulting protecting-group-free strategy provides scalable access to high-molecular-weight conjugated polymers bearing diverse functionalities, including the notoriously catalyst-deactivating amines, and expands the synthetic toolkit for functional conjugated polymers in organic electronics, biointerfaces, and energy applications.