Toward eco-friendly protocols: insights into direct arylation polymerizations under aerobic conditions in anisole

Abstract

Direct arylation polymerization (DArP) represents an ecological alternative to the conventional polycondensation methodologies for the obtainment of selected conjugated polymers. To further improve the sustainability of the synthetic protocol, efforts have been focused on bypassing the use of toxic solvents or managing them under dried conditions and inert atmospheres. Although the implementation of eco-friendly and low-toxic solvents from the safety, health and environment viewpoint has recently been proposed, their compatibility with undried and aerobic reaction conditions has remained thus far unexplored. Herein, we investigated the viability of applying anisole in the preparation of poly(9,9-dioctylfluorene-2,2′-bithiophene) under undried and aerobic conditions by employing the catalytic system comprising (PPh₃)₂PdCl₂/P(o-Anisyl)₃/Cs₂CO₃ in the presence of pivalic acid as the proton transfer agent. We assessed that the polymerization afforded satisfactory results without activating radical pathways or incorporation of structural defects in the obtained polymers. The same aerobic conditions were adopted for the copolymerization of differently structured units affording molecular weights up to 16 500 Da, thus consolidating the C–H activation route as an eco-friendly protocol for the preparation of conjugated polymers.