Tuning 'Ligandless' Direct Arylation Polymerization toward Less-Branching EDOT Polymers

Abstract

Direct arylation polymerization conditions can be classified into phosphine-assisted and "ligandless" conditions. We compared the outcomes of five poly[thiophene-derivates-alt-EDOT]s and PEDOTF polymerized under two kinds of conditions. The results revealed that the "ligandless" conditions led to higher polymerization efficiency compared to phosphine-assisted conditions when employing n-hexyl functionalized EDOT as arylative substrate and various dibromoarenes as oxidative substrates. Computational studies revealed that the phosphine-assisted conditions follow the standard concerted metalation-deprotonation (CMD). In contrast, the amide-assisted conditions follow electrophilic CMD. This mechanistic difference provides a reasonable explanation for the preference of "ligandless" conditions towards activation of electron-donating arenes. Additionally, the use of sterically hindered amide solvents and dibromoarenes helps reduce branching defects, preserving the desired linear polymer structure.