Intramolecular catalyst transfer on N-acyl dithieno[3,2-b:2′,3′-d]pyrroles in nonstoichiometric Suzuki-Miyaura polycondensation toward high molecular weight conjugated copolymers at room temperature

Abstract

Traditional step-growth polycondensation generally requires a strict stoichiometric balance of monomers, high temperature, and long reaction time conditions to obtain a high number average molecular weight (Mn). To overcome the challenge of these disadvantages, we demonstrate that the nonstoichiometric Suzuki–Miyaura polycondensation using commercially available t-Bu3PPd G2 precatalyst is an efficient method for synthesis of high Mn various alternating π-conjugated copolymers based on N-acyl dithieno[3,2-b:2′,3′-d]pyrroles (N-acyl DTPs) in a short time at room temperature. Initially, the intramolecular transfer ability of t-Bu3P-ligated Pd catalyst on dibromo-N-acyl DTPs was examed by model reaction with 1 equiv of 3-isobutoxyphenylboronic acid. The result showed that disubstituted product was selectively obtained, indicating the Pd catalyst efficiently walked on these N-acyl DTPs. Thus, a series of novel N-acyl DTP-based π-conjugated copolymers with very high Mn (up to 195 kDa) were successfully prepared under nonstoichiometric reaction conditions using excess dibromo-N-acyl DTPs with arylenediboronic acid esters. Notably, the utilization of K3PO4 as a base was essential for fast couplings at room temperature within 3 h. Furthermore, these copolymers showed tunable optical band gaps and exhibited highly fluorescent emission ranges. These findings should be useful for the precision synthesis of N-acyl DTP-based polymers with controlled Mn and narrow dispersity via chain-growth Suzuki–Miyaura polycondensation.