A Highly Efficient Catalyst for the Synthesis of Alternating Copolymers with Thieno[3,4-c]pyrrole-4,6-dione Units via Direct Arylation Polymerization

Abstract

π-Conjugated polymers with a donor–acceptor (DA) combination of repeating units possess a narrow HOMO–LUMO gap, thus resulting in a high device performance in solar cells. This paper reports an improved catalytic system for the synthesis of DA polymers containing 5-(2-hexyldecyl)-5H-thieno[3,4-c]pyrrole-4,6-dione-1,3-diyl (TPD) group as the acceptor unit via palladium-catalyzed direct arylation polymerization. Although a related study has been reported (Angew. Chem. Int. Ed. 2012, 51, 2068), we attempted to reduce the catalyst loading because the palladium residue in π-conjugated polymers has been known to produce a detrimental effect on device performance. As a result, the amount of palladium could be reduced to 1/8 by using PdCl2(MeCN)2 and P(C6H4-o-OMe)3 (L1) as catalyst precursors. The polymerization smoothly proceeds at 100 °C in THF in the presence of pivalic acid and Cs2CO3 to afford TPD-based DA polymers 3a–3d containing the following donor units in almost quantitative yields: 4,4′-dioctyl-2,2′-bi...