Optimization of the Reaction Conditions for Direct Arylation Polymerizations in a Sustainable Solvent

Abstract

Direct arylation polymerization (DArP) relieves the synthesis of conjugated polymers from the use of hazardous and toxic reagents typical of the traditional protocols. However, the compatibility with environmentally benign, nonhazardous, and low‐cost solvents still represents the critical aspect for projecting DArP as an industrial‐scale method for the preparation of conjugated polymers. In this study, a “green” solvent (i.e., cyclopentyl methyl ether) is implemented for the obtainment of poly(3‐hexylthiophene) by DArP reaction, in order to explore sustainable reaction conditions also regarding the catalytic system and the base quantity, which equally undermine the sustainability of the DArP protocol. Considering the molecular weights as the indicator of precatalyst performance in determined conditions, it is established that the cheapest palladium source (i.e., PdCl2) combined with two equivalents of (o‐anisyl)3P is able to yield the best results in the green ethereal solvent. Furthermore, it is found how, with respect to the common DArP protocols, the quantity of the expensive base (i.e., Cs2CO3) can be reduced in these reaction conditions without compromising molecular weights and regioregularity of the resulting polymer. These optimized reaction conditions can be extended to the copolymerization of other monomer units with satisfactory results in terms of molecular weights.

A Mixed-Ligand Strategy to Modulate P3HT Regioregularity for High-Efficiency Solar Cells

“…The RR gained with L1 was 90%, whereas L2 caused a high RR of 98%, consistent with Ozawa et al’s results . It was reported that the C–H bond activation may take place at the trans position in the concerted metalation–deprotonation (CMD) step. , This process will result in homocoupling and H/Br exchange thiophene species, which can subsequently be incorporated into the polymer backbone leading to T–T and H–H linkages, respectively (Figure S2). To gain insights into the effect of L1 and L2 on RR, the pathways for the formation of H–T, T–T, and H–H linkages shown in Figure S2 were examined by density functional theory (DFT) calculation (Figure ).…”

Sustainable protocols for direct C–H bond arylation of (hetero)arenes

“…231 Very recently, Thompson et al also reported the first synthesis of poly(3-alkylamide thiophenes) by direct arylation polymerization in CPME as the solvent, showing M n up to 15.4 kDa and yields up to 90%, 232 as well as of other polythiophene derivatives by direct C-H bond arylation polymerization in CPME of thiophene-based monomers bearing suitable ester directing groups, in order to study the inhibition of defect formation. 233 In 2020, the homo-polymerization of 2-bromo-3-hexylthiophene, as well as the co-polymerization of a bis-thienylDPP derivative with dibromoarenes, by direct arylation reactions in CPME as sustainable reaction medium, was described by Grisorio et al 234 3.3.2. Direct C-H bond arylation of (hetero)arenes in organic carbonates.…”

Improving the efficiency and sustainability of catalysts for direct arylation polymerization (DArP)

“…136,150 This result demonstrates that the L1-based Pd catalytic system displays more outstanding performance in the sustainable solvent CPME. 141,143,150,151 Besides the use of 2-MeTHF and CPME, the use of bioderived solvent anisole has also emerged for DArP. 152,153 Recently, Thompson et al also identified a bio-renewable, naturally sourced aromatic solvent, p-cymene (Figure 5), in the application of DArP for the first time.…”