Chain-Growth Polymerization of Benzotriazole Using Suzuki–Miyaura Cross-Coupling and Dialkylbiarylphosphine Palladium Catalysts

Abstract

Electron-deficient (n-type) conjugated materials are commonly prepared via step-growth methods with limited control over the molecular weight and molecular weight distribution of the resulting polymers. In this communication, we demonstrate that Pd-dialkylbiarylphosphine catalysts enable the chain-growth polymerization of benzo[1,2,3]triazole using Suzuki-Miyaura coupling with molecular weight control and modest molecular weight distributions (Đ ∼ 1.2−1.6). The importance of a free ligand in the reaction mixture during polymerization was established by analysis of polymer samples using GPC and MALDI-TOF mass spectrometry. A block copolymer with poly(3hexylthiophene) was also synthesized by sequential monomer addition. The success of these commercially available catalysts for polymerization of benzotriazole highlights their potential for chain-growth reactions with other bicyclic arenes in the future.

Pairing Suzuki–Miyaura cross-coupling and catalyst transfer polymerization

“…In our own work, we have also noted the importance of additional equivalents of phosphine and diphosphine ligand in chain-growth polymerizations (with both Pd and Ni). 33,34,41 Choi also noted that dialkylbiarylphosphines result in superior control as compared to P t Bu 3 in the polymerization of 3-alkylthiophenes.…”

“…7). 31,33,39,40,44,45 Recent advances with allyl or indenyl precatalysts may prove to be beneficial for SM CTP in the future. [109][110][111][112] The externally initiated catalysts with a ligand, a halide and an arene (LM(Ar)Br) produce well-defined chain-ends and narrow molar mass distributions in SM CTP.…”

“…In CTP, two dialkylbiaryl ligands have received considerable attention, namely SPhos and RuPhos. 31,33,39,69,115,116 The first example of these ligands being used in SM CTP of 3-alkylthiophenes appeared in 2006 from Higgins. 69 Though chaingrowth polymerization was not the focus of that work, it is clear from the data obtained that the obtained P3HT was highly regioregular, with a narrow molecular weight distribution.…”

“…Building from these reports, our group recently reported on the chain-growth polymerization of benzotriazole. 33 SPhos, RuPhos, and DavePhos Pd catalysts were used to prepare polybenzotriazole with relatively narrow dispersities and high molecular weights under mild conditions. 33 In that work, we also noted that the benzotriazole monomer, which bears a pinacol boronic ester, partially hydrolysed during polymerization.…”

“…33 SPhos, RuPhos, and DavePhos Pd catalysts were used to prepare polybenzotriazole with relatively narrow dispersities and high molecular weights under mild conditions. 33 In that work, we also noted that the benzotriazole monomer, which bears a pinacol boronic ester, partially hydrolysed during polymerization. A polybenzotriazole-poly(3-hexylthiophene) block copolymer could be synthesized by sequential addition of the benzotriazole and thiophene monomers.…”