An Active Catalyst System Based on Pd (0) and a Phosphine-Based Bulky Ligand for the Synthesis of Thiophene-Containing Conjugated Polymers.

Meifang Liu,Dan Li,Li Liu,Meixiu Wan,Zhihui Zhang,Huanmei Guo

doi:10.3389/fchem.2021.743091

Meifang Liu, Dan Li + Show 4 more

Open Access

https://doi.org/10.3389/fchem.2021.743091

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Abstract

To address the limitations of conventional Pd catalysts in the polymerization of thiophene-containing conjugated polymers, an active catalyst system based on Pd (0) and a phosphine-based bulky ligand, L1, is explored systematically in Suzuki–Miyaura polymerizations using thiophene boronic acid pinacol ester as one of the monomers. This active catalyst is found very efficient in synthesizing a series of thiophene-containing linear and hyperbranched conjugated polymers. First, as a model example, coupling reactions between electron-rich/moderately hindered aryl or thienyl halides and thiophene boronic acid pinacol ester give excellent yields with lower catalyst loading and can be completed in a shorter reaction time relative to Pd(PPh3)4. Notably, high molecular weight thiophene-containing polymers are successfully synthesized by Suzuki–Miyaura polycondensation of 2,5-thiophene bis(boronic acid) derivatives with different dibromo- and triple bromo-substituted aromatics in 5–15 min.

Highlights

The palladium-catalyzed Suzuki–Miyaura cross-coupling is a mild and efficient reaction to construct the carbon–carbon bonds among aromatics (Bellina et al, 2004; Han, 2013; Paul et al, 2015; Qiu et al, 2018; Rizwan et al, 2018; Ayogu and Onoabedje, 2019; Zhang et al, 2019)
The catalyst system consisting of Pd (0) and L1 shows high efficiency for the Suzuki–Miyaura cross-coupling of thiophene-2-boronic ester and aryl halide (Liu et al, 2013)
When the reaction time was shortened to 15 min, there was little effect on the yield of the reaction, and the product was gained in good yields of 85–95% under similar conditions with an increase in the values of turnover numbers (TONs) and turnover frequencies (TOFs) (Table 1, entries 3–7)

Summary

INTRODUCTION

Π-Conjugated polymers have received considerable interest for their potential in a variety of applications, such as optoelectronics, chemical sensors, and biological sensors (Ponder et al, 2018; Yue et al, 2019; Li and Pu, 2019; González et al, 2019; Ochieng, et al, 2020; Abdollahi and Zhao, 2020). Few groups reported that high molecular weight polymers were obtained by Suzuki polymerization based on 2,5-thiophenebis (boronic acid pinacol ester)s using Pd(PPh3) as the catalyst precursor (Lu et al, 2008; Liu et al, 2013; Nguyen et al, 2014). Compared with the traditional palladium source Pd(PPh3), the catalyst Pd2(dba)3/L1 showed higher performance in generating TON and TOF This catalyst system can be conducted for Suzuki polycondensation of polymers based on 2,5-thiophenebis (boronic acid pinacol ester), and high molar mass polymers can be gained within 15 min. The gel permeation chromatography (GPC) measurements were performed on a Waters chromatography system connected to a Shimadzu LC-20AD differential refractometer with THF as an eluent or at 150°C with 1,2,4-trichlorobenzene as an eluent and calibration with polystyrene standards

METHODS

RESULTS AND DISCUSSION

DATA AVAILABILITY STATEMENT

CONCLUSIONS