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

Abstract

In the past decade, direct arylation polymerization (DArP) has rapidly developed as a sustainable synthetic protocol for cost-effective, atom-economical preparation of conjugated polymers. By circumventing monomer functionalization with toxic transmetallating reagents such as organostannane and organoboron required for Stille-Migita and Suzuki-Miyaura polymerization methods, DArP proceeds through a metal-catalyzed C H activation pathway for the preparation of highperformance conjugated polymer materials. This review evaluates the development of several classes of efficient catalysts/catalytic systems from small-molecule studies to polymerizations, including the mechanisms involved in these transformations and how they inspire catalyst and monomer design for defect-free conjugated polymer synthesis. Recent advances in developing more sustainable first-row transition metal catalysts for DArP are also highlighted, and the fundamental understanding of these efficient and sustainable catalysts should motivate the pursuit for the next generation of catalytic design to enable more effective and environmentally friendly conjugated polymer synthesis.

Group 16 conjugated polymers based on furan, thiophene, selenophene, and tellurophene

“…91,92 Choices of ligands, catalytic systems, additives, and solvents are shown to help minimize the defects. 93,94…”

Recycling Heterogenous Catalysts for Multi-Batch Conjugated Polymer Synthesis via Direct Arylation Polymerization

“…23−26 Moreover, the recyclability of SiliaCat DPP-Pd has previously been showcased in various small-molecule Stille and Suzuki coupling reactions and further extended to large-scale synthesis in commercial flow reactors. 25−27 Although Leclerc et al have previously demonstrated the high reactivity of this heterogeneous catalyst in DArP using Ozawa-derived conditions (i.e., in nonpolar solvents), 8,18 our preliminary efforts revealed that the recovered SiliaCat DPP-Pd was not reusable after the initial polymerization under similar conditions (see SI for details). This may be attributed to the longer reaction time usually required for these polymerizations (24 h or more) compared to those for small-molecule cross-coupling reactions (∼30 min), 25,26 which likely results in significant leaching of Pd from the solid support suppressing the catalytic activity of the recovered Pd species.…”

“…Specifically, the generation of stoichiometric, highly toxic organotin byproducts and a multistep preparation of unstable stannylated monomers makes Stille impractical for the large-scale synthesis of CPs. 8 In recent years, direct arylation polymerization (DArP) has emerged as a facile synthetic tool for the preparation of highquality CPs through an atom-economical C−H activation pathway, alleviating the need for hazardous, pyrophoric reagents, and reducing toxic waste production (Scheme 1a). 8−10 Recent advances in replacing traditional, hazardous solvents with biorenewable green alternatives such as cyclopentyl methyl ether (CPME) and p-cymene have further enhanced the sustainability of DArP protocols.…”

“…Conjugated polymers (CPs) are flexible low-cost materials that attract great interest for a wide range of applications, such as organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), electrochromics, and bioelectronics. − Recently, with progress toward commercialization and the emergence of large-area roll-to-roll processing, the demand for industrial-scale CP synthesis has grown rapidly. , To synthesize CPs, the Stille polycondensation is one of the most widely employed traditional cross-coupling methods, which however has significant drawbacks. Specifically, the generation of stoichiometric, highly toxic organotin byproducts and a multistep preparation of unstable stannylated monomers makes Stille impractical for the large-scale synthesis of CPs …”

Circular Discovery in Small Molecule and Conjugated Polymer Synthetic Methodology

“…A wealth of information on DArP can be found in the numerous review articles previously published. − Topical review articles are also available, addressing topics such as defects in DArP-produced polymers , and improving DArP’s sustainability. − To ameliorate the existing literature, this perspective article presents a strategy in developing new methodologies for conjugated polymer synthesis. DArP is focused on as a useful example, with guidance on how to adapt existing small molecule methodologies to develop novel polymerizations.…”