A General Protocol for the Polycondensation of Thienyl N-Methyliminodiacetic Acid Boronate Esters To Form High Molecular Weight Copolymers

Josue Ayuso Carrillo,Michael J. Ingleson,Michael L. Turner

doi:10.1021/jacs.6b07666

Josue Ayuso Carrillo, Michael J. Ingleson + Show 1 more

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https://doi.org/10.1021/jacs.6b07666

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Abstract

Thienyl di-N-methyliminodiacetic acid (MIDA) boronate esters are readily synthesized by electrophilic C–H borylation producing bench stable crystalline solids in good yield and excellent purity. Optimal conditions for the slow release of the boronic acid using KOH as the base in biphasic THF/water mixtures enables the thienyl MIDA boronate esters to be extremely effective homo-bifunctionalized (AA-type) monomers in Suzuki–Miyaura copolymerizations with dibromo-heteroarenes (BB-type monomers). A single polymerization protocol is applicable for the formation of five alternating thienyl copolymers that are (or are close analogues of) state of the art materials used in organic electronics. The five polymers were produced in excellent yields and with high molecular weights comparable to those produced using Stille copolymerization protocols. Therefore, thienyl di-MIDA boronate esters represent bench stable and low toxicity alternatives to highly toxic di-trimethylstannyl AA-type monomers that are currently ubiquitous in the synthesis of these important alternating copolymers.

Highlights

Thiophene moieties, including annulated derivatives, are key constituents of many polymers used in organic electronic devices.[1]
An iterative coupling approach to oligothiophenes requires sequential deprotection, cross-coupling, and purification cycles and is not readily applicable to the formation of polymers, a quaterthiophene has been made via this strategy.11b we report the facile synthesis of highly pure and crystalline AA-type thienyl di-methyliminodiacetic acid (MIDA) boronate ester monomers and show that using these monomers a single polycondensation protocol is viable for the formation of a wide range of important alternating copolymers that are produced in excellent yield and with high molecular weights that are comparable to those afforded by Stille cross-coupling polymerization reactions
We reported the synthesis of 5-bromo-4-hexylthien2-yl-MIDA boronate ester, 1 (Figure 3 inset bottom left), by electrophilic C−H borylation of 2-bromo-3-hexylthiophene.[12,13]

Summary

■ INTRODUCTION

Thiophene moieties, including annulated derivatives, are key constituents of many polymers used in organic electronic devices.[1]. TBTT) that have desirable properties (e.g., high charge mobility).[3] thienyl containing alternating D−A polymers are among the state of the art active components in organic photovoltaic devices (enabling power conversion efficiencies (PCEs) of over 10%).[2,3] While parameters such as charge mobility and PCE are crucial markers of polymer performance in devices, another important but often overlooked criteria is the efficiency of monomer and polymer synthesis.[4] Low toxicity monomers that are available in good yield and excellent purity via simple synthetic routes and that undergo highly effective polymerization are crucial for the large scale development of printed electronics.[4] the copolymerization of an AA-type thienyl monomer with a BB-type acceptor monomer is dominated by the Stille cross-coupling reaction (Figure 2), which generally uses distannylated thienyl monomers.4d,5 This has drawbacks, including obtaining the distannylated thienyl monomer in sufficient purity (due to facile cleavage of thienyl− Sn bonds) making the precise control of stoichiometry in copolymerizations challenging.[6] stoichiometric toxic tin waste is produced, which is problematic with the Me3Sn−thienyl derivatives (which generate volatile tin byproducts but are still widely used due to the crystalline nature of many Me3Sn monomers).1,4d,5 Significant advances have been recently reported using direct (hetero)arylation polymerization (DHAP), which is a more efficient methodology An iterative coupling approach to oligothiophenes requires sequential deprotection, cross-coupling, and purification cycles and is not readily applicable to the formation of polymers, a quaterthiophene has been made via this strategy.11b we report the facile synthesis of highly pure and crystalline AA-type thienyl di-MIDA boronate ester monomers and show that using these monomers a single polycondensation protocol is viable for the formation of a wide range of important alternating copolymers that are produced in excellent yield and with high molecular weights that are comparable to those afforded by Stille cross-coupling polymerization reactions

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES