Identifying Homocouplings as Critical Side Reactions in Direct Arylation Polycondensation

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• 作者：Florian Lombeck ; Hartmut Komber ; Serge I. Gorelsky ; Michael Sommer
• 刊名：ACS Macro Letters
• 出版年：2014
• 出版时间：August 19, 2014
• 年：2014
• 卷：3
• 期：8
• 页码：819-823
• 全文大小：315K
• ISSN：2161-1653

文摘

Homocouplings are identified as major side reactions in direct arylation polycondensation (DAP) of 4,7-bis(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (TBT) and 2,7-dibromo-9-(1-octylnonyl)-9<i>Hi>-carbazole (CbzBr₂). Using size exclusion chromatography (SEC) and NMR spectroscopy, we demonstrate that both TBT and Cbz homocouplings occur at a considerable extent. TBT homocoupling preferentially occurs under phosphine-free conditions but can be suppressed in the presence of a phosphine ligand. Cbz homocoupling is temperature-dependent and more prevalent at higher temperatures. By contrast, evidence for chain branching as a result of unselective C鈥揌 arylation is not found for this monomer combination. These results emphasize that particular attention has to be paid to homocouplings in direct arylation polycondensations as a major source of main-chain defects, especially under phosphine-free conditions.