期刊
DALTON TRANSACTIONS
卷 43, 期 40, 页码 15143-15150出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4dt01617c
关键词
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资金
- Iran's National Foundation of Elites
- Spanish MINECO for a Ramon y Cajal [RYC-2009-05226]
- European Commission for a Career Integration Grant [CIG09-GA-2011293900]
In this study we have investigated computationally the mechanism of polymerization of 2,5-dibromo 3-butylthiophene via the GRIM method, with the focus on the origin of the head to tail (HT) selectivity. To this end, first the Grignard reagent underwent oxidative addition to the monomer to afford the 2-bromo5-chloromagnesio-3-butylthiophene (intermediate I1) or the 2-chloromagnesio 5-bromo-3-butylthiophene (intermediate I2) regioisomers. Then intermediates I1 and I2 were polymerized catalytically to a series of regiospecific poly-3-butyithiophenes using the commonly used Ni(dppp)Cl-2 [dppp: 1,3-bis(diphenylphosphino) propane] and Pd(dppp)Cl-2 catalysts. Due to the asymmetric nature of I1 and I2 that act as the active monomeric species, 6 coupling modes may occur. The whole energy profile of all modes has been studied by considering a three-stage mechanism, including coordination, transmetalation, and reductive elimination, to compare quantitatively the ability of so-called catalysts in selective coupling of desired isomers to produce regioregular poly-3-butylthiophene. Finally, to quantify the steric role of the dppp in regioselectivity, analysis of the buried volume in terms of steric maps was performed.
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