Stereospecific Polymerization of 3- buthythiophene: A DFT Study

In this study we have investigated computationally the mechanism of polymerization of 2,5-dibromo 3-butylthiophene (1) via GRIM method, with a focus on the origin of the Head to Tail (HT) selectivity. To this end, first Grignard reagent underwent oxidative addition to monomer (1) to afford the 2-bromo-5-chloromagnesio-3-butylthiophene (intermediate I1) or the 2-chloromagnesio 5-bromo-3-butylthiophene (intermediate I2) regioisomers. The mechanism of polymerization of I1 or I2 with Ni(dppp)Cl2 [dppp: 1,3-bis(diphenylphosphino) propane] catalyst involves three main catalytic steps: oxidative addition, transmetalation, and reductive elimination, which will be studied in the present work in more detail.