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Metal-Catalyzed Condensation Polymerization
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
Thiophene-containing polymers have emerged as the frontrunners among conjugated polymers. Stille reaction involves palladium-catalyzed coupling of organostannanes with aryl halides, triflates, and acyl chlorides.10 Stannyl groups attached to the benzene ring of monomer were shown to give poor reactivity with aryl halides under Stille coupling conditions.11 However, this coupling gives excellent yields in preparation of polythiophenes and hence is the method of choice for their synthesis.12 It is a stereospecific and regioselective reaction. Organotin compounds can be prepared without the need for protection–deprotection chemistry. They are less oxygen- and moisture-sensitive than other organometallic species such as Grignard reagents and organolithium reagents.
BNPs@Cur-Pd as a versatile and recyclable green nanocatalyst for Suzuki, Heck and Stille coupling reactions
Published in Journal of Experimental Nanoscience, 2020
Muhammed Ali Jani, Kiumars Bahrami
In the absence of nanocatalyst, no coupling reaction has occurred in entry 1. In the beginning, PEG was used as a solvent and Na2CO3 as a base by using of 5–15 mg of BNPs@Cur-Pd at 80 °C (entries 2–5). The optimum results were obtained by 12 mg (0.043 10−5 mol g−1) of the BNPs@Cur-Pd nanocatalyst (entry 4). Increasing the amount of nanocatalyst did not give rise to a sensible improvement in the efficiency of the reaction (entry 5). Then, changing the solvent was conducted in order to evaluate solvent effects by using DMF, DMSO, and H2O instead of PEG (entries 6–8). The results revealed that the PEG solvent was the best in comparison with others. As can be seen in Table 3, DMF, and DMSO (as aprotic solvents) present the better results versus H2O as a protic solvent which can be due to the nature of curcumin as an organic ligand in BNPs@Cur-Pd. Also, like what was observed in Suzuki coupling reaction, here, PEG solvent promotes the basicity of Na2CO3 and increases the solubility of other precursors. Next, the optimization was conducted on the effect of various bases such as KOH, Et3N, and NaOEt in the Stille reaction (entries 9–11). The results indicate that sodium carbonate is the best choice to obtain a high yield of product. Finally, the temperature effect was appraised in 25 °C, 60 °C and 80 °C to choose the best reaction temperature. As shown in Table 3 (entries 4, 12 and 13), the Stille reaction proceeds effectively at 80 °C.