將氮雜環碳烯鈀金屬錯合物催化的直接碳氫鍵芳基化反應運用於聚（3-己基噻吩）、聚（3-己基硒吩）及噻吩硒吩交替共聚物的合成

Utilization of N-Heterocyclic Carbene Palladium Complexes in Synthesis of Poly(3-hexylthiophene), Poly(3-hexylselenophene) and Poly(3-hexylselenophene-alt-3-hexylthiophene) by Direct C-H Arylation Polymerization

賴育英(Yu-Ying Lai) ； 童子謙(Tsu-Chien Tung) ； 鄭彥如(Yen-Ju Cheng)

《化學》 73卷2期 (2015/06) Pp. 139-149

https://doi.org/10.6623/chem.2015014

摘要

本研究成功地將氮雜環碳烯鈀金屬錯合物引入直接碳氫鍵芳基化的催化反應中，並且利用氮雜環碳烯鈀金屬錯合物催化劑進行直接碳氫鍵芳基化反應合成聚(3-己基噻吩) (P3HT)、聚 (3-己基硒吩)(P3HS) 與噻吩硒吩交替共聚物 (P3HTS) 三種不同的高分子光電材料。在我們的催化系統下，合成出來的P3HT 具有高分子量(Mn = 26.9K g/mol) 及高立體規則度 (94%) 等特性。我們同樣以此方法合成了P3HS，目前文獻中尚未有以直接碳氫鍵芳基化反應合成P3HS 的研究報導。氮雜環碳烯鈀金屬錯合物催化系統有寬廣的反應溫度 (70 °C 到140 °C)，相較於以膦配體醋酸鈀 (Pd(OAc)_2) 作為催化劑有較好的穩定性，反應的再現性也有明顯地提升。我們亦發現使用外加的配體，如P(MeOPh)_3，有助於提升醋酸鈀(Pd(OAc)_2)系統的催化效率，其原因有可能是P(MeOPh)3 上的氧原子會配位至鈀金屬，穩定鈀金屬的催化中間體，進而提升聚合的效率。我們也利用直接碳氫鍵芳基化反應，第一個成功地合成高立體規則度的噻吩硒吩交替共聚物(Alt-P3HST)，產物的分子量高達20,000 g/mol。本研究結果利用碳氫鍵直接芳基化反應，提供了更方便、也更經濟的方法，進行噻吩與硒吩的交替共聚物的合成。也為其它噻吩、硒吩和碲吩等不同的共聚物合成，提供了一個可行的方向。

關鍵字

氮雜環碳烯 ； 鈀催化 ； 直接碳氫鍵芳基化反應 ； 密度泛函理論計算 ； 噻吩硒吩交替共聚物

並列摘要

N-heterocyclic carbene (NHC) palladium-based and Pd(OAc)2-based systems have been utilized to conduct direct arylation polymerization of 2-bromo-3-hexylselenophene and 2-bromo-3-hexylthiophene. The reaction catalyst, temperature, time, additive, base, ligand, and sovlent are screened and optimized. When [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]chloro[3-phenylallyl] palladium(II) (Pd-IPr) was used as the catalytic precusor, high molecular weight poly(3-hexylthiohphene) (P3HT) (Mn = 26.9K g/mol) with high head-to-tail regioregularity (94%) can be achieved. Pd-IPr possesses high thermal stability and good catalytic reproducibility in the direct arylation polymerization, which is ascribed to the presence of the electron-rich NHC ligand. For the Pd(OAc)_2 system, an additional phosphine ligand, such as tris(o-methoxyphenyl)phosphine, is beneficial for enhancing the direct arylation polymerization efficiency. It is postulated that the phophine coordination effect can stabilize the catalytic intermediates and thus increase the catalytic efficiency. Poly(3-hexylselenophene) (P3HS) was also synthesized by direct-arylation polymerization for the first time. Presumably due to the poor solubility of P3HS in the reaction solvents, the obtained P3HS possesses modest molecular weight. The postulated reaction mecha-nisms for the catalytic systems in this research were investigated by Density-functional-theory (DFT) calculations. The ligand effect for the palladium-catalyzed direct arylaiton polymerization was then studied. More importantly, Pd-IPr-catalyzed direct-arylation polymerization of 2-bromo-3-hexyl-5-(3-hexylselenophen-2-yl)thiophene leads to the formation of a main-chain alternating and sidechain regioregular (head to tail = 94%) high molecular weight (20.0K g/mol) poly(3-hexylselenophene-alt-3-hexylthiophene) (Alt-P3HST). To our knowledge, it is the first approach to synthesizing 3-hexylselenophene and 3-hexylthiophene alternating copolymer. This research demonstrates in-depth investigation on the NHC-based palladium catalysts for the synthesis of conjugated polymers via direct C-H bond polymerization.

並列關鍵字

N-Heterocyclic carbene ； Palladium catalysis ； Direct arylation polymerization ； DFT calculations ； Selenophene and thiophene alternating copolymer