Ren Jindong, Klaasen Henning, Witteler Melanie C, Viergutz Lena, Neugebauer Johannes, Gao Hong-Ying, Studer Armido, Fuchs Harald
Center for Nanotechnology (CeNTech), Heisenbergstraße 11, 48149, Münster, Germany.
Physikalisches Institut, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Straße 10, 48149, Münster, Germany.
Chemistry. 2020 Dec 15;26(70):16727-16732. doi: 10.1002/chem.202002486. Epub 2020 Nov 9.
The reactivity of aryl triflates in on-surface C-C coupling is reported. It is shown that the triflate group in aryl triflates enables regioselective homo coupling with preceding or concomitant hydrodetriflation on Cu(111). Three different symmetrical π-systems with two and three triflate functionalities were used as monomers leading to oligomeric conjugated π-systems. The cascade, comprising different intermediates at different reaction temperatures as observed for one of the molecules, proceeds via initial removal of the trifluoromethyl sulfonyl group to give an aryloxy radical which in turn is deoxygenated to the corresponding aryl radical. Thermodynamically driven regioselective 1,2-hydrogen atom transfer leads to a translocated aryl radical which in turn undergoes coupling. For a sterically more hindered bistriflate, where one ortho position was blocked, dehydrogenative coupling occurred at remote position with good regioselectivity. Starting materials, intermediates as well as products were analyzed by scanning tunneling microscopy. Structures and suggested mechanism were further supported by DFT calculations.
报道了芳基三氟甲磺酸酯在表面C-C偶联中的反应活性。结果表明，芳基三氟甲磺酸酯中的三氟甲磺酸酯基团能够在Cu(111)上实现区域选择性均相偶联，并伴随着氢脱三氟甲磺酸反应。使用三种具有两个和三个三氟甲磺酸酯官能团的不同对称π体系作为单体，得到了低聚共轭π体系。对于其中一个分子，在不同反应温度下观察到的包含不同中间体的级联反应，首先是三氟甲基磺酰基的去除，生成芳氧基自由基，该自由基再脱氧生成相应的芳基自由基。热力学驱动的区域选择性1,2-氢原子转移导致芳基自由基发生移位，进而发生偶联。对于一种空间位阻更大的双三氟甲磺酸酯，其中一个邻位被阻断，脱氢偶联在远程位置发生，具有良好的区域选择性。通过扫描隧道显微镜对起始原料、中间体和产物进行了分析。密度泛函理论计算进一步支持了结构和提出的机理。
