Physics Department E20, Technical University of Munich , James-Franck Straße 1, 85748 Garching, Germany.
Physics Department, Paderborn University , Warburger Straße 100, 33098 Paderborn, Germany.
ACS Nano. 2017 Mar 28;11(3):3383-3391. doi: 10.1021/acsnano.7b00766. Epub 2017 Mar 1.
Radical cyclization is among the most powerful and versatile reactions for constructing mono- and polycyclic systems, but has, to date, remained unexplored in the context of on-surface synthesis. We report the controlled on-surface synthesis of stable corrole radicals on Ag(111) via site-specific dehydrogenation of a pyrrole N-H bond in the 5,10,15-tris(pentafluoro-phenyl)-corrole triggered by annealing at 330 K under ultrahigh-vacuum conditions. We reveal a thermally induced regioselective cyclization reaction mediated by a radical cascade and resolve the reaction mechanism of the pertaining cyclodefluorination reaction at the single-molecule level. Via intramolecularly resolved probing of the radical-related Kondo signature, we achieve real space visualization of the distribution of the unpaired electron density over specific sites within the corrole radical. Annealing to 550 K initiates intermolecular coupling reactions, producing an extended π-conjugated corrole system.
自由基环化反应是构建单环和多环体系最强大、最通用的反应之一，但迄今为止，在表面合成的背景下，该反应仍未得到探索。我们通过在超真空条件下于 330 K 退火，报告了在 Ag(111)上通过特定位置的吡咯 N-H 键脱氢，可控地合成稳定的卟啉自由基。我们揭示了一种由自由基级联介导的热诱导区域选择性环化反应，并在单分子水平上解析了相关的脱氟环化反应的反应机制。通过对自由基相关的 Kondo 特征的分子内分辨探测，我们实现了在卟啉自由基内特定位置的未配对电子密度分布的实空间可视化。退火至 550 K 会引发分子间偶联反应，生成扩展的π共轭卟啉体系。
