新加坡国立大学Andrew Thye Shen Wee团队取得一项新突破。他们的最新研究实现了石墨上自组装有序分子阵列表面环加成反应的重定向。相关论文于2025年2月5日发表于国际顶尖学术期刊《德国应用化学》杂志上。

在这项研究中，研究团队用扫描隧道显微镜在石墨上，在高度有序π共轭分子阵列中，通过温和退火（~210℃）触发了一个非同寻常的[2+2]+[2+2]环加成。与通常在金属基质上获得的不规则树枝状碎片相比，在这里观察到超过30%的环加成产物和其他聚合物的大超分子岛，它们作为有缺陷的个体或链（晶界）嵌入。

第一性原理计算表明，多重脱卤、脱氢和环加成反应的能垒被催化铁原子降低，但能量上仍然是不利的。对于惰性表面上的重定向反应，研究者提出了一种独特的驱动机制，其中额外的分子间偶联，位阻和/或界面相互作用起重要作用。本研究为理解非金属衬底上的表面合成提供了一个新的范例。

据了解，超高真空下原子精密碳纳米结构的合成，在金属表面上取得了广泛的进展。然而，这在化学惰性表面上仍然具有挑战性。这是因为热活化的C-C耦合在弱相互作用的底物上，遇到了严重的“解吸问题”。

附：英文原文

Title: Redirecting On-surface Cycloaddition Reactions in a Self-assembled Ordered Molecular Array on Graphite

Author: Yuli Huang, Ke Yang, Jing Yang, Sisheng Duan, Yihe Wang, Mingyue Sun, Yong-Wei Zhang, Ming Yang, Andrew Thye Shen Wee

Issue&Volume: 2025-02-05

Abstract: The synthesis of atomically precise carbon nanostructures in ultra-high vacuum has seen extensive progress on metal surfaces. However, this remains challenging on chemically inert surfaces. It is because the thermally activated C-C coupling encounters a severe “desorption problem” on weakly interacting substrates. In this study, we report an extraordinary [2+2]+[2+2] cycloaddition triggered by mild annealing (~210°C) in a highly ordered π-conjugated molecular array on graphite using scanning tunneling microscopy. In contrast to irregular dendritic fragments typically obtained on metal substrates, large supramolecular islands are observed here with cycloaddition products and other polymers over 30%, which are embedded as defective individuals or chains (grain boundaries). First-principles calculations reveal that the energy barriers of the multiple dehalogenation, dehydrogenation, and cycloaddition reactions are reduced by catalytic Fe atoms but remain energetically unfavorable. A distinct driving mechanism is proposed for redirecting the reactions on inert surfaces, where additional intermolecular coupling, steric hindrance, and/or interfacial interactions play significant roles. This study introduces a new paradigm for understanding on-surface synthesis on non-metal substrates.

DOI: 10.1002/anie.202425185

Source: https://onlinelibrary.wiley.com/doi/10.1002/anie.202425185