Key Laboratory for Advanced Materials and Feringa Nobel Prize Scientist Joint Research Center, Frontiers Science Center for Materiobiology and Dynamic Chemistry, State Key Laboratory of Chemical Engineering, School of Chemistry and Molecular Engineering, East China University of Science & Technology, 130 Meilong Road, Shanghai 200237, China.
J Am Chem Soc. 2023 Jun 21;145(24):13048-13058. doi: 10.1021/jacs.3c00962. Epub 2023 Jun 8.
Two-dimensional (2D) crystal-to-crystal transition is an important method in crystal engineering because of its ability to directly create diverse crystal materials from one crystal. However, steering a 2D single-layer crystal-to-crystal transition on surfaces with high chemo- and stereoselectivity under ultra-high vacuum conditions is a great challenge because the transition is a complex dynamic process. Here, we report a highly chemoselective 2D crystal transition from radialene to cumulene with retention of stereoselectivity on Ag(111) via retro-[2 + 1] cycloaddition of three-membered carbon rings and directly visualize the transition process involving a stepwise epitaxial growth mechanism by the combination of scanning tunneling microscopy and non-contact atomic force microscopy. Using progression annealing, we found that isocyanides on Ag(111) at a low annealing temperature underwent sequential [1 + 1 + 1] cycloaddition and enantioselective molecular recognition based on C-H···Cl hydrogen bonding interactions to form 2D triaza[3]radialene crystals. In contrast, a higher annealing temperature induced the transformation of triaza[3]radialenes to generate -diaza[3]cumulenes, which were further assembled into 2D cumulene-based crystals through twofold N-Ag-N coordination and C-H···Cl hydrogen bonding interactions. By combining the observed distinct transient intermediates and density functional theory calculations, we demonstrate that the retro-[2 + 1] cycloaddition reaction proceeds via the ring opening of a three-membered carbon ring, sequential dechlorination/hydrogen passivation, and deisocyanation. Our findings provide new insights into the growth mechanism and dynamics of 2D crystals and have implications for controllable crystal engineering.
二维（2D）晶体到晶体的转变是晶体工程中的一种重要方法，因为它能够直接从一种晶体中创造出多种晶体材料。然而，在超高真空条件下，通过化学和立体选择性来引导 2D 单层晶体到晶体的转变是一个巨大的挑战，因为该转变是一个复杂的动态过程。在这里，我们通过三员环的逆[2+1]环加成反应和扫描隧道显微镜与非接触原子力显微镜的结合，报道了在 Ag(111)表面上具有高化学选择性和立体选择性的从径向烯到累积烯的 2D 晶体转变，并且直接观察到涉及逐步外延生长机制的转变过程。通过程序升温退火，我们发现 Ag(111)上的异氰化物在较低的退火温度下经历了顺序的[1+1+1]环加成和基于 C-H···Cl 氢键相互作用的对映选择性分子识别，以形成二维三氮[3]径向烯晶体。相比之下，较高的退火温度诱导三氮[3]径向烯的转变生成-二氮[3]累积烯，它们通过两倍的 N-Ag-N 配位和 C-H···Cl 氢键相互作用进一步组装成基于累积烯的二维晶体。通过结合观察到的明显瞬态中间体和密度泛函理论计算，我们证明了逆[2+1]环加成反应通过三元环的开环、顺序脱氯/氢钝化和脱异氰化进行。我们的发现为二维晶体的生长机制和动力学提供了新的见解，并对可控晶体工程具有启示意义。
