Visualizing and Understanding Ordered Surface Phases during the Ullmann Coupling Reaction
Visualizing and Understanding Ordered Surface Phases during the Ullmann Coupling Reaction
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DOI：
10.1021/acs.jpcc.1c00462
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发表时间：
2021-04-01
影响因子：
3.7
通讯作者：
Sykes，E. Charles H.
中科院分区：
文献类型：
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作者：
Balema，Tedros A.;Miao，Jiayuan;Sykes，E. Charles H.
金属铜催化卤代芳烃的Ullmann偶联反应已有一个多世纪的历史，作为一种基于表面C-C偶联的扩展2D结构自组装的方法，引起了纳米科学界的新兴趣。此外，最近的实验表明，Ullmann偶联不是一个直接的过程，而是通过一个被移除的铜表面原子配位两个苯基组成的有机金属中间体进行的。我们进行了低温扫描隧道显微镜研究，研究了表面结合的反应物、有机金属中间体和产物的相互作用和有序性，发现这些物种都自组装成致密的2D岛，模拟了典型的Ullmann偶联反应条件下预期的高表面覆盖率。通过对一系列取代溴苯反应物的比较和对比，我们发现2D堆积密度和结构强烈地依赖于取代基的官能度。此外，我们对中间体和产物中电荷分布的计算解释了观察到的高度有序的2D相的堆积结构。这项研究提供了这一重要反应的催化表面的原子尺度快照，并可以指导进一步的乌尔曼偶联反应分子尺度机理的模型研究。
The more than century old copper metal-catalyzed Ullmann coupling reaction of aryl halides has seen renewed interest from the nanoscience community as a means to perform on-surface C–C coupling based self-assembly of extended 2D structures. Furthermore, recent experiments have revealed that Ullmann coupling is not a direct process, rather it proceedsviaan organometallic intermediate composed of a removed Cu surface atom that coordinates two phenyl groups. We have undertaken a low-temperature scanning tunneling microscopy study to investigate the interaction and ordering of the surface-bound reactants, organometallic intermediates, and products and found that these species all self-assemble into dense 2D islands that mimic the high surface coverages expected during typical Ullmann coupling reaction conditions. By comparing and contrasting a series of substituted bromobenzene reactants, we found that the 2D packing density and structure depend strongly on the functionality of the substituents. Furthermore, our calculations of the charge distribution in the intermediates and products explain the observed packing structures of the highly ordered 2D phases. This study provides atomic-scale snapshots of the catalytic surface of this important reaction and can guide further model studies of the molecular-scale mechanism of the Ullmann coupling reaction.