Lawrence James, Mohammed Mohammed S G, Rey Dulce, Aguilar-Galindo Fernando, Berdonces-Layunta Alejandro, Peña Diego, de Oteyza Dimas G
Donostia International Physics Center, 20018 San Sebastián, Spain.
Centro de Física de Materiales, 20018 San Sebastián, Spain.
ACS Nano. 2021 Mar 23;15(3):4937-4946. doi: 10.1021/acsnano.0c09756. Epub 2021 Feb 25.
The combination of alkyne and halogen functional groups in the same molecule allows for the possibility of many different reactions when utilized in on-surface synthesis. Here, we use a pyrene-based precursor with both functionalities to examine the preferential reaction pathway when it is heated on an Au(111) surface. Using high-resolution bond-resolving scanning tunneling microscopy, we identify multiple stable intermediates along the prevailing reaction pathway that initiate with a clearly dominant Glaser coupling, together with a multitude of other side products. Importantly, control experiments with reactants lacking the halogen functionalization reveal the Glaser coupling to be absent and instead show the prevalence of non-dehydrogenative head-to-head alkyne coupling. We perform scanning tunneling spectroscopy on a rich variety of the product structures obtained in these experiments, providing key insights into the strong dependence of their HOMO-LUMO gaps on the nature of the intramolecular coupling. A clear trend is found of a decreasing gap that is correlated with the conversion of triple bonds to double bonds hydrogenation and to higher levels of cyclization, particularly with nonbenzenoid product structures. We rationalize each of the studied cases.
在同一分子中炔基和卤素官能团的组合，使得其在表面合成中能够发生多种不同的反应。在此，我们使用一种兼具两种官能团的芘基前驱体，来研究其在Au(111)表面加热时的优先反应路径。利用高分辨率键分辨扫描隧道显微镜，我们确定了主要反应路径上的多个稳定中间体，该路径以明显占主导的格拉泽偶联反应开始，同时还产生了大量其他副产物。重要的是，对缺乏卤素官能化的反应物进行的对照实验表明，不存在格拉泽偶联反应，而是显示出非脱氢头对头炔烃偶联反应占主导。我们对这些实验中获得的丰富多样的产物结构进行了扫描隧道光谱分析，从而深入了解了它们的HOMO-LUMO能隙对分子内偶联性质的强烈依赖性。发现了一个明显的趋势，即能隙减小与三键向双键的氢化转化以及更高程度的环化相关，特别是对于非苯型产物结构。我们对每个研究案例进行了合理的解释。
