Kinetics of On-Surface Dechlorinated Aryl-Aryl Coupling

Dehalogenative aryl-aryl coupling has been the key strategy in on-surface synthesis for crafting covalently bonded carbon-based nanomaterials. However, comprehensive studies focusing on the kinetics of these reactions are notably rare. Moreover, the existing literature predominantly addresses debromination, often neglecting dechlorination, a critical reaction requiring higher energies but with profound implications for environmental protection and advancement of sustainable chemistry practices. Here, we combined synchrotron-based X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) to study the dehalogenated coupling reactions of chlorinated and brominated aromatic hydrocarbons on the Au(111) surface. The high-resolution surface-sensitive techniques allow to identify the reactants and products. We find that extended annealing facilitates setting the activation temperature for dechlorinated coupling to around 473 K, a notable decrease from the previously considered 573 K, highlighting the significant impact of kinetic effects on the on-surface reaction process. Using the temperature-programmed XPS measurement, we are able to extract the kinetic curves of the dechlorinated coupling reactions and obtain detailed insight into the reaction process. This research enhances our mechanistic understanding of the widely utilized on-surface dehalogenative coupling reaction, serving as a fundamental step toward optimizing its efficiency and selectivity.