Stolz Samuel, Di Giovannantonio Marco, Urgel José I, Sun Qiang, Kinikar Amogh, Borin Barin Gabriela, Bommert Max, Fasel Roman, Widmer Roland
Empa, Swiss Federal Laboratories for Materials Science and Technology, nanotech@surfaces Laboratory, 8600, Dübendorf, Switzerland.
Institute of Physics, École Polytechnique Fédérale de Lausanne, Laboratory of Nanostructures at Surfaces, 1015, Lausanne, Switzerland.
Angew Chem Int Ed Engl. 2020 Aug 10;59(33):14106-14110. doi: 10.1002/anie.202005443. Epub 2020 May 28.
In the emerging field of on-surface synthesis, dehalogenative aryl-aryl coupling is unarguably the most prominent tool for the fabrication of covalently bonded carbon-based nanomaterials. Despite its importance, the reaction kinetics are still poorly understood. Here we present a comprehensive temperature-programmed x-ray photoelectron spectroscopy investigation of reaction kinetics and energetics in the prototypical on-surface dehalogenative polymerization of 4,4''-dibromo-p-terphenyl into poly(para-phenylene) on two coinage metal surfaces, Cu(111) and Au(111). We find clear evidence for reversible dehalogenation on Au(111), which is inhibited on Cu(111) owing to the formation of organometallic intermediates. The incorporation of reversible dehalogenation in the reaction rate equations leads to excellent agreement with experimental data and allows extracting the relevant energy barriers. Our findings deepen the mechanistic understanding and call for its reassessment for surface-confined aryl-aryl coupling on the most frequently used metal substrates.
在表面合成这个新兴领域中，脱卤芳基-芳基偶联无疑是制备共价键合碳基纳米材料最突出的工具。尽管其很重要，但反应动力学仍未得到充分理解。在此，我们展示了一项全面的程序升温X射线光电子能谱研究，该研究针对在两种铸币金属表面（Cu(111)和Au(111)）上4,4''-二溴对三联苯的典型表面脱卤聚合反应生成聚对亚苯基的反应动力学和能量学进行。我们发现了在Au(111)上存在可逆脱卤的明确证据，而在Cu(111)上由于有机金属中间体的形成，这种可逆脱卤受到抑制。将可逆脱卤纳入反应速率方程后，与实验数据取得了极好的一致性，并能够提取相关的能垒。我们的研究结果加深了对其机理的理解，并呼吁对在最常用金属基底上的表面受限芳基-芳基偶联进行重新评估。
