Synthesis of covalently bonded molecular nano-architectures on surfaces modeled from first principles

在过去的十年里，基于非共价键的各种高度规则的超分子结构已经在单晶金属表面实现。然而，许多潜在的应用，例如在自下而上的器件技术中，需要只有通过共价键才能提供的热稳定性和化学稳定性。作为对这一需求的响应，最近已经进行了许多尝试，以在单晶金属表面上制备共价互连的聚合物网络。因此，人们注意到，当反应伙伴被限制在二维时，从3D化学中已知的一些反应发生的方式不同，在某些情况下，报道了全新的反应路径。在这里，我们提出密度泛函理论(DFT)计算，以详细探讨表面对化学反应热力学和动力学的影响。特别是，我们的目标是识别和探索系统，其中底物同时充当模板和催化剂，因为它们似乎特别有希望在表面进行可控的反应。因此，我们集中于典型的例子，如表面支撑的嘧啶基团的互变异构化，Ullmann偶联，胺和酸酐的亚胺化缩合，硼酸和二醇基团的酯化，醛和胺的生成亚胺，以及活化的卟啉在金属底物上的反应。我们将对硬币金属(111)、(110)和(001)表面的空间位阻、电子转移和屏蔽效应、与衬底的化学相互作用以及衬底原子在反应中的直接参与等各种潜在机制进行研究，以建立化学趋势，并对表面的共价合成得到更深入和彻底的了解。

A wide variety of highly regular supramolecular architectures, based on noncovalent bonds, has been realized on single crystal metal surfaces over the past decade. Many potential applications, e.g., in bottom-up device technology, however, require a thermal and chemical stability that can only be provided by covalent bonding. In response to this need a number of attempts to fabricate covalently interlinked polymeric networks on single crystal metal surfaces have recently been made. Thereby it was noted that some reactions known from 3D chemistry occur differently when the reaction partners are confined to two dimensions and in some cases entirely novel reaction pathways were reported. Here we propose density-functional theory (DFT) calculations in order to explore in detail the influence of the surface on the thermodynamics and kinetics of chemical reactions. In particular we aim at identifying and exploring systems, where the substrate acts simultaneously as a template and a catalyst, as they seem especially promising for controllable reactions at surfaces. Thereby we focus on prototypical examples such as surface-supported tautomerization of pyrimidine groups, Ullmann couplings, imidization condensation of amines and anhydrides, esterification between boronic acid and diol groups, imine formation from aldehydes and amines, and the reaction of activated porphyrins on metal substrates. Various potential mechanisms like steric hindrances, electron transfer and screening effects, chemical interactions with the substrate as well as the direct involvement of substrate atoms in the reaction will be investigated for the coin metal (111), (110), and (001) surfaces in order to establish chemical trends and arrive at a deep and thorough understanding of the covalent synthesis at surfaces.