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

在过去的十年中，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上实现。然而，许多潜在的应用，例如自下而上的设备技术，需要只有共价键才能提供的热稳定性和化学稳定性。为了满足这一需求，最近已经进行了许多在单晶金属表面上制造共价互连聚合物网络的尝试。因此，人们注意到，当反应伙伴被限制在二维空间中时，一些从三维化学中已知的反应发生了不同的变化，在某些情况下，报道了全新的反应途径。在此，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，其中底物同时作为模板和催化剂，因为它们似乎特别有希望在表面上进行可控反应。因此，我们关注的是典型的例子，如嘧啶基团的表面支持的互变异构化，乌尔曼偶联，胺和酸酐的亚胺化缩合，硼酸和二醇基团之间的酯化反应，醛和胺生成亚胺，以及活化卟啉在金属底物上的反应。各种潜在的机制，如空间位阻、电子转移和筛选效应、与底物的化学相互作用以及底物原子在反应中的直接参与，将对硬币金属（111）、（110）和（001）表面进行研究，以建立化学趋势，并对表面上的共价合成有一个深入而彻底的理解。

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.