Synthesis and Reactivity of molecular Silicas with and without Oxygen Defects and Their Chalcogen Analogues

二氧化硅及其重同源物对各种底物（例如，为了固定这些表面上的金属位点或金属基簇）的各种令人着迷的反应性强烈依赖于末端基团和氧缺陷的化学性质。就二氧化硅而言，水和/或氧缺陷的存在不仅决定了末端Si-OH基团的浓度，而且还会影响其形态稳定性，即其发生后团聚的倾向。利用具有不同末端的分子模型，如Si-O-Si， Si(OH)n, Si=O基团，甚至氧缺乏，提供了一种在分子水平上揭示这类材料结构-反应性关系的方法。然而，由于缺乏合适的分子前体，可靠的模型化合物的合成途径仍然非常有限。这就是为什么该项目致力于开发前所未有的合成方法，以生成定义良好的二氧化硅分子模型及其重同源物。我们研究的起点是先前开发的（“无水”）选择性硫代作用，一种双n杂环碳稳定的零价硅配合物（“硅酮”），它可以合成和分离相应的含有单核6，SiX2 （X = O， S, Se, Te）和Si(CO3)2分子的化合物。后者与双碳配体的供体-受体相互作用阻止了它们的聚合。有了这些化合物，我们将研究这些实体对水和相关含OH化合物的反应性，旨在（通过连续选择性水解）合成相应的配体支持的单核Si(OH)n化合物（n = 2,3,4），包括试图分离难以找到的硅酸Si(OH)4的配合物。此外，我们将从辛科2n型（n = 5,6）的无环和环氯硅烷及其转化为相应的硅氧基和羟基取代的环硅烷开始，继续研究它们作为缺氧二氧化硅分子模型的能力，以及通过非水解途径作为分子前体生成二氧化硅等缺氧二氧化硅的能力。

The fascinatingly diverse reactivity of silica and its heavy homologues towards various substrates (e.g., in order to immobilize metal sites or metal-based clusters on such surfaces) is strongly dependent on the chemical nature of the terminal groups and oxygen defects. In the case of silica, the presence of water and/or oxygen defects not only determines the concentration of terminal Si-OH groups but will also influence its morphological stability, that is, its tendency to undergo post-agglomerization. One way to unravel structure-reactivity relationships of such materials on the molecular level is provided by taking ad-vantage of molecular models featuring different sorts of terminations such as Si-O-Si, Si(OH)n, Si=O moieties, and even oxygen deficiency. However, the synthetic access to reliable model compounds is still very limited due to the lack of suitable molecular precursors. This is why the project is devoted to the development of unprecedented synthetic methods for the generation of well-defined molecular models of silica and its heavy homologues.Starting point of our investigation is the previously developed (‘water-free’) selective chalcogenation a bis-N-heterocyclic carbene stabilized zero-valent silicon complex (‘silylone’) which enabled the synthesis and isolation of corresponding compounds bearing mononuclear SiX, SiX2 (X = O, S, Se, Te) and Si(CO3)2 molecules. The donor-acceptor interaction of the latter with the bis-carbene ligands prevents them from polymerization. With this compounds in hand we will study the reactivity of these entities towards water and related OH containing compounds aiming at the synthesis (via consecutive selective hydrolysis) of the corresponding ligand supported mononuclear Si(OH)n compounds (n = 2,3,4), including attempts to isolate a complex of the elusive silic acid, Si(OH)4. Moreover, starting from acyclic and cyclic chlorosilanes of the type SinCl2n (n = 5,6) and their transformation to the corresponding siloxy- and hydroxo-substituted cyclosilanes, we will continue to investigate their ability to serve as molecular models of oxygen-deficient silicas and to act as molecular precursors to give oxygen-deficient silicas such as SiO by a non-hydrolytic pathway.