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Structure and reactivity of oxametallacycle intermediates on silver surfaces: A combined experimental/theoretical approach.

机译：在银表面上的氧杂金属环中间体的结构和反应性：组合的实验/理论方法。

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The silver-catalyzed epoxidation of olefins represents an important class of reactions in heterogeneous catalysis. Despite much study, however, the detailed mechanism for these reactions is not well understood. In an effort to better understand the mechanism of olefin epoxidation, the research described in this dissertation has been focused on synthesizing and studying oxametallacycle intermediates that may be formed during these reactions. By combining the results from experimental surface science studies with insights from theoretical calculations, it is possible to obtain a detailed understanding of the structure and reactivity of oxametallacycle intermediates on silver surfaces.; The recent commercialization of a new process for the silver-catalyzed epoxidation of 1,3-butadiene has created new opportunities for exploring the mechanism of epoxidation reactions on silver surfaces. The product of butadiene epoxidation, 1-epoxy-3-butene (EpB), has been reported to exist in a strongly adsorbed state on the catalyst used in the industrial process. We have utilized a combination of experimental surface science techniques and density functional theoretical calculations to study the nature of this intermediate on model silver surfaces. These studies have confirmed that the strongly adsorbed species is in fact an oxametallacycle intermediate—a cyclic -O-C-C- species in which both oxygen and carbon atoms are bound to the surface. Our combined experimental/theoretical studies have enabled us to examine the structure and reactivity of the isolated oxametallacycle in great detail, and to establish the importance of this intermediate in the industrial process.; A similar experimental/theoretical approach has been used to study oxametallacycle intermediates of potential importance in related oxidation processes, including ethylene, propylene, and isobutylene epoxidation, in order to determine how changes in oxametallacycle structure may alter reaction pathways. These investigations can identify explanations for observed reactivity differences for different epoxidation reactions, and can ultimately be used to obtain a more detailed understanding of the mechanism for olefin epoxidation. Furthermore, these studies demonstrate the incisiveness of the synergistic application of computational chemistry and experiment in pursuit of reaction mechanisms, and point toward a direction in which this approach can be used to shed light on a wide array of surface phenomena.
机译：烯烃的银催化的环氧化代表了非均相催化中重要的一类反应。然而，尽管进行了大量研究，但对于这些反应的详细机理尚不十分了解。为了更好地理解烯烃环氧化的机理，本论文描述的研究一直集中在合成和研究在这些反应过程中可能形成的氧杂金属环中间体上。通过将表面实验研究的结果与理论计算的见解相结合，有可能获得对银表面金属杂草环中间体的结构和反应性的详细了解。银催化的1，3-丁二烯环氧化新工艺的最新商业化为探索银表面上环氧化反应的机理创造了新的机会。据报道，丁二烯环氧化产物1-环氧-3-丁烯（EpB）以强吸附状态存在于工业过程中使用的催化剂上。我们结合了实验表面科学技术和密度泛函理论计算，研究了模型银表面上该中间体的性质。这些研究已经证实，吸附力强的物质实际上是氧杂金属环中间体-一种环状-O-C-C-物质，其中氧原子和碳原子都结合在表面上。我们的实验/理论研究相结合，使我们能够详细检查分离出的金属氧杂环化合物的结构和反应活性，并确定该中间体在工业过程中的重要性。为了确定氧杂金属环结构的变化如何改变反应途径，已经使用了类似的实验/理论方法来研究在相关氧化过程中具有潜在重要性的氧杂金属环中间体，包括乙烯，丙烯和异丁烯环氧化。这些研究可以为不同的环氧化反应确定观察到的反应性差异的解释，并最终可以用来更详细地了解烯烃环氧化的机理。此外，这些研究证明了计算化学和实验的协同应用在追求反应机理方面的敏锐性，并指出了该方法可用于阐明各种表面现象的方向。

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