Velocity resolved kinetics of enantioselective olefin epoxidation on chiral surfaces

手性表面上对映选择性烯烃环氧化的速度解析动力学

• 批准号: 457424069
• 负责人: Dr. Tim Schäfer
• 金额: --
• 依托单位: Institut für Physikalische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/457424069?language=en
• 关键词: Velocity; resolved; kinetics; enantioselective; olefin

In the here proposed project we intend to study the dynamics and kinetics of enantioselective olefin epoxidation on chiral surfaces by combining molecular beam surface scattering experiments with velocity map imaging techniques. The epoxidation of olefins on metal surfaces is a technologically important class of chemical reactions, and so far corresponding reactions have been extensively investigated in high detail under ultra-high vacuum conditions. However, none of these studies focuses on the reaction’s enantioselectivity when the reaction occurs on chiral surfaces, as chirality detection is demanding for surface desorbing reaction products at low concentration in the gas phase. We plan to identify the reaction products’ chirality by measuring the multi-photon photoelectron circular dichroism (MP-PECD) after pulsed laser 2+1 resonant enhanced multi-photon ionization (REMPI) of the epoxides at 400 nm. Experiments will be performed similar to pump-probe laser experiments. A short molecular beam pulse of the prochiral olefin initiates the reaction by adsorption at the surface (pump) and reaction products will be probed after desorption by laser ionization. By time delaying molecular beam pulse and laser ionization, reaction kinetics can be inferred on a microsecond timescale. We record either photoelectrons for chirality detection or photoions for product assignment by time-of-flight mass spectrometry (ToF-MS). The same detector provides velocity map images of reaction products, which are used to record dynamics of site specific reaction channels. We will investigate the reactions of the prochiral olefins styrene, 3,3-dimethyl-1-butene, and trans-methyl-styrene on chiral coinage metals. On achiral coinage metal surfaces all these olefins partially oxidize to racemic mixtures of corresponding chiral epoxides when reacting with oxygen. We will introduce enantioselectivity to the reaction by performing the reaction on chiral surfaces. For this, we will follow two approaches: at first, we will perform epoxidation experiments on naturally chiral surfaces, which have intrinsically chiral atomic structures. In a second approach, we plan to investigate the epoxidation on chirally modified surfaces. We will produce such surfaces by the adsorption of functionalized chiral organic molecules. The experiments will produce valuable data for the microscopic understanding of heterogeneously catalyzed enantioselective reactions by addressing among others the following questions: how does the epoxidation reaction rate of chosen olefin molecules depend on the combination of chiral reaction product and surface chirality? Are there systematic trends when changing the prochiral olefin reactants? Can we induce enantioselectivity when adsorbing chiral modifier molecules at the surface?

在此提出的项目中，我们打算通过将分子束表面散射实验与速度图成像技术相结合，研究手性表面上对映选择性烯烃环氧化的动力学和动力学。金属表面上烯烃的环氧化是一类技术上重要的化学反应，迄今为止，相应的反应在超高真空条件下已得到广泛、详细的研究。然而，这些研究都没有关注反应发生在手性表面上时的对映选择性，因为手性检测对气相中低浓度的表面解吸反应产物要求较高。我们计划通过在 400 nm 处对环氧化物进行脉冲激光 2+1 共振增强多光子电离 (REMPI) 后测量多光子光电子圆二色性 (MP-PECD) 来鉴定反应产物的手性。实验将类似于泵浦探测激光实验进行。前手性烯烃的短分子束脉冲通过在表面（泵）处的吸附来引发反应，并且在通过激光电离解吸后将探测反应产物。通过延迟分子束脉冲和激光电离，可以在微秒时间尺度上推断反应动力学。我们通过飞行时间质谱 (ToF-MS) 记录用于手性检测的光电子或用于产品分配的光离子。同一检测器提供反应产物的速度图图像，用于记录特定位点反应通道的动态。我们将研究前手性烯烃苯乙烯、3,3-二甲基-1-丁烯和反式甲基苯乙烯在手性造币金属上的反应。在非手性造币金属表面上，当与氧气反应时，所有这些烯烃都部分氧化成相应手性环氧化物的外消旋混合物。我们将通过在手性表面上进行反应来引入对映选择性。为此，我们将遵循两种方法：首先，我们将在具有本质手性原子结构的自然手性表面上进行环氧化实验。在第二种方法中，我们计划研究手性改性表面上的环氧化。我们将通过吸附功能化的手性有机分子来生产这样的表面。这些实验将通过解决以下问题，为非均相催化对映选择性反应的微观理解提供有价值的数据：所选烯烃分子的环氧化反应速率如何取决于手性反应产物和表面手性的组合？改变前手性烯烃反应物时是否存在系统趋势？当手性改性剂分子吸附在表面时，我们可以诱导对映选择性吗？