Dynamics of C-C coupling reactions of activated carbon centers by crossed beam imaging

通过交叉光束成像研究活性炭中心 C-C 偶联反应的动力学

• 批准号: 500279291
• 负责人: Dr. Jennifer Meyer
• 金额: --
• 依托单位: Institut für Ionenphysik und Angewandte Physik
• 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/500279291?language=en
• 关键词: Dynamics; coupling; reactions; activated; carbon

Carbon-carbon coupling reactions are an integral part of synthetic protocols and often make use of organometallic catalysts with intermediate reactive carbon centers being formed through interaction with a metal center. This project focuses on two types of reactive carbon centres (1) alkylidens M-CH3 and (2) carbenes M=CH2 with the first important in Ziegler-Natta type chemistry and the second in olefin metathesis. Despite the very different nature of the metal carbon bond, it is accepted that for both intermediates the coupling reaction passes through a four-membered cyclic transition state. The currently used transition metals are foremost from the 4d and 5d series. These elements are rare and expensive, thus research tries to replace them by more abundant 3d transition metals, for example iron or cobalt which will be our transition metals of choice. The outcome of transition metal chemistry is hard to predict due to the number of close lying electronic states of the metal which can for example lead to state-selective reactivity, non-statistical product formation or efficient crossing of spin-surfaces. The aim of this project is to investigate the underlying atomistic dynamics of the carbon bond forming reactions in gas phase using M-CH3+ and M=CH2+ model systems in reactions with small olefines, namely ethene and propene. In-situ ion formation in an radio frequency multipole ion trap allows us to omit any stabilizing ligands needed in condensed phase. We will use crossed beam 3D velocity map imaging to investigate the atomic-level dynamics to record product ion velocity distributions, i.e. differential cross sections. From the experimental data, we can extract information on the atomistic mechanisms, that means how atoms rearrange during the reactive encounter and if a reaction is direct or indirect. Further, we learn about the influence of barriers along the reaction coordinate or if reaction follows may be non-statistical. Recording the full velocity vector allows us to investigate competing product channels in the same experiment and derive branching ratios. Collision energy dependent experiments will give additional insight into these competitions, importance of barriers and stability of encounter complexes. We will study the benchmark reaction of methane coupling by Ta+ for which the first step is the Ta=CH2+ formation followed by a reaction with a second methane molecule. We will concentrate on the role of the four-membered transition state and if direct reaction dynamics are possible despite the complex transition state structure and if a common signature emerges. Depending on the chosen transition metal, barriers along the reaction coordinate might be submerged or not. Their role will be studied in reactions with M-CH3+. Bond insertion reactions are a competing with metathesis reactions, therefore we will carefully study this competition as function of collision energy.

碳-碳偶联反应是合成方案的组成部分，并且通常利用有机金属催化剂，其中中间活性碳中心通过与金属中心的相互作用形成。该项目重点关注两种类型的活性碳中心（1）亚烷基M-CH 3和（2）卡宾M= CH 2，第一种在齐格勒-纳塔型化学中很重要，第二种在烯烃复分解中很重要。尽管金属碳键的性质非常不同，但对于两种中间体来说，偶合反应都通过四元环过渡态。目前使用的过渡金属主要是4d和5d系列。这些元素是稀有和昂贵的，因此研究试图用更丰富的3d过渡金属来取代它们，例如铁或钴，这将是我们选择的过渡金属。过渡金属化学的结果很难预测，因为金属的紧密电子态的数量可能导致例如状态选择性反应性，非统计产物形成或自旋表面的有效交叉。本项目的目的是研究在气相中使用M-CH 3+和M= CH 2+模型系统与小烯烃，即乙烯和丙烯反应中的碳键形成反应的原子动力学。在射频多极离子阱中原位离子形成允许我们省略凝聚相中所需的任何稳定配体。我们将使用交叉束三维速度图成像来研究原子级动力学，以记录产物离子的速度分布，即微分截面。从实验数据中，我们可以提取原子机制的信息，这意味着原子在反应相遇过程中如何重新排列，以及反应是直接还是间接的。此外，我们了解了沿反应坐标沿着势垒的影响，或者反应是否遵循可能是非统计的。记录全速度矢量使我们能够在同一实验中研究竞争产物通道并得出分支比。碰撞能量依赖的实验将提供更多的洞察这些竞争，障碍的重要性和稳定性的遭遇复杂。我们将研究由Ta+进行的甲烷偶联的基准反应，其中第一步是Ta= CH 2+形成，然后与第二个甲烷分子反应。 我们将集中在四元过渡态的作用，如果直接反应动力学是可能的，尽管复杂的过渡态结构，如果一个共同的签名出现。根据所选择的过渡金属，沿着反应坐标的屏障可能会被淹没或不被淹没。它们的作用将在与M-CH 3+的反应中进行研究。键插入反应与复分解反应是竞争反应，因此我们将仔细研究这种竞争作为碰撞能的函数。