Development of a Dual-Mode Microwave-EPR Cavity for Studies of Paramagnetic Systems

在催化体系中，特别是在原位条件下，研究反应中间体的机理和形态存在许多挑战。通常，这些物种的寿命和浓度都低于询问光谱技术的检测下限。对于顺磁反应中间体来说尤其如此。为了应对这些挑战，我们正在开发一种用于电子顺磁共振(EPR)光谱的独特的双中等作用器-谐振器，利用微波(MWs)令人难以置信的高效加热能力来产生测量和快速样品加热(温度跳跃或TJ能力)，以更好地了解MWs在提高反应和化学转化速度方面的拟议作用。常规EPR腔(谐振器)的TE102模式将监测EPR信号，而较低频率的TE101模式将通过外部连续波或脉冲微波源同时访问，以感应样品加热(电感应器)。快速加热有多种好处，不仅可以加速反应，还可以改变不稳定物种的产物分布和比例，从而能够使用EPR光谱仪进行TJ驰豫测量。在这个实验项目中，我们将专门使用双模谐振器来初步研究三个关键的应用领域。首先，将利用共振器来研究有机自由基中交换反应的动力学，特别是探索溶剂在这些电子转移事件中的作用和行为。其次，我们将研究一系列低价过渡金属离子用于微波辅助交叉偶联反应。在某些情况下，已经提出了反应产物的分子量增强的建议，我们将试图调查这些建议的加速的根本来源。最后，我们还将研究使用含钴络合物进行氧化催化所涉及的活性物种。这些络合物不仅与均相催化有关，而且也是研究自旋交叉化合物的模型系统，可以通过共振器的可变原位加热能力来操纵。了解远离平衡的反应的化学是化学和物理科学中的一个重要愿望。虽然有许多T跳跃摄动技术可用，但这种就地快速加热EPR的好处将为英国提供一种新的能力。虽然该项目的一个主要焦点是测试应用于反应动力学和催化问题的双中间反应-共振器，但必须认识到，尽管在合成化学转化中越来越多地使用微波辐射，但对微波如何与材料相互作用的基本知识仍然知之甚少。还必须指出，催化是EPSRC投资组合中的一个重要研究领域。因此，本项目的研究将服务于这两个主要挑战和研究领域。

There are many challenges in studying the mechanisms and speciation of reactionintermediates in catalytic systems, particularly under in situ conditions. Quite often thelifetime and concentrations of these species are below the detection limits of theinterrogating spectroscopic technique. This is particularly true for paramagneticreaction intermediates. To address these challenges, we are developing a unique dualmodereactor-resonator for Electron Paramagnetic Resonance (EPR) spectroscopy,utilising the incredibly efficient heating capabilities of microwaves (MWs) to generatevolumetric and rapid sample heating (a temperature jump, or TJ, capability), to betterunderstand the proposed role of MWs in enhancing the rate of reactions and chemicaltransformations. The TE102 mode of a conventional EPR cavity (the resonator) willmonitor the EPR signals whilst a lower frequency TE101 mode will be simultaneouslyaccessed via an external CW or pulsed MW source to induce the sample heating (thereactor). The rapid heating offers multiple benefits, not only to accelerate a reaction, butalso to alter the product distribution and proportion of unstable species and therebyenable TJ-relaxation measurements to be performed using EPR spectroscopy.In this experimental project, we will specifically employ the dual mode resonator toinitially study three key application areas. Firstly, the resonator will be utilised toinvestigate the kinetics of exchange reactions in organic radicals, and particularlyexplore the role and behaviour of the solvent in these electron transfer events. Secondly,we will study a series of low valent transition metal ions for MW assisted cross couplingreactions. In some cases, a proposed MW enhancement of reaction products has beenproposed, and we will seek to investigate the fundamental origins of these proposedaccelerations. Finally, we will also examine the reactive species involved in oxidationcatalysis employing cobalt bearing complexes. These complexes are relevant not only tohomogeneous catalysis, but also as model systems for studies of spin-cross overcompounds, which can be manipulated using the variable in situ heating capabilities ofthe resonator.Understanding the chemistry of reactions shifted far from equilibrium is an importantaspiration in the chemical and physical sciences. Although many T-jump perturbationtechniques are available, the benefits of this in situ rapid heating EPR will provide a newcapability to the UK. Whilst a major focal point of this project is the testing of the dualmodereactor-resonator, applied to problems in reaction kinetics and catalysis, it mustbe recognised that the fundamental knowledge of how MWs interact with materialsremains poorly understood, despite the growing use of MW-radiation in syntheticchemical transformations. It must also be stated that catalysis is an important researcharea within the EPSRC portfolio. Therefore, the research in this project will serve tounderpin both of these major challenges and research areas.