Visualising Inner and Outer Sphere Metal-Ligand Interactions in Enantioselective Homogeneous Catalysts by ENDOR Spectroscopy and Computer Modelling

分子的化学反应能力和性质常常严重地取决于它们的形状或结构。例如，分子形状控制着从颜色、气味和味道到一种物质是固体、液体还是气体的一切。科学家使用不同的工具来研究这些形状，从而探索一个分子将如何根据其形状与另一个分子反应。这通常是很难实现的，特别是当分子处于溶液中，当它们与其他分子的相互作用非常弱时，它们几乎是任何分析技术都看不见的。因此，科学家们多年来一直致力于如何选择性地或以纯形式合成手性(手性)化合物，而不是作为具有不同三维结构或立体化学的镜像形式(称为对映体)的混合物。虽然大自然非常擅长这些所谓的对映选择性反应，但科学家们现在才学会在设计和合成新型手性催化剂时从这些天然催化剂中汲取灵感。在这个项目中，我们将首次使用脉冲EPR方法(Endor和HYSCORE)来了解溶液中手性金属络合物-配体相互作用的性质。我们选择手性体系有两个原因：1)了解手性相互作用对于合理开发新的均相催化剂很重要；2)控制手性识别的相互作用往往非常微弱，通过使用手性催化剂或其模型，可以通过进行镜像或非对映等效实验来确定结果的准确性。由于这些弱相互作用只在溶液中观察到，因此对于一系列不对称均相体系，可以推导出现实的底物-络合物相互作用模型。我们将探索手性信息如何从催化剂的活性位置转移(立体诱导)到反应底物，从而开发一种新的方法，使我们能够生成溶液中分子的三维可视化，揭示手性分子相互作用时发生的非常微小的结构变化。这项研究将使我们能够更好地了解这些特权手性催化剂是如何工作的，从而帮助我们对未来改进的催化剂设计做出总体预测。

The chemical reactivity and properties of molecules often depend critically on their shape or structure. For example, molecular shapes govern everything from colour, odour and taste to whether a substance is a solid, liquid or gas. Scientists use different tools to study these shapes, and thereby explore how one molecule will react with another depending on its shape. Quite often this is very hard to achieve, particularly when the molecules are in solution and when their interactions with other molecules are so weak, that they are virtually invisible to any analytical technique. Therefore scientists have been engaged for many years on how to synthesize handed (chiral) compounds selectively, or in pure form, rather than as mixtures of the mirror-image forms (called enantiomers) with different three dimensional structures or stereochemistries. While Nature is very good at these so-called enantioselective reactions, scientists are only now learning to draw inspiration from these natural catalysts in the design and synthesis of novel chiral catalysts. In this project, we will utilise for the first time, pulsed EPR methodologies (ENDOR and HYSCORE) to understand the nature of chiral metal complex-ligand interactions in solution. We have chosen chiral systems for two reasons: 1) understanding chiral interactions is important to the rational development of new homogeneous catalysts, and 2) the interactions governing chiral discrimination are often extremely feeble and by using chiral catalysts, or models thereof, the veracity of a result may be established by performing 'mirror-image' or diastereomerically equivalent experiments. Since these weak interactions are only observed in solution, realistic models of substrate-complex interactions can be derived for a range of asymmetric homogeneous systems. We will explore how the chiral information is transferred (the stereoinduction ) from the active site of the catalyst to a reacting substrate, and thereby develop a new approach enabling us to generate a 3-dimensional visualisation of molecules in solution, revealing the very small changes in structure that occur when chiral molecules weakly interact with each other. This study will enable us to understand better how these privileged chiral catalysts operate, and therefore help us to make general predictions for future improved catalyst designs.