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

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.