The metathesis reaction, studied by single-molecule chemistry

点击翻译按钮获取中文摘要

The description of chemical reaction in textbooks relies on the transformation of single molecules, but chemists hardly perform experiments on suchlike concentration levels. Understanding chemistry requires a huge level of abstraction in deducing molecular properties from physical properties of the material. Thus, direct access to molecular dynamics will not only help adding knowledge about reaction mechanisms and pathways but may also help simplifying the understanding of chemistry in general. Recently, the authors of this proposal studied the well-known epoxidation of double bonds by single-molecule fluorescence spectroscopy. In their experiments, they exploited the change of the emission wavelength of a fluorescent probe molecule during the transformation and found a yet unknown bifurcation in the reaction pathway to the epoxide. The experiments were carried out in special reaction chambers resistive to organic solvents using a single-molecule sensitive TIRF-microscope.In the applied project we plan to transfer this experimental approach to the ruthenium-catalyzed metathesis reaction. Despite the catalysis being well-understood for a plethora of synthetic applications, the initial reaction deserves further investigation as preliminary experiments revealed hints to both the associative and the dissociative reaction mechanism. The aim of the present project is to familiarize chemists with the opportunities of single-molecule chemistry, exemplified on the ambiguous activation of ruthenium-based metathesis catalysts. We plan to address the role of phosphine dissociation in the regioselectivity by following fluorescence trajectories on immobilized targets. Controlled supply of further chemicals is warranted by use of microfluidics.