Gehrke, Sascha: The Influence of Solvent Reorganization on Organocatalytic Reactions. - Bonn, 2021. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Sascha Gehrke}},
title = {The Influence of Solvent Reorganization on Organocatalytic Reactions},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = apr,

note = {In the last decades N-heterocyclic carbenes have shown a certain potential as organocatalysts. In addition to the formation of regio- and stereoselective C-C coupling reactions, their scope of application includes the activation of CO2. The active site of the carbene - the electron lone pair on the hypovalent carbon atom - is on the one hand a very strong nucleophile, but on the other hand it also serves as a potential interaction acceptor site for hydrogen bonds and can therefore be blocked by solvents with appropriate functional groups. In order to develop efficient catalyst-solvent systems, a deeper understanding of this interplay is essential. This thesis makes a valuable contribution to this issue by the aid of quantumchemical calculations and classical molecular dynamics simulations. First, a summary of the current state of research in the field of carbenes is included in chapter 1.1. Thereby, the main focus is on a discussion of the assumed reaction mechanism and the observed influences by the respective solvent on the reactivity and selectivity of the catalyst. This is followed by the short chapter 1.2, which summarizes the basic knowledge about hydrogen bonds. Based on this level of knowledge, some target questions are formulated in chapter 1.3 and the work steps required to answer them are marked out in the form of milestones. In order to process these milestones, besides others an advanced method for analyzing the dynamic properties of hydrogen bonds is required. As such a method the Reactive Flux approach is introduced and the corresponding mathematics are derived in chapter 2.1.
The first milestone consists of the development of a molecular dynamics model which is suitable for simulations of catalyst-solvent systems of sufficient size over a period which is long enough to represent the reorganization of the hydrogen bond network formed by the solvent with the catalyst incorporated therein. Such a model is presented in chapter 3.1 and applied to a first test in chapter 3.2. As a second milestone, an implementation of the Reactive Flux approach was proposed. The successful completion of this task is described in chapter 3.3 and the robustness of the method is demonstrated in the following chapter 3.4. The processing of the third milestone requires simulations of various potential catalysts in different solvents with the aid of the model developed in milestone 1 and a subsequent analysis of the structure of the corresponding hydrogen bonds, as well as their dynamic behavior using the method from milestone 2. This central study is described in chapter 3.5. Finally, milestone 4 requires an investigation of the activation step of the catalytic cycle by means of quantum chemical calculations in order to achieve a complete picture. In this first reaction step a precursor cation is first deprotonated and the formed carbene afterwards performs a nucleophilic attack on the substrate to form the so-called Breslow-Intermediate. In the investigations presented in chapter 3.6, a new, energetically much more favorable transition state is presented, which enables these two reactions in a single concerted step. Finally, in chapter 3.8 some observations that initially appear to be contradictory are discussed and brought into line with the results shown above.},

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