Organocatalysis
Dr. Thomas Werner
Novel organocatalysts and cooperative catalytic procedures for the use of CO2 as synthetic building block
The global climate change is closely connected to the emission of anthropogenic greenhouse gases. The by far largest part of this emission is accounted to carbon dioxide (CO2). Beside the reduction of CO2 its use as synthetic building block is the central point of the overall CO2 management strategy. The atom economic and efficient utilization of CO2 as synthetic building block is closely connected to the effective activation of this very stable molecule.
The aim of our work is the development of novel metal free catalysts, so called organocatalysts, for the synthesis of industrially relevant products with CO2 as C1-building block. The utilization of inter- and intra molecular cooperative effects as well as the combination of those catalysts with metal or enzyme catalyzed procedures in (sequential) one pot reactions shall lead to innovative and sustainable catalytic systems with high selectivity and energy efficiency, respectively. Those alternative methods with inclusion of up- and downstream steps shall afford a change and extension of the raw material base under utilization of CO2. Objects of our studies are transformations and products of high industrial interest and large CO2-fixation potential (synthesis of cyclic carbonates (A), polycarbonates (B), β‑keto esters and β‑hydroxy acids (C), Figure 1).
Figure 1. Utilization of CO2 via direct fixation
This project is funded by the Federal Ministry of Education and Research (BMBF) within the funding initiative "Technologies for Sustainability and Climate Protection – Chemical Processes and Use of CO2"
Novel organocatalytic procedures based on phosphorous containing catalysts
Homogenous metal catalysis plays a major role in research and industry. Even though organocataysis is long known it was not until the end of the last century that this field of research received adequate attention. In particular asymmetric organocatalysis has seen enormous progress over the past 15 years. Especially well developed is the utilization of N-based catalysts.
Phosphines are an important class of ligands in metal complexes. Due to their outstanding capacity in homogenous catalysis numerous publications concerning the synthesis of achiral and chiral phosphine based ligands have been reported. In addition many of them are commercially available. Phosphines and their derivatives are also important reagents in organic synthesis. For example, they mediate the conversion of alcohols to halides (Appel reaction), the olefination of ketones and aldehydes (Wittig reaction) and the synthesis of imines via Aza-Wittig reaction. In contrast to their tremendous importance as ligands and reagents the application of phosphines as organocatalysts is not very well established.
- Figure 2. Phosphines and Phosphonium salts – potential Lewis-basic and Lewis-acidic organocatalysts.
Our aim is to develop catalytic variants of procedures in a first step in which phopsphines are usually employed in stoichiometric amounts. In a second step asymmetric versions of those reactions will be developed based on these new procedures. Moreover we are exploring the application of chiral phosphines and phosphonium salts as Lewis-basic and Lewis-acidic phosphonium salts respectively (Figure 2).
