1. What is the new discovery that you made?
In our group we look for sustainable and efficient methods to use CO2 for chemical synthesis. In this last publication we developed a sustainable, salt-free strategy for CO2-insertion into non-activated C-H bonds. We found a copper(I) catalyst that enables the carboxylation step of terminal alkynes with CO2 in the presence of a very mild base, for example an amine. By using a mild base, the hydrogenation step of the resulting carboxylate becomes thermodynamically feasible. In fact, the obtained ammonium salt is only marginally stabilized compared to more stable inorganic carboxylates. The salt can thus be hydrogenated to the primary alcohol with a rhodium/molybdenum catalyst. In this step, only water is released and the regenerated amine can be recovered, making the overall process waste-free.
2. What is its significance?
In general, the chemical use of CO2 in industrial processes could help to reduce anthropogenic CO2 emissions. With our development of a salt-free hydroxymethylation process we have demonstrated that it is possible to chemically use CO2 in a highly sustainable way without salt waste. Our methodology surpasses current strategies for C-C bond-forming reactions with CO2 as a C1 building block. Those carboxylation processes are based on prefunctionalized compounds, such as organometallic reagents or carbon electrophiles that react with stoichiometric metal-based reducing agents - approaches inevitably lead to salt waste, therefore limiting sustainability. Moreover, we are currently investigating the reaction of carbon dioxide with acetylene to synthesize the platform chemical butanediol. This would be an economically and ecologically advantageous entry to C4 chemicals. However, the process must be vastly improved to allow industrial application.
3. Is this related to Solvation Science? If yes, how?
In the reaction, mixtures of CO2 and conventional solvents are used, and the acidity of the solvent is strongly dependent on the CO2 partial pressure. Numerous experiments were required to empirically optimize reaction conditions. In an ongoing project, we systematically investigate the influence of CO2 pressure on the solvent properties and try to find alternative descriptors to the classical pH value to assess the acidity of the system. In extension to this work we are currently developing alternative strategies based on esterification.
Original Publication:
T. Wendling, E. Risto, T. Krause, L. J. Gooßen, Salt-Free Strategy for the Insertion of CO2 into C-H Bonds: Catalytic Hydroxymethylation of Alkynes, Chem. Eur. J. 2018, 24