Catalytic Activation of CO2 towards Carboxylic Acids and Esters Mediated by Organometallic Precursors – CO22CHEM

A smooth and straightforward scenario for catalytic synthesis of carboxylate platforms has been envisaged and investigated, based on an efficient catalytic coupling reaction of CO2 with commodity alkenes (ethylene), followed by reduction with: A) molecular hydrosilanes (R3SiH) as model reductants, which would afford valuable and technologically relevant carboxylic acid silyl esters, and B) economical dihydrogen, which could provide direct, fully atom-economic access to the corresponding carboxylic acids. Upon using High-Throughput Experimentation (first at Argonne National Laboratory, USA, then at the Realcat platform of UCCS, Lille), among >150 combinations of different transition-metal precursors with various ligands have been used in tests. Several promising hits have been pinpointed and then, successfully implemented on a larger scale. Through stoichiometric studies, several key catalytic intermediates were isolated, identified and assessed computationally (collaboration with LPCNO, INSA Toulouse) in order to build up the putative mechanism of the global process. Further optimization of these catalytic systems allowed significant improving selectivities toward the formation of propionate or acrylate silyl esters, which, after hydrolysis, can afford the corresponding carboxylic acids.

A dozen of combinations of metal precursors and ligands have been identified, which are competent of reductive coupling of CO2 with ethylene towards carboxylate platforms. Several optimized catalytic systems have been elaborated for selective production of propionic and acrylic silyl esters. Unusual reactive intermediates such as metal-acrylate species has been isolated and structurally authenticated and used for understanding the mechanism of coupling. The obtained results are used for setting up new ANR PRC project focused specifically on the utilization of hydrogen or other hydrogen surrogates (water, methane) as reductants for this process. The established Partnership between Rennes, Lille and Toulouse will stay operational within the frames of the new project.

Efficient activation of small molecules such as CO2 or methane still remains a true scientific and technological burden, as no truly effective catalytic system does exist. In the continuation of the CO22CHEM project, we aim at developing new homogeneous catalytic processes using H2 and its surrogates (H2O, alcohols, CH4) to enable the straightforward, direct carboxylation of alkenes into the corresponding acids or esters, in an atom- and cost-effective, industrially attractive but also more challenging way. In a longer-term perspective, the fundamental data harvested in this challenging project will be of high interest for extrapolation to other related chemical processes associated with metal-mediated protocols of chemical conversion and/or sequestration/recycling of both CO2 and methane.

1) Kunihiro, K.; Heyte, S.; Paul, S.; Roisnel, T.; Carpentier, J.-F.; Kirillov, E. Ruthenium-Catalyzed Coupling Reactions of CO2 with C2H4 and Hydrosilanes towards Silyl Esters. Chem. Eur. J. 2021, 27, 3997-4003. /Hot paper/
2) Kunihiro, K.; Thayalan, R.; Maron, L. Heyte, S.; Paul, S.; Roisnel, T.; Carpentier, J.-F.; Kirillov, E. Studies on the Mechanism of Ruthenium-Catalyzed Coupling Reactions of CO2 with C2H4. Manuscript in preparation.
3) Huang, W.; Roisnel, T. Dorcet, V.; Orione, C.; Kirillov, E. Reduction of CO2 by Hydrosilanes in the Presence of Formamidinates of Groups 13 and 12 Elements. Organometallics 2020, 39, 698-710.
4) Qu, L.; Roisnel, T.; Cordier, M.; Yuan, D.; Yao, Y.; Zhao, B.; Kirillov, E. Rare-Earth Metal Complexes Supported by Polydentate Phenoxy-Type Ligand Platforms: C?H Activation Reactivity and CO2/Epoxide Copolymerization Catalysis. Inorg. Chem. 2020, 69, 16976-16987.
5) Kunihiro, K.; Carpentier, J.-F.; Kirillov, E. Catalytic Activation of CO2 towards Carboxylic Acids and Esters Mediated by Organometallic Precursors. HTCD 2021 - 1st International Symposium on High-throughput Catalyst Design, Centrale Lille, Villeneuve d’Acsq, 2021, oral presentation.
6) Kunihiro, K.; Carpentier, J.-F.; Kirillov, E. Catalytic Activation of CO2: Ruthenium-Catalyzed Coupling Reactions of CO2 with C2H4 and Hydrosilannes towards Silyl Esters. SECO 57th – Semaine d’Etudes de Chimie Organique, Léon, France, 2020, oral presentation.
7) Kunihiro, K.; Heyte, S.; Paul, S.; Carpentier, J.-F.; Kirillov, E. Catalytic Activation of CO2 towards Carboxylic Acids and Esters Mediated by Organometallic Precursors. GECOM, Erquy, France, 2019, poster presentation.

This project is focused on the discovery and elaboration of homogeneous catalytic processes for the efficient transformation of CO2 and alkenes into industrially relevant commodity and fine chemicals. The principal goals are: (i) understanding of the key elementary steps of selective coupling of CO2 with alkenes towards carboxylic acids and esters, using H2 as a most preferred co-reductant or hydrosilanes as model co-reductants; and (ii) development of effective catalytic systems, based on transition and non-transition metals complexes, reconciling these elementary steps for selective production of carboxylic acids using alkenes, CO2 and H2 as reductant. The methodology will rely on High-Throughput Screening (HTS) and experimental / computational techniques for initial discovery and fundamental studies, along with catalytic engineering developments. The CO22CHEM project has been selected twice for stage 2 in the framework of the ANR generic call programs in 2014/2015 and 2015/2016, after which it was each time recommended by panels of 5 and 9 referees, respectively, for funding within the budget available for the project call.