Tailored Ruthenium–N‐Heterocyclic Carbene Hybrid Catalytic Materials for the Hydrogenation of Carbon Dioxide in the Presence of Amine

Abstract

Dedicated to Christian Bruneau on the occasion of his 60th birthdayThe use of CO 2 as a C 1 building block is one possible solution for CO 2 remediation; a point of particular interest considering that the atmospheric concentration of CO 2 is reaching critical values.[1] For instance, the hydrogenation of CO 2 back into chemicals and fuels [2] can be a potential approach. For this particular chemical process, homogeneous catalysts based on noble metals were first discovered in the 1970s, [3,4] but one critical advance was the use of ruthenium trimethylphosphine complexes and supercritical CO 2 as a "solvent". Depending on the additives present during the reaction, formic acid, [5] formamides, [6] or formate esters [7] are produced. The introduction of bidentate chelating ligands led to further improvements for the hydrogenation of CO 2 to formamides.[8] Ruthenium and iridium complexes with phosphorus-nitrogen-phosphorus pincer (PNP) [9] or bis-N-heterocyclic carbene (NHC) ligands [10] were also very effective for the hydrogenation of CO 2 to formic acid. Although homogeneous catalytic systems of this type are numerous, there are only a few examples of heterogeneous catalysts. Two main strategies have been developed to date: the coordination of different metal precursors to aminopropylfunctionalised materials [10] and the incorporation of trialkoxysilane-containing ruthenium phosphine complexes during a sol-gel process.[11] Whereas the former approach leads to significant metal leaching, the latter suffers from lower catalytic performances than their homogeneous analogues, owing possibly to reactant diffusion difficulties.[12] Considering the advantages of heterogeneous catalysts, there is still the need to develop supported catalysts by using a much more controlled approach, allowing the control of the distribution of active sites, and avoiding any problem of accessibility of the reactants to these sites. Based on the direct synthesis of hybrid materials synthesis, we recently developed imidazolium-functionalised materials and the corresponding iridium [14] and ruthenium [13,14] NHC catalytic materials for H/D exchange and alkene metathesis reactions. Their very high catalytic performances, typically equalling or exceeding those of their homogeneous counterparts, are owed to the control of the synthesis of the catalytic material at the molecular level. We therefore developed catalytic materials based on RuÀNHC species, which display promising catalytic performances, for the hydrogenation of CO 2 to amides.Firstly, the synthesis of the molecular complex [RuCl 2 (pcymene)(1-mesityl-3-{(3-triisopropoxysilyl)propyl}imidazol-2-ylidene)], Ru Cym , was performed (Scheme 1). It involved the formation of a free NHC (step 1) and the subsequent coordination of [{RuCl 2 (p-cymene)} 2 ] (step 2). The optimal experimental conditions were the deprotonation of 1-mesityl-3-[3-(triisopropoxysilyl)propyl]imidazolium iodide with KHDMS in THF followed by subsequent treatment with [{RuCl 2 (p-cymene)} 2 ]. The expected Ru Cym complex ...

A DFT Study of CO2 Hydrogenation on Faujasite‐Supported Ir4 Clusters: on the Role of Water for Selectivity Control

“…Metal oxide supported Au nanoparticles have also been studied for the liquid‐phase CO 2 hydrogenation ,. In addition, grafting of Ir and Ru complexes onto mesoporous supports has been considered as a promising strategy towards heterogeneous CO 2 hydrogenation catalysts ,,…”

Solid-state NMR: An EYE Opener in Surface Chemistry

“…[24,25] This approach is quite general, and we have reported materials containing imidazolium compounds, which are precursors to N-heterocyclic carbene metal complexes. These NHC-M containing materials have been shown to be effective catalysts for Ir-catalyzed H/D exchange, [26] and Ru-catalyzed olefin metathesis [27] and CO 2 reduction [28] with performance close the analogous homogeneous catalysts. However, the solid-state NMR characterization of the imbedded ligands and the resulting organometallic complexesh ave remained a challenge, since by design these materials have very loworganic concentrations (ca.…”

“…Indeed, many solid-state NMR studies of hybrid materials require tedious isotopic enrichment to obtain reasonable 1D 13 C NMR spectra. [26][27][28] Similarly, 29 Si NMR can require many days to obtain a spectrum under inert conditions.…”

Surface and Interfacial Chemistry

“…3). [20][21][22] This promising approach is clearly applicable to a broad range of ligands so that most -if not all -homogeneous catalysts can be made heterogeneous and so that the development of functional materials for various applications is possible.…”