Tuning the Reactivity of a Heterogeneous Catalyst using N‐Heterocyclic Carbene Ligands for C−H Activation Reactions

Abstract

We report the dramatic impact of the addition of N‐heterocyclic carbenes (NHCs) on the reactivity and selectivity of heterogeneous Ru catalysts in the context of C−H activation reactions. Using a simple and robust method, we prepared a series of new air‐stable catalysts starting from commercially available Ru on carbon (Ru/C) and differently substituted NHCs. Associated with C−H deuteration processes, depending on Ru/C‐NHC ratios, the chemical outcome can be controlled to a large extent. Indeed, tuning the reactivity of the Ru catalyst with NHC enabled: 1) increased chemoselectivity and the regioselectivity for the deuteration of alcohols in organic media; 2) the synthesis of fragile pharmaceutically relevant deuterated heterocycles (azine, purine) that are otherwise completely reduced using unmodified commercial catalysts; 3) the discovery of a novel reactivity for such heterogeneous Ru catalysts, namely the selective C‐1 deuteration of aldehydes.

Tailoring graphene-supported Ru nanoparticles by functionalization with pyrene-tagged N-heterocyclic carbenes

“…28 Pieters et al also controlled the selectivity of Ru NPs supported on carbon in the isotopic H/D exchange by modifying the surface metal with NHCs. 29 However, the surface modification of supported MNPs with NHCs not only may improve their selectivity, but also is able to increase their stability. Recently, it has been shown that NHCs bearing a pyrene group can enhance the stability of graphenesupported MNPs via non-covalent π-interactions between the pyrene tag and the graphene layer.…”

Boosting the catalytic performance of graphene-supported Pt nanoparticlesviadecorating with –SnBun: an efficient approach for aqueous hydrogenation of biomass-derived compounds

“…On the other hand, under the same catalytic conditions (0.1 mol% Pt, H 2 O, 5 bar H 2 , 25 °C, 5 h) the monometallic catalyst Pt@rGO presented a conversion of 82.9% and a slightly lower selectivity to the corresponding alcohol (8), due to the formation of a small amount of the HDO product, 2-methoxy-4-methylphenol (9) (see Table 1, entries 5 and 6). In the hydrogenation of levoglucosenone (10) with Pt@rGO/Sn 0.8 we observed complete conversion in 5 hours, and a selectivity of 58% towards the fully hydrogenated product, levulinyl alcohol (12) (see Table 1, entry 7). However, at the same reaction time, Pt@rGO showed a slower conversion (91.2%) and 92% selectivity to the product (11), due to its lower reactivity in the hydrogenation of CvO bonds compared to the functionalized catalyst (see Table 1, entry 8).…”

Bringing Selectivity in H/D Exchange Reactions Catalyzed by Metal Nanoparticles through Modulation of the Metal and the Ligand Shell

“… 15 More recently, water-soluble Ru NPs stabilized by sulfonated NHC ligands were also reported in the H/D exchange of l -lysine. 16 These catalytic systems allowed an efficient and selective late-stage H/D exchange in complex molecules.…”

“…Following the same methodology, the enantiospecific deuterium incorporation at the stereogenic center of amino acids was also achieved . More recently, water-soluble Ru NPs stabilized by sulfonated NHC ligands were also reported in the H/D exchange of l -lysine . These catalytic systems allowed an efficient and selective late-stage H/D exchange in complex molecules.…”