Metal–ligand cooperation (MLC) allows cooperative action between active sites at both the metal and the ligand for transferring hydrogen to the substrate using hydride and proton transfer. Despite their utility in the development of green and sustainable synthetic transformations from a single source, these transfers using two different sources remain limited. Herein, we presented a bench-stable bifunctional 2,2′-bibenzimidazole (BiBzImH2)-based Ru(II)-para-cymene for selective and efficient hydrogenation of unsaturated carbonyl/nitro to saturated carbonyl/nitro using hydride and proton transfer from two different sources (silane for hydride and methanol for proton) via substrate-mediated interconvertible coordination modes (imino N → Ru and amido N–Ru) of the active catalyst. Remarkably, the generation of Ru–H and the presence of N–H of the coordinated BiBzImH2 are important for the generation of interconvertible coordination modes, which in turn is not operative without the N–H. The initial rate kinetics under standard reaction conditions showed a broken positive order in the substrate, first order in the catalyst, and first order in the hydrogen donor (TES). Mechanistic studies, evaluated from spectroscopic, kinetic, Hammett study, kinetic isotope effects (KIEs), and a few other controlled experiments, further reveal that both solvent-mediated proton transfer via the interconvertible coordination mode and hydride transfer between the substrate-coordinated intermediate and Ru–H might be involved in two separate rate-determining steps. The catalyst demonstrated good efficiency, selectivity (>98%), and functional group tolerance and displayed a broad scope with unsaturated ketones and β nitrostyrenes, affording their saturated keto and nitro products with excellent selectivity and emphasizing its potential synthetic utility.
Catalysts consisting of metal−metal hydroxide/oxide interfaces are highly in demand for advanced catalytic applications as their multicomponent active sites will enable different reactions to occur in close proximity through synergistic cooperation when a single component fails to promote it. To address this, herein we disclosed a simple, scalable, and affordable method for synthesizing catalysts consisting of nanoscale nickel−nickel oxide−zinc oxide (Ni−NiO−ZnO) heterojunctions by a combination of complexation and pyrolytic reduction. The modulation of active sites of catalysts was achieved by varying the reaction conditions of pyrolysis, controlling the growth, and inhibiting the interlayer interaction and Ostwald ripening through the efficient use of coordinated acetate and amide moieties of Zn−Ni materials (ZN−O), produced by the reaction between hydrazine hydrate and Zn−Ni−acetate complexes. We found that the coordinated organic moieties are crucial for forming heterojunctions and their superior catalytic activity. We analyzed two antagonistic reactions to evaluate the performance of the catalysts and found that while the heterostructure of Ni−NiO−ZnO and their cooperative synergy were crucial for managing the effectiveness and selectivity of the catalyst for dehydrogenation of aryl alkanes/alkenes, they failed to enhance the hydrogenation of nitro arenes. The hydrogenation reaction was influenced by the shape, surface properties, and interaction of the hydroxide and oxide of both zinc and nickel, particularly accessible Ni(0). The catalysts showed functional group tolerance, multiple reusabilities, broad substrate applicability, and good activity for both reactions.
A versatile, selective, solvent (methanol vs ethanol)- and base (potassium vs lithium carbonate)-assisted switchable synthesis of saturated ketone and α-methyl saturated ketone from α,β-unsaturated ketone is developed. Mechanistic aspects, evaluated from spectroscopic studies, in situ monitoring of the reaction progress, control studies, and labeling studies, further indicate the involvement of a tandem dehydrogenation–condensation–hydrogenation sequence in the reaction, in which the interconvertible coordination mode (imino N → Ru and amido N–Ru) of coordinated imidazole with Ru(II)–para-cymene is crucial, without which the efficiency and selectivity of the catalyst are completely lost. The catalyst demonstrates good efficiency, selectivity, and functional group tolerance and displays a broad scope (69 examples) for monomethylation and hydrogenation of unsaturated chalcones, double methylation of ketones, and N-methylation of amines.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.