Dehydrogenation of Formic Acid Catalyzed by a Ruthenium Complex with an N,N′-Diimine Ligand

Abstract

We report a ruthenium complex containing an N,N'-diimine ligand for the selective decomposition of formic acid to H and CO in water in the absence of any organic additives. A turnover frequency of 12 000 h and a turnover number of 350 000 at 90 °C were achieved in the HCOOH/HCOONa aqueous solution. Efficient production of high-pressure H and CO (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO. Mechanistic studies by NMR and DFT calculations indicate that there may be two competitive pathways for the key hydride transfer rate-determining step in the catalytic process.

Dehydrogenation of Formic Acid Catalyzed by Water‐Soluble Ruthenium Complexes: X‐ray Crystal Structure of a Diruthenium Complex

“…It is evident that the treatment of C‐2/C‐4 with sodium formate led to the formation of the species C‐2A/C‐4A , which eventually dimerize to the stable diruthenium complex C‐2A′/C‐4A′ , plausibly the catalyst resting state (Schemeà). [10g], Analogous unsaturated species [Ru(η 6 ‐C 10 H 14 )(Imd‐H)] + (Imd = 2,2′‐bi‐2‐imidazole), generated in situ from [Ru(η 6 ‐C 10 H 14 )Cl(2,2′‐bi‐2‐imidazole)] + in the presence of sodium formate, was reported to play an important role in the formic acid dehydrogenation process . Interesting to note here, that literature also revealed that such coordinatively unsaturated species are unstable and may undergo dimerization .…”

“…The initial rates for the formic acid dehydrogenation over complex C‐4 followed Arrhenius behavior in the temperature range of 60–90 °C (Figureà). The obtained apparent activation energy of 87.9 kJ/mol is in line with the activation energies reported for formic acid dehydrogenation over the analogous system Subsequently, the dependence of the rate of formic acid dehydrogenation on the catalyst concentration was determined by varying the catalyst concentration between 0.005 mmol and 0.03 mmol, while keeping the formic acid concentration constant (2.0 m , 2.5 mL) at 90 °C. The double logarithmic plots of the initial reaction rates against the concentration of C‐4 catalyst follows a linear dependence on catalyst concentration.…”

“…A Ru‐hydride species C‐2C/C‐4C is expected to be formed, upon extrusion of CO 2 from C‐2B/C‐4B . This step is most probably the rate‐determining step in the catalytic cycle as indicated by kinetic isotope effect studies, where the deuterated formic acid (DCOOD) substrate (KIE: 2.9, Tableà, entry 3) is more influential than deuterated H 2 O (D 2 O) (KIE: 1.9, Table , entry 2) on the reaction rate, indicating that C‐H bond cleavage of formic acid is the rate‐determining step , …”

Picolinamide‐Based Iridium Catalysts for Dehydrogenation of Formic Acid in Water: Effect of Amide N Substituent on Activity and Stability

“…Discovering ways for reversibly converting H 2 into liquid chemicals has been regarded as ap ossible approachf or using H 2 as af uel. [11][12][13] These resultsp roved that FA has the potentialt obe av iable H 2 carrier that has more favorable properties than other H 2 carriers, such as methylcyclohexane. In 2008, Beller and co-workers [10] and Laurenczy and co-workers [11] independently reported efficient and selectiveR u complex catalysts for FA dehydrogenation under mild reaction conditions.…”

Catalytic Hydrogenation of Arenes in Water Over In Situ Generated Ruthenium Nanoparticles Immobilized on Carbon

“…Notably, in transfer hydrogenation catalysts, ligands that have N−H bonds play a determining role particularly to help in the activation of the H source . It is evident from previous studies that among the Ru‐based catalysts explored for HCOOH to H 2 conversion or hydrogenation using HCOOH, the most active catalysts are those that have N‐based ligands . The presence of nitrogen was advantageous in these complexes because of its crucial involvement to provide protic (−NH) hydrogen and, subsequently, in the facile release of H 2 gas by stabilising various intermediates with H bonds.…”