Homogeneously catalysed conversion of aqueous formaldehyde to H2 and carbonate

Abstract

Small organic molecules provide a promising solution for the requirement to store large amounts of hydrogen in a future hydrogen-based energy system. Herein, we report that diolefin–ruthenium complexes containing the chemically and redox non-innocent ligand trop2dad catalyse the production of H2 from formaldehyde and water in the presence of a base. The process involves the catalytic conversion to carbonate salt using aqueous solutions and is the fastest reported for acceptorless formalin dehydrogenation to date. A mechanism supported by density functional theory calculations postulates protonation of a ruthenium hydride to form a low-valent active species, the reversible uptake of dihydrogen by the ligand and active participation of both the ligand and the metal in substrate activation and dihydrogen bond formation.

3-Methylindole-Based Tripodal Tetraphosphine Ruthenium Complexes in N2 Coordination and Reduction and Formic Acid Dehydrogenation

“…Ex-situ 31 P NMR spectroscopy of the RuCl 2 L1 H catalytic system showed the absence of the signals of the ruthenium complex pointing to decomposition of the pre-catalyst under the applied conditions. Next, we investigated the potential of these Ru-species in the catalytic dehydrogenation of formic acid (Figure 13), given our interest in the reversible storage of H 2 into liquid fuels [27][28][29][30][31][32][33]. For Ru-catalysts, formic acid dehydrogenation is accelerated when more electron-rich ligands are employed, as was shown by Himeda et al, who used a series of bipyridine ligands with various substituents at the para position (-OH, -OMe, -Me, -CO 2 H, and -H) [34].…”

Chemoenzymatic Hydrogen Production from Methanol through the Interplay of Metal Complexes and Biocatalysts

“…Another methanol-active catalyst, the dibenzotropyl-based ruthenium complexb yG r ützmacher,w as evaluated against aqueous formalin as the hydrogen donora nd provede ffective as mediator in the hydrogen evolution from this C 1 donor. [16,21] Similart ot he iridium-based systems, also the Grützmacher's catalystr equires rather basic reaction conditions, yet reaches good TONs of close to 1800 at moderate heatingt o6 08C. Both in Fujita and Yamaguchi's and Grützmacher's approaches, the metal center is coordinated by ac hemically and electronically non-innocent cooperative ligand.T his non-innocent coordination environment helps the metal centers to readily change their oxidations tate.…”

“…The previously introduced methanol‐active iridium bipyridonate naturally also exhibited activity in the H 2 ‐liberating decomposition of formalin reaching moderate turnover numbers (TONs) of up to 178 upon heating under slightly basic conditions. Another methanol‐active catalyst, the dibenzotropyl‐based ruthenium complex by Grützmacher, was evaluated against aqueous formalin as the hydrogen donor and proved effective as mediator in the hydrogen evolution from this C 1 donor . Similar to the iridium‐based systems, also the Grützmacher's catalyst requires rather basic reaction conditions, yet reaches good TONs of close to 1800 at moderate heating to 60 °C.…”

An In-Depth Mechanistic Study of Ru Catalysed Aqueous Methanol Dehydrogenation and Prospects for Future Catalyst Design

“…undergoes a solvent mediated rearrangement to form complex 2' containing a Ru II center. [19][20][21] We used static DFT models with a small number of solvent molecules to demonstrate that solvent molecules participate directly in the dehydrogenation of methanol to formaldehyde catalysed by complex 2', involving several hydrogen bond interactions with the anionic oxygen and hydride moieties (in CH 3 O À ). Interestingly, explicit solvent effects did not play an important role in the computed mechanism of aqueous methanol dehydrogenation by the [Ru (trop 2 dad)] complex 1.…”