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

Abstract

Dehydrogenation of formic acid over various Ru‐arene complexes containing N‐donor chelating ligands was investigated in H2O and isolated and characterized several important catalytic intermediate species to elucidate the reaction pathway for formic acid dehydrogenation. Among the studied complexes, Ru‐arene complexes, namely [(η6‐C6H6)Ru(κ2‐NpyNH2‐AmQ)Cl]+ (C‐2), [(η6‐C10H14)Ru(κ2‐NpyNH2‐AmQ)Cl]+ (C‐3) and [(η6‐C6H6)Ru(κ2‐NpyNHMe‐MAmQ)Cl]+ (C‐4) [AmQ = 8‐aminoquinoline and MAmQ = 8‐(N‐methylamino)quinoline] were proved to be the efficient catalysts for formic acid dehydrogenation at 90 °C, even in the absence of base. With an initial TOF of 940 h–1, complex C‐4 displayed the highest catalytic activity for formic acid dehydrogenation in H2O and it can be recycled up to 5 times with a TON of 2248. Effect of temperature, pH, formic acid and catalyst concentration on the reaction kinetics were also investigated in detail. Extensive mechanistic investigations using mass spectrometry and NMR evidenced the formation of a coordinatively unsaturated species [(η6‐C6H6)Ru(κ2‐NpyNH‐AmQ)]+ (C‐2A)/[(η6‐C6H6)Ru(κ2‐NpyNMe‐MAmQ)]+ (C‐4A) as the active component during the catalytic dehydrogenation of formic acid. We further characterized the dimer‐form of C‐2A, possibly the catalyst resting state, by single‐crystal X‐ray crystallography.

Recent Advances in Homogeneous/Heterogeneous Catalytic Hydrogenation and Dehydrogenation for Potential Liquid Organic Hydrogen Carrier (LOHC) Systems

“…In 2019, Singh et al reported the catalytic dehydrogenation of formic acid using a water-soluble Ru-arene complex containing N-H moiety [32]. The use of water-soluble catalysts in aqueous solutions allows for environmentally friendly catalysis by avoiding toxic organic solvents.…”

“…The pathway of formic acid/formaldehyde dehydrogenation using various catalysts. Data obtained from [27][28][29][30][31][32][33][34][35][36]44,45]. Recently, Singh and colleagues reported the ruthenium-catalyzed dehydrogenation of aqueous formaldehyde and paraformaldehyde to produce hydrogen [45].…”

“…The pathway of formic acid/formaldehyde dehydrogenation using various catalysts. Data obtained from [27][28][29][30][31][32][33][34][35][36]44,45].…”

Selective Hydrogen Production from Glycerol over Ruthenium Catalyst

“…Further, to utilize biomass‐derived substrates for the production of hydrogen gas, which is identified as a clean fuel of the future, will not only have a crucial role in diminishing CO 2 emission, but also provide a sustainable route to utilize biomass waste [3–5] . Hydrogen is being produced at an industrial scale by electrolysis of water, [6] methane reforming, [7] enzymatic pathway, [8,9] gasification of biomass waste, [10] steam reforming, [11] aqueous phase reforming [12] and catalytic dehydrogenation of liquid hydrogen carriers [13–19] . However, globally efforts are also being made to explore alternate and effective ways to produce hydrogen gas, and therefore the selection of the sustainable resources and mild reaction conditions for hydrogen production are few of the crucial factors which need specific attention.…”

A Process for Hydrogen Production from the Catalytic Decomposition of Formic Acid over Iridium—Palladium Nanoparticles

“…Sinjay et al synthesized ruthenium complexes [(η 6 -arene)Ru(κ 2 -L)] n+ (n = 0.1) ([Ru]-1 − [Ru]-9) ligated with pyridine-based ligands and used them to produce hydrogen from formic acid in water. They obtained a very effective and stable catalyst in water, which could be used up to seven times, and they achieved a total turnover frequency (TOF) of 6050 h −1 [41,42].…”