Catalytic Hydrogen Production by Ruthenium Complexes from the Conversion of Primary Amines to Nitriles: Potential Application as a Liquid Organic Hydrogen Carrier

Abstract

The potential application of the primary amine/nitrile pair as a liquid organic hydrogen carrier (LOHC) has been evaluated. Ruthenium complexes of formula [(p-cym)Ru(NHC)Cl ] (NHC=N-heterocyclic carbene) catalyze the acceptorless dehydrogenation of primary amines to nitriles with the formation of molecular hydrogen. Notably, the reaction proceeds without any external additive, under air, and under mild reaction conditions. The catalytic properties of a ruthenium complex supported on the surface of graphene have been explored for reutilization purposes. The ruthenium-supported catalyst is active for at least 10 runs without any apparent loss of activity. The results obtained in terms of catalytic activity, stability, and recyclability are encouraging for the potential application of the amine/nitrile pair as a LOHC. The main challenge in the dehydrogenation of benzylamines is the selectivity control, such as avoiding the formation of imine byproducts due to transamination reactions. Herein, selectivity has been achieved by using long-chain primary amines such as dodecylamine. Mechanistic studies have been performed to rationalize the key factors involved in the activity and selectivity of the catalysts in the dehydrogenation of amines. The experimental results suggest that the catalyst resting state contains a coordinated amine.

Catalytic Dehydrogenative Coupling of Hydrosilanes with Alcohols for the Production of Hydrogen On‐demand: Application of a Silane/Alcohol Pair as a Liquid Organic Hydrogen Carrier

“…Most probably, the rGO material is stabilizing the catalytic active species. We have observed a similar effect when using molecular catalysts immobilized on the surface of graphene for different catalytic reactions …”

“…The ruthenium complexes [Ru( p ‐cym)(Cl) 2 (NHC)] dissociate a Cl − anion generating the [Ru( p ‐cym)Cl(NHC)] + species, which is a highly electrophilic ruthenium cation. The equilibrium between these two species has previously been observed and depends on the solvent, the pH and the presence of nucleophiles . The 1 H NMR spectrum of the ruthenium complex [Ru( p ‐cym)(Cl) 2 (NHC)] in CDCl 3 displays one set of sharp signals, in contrast, the presence of different species was observed when the 1 H NMR spectrum was carried in CD 3 OD.…”

“…For that purpose, we evaluated the catalytic activity of a ruthenium complex immobilized on the surface of graphene by π–π interactions using a pyrenyl tag attached to the NHC ligand (see structure in Table and Figure ) . This supported catalyst has recently been developed by us and is very efficient in the dehydrogenation of alcohols and amines . The initial catalytic tests show that properties of the supported ruthenium catalyst in terms of stability and recyclability are very promising.…”

High Production of Hydrogen on Demand from Silanes Catalyzed by Iridium Complexes as a Versatile Hydrogen Storage System

“…We have observed that the pyrene tag forms strong π-interactions with graphene, which prevents desorption of the molecular complex during the catalytic experiments. 44,45 Direct evidence for π-stacking interactions due to the pyrene tag was observed using single-crystal X-ray diffraction of compound 2 (Figure 1). Suitable single crystals were obtained after halide exchange using NaBr.…”

Understanding the mechanism of the competitive adsorption in 8-methylquinoline hydrogenation over a Ru catalyst

“…[1][2][3] Both partially hydrogenated products and fully hydrogenated products are valuable chemicals as well as liquid organic hydrogen storage materials. [4][5][6][7][8] Therefore, the role of reaction parameters in the selectivity of QLs hydrogenation is widely investigated for obtaining the required product. [9][10][11][12][13] Two hydrogenated intermediates, 1,2,3,4-4H-QL and 5,6,7,8-4H-QL, were generated along with the completely hydrogenated product, 10H-QL.…”