Highly Efficient Reversible Hydrogenation of Carbon Dioxide to Formates Using a Ruthenium PNP‐Pincer Catalyst

Abstract

The front cover artwork for Issue 6/2014 is provided by the research group of Inorganic Materials Chemistry and the Institute for Complex Molecular Systems, Eindhoven University of Technology (The Netherlands). The image shows a concept of a hydrogen battery in which H2 storage and its release are achieved through reversible hydrogenation of CO2 catalysed by an Ru‐PNP pincer complex. See the Communication itself at .

From Homogeneous to Heterogenized Molecular Catalysts for H2 Production by Formic Acid Dehydrogenation: Mechanistic Aspects, Role of Additives, and Co-Catalysts

“…Immobilization of the complex on SiO2 increased the TOFs by 170% vs. the analogous homogeneous system. Importantly, in this work [23], an heterogenized catalyst was demonstrated, for the first time, to have high efficiency and robustness in a wide range of temperatures, being able to produce up to 14 lt of H2 within 6 h of continuous operation. Thus, the covalent immobilization strategy of the metal-complex or/and the co-catalyst can provide definitive advantages paving the road towards the continuous-operation standards where durability and recyclability will be of primary importance.…”

“…The best results were obtained for the Pd-S-SiO 2 (TOF = 700 at 85 • C). More recently, heterogenization of an iron-phosphine complex Fe/(tris[(2-diphenylphosphino)ethyl]phosphine) was presented by our group [23]; see Figure 15. Immobilization of the complex on SiO 2 increased the TOFs by 170% vs. the analogous homogeneous system.…”

“…(iv) The poisonous effect of H 2 O and Inorganic Anions: In aprotic solvents, the presence of trace amounts of water can be a limiting factor. For example, we have found [23] that the performance of [Fe/PPh 3 /propylene carbonate] system can be severely inhibited when H 2 O was present over a certain limiting amount i.e., 6% [23]. Notice that commercial formic acid typically contains at least 2-3% of water to sustain its liquid phase.…”

“…Such grafting technology has been exploited for many years by our group for immobilization of oxidation catalysts i.e., Mn complexes [68] and Fe complexes on SiO 2 -based [69] or carbonaceous-based supports [70]. However, the grafting technology for H 2 production from FA has been exploited only recently by us [23] (see Figure 15) and others. In 2009, Gan et al [71] had immobilized a homogeneous Ru[meta-trisulfonatedtriphenylphospine] complex on various matrices i.e., polymers and zeolites.…”

“…The catalytic H 2 generation from homogeneous metal complexes has been reviewed by Wills et al [10] with focus on the type of substrate, by Singh et al [21] with focus on FA as energy carrier, and recently by Sordakis et al [19], Onishi et al [22], and Filonenko et al [23], comprehensively reviewing the type of metal complex, substrate used, and the reaction conditions and the reversibility of the procedure. Recently, Inglesias and Oro reviewed the homogenous FA dehydrogenation [24].…”