Over the last decade, the hydrogenation of arenes catalysed by soluble nanoparticles has attracted much interest from both academic and industrial research groups due to the milder conditions and the interesting selectivities achieved when compared to those obtained with classical heterogeneous catalysts. When substituted arenes are used as substrates in this reaction, the stereoselectivity is a key objective, and high levels of enantioselectivity are yet to be achieved.

Going against tradition: Uniformly distributed Pd nanoparticles on imidazolium‐ionic‐liquid‐modified Al2O3 surfaces are prepared by a top down approach by using a new sputtering chamber. The hydrogenation of 1,3‐cyclohexadiene is used to probe the surface properties of these new Pd nanoparticles.

Ionic liquid (IL)-hybrid organosilicas based on 1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic and hydrophobic anions decorated with well dispersed and similar sized (1.8-2.1 nm) Pd nanoparticles (PdNPs) are amongst the most active and selective catalysts for the partial hydrogenation of conjugated dienes to monoenes. The location of the sputter-imprinted Pd-NPs on different supports, as determined by RBS and HS-LEIS analysis, is modulated by the strength of the contact ion pair formed between the imidazolium cation and the anion, rather than the IL-hybrid organosilica pore size and surface area. In contrast, the pore diameter and surface area of the hybrid supports display a direct correlation with the anion hydrophobicity. XPS analysis showed that the Pd(0) surface component decreases with increasing ionic bond strength between the imidazolium cation and the anions (contact ion pair). The finding is corroborated by changes in the coordination number associated with the Pd-Pd scattering in EXAFS measurements. Hence, the interaction of the IL with the metal surface is found to occur via IL contact pairs (or aggregates). The observed selectivities of ≥99% to monoenes at full diene conversion indicate that the selectivity is intrinsic to the electron deficient Pd-metallic surfaces in this "restricted" ionic environment. This suggests that ILhybrid organosilica/Pd-NPs under multiphase conditions ("dynamic asymmetric mixture") operate akin to catalytically active membranes, i.e. far from the thermodynamic equilibrium. Detailed kinetic investigations show that the reaction rate is zero-order with respect to hydrogen and dependent on the fraction of catalyst surfaces covered by either the substrate and/or the product. The reaction proceeds via rapid inclusion and sorption of the diene to the IL/Pd metal surface saturated with H species. This is followed by reversible hydride migration to generate a π-allyl intermediate. The reductive elimination of this intermediate, the formal ratedetermining step (RDS), generates the alkene that is rapidly expelled from the IL phase to the organic phase.

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Dedicated to the memory of Prof. Roberto F. Souza, one of the pioneers of ionic liquid phase organometallic catalysisThe reaction of [BMI·Cl] (BMI = 1-butyl-3-methylimidazolium) or [BMMI·Cl] (BMMI = 3-butyl-1,2-dimethylimidazolium) with Ru 3 (CO) 12 generates Ru-hydride-carbonyl-carbene species in situ that are efficient catalysts for a reverse water gas shift/ hydroformylation/hydrogenation cascade reaction. The addition of H 3 PO 4 increased the catalytic activity of the first step (i.e., the hydrogenation of CO 2 to CO). Under the optimized reaction conditions [120 8C and 6.0 MPa CO 2 /H 2 (1:1) for 17 h], cyclohexene and 2,2-disubstituted alkenes were easily functionalized to alcohols through sequential hydroformylation/carbonyl reduction.Carbon dioxide sequestration and its use as a feedstock in industrial processes are major challenges in the development of alternative greener and sustainable processes. [1] Indeed, several catalytic processes are under investigation, and they include the incorporation of CO 2 through the addition to epoxides to generate organic carbonates, diols, and polycarbonates by using either organic or metal-based catalysts. [2] However, the substitution of carbon monoxide (CO) by carbon dioxide (CO 2 ) in carbonylation reactions [3][4][5][6] may allow for new applications with broader use for this important and abundant but poorly reactive substrate. Indeed, at the industrial scale, the hydroformylation [7,8] of alkenes is one of the most important applications of homogeneous catalysis, and over 9 million tons of socalled oxo products, such as aldehydes and alcohols, are produced each year. [9] Rh-modified systems are the catalysts of choice for this reaction, as they are highly active and selective for the formation of aldehydes, [7,8] as well as for cascade reactions involving hydroformylation/Witting, [10] hydroaminomethylation sequences, [11,12] and hydroformylation/cyclization reactions. [13][14][15][16] Other metals, such as Pt and Ru, have been much less studied owing to their high hydrogenation activity, which results in the formation of large amounts of alkanes as byproducts. [17][18][19][20] However, the use of Rh-Ru bimetallic systems is of interest for the production of alcohols by hydroformylation/hydrogenation se-quences. [21][22][23][24][25] The differences in selectivity could be easily understood if we look at the hydroformylation and hydrogenation mechanisms catalyzed by Rh I and Ru 0 systems, as the active catalytic species under hydroformylation conditions are the RhÀH and the RuÀ(H) 2 species. [7][8][9]26] The accepted mechanism for the formation of MÀ(H) 2 is the homolytic cleavage of the HÀH bond, as the formation of MÀH occurs either by intramolecular (ligands) or intermolecular (external base) heterolysis of the HÀH bond, which favors the formation of MÀH species. [12,27,28] For instance, cationic [RuÀH] + species species are described as the catallytically active species in the Ru-catalyzed hydrogenation of acids, cyclic carbonates, and CO 2 to alcohol. [...