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Two imidazolylidene (Im) complexes of the general formula trans -[PdX2(Im)(pyridine)] (X = Cl (2), Br (3)), in which the N -heterocyclic carbene ligand has one of its nitrogen atoms substituted by a bulky 9-propyl-9-fluorenyl group (Pr F), have been prepared and fully characterised by spectroscopic methods and single-crystal X-ray structure analyses. In the solid state, the Im ring plane and the coordination plane of each complex are nearly orthogonal, thereby minimising the steric interactions between the N-substituents and the halide atoms. In both structures two methylenic C–H bonds sit near the d z 2 axis point to the palladium atom, resulting in CH⋯Pd separations of 2.58/2.95 Å in 2 and 2.74/2.74 Å in 3. NMR measurements and DFT calculations indicate that these methylene groups are involved in anagostic CH⋯M interactions but not in significant H⋯X bonding. The stepwise synthesis of two palladium(II) complexes containing an N -heterocyclic carbene ligand substituted by the bulky 9-propyl-9-fluorenyl group is described. In both complexes, two methylenic H atoms of the propyl group interact with the metal atom in an anagostic manner. [ABSTRACT FROM AUTHOR]

A series of new Pd–PEPPSI complexes containing imidazolylidene ligands with a mixed 9-alkyl-9-fluorenyl/aryl N,N′-substitution pattern have been synthesised. Single crystal X-ray diffraction studies were carried out for four complexes, which revealed that the N-heterocyclic carbene ligands display a semi-open, unsymmetrical space occupancy about the metal. Despite their particular unsymmetrical shape, the new complexes were found to perform as well in Suzuki–Miyaura cross coupling (dioxane, 80 °C) as previously reported, highly active analogues bearing two sterically protecting 9-alkylfluorenyl substituents. They were further found to be considerably more active than the standard Pd–PEPPSI complexes [PdCl2IMes(pyridine)] and [PdCl2IPr(pyridine)]. Surprisingly, unlike the latter, the unsymmetrical complexes of this study were practically inactive in isopropanol at 80 °C. Under these conditions the complexes appear to decompose with formation of non-stabilised nanoparticles. [ABSTRACT FROM AUTHOR]

Bimetallic platinum-ruthenium nanoparticles stabilised by pyridine- and monophosphine-based ligands were prepared either in supercritical CO2 or in THF. TEM analyses evidenced a tendency of the nanoparticles prepared in supercritical CO2 to agglomerate. Both types of bimetallic nanoparticles were further confined into functionalised multiwalled carbon nanotubes. Upon confinement, PtRu nanoparticles stabilised by phosphine ligands appeared more agglomerated than those stabilised by the pyridine ligand. These materials were applied to cinnamaldehyde hydrogenation. Confined PtRu nanoparticles showed higher catalytic activity and selectivity than unsupported nanoparticles. [ABSTRACT FROM AUTHOR]

Hydrogenation of cinnamaldehyde in water in the presence of cyclodextrin and supported metallic catalyst has been investigated. The nature of the metal plays the main role in the selectivity of the reaction. The formation of allylic alcohol was achieved in the presence of Pt/C and was slightly improved after addition of cyclodextrin substituted with triazole moiety. However, the contribution of cyclodextrin is modest due to the partial solubility of cinnamaldehyde in water. [ABSTRACT FROM AUTHOR]

Catalysts based on molybdenum carbide or nitride nanoparticles (2-5 nm) supported on titania were prepared by wet impregnation followed by a thermal treatment under alkane (methane or ethane)/hydrogen or nitrogen/hydrogen mixture, respectively. The samples were characterized by elemental analysis, volumetric adsorption of nitrogen, X-ray diffraction, and aberration-corrected transmission electron microscopy. They were evaluated for the hydrogenation of CO 2 in the 2-3 MPa and 200-300°C ranges using a gas-phase flow fixed bed reactor. CO, methane, methanol, and ethane (in fraction-decreasing order) were formed on carbides, whereas CO, methanol, and methane were formed on nitrides. The carbide and nitride phase stoichiometries were tuned by varying the preparation conditions, leading to C/Mo and N/Mo atomic ratios of 0.2-1.8 and 0.5-0.7, respectively. The carbide activity increased for lower carburizing alkane concentration and temperature, i.e., lower C/Mo ratio. Enhanced carbide performances were obtained with pure anatase titania support as compared to P25 (anatase/rutile) titania or zirconia, with a methanol selectivity up to 11% at 250°C. The nitride catalysts appeared less active but reached a methanol selectivity of 16% at 250°C., (Copyright © 2020 Abou Hamdan, Nassereddine, Checa, Jahjah, Pinel, Piccolo and Perret.)

A series of new Pd-PEPPSI complexes containing imidazolylidene ligands with a mixed 9-alkyl-9-fluorenyl/aryl N,N'-substitution pattern have been synthesised. Single crystal X-ray diffraction studies were carried out for four complexes, which revealed that the N-heterocyclic carbene ligands display a semi-open, unsymmetrical space occupancy about the metal. Despite their particular unsymmetrical shape, the new complexes were found to perform as well in Suzuki-Miyaura cross coupling (dioxane, 80 °C) as previously reported, highly active analogues bearing two sterically protecting 9-alkylfluorenyl substituents. They were further found to be considerably more active than the standard Pd-PEPPSI complexes [PdCl 2 IMes(pyridine)] and [PdCl 2 IPr(pyridine)]. Surprisingly, unlike the latter, the unsymmetrical complexes of this study were practically inactive in isopropanol at 80 °C. Under these conditions the complexes appear to decompose with formation of non-stabilised nanoparticles.