ABSTRACT
Treatment of aromatic N-substituted N-heterocyclic carbenes (NHCs) with trimethyl-gallium and -indium yielded the new Lewis acid-base adducts, IMes·GaMe3 (1), SIMes·GaMe3 (2), IPr·GaMe3 (3), SIPr·GaMe3 (4), IMes·InMe3 (5), SIMes·InMe3 (6), IPr·InMe3 (7), and SIPr·InMe3 (8), with all complexes being identified by X-ray diffraction, IR, and multinuclear NMR analyses. Complex stability was found to be largely dependent on the nature of the constituent NHC ligands. Percent buried volume (%VBur) and topographic steric map analyses were employed to quantify and elucidate the observed trends. Additionally, a detailed bond snapping energy (BSE) decomposition analysis focusing on both steric and orbital interactions of the M-NHC bond (M = Al, Ga and In) has been performed.
ABSTRACT
Highly active and selective aerobic oxidation of KA-oil to cyclohexanone (precursor for adipic acid and É-caprolactam) has been achieved in high yields using continuous-flow chemistry by utilizing uncapped noble-metal (Au, Pt & Pd) nanoparticle catalysts. These are prepared using a one-step in situ methodology, within three-dimensional porous molecular architectures, to afford robust heterogeneous catalysts. Detailed spectroscopic characterization of the nature of the active sites at the molecular level, coupled with aberration-corrected scanning transmission electron microscopy, reveals that the synthetic methodology and associated activation procedures play a vital role in regulating the morphology, shape and size of the metal nanoparticles. These active centers have a profound influence on the activation of molecular oxygen for selective catalytic oxidations.
Subject(s)
Metal Nanoparticles/chemistry , Oils/chemistry , Platinum/chemistry , Aerobiosis , Cyclohexanes/chemistry , Oxidation-ReductionABSTRACT
Treatment of a series of aromatic NHCs (IMes, SIMes, IPr and SIPr) with trimethylaluminium produced their corresponding Lewis acid-base adducts: IMes·AlMe3 (1), SIMes·AlMe3 (2), IPr·AlMe3 (3), and SIPr·AlMe3 (4). These complexes expand the few known examples of saturated NHC stabilised Group 13 complexes. Furthermore, compounds 1-4 show differential stability depending on the nature of the NHC ligand. Analyses of topographic steric maps and NHC %V(Bur) were used to explain these differences. All the compounds have been fully characterised by multinuclear NMR spectroscopy, IR and single crystal X-ray analysis together with computational studies.
ABSTRACT
By using platinum nanoparticle catalysts that are generated in situ by extrusion from a porous copper chlorophosphate framework, the role of oxidants in the selective oxidation of benzyl alcohol to benzaldehyde was evaluated, with a view to establishing structure-property relationships. With a detailed study of the kinetic properties of the oxidation reaction, it has been determined that the aerobic oxidation pathways progress with lower levels of product selectivity and higher activation energies (72.4â kJ mol-1 ) than the peroxide-based ones (23.6â kJ mol-1 ); affording valuable insights in the design of solid catalysts for selective oxidation reactions. Furthermore, through the use of X-ray absorption spectroscopy, the effect of calcination temperature on the degree of extrusion and its influence on nanoparticle formation have been evaluated, leading to the establishment of structure-activity correlations between the observed activation energies and the proportion of nanoparticle species generated.
ABSTRACT
The frontispiece shows a novel inâ situ method of generating metal nanoparticles within porous molecular frameworks, thereby affording highly active and selective single-site heterogeneous catalysts for industrially significant aerobic oxidations. The Communication on pageâ 1226 by Robert Raja and Andy Hor etâ al. highlights the importance of spectroscopic and kinetic studies in establishing structureproperty correlations that are fundamental in the design of sustainable heterogeneous catalysts.
