214 research outputs found
A new mechanism for the rearrangement of the icosahedral carboranes
No full textA new mechanism which involves the anticubeoctahedron as the complementary geometry is postulated to rationalise previously reported data on the rearrangement of various icosahedral carboranes
A new approach to the design of heterogeneous single-site enantioselective catalysts
No full textWe analyze the merits of an approach to the design of enantioselective catalysts that relies on constraining an anchored organometallic complex at the inner walls of mesoporous silica. Two distinct metal centers {Rh(I) and Pd(II)}, three distinct diamino ligands {(S)-(-)-2-aminomethyl-1-ethylpyrrolidine, (AMP), (S)-(+)-(2-pyrrolidinyl-methyl)pyrrolidine, (PMP), and (1R,2R)-(+)-1,2-diphenylethylenediamine, (DED)}, two distinct methods of anchoring (a covalent and a noncovalent one), and two specific examples of enantioselective hydrogenation (the asymmetric hydrogenation of the C=C bond in E--phenylcinnamic acid and the asymmetric hydrogenation of the C=O bond in methyl benzoylformate) have been investigated. Values of enantiomeric excess (ee) ranging from a low of 66 to a high of 93 have been achieved by this approach. Moreover, the catalysts are robust and stand up well to recycling
Constraining asymmetric organometallic catalysts within mesoporous supports boosts their enantioselectivity
No full textBy constraining tethered asymmetric organometallic catalysts within the nanopores of silica supports so as to increase the interaction between the pore wall and the active center (and hence to restrict access of the reactant to the catalyst) a significant improvement in enantioselectivity is achieved. A schematic illustration of a cationic chiral, organometallic catalyst, [Rh(I)(COD)PMP] {(S)-(+)-1-(2-pyrrolidinylmethyl)-pyrrolidine and cyclooctadiene}, which is non-covalently anchored, via a N–H••••F hydrogen bond with the triflate ion, CF3SO3-, to the curved inner surface of a 38 Å diameter pore of a silica support, for the asymmetric hydrogenation of the C=O bond in methyl benzoylformate to the corresponding methyl mandelate is shown. Rh (purple); N (blue); H (white); F (green); C (grey); S (yellow); O (red)
Bimetallic nanocatalysts for the conversion of muconic acid to adipic acid
No full textAdipic acid (2) production currently entails use and generation of environmentally harmful materials: an efficient catalyst, consisting of nanoparticles of Ru10Pt2 anchored within the pores of mesoporous silica, facilitates the production of (2) by hydrogenating muconic acid, that may be derived biocatalytically from D-glucose. Industrially desirable chemical products such as adipic acid may be produced in good yields and selectivities from plant-crop sources, using highly active bimetallic nanocatalysts anchored onto mesoporous silica
Rhodium(I) and palladium(II) complexes with the Schiff base 2,2'-bis((4S)-4-benzyl-2-oxazoline)
No full textThe Schiff base 2,2?-bis((4S)-4-benzyl-2-oxazoline) (I) and its coordination complexes with rhodium(I) and palladium(II) (and with 1,5-cyclo-octadiene and allyl ligands) have been characterised by single-crystal X-ray diffraction, mass spectrometry, 13C and 1H NMR spectroscopy: [Rh(C20H20N2O2)(C8H12)][Rh2(C20H20N2O2)2](CF3SO3)3 · (CH3CH2O) (II) and [Pd(C20H20N2O2)(C3H5)]CF3SO3 (III). We discuss the reasons for the formation of two complex cations for Rh(I), [Rh(C20H20N2O2)(C8H12)]+ (IIa) and [Rh2(C20H20N2O2)2]2+ (IIb), and only one for Pd(II)
Novel ruthenium(II) diamine complexes
No full textThe complex cations [Ru(C7H16N2)(C10H14)Cl]+, [Ru(C7H16N2)(C6H6)Cl]+, [Ru(C9H18N2)(C6H6)Cl]+, [Ru(C9H18N2)(C10H14)Cl]+ and [Ru(C14H16N2)(C10H14)Cl]+ have been synthesised from the reaction between the ruthenium-arene complexes [with C6H6 (benzene) or C10H14 (p-cymene)] and the respective chiral diamines [C7H16N2=(S)-(?)-2-aminomethyl-1-ethylpyrrolidine, C9H18N2=(S)-(+)-2-(pyrrolidinylmethyl)-pyrrolidine, or C14H16N2=(1R,2R)-(+)-1,2-diphenylethylenediamine], isolated and characterised as chloride salts using single-crystal X-ray diffraction. All complexes were fully characterised by elemental analysis, mass spectrometry, 13C and 1H NMR, and also found to exhibit catalytic activity in the transfer hydrogenation of acetophenone to 1-phenylethanol at 50 °C (enantiomeric excesses range from ca. 25% to 60%, and conversions from ca. 30% to 50%)
Highly efficient catalysts for the hydrogenation of nitro-substituted aromatics
No full textNanoparticles of Co and NiPd, derived from colloidal precursors and supported on commercially available nonordered mesoporous silica, are highly effective, cheap, recyclable and industrially viable catalysts for the hydrogenation of a range of nitro-substituted aromatics under mild conditions.</p
The construction of Hadrian's Wall
No full textEThOS - Electronic Theses Online ServiceGBUnited Kingdo
Application of the ligand polyhedral model to dicobalt octacarbonyl
No full textApplication of the ligand polyhedral model (LPM) to dicobalt octacarbonyl, [Co2(CO)8], leads to an explanation of the mu-2-bridged structure that the molecule adopts in the solid state and also of the isomeric forms which coexist in equilibrium in solution. It further provides a convenient explanation of both the observed low energy interconversion of these isomers and the fluxional behaviour they exhibit
- …
