Douglas S. Shephard

Preparation, characterisation and performance of encapsulated copper-ruthenium bimetallic catalysts derived from molecular cluster carbonyl precursors

High-performance, bimetallic nanoparticle catalysts (M1+M2) were obtained by gentle thermolysis of their precursor metal-cluster carbonylates physisorbed inside the mesoporous channels of silica (the hexagons in the figure). The Cu–Ru catalyst anchored on silica is stable in use and has been tested in the catalytic hydrogenation of hex-1-ene, diphenylacetylene, phenylacetylene, stilbene, cis-cyclooctene, and D-limonene.

Constrained chiral catalysts

Some of the approaches previously used to perform reactions enantioselectively using heterogeneous catalysts, together with a few illustrative examples, are first briefly summarised. We then outline various advantages and opportunities that nowadays exist for the confinement of large and rather complicated chiral organometallic catalytic entities as well as reactant and product species inside the cavities of mesoporous silicas, the pore diameters of which fall in the range 25 to 100 A. The unique opportunities afforded by chiral chelate ligands based on bis-diphenyl-phosphinoferrocene (BPPFA) held within mesoporous silica are adumbrated. Examples of potentially useful reaction systems and general synthetic possibilities are discussed with the view to highlight the emerging potential of the mesoporous dimension in regio- and enantioselective catalysis.

CVD synthesis of carbon nanotubes

Abstracts are not published in this journal

New catalysts for clean technology

The preparation, characterisation and catalytic performance of both bimetallic nanoparticles and chiral homogeneous catalysts anchored along the interior walls of mesoporous silica (MCM-41) are described. The bimetallic nanoparticles are prepared from Ru 6Pd 6 and Ru 6CSn carbonyl clusters and the resulting MCM derivatives are characterised by a number of methods, including EXAFS, FTIR and STEM. The solvent-free hydrogenation of naphthalene and cyclic polyenes using these catalysts are described, with the Ru 6CSn based catalyst giving a 90% selectivity for the corresponding monoenes while the Ru 6Pd 6 produces the fully hydrogenated product in high yield. The homogeneous catalysts 1-[-(R)-1′2-bis(diphenylphosphino)ferrocenyl] ethyl-N-N′-dimethylethylenediamine palladium dichloride was heterogenised by anchoring along the inside walls of MCM-41. The catalysed reaction between cinnamylacetate and benzylamine was studied and the catalyst produced 51% of the branched chain product possibly with 100%ee.

Effects of electron-beam exposure on a ruthenium nanocluster polymer

The properties of the ruthenium nanocluster polymer of formula [Ru6C(CO)15P(C6H5)2CCP(C6H5)2]n are studied by atomic-force microscopy, Fourier-transform infrared spectroscopy, and electron microscopy as a function of electron-beam exposure. These properties are related to the electrical conductivity, which is measured at various temperatures and electric fields. A hopping correlation length of 240 nm is deduced and explained on the basis of the formation of ruthenium superclusters in an insulating matrix.

Superior performance of a chiral catalyst confined within mesoporous silica

A chiral catalyst from the ligand 1,1′-bis(diphenylphosphino)ferrocene (dppf) anchored to the inner walls of the mesoporous support MCM-41 and co-ordinated to PdII has been shown to exhibit a degree of regioselectivity and enantiomeric excess, in the allylic amination of cinnamyl acetate, which is far superior to that of its homogeneous counterpart or that of a surface-bound analogue attached to a non-porous silica.

Modelling the active sites of heterogeneous titanium-centred epoxidation catalysts with soluble silsesquioxane analogues

By synthesising and structurally characterising new soluble titanosilsesquioxanes, and by following the dynamics of epoxidation of cyclohexene in their presence, the tripodally anchored TiIV active sites in Ti–SiO2 heterogeneous catalysts are modelled structurally and catalytically.

Novel behaviour and reactivity in 1,1′-bis(diphenylphosphino)ferrocene and 1,1′-bis(diphenylphosphino)cobaltocene cluster derivatives

The clusters [Ru 6 C(CO) 16 {Fe(C 5 H 4 P(Ph) 2 ) 2 }] 2 and [Ru 6 C(CO) 15 { μ -Fe(C 5 H 4 P(Ph) 2 ) 2 }] 3 have been synthesised from the reaction of the parent cluster [Ru 6 C(CO) 17 ] 1 with 1,1′-bis(diphenylphosphino)ferrocene (dppf) in THF. The related compound [Ru 5 C(CO) 13 { μ -Fe(C 5 H 4 P(Ph) 2 ) 2 }] 4 is produced from 2 and 3 in more forcing conditions. Both clusters 3 and 4 have been structurally characterised by single crystal X-ray analysis. In 3 the dppf ligand is coordinated in the vicinal form and the cluster core is a highly distorted octahedron. In 4 the vicinal mode is retained but the dppf ligand is coordinated to adjacent basal atoms of a square-base pyramid. The 31 P-NMR spectra of 3 and 4 in CD 2 Cl 2 at various temperatures show a high degree of stereochemically non-rigid behaviour. Magnetic susceptibility measurements across a range of temperatures indicate that 3 is paramagnetic at all temperatures. An electrochemical study of 1 , 3 , 4 and the related [Ru 6 C(CO) 15 { μ -dppm}] 5 has demonstrated a significant degree of communication between the redox-active sites in 3 and 4 . The cluster [Ru 5 C(CO) 13 { μ -Co(C 5 H 4 P(Ph) 2 ) 2 }] 7 has also been synthesised from the direct reaction of the parent cluster [Ru 5 C(CO) 15 ] 6 with 1,1′-bis(diphenylphosphino)cobaltocene (dppc). Synthesis of the dppc analogue of 3 was attempted but was thwarted by unfavourable redox chemistry. EPR spectra have been obtained for both dppc and 7 . The oxidation product of 7 has also been produced ( 7 + ) and displays a high degree of stereochemically non-rigid behaviour in a fashion similar to 3 and 4 . The magnetic suceptibility of 7 has also been measured, showing an extraordinarily large magnetic moment at ambient temperature.

Modified mesoporous silicate MCM-41 materials: immobilised perruthenate—a new highly active heterogeneous oxidation catalyst for clean organic synthesis using molecular oxygen

A new oxidation catalyst containing perruthenate immobilised within MCM-41 has been prepared and used in the clean oxidation of alcohols to carbonyl compounds with molecular oxygen.

Synthesis of high purity single-walled carbon nanotubes in high yield

A simple method for the synthesis of high purity single wall carbon nanotubes has been developed by using nickel formate as a precursor for the formation of nearly mono-dispersed nickel seed-nanoparticles as catalysts in the CVD growth process.