Antony J. Ward

Catalytic hydrosilylation of acetylenes mediated by phosphine complexes of cobalt(I), rhodium(I), and iridium(I)

Abstract The complexes [Co(PPh 3 ) 3 Cl] ( 1 ), [Co(PPh 3 ) 2 (CO) 2 Cl] ( 2 ), [Co(PMe 3 ) 3 Cl] ( 3 ), [Co(PMe 3 ) 2 (CO) 2 Cl] ( 4 ), [Rh(dppe)(CO)Cl] ( 5 ), [Rh(PPh 2 Me) 2 (CO)Cl] ( 6 ), [Ir(dppe)(CO)Br] ( 7 ), and [Ir(PPh 2 Me) 2 (CO)Cl] ( 8 ) catalyse the hydrosilylation of a range of acetylenes including 1-hexyne, phenylacetylene, and 1-phenyl-1-propyne with triethylsilane. In the case of 1-hexyne and 1-phenyl-1-propyne, only the expected hydrosilylation products were observed; however, when the substrate was phenylacetylene, cyclotrimerisation and dimerisation products were observed in addition to the expected vinylsilanes. No hydrosilation was observed with alkene substrates; however, in the presence of some metal complexes, there was double bond migration and cis / trans -isomerisation probably mediated by the formation of metal hydrides in the reaction mixture.

The Formation of High‐Order Polybromides in a Room‐Temperature Ionic Liquid: From Monoanions ([Br5]− to [Br11]−) to the Isolation of [PC16H36]2[Br24] as Determined by van der Waals Bonding Radii

An unprecedented diversity of high-order bromine catenates (anionic polybromides) was generated in a tetraalkylphosphonium-based room temperature ionic liquid system. Raman spectroscopy was used to identify polybromide monoanions ranging from [Br5 ](-) to [Br11 ](-) in the bulk solution, while single-crystal X-ray diffraction identified extended networks of linked [Br11 ](-) units, forming a previously unknown polymeric [Br24 ](2-) dianion. This represents the largest polybromide species identified to date. In combination with recent work, this suggests that other, higher order molecular polybromide ions might be isolated.

Metallasilsesquioxanes: Molecular Analogues of Heterogeneous Catalysts

As soluble molecular analogues of silica surfaces, polyhedral oligosilsesquioxanes (POS or POSS®) have been used extensively, along with alkylsilanols, to mimic the structure and chemistry of silica surfaces (Figure 3.1).

The use of acidic task-specific ionic liquids in the formation of high surface area mesoporous silica

The acidic ionic liquids 1-alkyl-3-methylimidazolium hydrogen sulfate [CnMIM]HSO4 (n = 8, 10, 12, 16) were synthesised using a one-pot method and then used as new acidic templates to generate high surface area ordered mesoporous silicas (>1000 m2 g−1) using a one-step synthetic route.

Solar Hydrogen from an Aqueous, Noble‐Metal‐Free Hybrid System in a Continuous‐Flow Sampling Reaction System

We introduce the visible-light photocatalytic H2 evolution reaction as catalyzed by a cobaloxime/carbon nitride (C3N4) noble-metal-free hybrid photosystem by using a continuous-flow sampling reaction system. The photocatalytic H2 evolution rate is highly dependent on the structure of C3N4, in which porous C3N4 shows the best activity compared with bulk C3N4 (lamellar) and C3N4 nanosheets. When using porous C3N4, the system is neither affected by the solution pH, nor the C3N4 concentration, nor the structure of the cobaloxime complex.

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

We discuss herein selected examples of metal complexes of polyhedral oligosilses-quioxanes (POSSs) as models of single-site heterogeneous surface catalysts. The utility of these compounds as such models is illustrated when employed as analogues of single-site titanium species supported on a silica surface. Deep insights into structure–functionality relationships can be gained. In particular, it was possible to probe the relationship between accessibility of the reactive centre and turnover frequencies in a manner that is impossible for a purely heterogeneous catalyst. We also report that the partially dehydroxylated SiO2 surface alone is an effective radical polymerization initiation catalyst. This surface reactivity is modelled by the solution reactions between the olefin substrate and two POSSs, the completely condensed triganol prism, Si6Cy6O9 (a6b0, Cy = Cyclohexyl, C6H11), and the incompletely condensed partial cube, Si7Cy7O9(OH)3 (a7b3). The former, with six-membered Si3O3 rings, is a catalyst. The latter, without this feature, is not. Similar reactivity discrimination is observed in the gas phase reactions of these POSSs with the olefin substrate, examined using atmospheric pressure chemical ionization- and collision-induced decomposition spectroscopies. Silsesquioxane a6b0, containing Si3O3 rings, reacts with the olefin, forming grafted olefin monomers and dimers, while this reactivity is not observed with silsesquioxane a7b3.

A Palladium‐Catalyzed Multicascade Reaction: Facile Low‐Temperature Hydrogenolysis of Activated Nitriles and Related Functional Groups

The facile hydrogenolysis of various nitriles, imines, and amines over Pd/C has been achieved by using straightforward and relatively mild conditions. Substrates that contain an aryl group adjacent to the nitrogen‐containing functionality were hydrogenolyzed most effectively. The stabilization of the proposed η2‐coordinated palladium intermediate by this group was partly responsible for this observation and is borne out by ab initio calculations.

Synthesis and molecular structures of dimeric assemblies of telluronium salts derived from o-C6H4(CH2TeMe)2 and PhMeTe

The ditelluroether, o-C6H4(CH2TeMe)(2) reacts with excess MeI in acetone to afford the bis(triorganotelluronium iodide), o-C6H4(CH2TeMe2I)(2), in high yield which has been characterised by H-1-, C-13{H-1}- and Te-125{H-1}-NMR spectroscopy, microanalysis and X-ray crystallography. The crystal structure of this species reveals a weakly associated dimer, assembled through a series of secondary (TeI)-I-... interactions to give a pseudo-cubane Te4I4 core, involving three-coordinate (pyramidal) iodine and six-coordinate (distorted octahedral) tellurium. The o-xylyl backbone units are oriented across the diagonal of two opposite faces of the cubane. This is the first crystallographic study of a triorganotelluronium halide salt derided from a ditelluroether, The crystal structure of PhTeMe2I shows a weakly associated mu(2)-diiodo bridged dimer, in this case with two-coordinate iodine and five-coordinate, distorted square pyramidal tellurium. The stereochemical activity of the Te-based lone pair is discussed for each system and the structures are compared with other related species.

Ionic liquid-templated preparation of mesoporous silica embedded with nanocrystalline sulfated zirconia

A series of mesoporous silicas impregnated with nanocrystalline sulphated zirconia was prepared by a sol-gel process using an ionic liquid-templated route. The physicochemical properties of the mesoporous sulphated zirconia materials were studied using characterisation techniques such as inductively coupled optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray microanalysis, elemental analysis and X-ray photoelectron spectroscopy. Analysis of the new silicas indicates isomorphous substitution of silicon with zirconium and reveals the presence of extremely small (< 10 nm) polydispersed zirconia nanoparticles in the materials with zirconium loadings from 27.77 to 41.4 wt.%.

Unprecedented blue-shift in bismuth oxide supported on mesoporous silica

A range of Bi-impregnated TUD-1-type mesoporous silicas have been prepared using the structure directing agent triethanolamine (TEA), with bismuth loadings ranging from 25 wt% to <0.001 mol%. These silicas have been characterized by surface area, pore size, pore volume, Raman spectroscopy, IR spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and ICP-AES. During the gelation phase the bismuth chemistry varies with its concentration and it is possible to prepare atomically dispersed as well as highly uniform nanoparticulate bismuth oxide that can be well characterised. Diffuse reflectance UV-Vis spectrophotometry was used to determine the band gap of the bismuth oxide nanoparticles and unprecedented blue shifts (due to quantum confinement) as compared to bulk α-Bi2O3, were observed with the maximum band gap observed being 5.17 eV.