Julian A. Davies

Hydroformylation of 1-hexene in supercritical carbon dioxide using a heterogeneous rhodium catalyst. 3. Evaluation of solvent effects

The heterogeneously catalyzed hydroformylation of 1-hexene in supercritical carbon dioxide is demonstrated as an alternative to homogeneous catalysis through the use of a rhodium–phosphine catalyst tethered to a silica support. Reaction over the heterogeneous catalyst in supercritical CO2 is compared with the use of this catalyst in liquid-phase toluene, and toluene expanded with CO2. Likewise, the performance of the tethered catalyst is compared with a homogeneous rhodium–phosphine catalyst, and shown to be equally effective under identical reaction conditions. Comparable reaction rates were obtained using the heterogeneous rhodium catalyst in supercritical CO2 and CO2-expanded toluene, both of which were superior to the reaction rate with the heterogeneous catalyst in liquid-phase toluene. Initial aldehyde selectivity obtained with the heterogeneous species was also comparable to that obtained with the homogeneous catalyst, but decreased over the course of the reaction. These results demonstrate the value of using phase behavior, and the importance of understanding this behavior in the development and analysis of greener solvent/catalyst systems.

Non-Gadolinium-Based MRI Contrast Agents

Contrast agents for magnetic resonance imaging based on metal ions other than gadolinium(III) including manganese(II), manganese(III), iron(III) and copper(II), have been investigated over the past decade. Although the intrinsic properties of these metal ions tend to make these agents less attractive than gadolinium(III)-based agents, the large volume of literature on the biochemistry of these metal ions has allowed for the development of viable contrast agents. Agents specific for tissues such as the liver, pancreas, adrenals, cancerous tumors, and even the insides of cells and neuronal tracts as well as non-specific agents have been developed and tested in animal models. Two manganese(II)-based agents, the liver-specific agent manganese(II)-dipyridoxal diphosphate (Teslascan®) and an oral agent containing manganese(II) chloride (Lumen Hance®), and one ferric ammonium citrate-containing oral agent (FerriSeltz®) are available clinically for human use. Information on the toxicity, relaxivity, image enhancement, and tissue specificity of agents is discussed here. In addition to agents designed for use in living systems, contrast agents that measure pH and redox reactions in non-living systems have also been investigated and will be discussed.

Photooxidation of aqueous ammonia with titania-based heterogeneous catalysts

The photoassisted oxidation of dilute aqueous ammonia (0–100 μM) to NO2− and NO3− was investigated over heterogeneous catalysts of TiO2 doped with iron oxide in quartz vessels and with radiation from mercury lamps. Effects on the reaction rate of varying concentration, radiation intensity, amount of catalyst, and pH were studied. The rate of ammonia consumption increased with radiation intensity and was independent of the amount of catalyst over the range of 0.1–1.0 g suspended in 50 ml of solution. In acidic solutions (pH 1–6), the simultaneous action of catalyst and radiation was needed, while in strongly basic solutions (pH 12) only illumination was required. Moreover, the nature and yields of products were dependent on pH: in acidic solutions NO3− was the main product and in basic solutions NO2− was the primary one. Control experiments showed that the reaction rate increased with pH in the absence of catalyst, and the catalyst was active only when irradiated. The reaction was first-order in NH3. The chemical reaction and the mechanism of the photooxidation of NH3 are discussed.

Solid state 31P NMR spectroscopic studies of tertiary phosphines and their complexes

A. Introduction . . . . . . . . . . . . . . . B. Solid state NMR methods . . (i) The MAS experiment . . . . (ii) The CP/MAS experiment. . . C. Tertiary phosphines . . . . . . . . . . . . D. Transition metal complexes . . . . (i) Complexes of the Group 8 metals. (ii) Complexes of the Group 9 metals. (iii) Complexes of the Group IO metals (iv) Complexes of the Group I I metals (v) Complexes of the Group 12 metals E. Concluding remarks . . . . . . Note added in proof. . . . . . References . . . .

I+-abstraction versus I−-displacement in the reactions of diiodocethylene with metal carbonyl anions: X-ray structure of [(OC)5MneCCMn(CO)5]

Abstract Solid diiodoacetylene, ICCI, reacts with THF solutions of the highly basic, third row, metal carbonyl anion, RE(CO) 5 − , exclusively by a formal I + -abstraction process producing ReI(CO) 5 and Re 2 I 2 (CO) 8 . Under the same conditions, the less basic, first row, metal carbonyl anion, Mn(CO 5 − reacts to produce not only Mn 2 I 2 (CO 8 ) by formal I + -abstraction but also (OC) 5 MnCCMn(CO 5 by I − -displacement. These results may be rationalized by HSAB arguments and consideration of charge distribution in the substrate as indicated by molecular orbital calculations. The X-ray structure of (OC) 5 MnCCMn(CO) 5 is reported. Crystals are triclinic, space group P 1 , with Z = 1 in a unit cell of dimensions a 6.421(2), b 6.425(2), c 9.520(2) A, α 81.86(2), β 88.55(2), γ 82.06(2)°, and D calc 1.79 g cm −3 . The structure was solved by the Patterson and Fourier methods and refined by full-matrix least squares to R = 0.024, R w = 0.033 for 1372 observed reflections with F 2 o > 30σ( F 2 o ). The complex is centrosymmetric and thus exhibits an eclipsed in the solid state.

Solid state NMR studies of d-block and p-block metal nuclei: Applications to organometallic and coordination chemistry

A. Introductio B. Properties of metal nuclei . . 204 C. Solid state NMR . . . 204 D. Studies of metal nuclei 209 (i) The d-block metals . 209 (a) Group 3 (SC, Y, La) . 209 (b) Group 4 (Ti, Zr, Hf) . . . . 211 (c) Group 5 (V, Nb, Ta) . 213 (d) Group 6 (Cr, MO, W) . . 214 (e) Group 7 (Mn, Tc, Re) . . 217 (f) Group 8 (Fe, Ru, OS) . 219 (g) Group 9 (Co, Rh, Ir) . . . 220 (h) Group 10 (Ni, Pd, Pt) 220 (i) Group 11 (Cu, Ag, Au) 222 (j) Group 12 (Zn, Cd, Hg) 223 (ii) The p-block metals . . 229 (a) Group 13 (Al, Ga, In, Tl) 229 (b) Group 14 (Ge, Sn, Pb) 230 (c) Group 15 (Sb, Bi) 238 E. Concluding remarks 238 References . . . . . . 239

Underappreciated role of regionally poor water quality on globally increasing antibiotic resistance.

Increasing Antibiotic Resistance David W. Graham,*,† Peter Collignon,‡ Julian Davies, D. G. Joakim Larsson, and Jason Snape †School of Civil Engineering & Geosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, U.K. ‡Australian National University and Canberra Hospital, Canberra 2605, Australia Department of Microbiology and Immunology, University of British Columbia, Vancouver V6T 1Z4, Canada Institute for Biomedicine, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden AstraZeneca U.K., Global Safety, Health and Environment, Alderley Park, Macclesfield, U.K.

Hydroformylation of 1-hexene in supercritical carbon dioxide using a heterogeneous rhodium catalyst. 1. Effect of process parameters

Abstract The hydroformylation of 1-hexene in supercritical carbon dioxide is catalyzed with a heterogeneous rhodium catalyst that is active, selective, and stable for the formation of heptanal. The aldehyde yield and regioselectivity can be affected through changes in catalyst support structure, CO2 solvent pressure, and reaction temperature. A complex reaction pathway model is described that allows determination of rate constants, which are in turn, evaluated as a function of temperature and pressure. Analysis reveals an activation volume of −474 cm3/mol and activation energy of 31.9 kJ/mol for the hydroformylation pathways.

An investigation of the putative photosynthesis of ammonia on iron-doped titania and other metal oxides

Abstract The reported heterogenous photocatalytic sythesis of NH 3 from N 2 and H 2 O in the presence of iron-doped TiO 2 or other semiconducting metal oxides has been investigated. Skepticism about this thermodynamically and mechanistically daunting process is appropriate, and the results reported here support a skeptical position. To assess the reproducibility of the results obtained by previous workers, we performed a large number of experiments under various conditions similar to those employed with apparent success by others. We also carried out 15 N isotope labelling experiments in which the lower limit of detection was around 0.2–1 nmol of added 15 NH 3 in 10 μmol of natural ammonia, i.e. two to three orders of magnitude below the levels reported in successful syntheses by others. All the catalysts tested promoted the photo-oxidation of ammonia under the conditions said to give ammonia photosynthesis. Photocatalytic nitrogen fixation was not found in any of the experiments, although in some cases results were obtained that could have been mistaken for nitrogen fixation. Our results suggest that the reported putative reaction does not occur. We recommend that any further research in this area should be based on standards of demonstration as rigorous as those applied in experiments on the biological fixation of nitrogen.

Ligand effects on the Pt(II) → Pt(0) reduction of dichlorobis(tertiary phosphine)platinum(II) complexes: Correlations between electrochemical data, spectroscopic data, and electronic ligand parameters

Abstract Cyclic voltammetry has been employed to study the diffusive, irreversible platinum(II) → platinum(0) reduction of three sets of structurally related complexes: cis-[PtCl2P{p-C6H4X}3)2] (X = H, CH3, Cl, F, OCH3, N(CH3)2); cis-[PtCl2(PPh2R)2] (R = CH3, n-C3H7, n-C5H11, n-C6H13, n-C12H25) and cis-[PtCl2(PR3)2] (R = CH3, C2H5, CH2ch2CN). Relationships between the peak potentials for the Pt(II) → Pt(0) reduction and thermodynamic parameters which measure the electronic properties of the ligands are shown to exist for complexes of P{p-C6H4X}3 ligands, implying a thermodynamic origin for the sensitivity of the peak potentials to structural change. Complexes of both P{p-C6H4X}3 and PPh2R ligands show correlations between peak potentials for reduction and the 31P{1H} NMR spectroscopic parameter, 1J(195Pt, 31P). Correlations with values of δ(31P) exist in both cases, but a correlation with the coordination chemical shift, Δδ(31P), exists for complexes of PPh2R, and not for complexes of P{C6H4X}3. Complexes of PR3 ligands show no correlation between the peak potentials measured for the Pt(II) → Pt(0) reduction and electronic or spectroscopic parameters, except possibly 1J(195Pt, 31P).