The comparison of fac and mer ruthenium(II) trischelate complexes in anion binding

The synthesis of three new homoleptic trischelate ruthenium( II) complexes bearing new 2,2'-bipyridine ligands, 5,5'-dibenzylamido-2,2'-bipyridine (L1) and 5-benzylamido-2,2'- bipyridine (L2) has been achieved. In the case of [Ru(L2)(3)](2+), the mer and fac isomers have been separated. H-1 NMR spectroscopic anion binding studies indicate that the two C-3-symmetric pockets provided by [ Ru(L1)(3)](2+) is conducive to receive a range of anions, although this is not readily reflected in the photophysical behaviour. The fac-isomer of [Ru(L2)(3)](2+) does appear to have an enhancement in the binding interactions over the mer form with dihydrogenphosphate salts, although the difference is much less marked with the spherical chloride ions. From X-ray crystallographic evidence, the ability to hold water in the "anion" binding cleft can inhibit the strength of the interactions with anions, giving rise to the observed selectivity for directional oxoanions such as dihydrogen phosphate.

Characterization of silica-supported dodecatungstic heteropolyacids as a function of their dehydroxylation temperature

Dodecatungsto-silicic H4SiW12O40 and -phosphoric acids H3PW12O40 were deposited on silica by a classical impregnation technique. The resulting materials were studied by in situ Raman and infrared spectroscopy, XPS and by solid-state H-1 MAS NMR as a function of their dehydroxylation temperature. The data show that in the case of H3PW12O40 three silanol groups are protonated while in the case of H4SiW12O40 at least one acidic proton remains. Upon heating this proton reacts leading to a disordered structure and a broadening of the W-O Raman bands.

Lanthanide-doped luminescent ionogels

Ionogels are solid oxide host networks con. ning at a meso-scale ionic liquids, and retaining their liquid nature. Ionogels were obtained by dissolving lanthanide(III) complexes in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C(6)mim][Tf2N], followed by confinement of the lanthanide-doped ionic liquid mixtures in the pores of a nano-porous silica network. [C(6)mim][Ln(tta)(4)], where tta is 2-thenoyltrifluoroacetonate and Ln = Nd, Sm, Eu, Ho, Er, Yb, and [choline](3)[Tb(dpa)(3)], where dpa = pyridine-2,6-dicarboxylate (dipicolinate), were chosen as the lanthanide complexes. The ionogels are luminescent, ion-conductive inorganic-organic hybrid materials. Depending on the lanthanide(III) ion, emission in the visible or the near-infrared regions of the electromagnetic spectrum was observed. The work presented herein highlights that the confinement did not disturb the first coordination sphere of the lanthanide ions and also showed the excellent luminescence performance of the lanthanide tetrakis beta-diketonate complexes. The crystal structures of the complexes [C(6)mim][Yb(tta)(4)] and [choline](3)[Tb(dpa)(3)] are reported.

Solventless continuous flow homogeneous hydroformylation of 1-octene

The hydroformylation of 1-octene under continuous flow conditions is described. The system involves dissolving the catalyst, made in situ from [ Rh(acac)(CO)(2)] (acacH = 2,4- pentanedione) and [RMIM][TPPMS] ( RMIM = 1-propyl (Pr), 1-pentyl (Pn) or 1-octyl (O)-3-methyl imidazolium, TPPMS = Ph2P(3-C6H4SO3)), in a mixture of nonanal and 1-octene and passing the substrate, 1-octene, together with CO and H-2 through the system dissolved in supercritical CO2 (scCO(2)). [PrMIM][TPPMS] is poorly soluble in the medium so heavy rhodium leaching (as complexes not containing phosphine) occurs in the early part of the reaction. [PnMIM][ PPMS] affords good rates at relatively low catalyst loadings and relatively low overall pressure (125 bar) with rhodium losses <1 ppm, but the catalyst precipitates at higher catalyst loadings, leading to lower reaction rates. [OMIM][ TPPMS] is the most soluble ligand and promotes high reaction rates, although preliminary experiments suggested that rhodium leaching was high at 5-10 ppm. Optimisation aimed at balancing flows so that the level within the reactor remained constant involved a reactor set up based around a reactor fitted with a sight glass and sparging stirrer with the CO2 being fed by a cooled head HPLC pump, 1-octene by a standard HPLC pump and CO/H-2 through a mass flow controller. The pressure was controlled by a back pressure regulator. Using this set up, [OMIM][ TPPMS] as the ligand and a total pressure of 140 bar, it was possible to control the level within the reactor and obtain a turnover frequency of ca. 180 h(-1). Rhodium losses in the optimised system were 100 ppb. Transport studies showed that 1-octene is preferentially transported over the aldehydes at all pressures, although the difference in mol fraction in the mobile phase was less at lower pressures. Nonanal in the mobile phase suppresses the extraction of 1-octene to some extent, so it is better to operate at high conversion and low pressure to optimise the extraction of the products relative to the substrate. CO and H2 in the mobile phase also suppress the extraction effciency by as much as 80%.

Designing ionic liquids with boron cluster anions: alkylpyridinium and imidazolium [nido-C(2)B(9)H(11)] and [closo-CB(11)H(12)] carborane salts

A range of new alkylpyridinium and imidazolium carborane salts with [nido-C2B9H12](-), [closo-CB11H12](-), and [RC2B11H11](-) (R = methyl or butyl) anions have been prepared and characterized by physical and thermal methods, including the solid state structures of five of the salts determined by single crystal X-ray diffraction. The tendency of the salts to form low-melting ionic liquids has been assessed; all the salts studied with [nido-C2B9H12](-) anions melted below 100 degrees C and, significantly, have melting points that are 25-85 degrees C lower than those of the corresponding [closo-CB11H12](-) analogs, demonstrating that a wider range of boron-rich ionic liquid materials can be readily accessed.

Crystal structures of imidazolium bis(trifluoromethanesulfonyl)imide 'ionic liquid' salts: the first organic salt with a cis-TFSI anion conformation

Crystal structures of two examples of an important class of ionic liquids, 1,3-dimethylimidazolium and 1,2,3-triethylimidazolium bis(trifluoromethanesulfonyl)imide have been characterized by single crystal X-ray diffraction. The anion in the 1,3-dimethylimidazolium example (mp 22 degreesC), adopts an unusual cis-geometry constrained by bifurcated cation-anion C-H...O hydrogen-bonds from the imidazolium cation to the anion resulting in the formation of fluorous layers within the solid-state structure. In contrast, in the 1,2,3-triethylimidazolium salt (mp 57 degreesC), the ions are discretely packed with only weak C-H...O contacts between the ions close to the van der Waals separation distances, and with the anion adopting the twisted conformation observed for all other examples from the limited set of organic bis( trifluoromethanesulfonyl) imide crystal structures. The structures are discussed in terms of the favorable physical properties that bis(trifluoromethanesulfonyl) imide anions impart in ionic liquids.

Changes in solar activity and Holocene climatic shifts derived from C-14 wiggle-match dated peat deposits

Closely spaced sequences of accelerator mass spectrometer (AMS) C-14 dates of peat deposits display century-scale wiggles which can be fitted to the radiocarbon calibration curve. By wiggle-matching such sequences, high-precision calendar age chronologies can be generated which show that changes in mire surface wetness during the Bronze Age/Iron Age transition (c. 850 cal. BC) and the 'Little Ice Age' (Wolf, Sporer, Maunder and Dalton Minima) occurred during periods of suddenly increasing atmospheric concentration of C-14. Replicate evidence from peat-based proxy climate indicators in northwest Europe suggest these changes in climate may have been driven by temporary declines of solar activity. Carbon-accumulation rates of two raised peat bogs in the UK and Denmark record low values during the 'Little Ice Age' which reflects reduced primary productivity of the peat-forming vegetation during these periods of climatic deterioration.

Speciation of chloroindate(III) ionic liquids

A range of chloroindate(III) ionic liquid systems was prepared by mixing of 1-alkyl-3-methylimidazolium chloride with indium(III) chloride in various ratios, expressed as the mol fraction of indium(III) chloride, chi(InCl3). For chi(InCl3) 0.50, the products were biphasic (suspensions of a solid in an ionic liquid). Speciation of these chloroindate(III) systems was carried out using a wide range of techniques: differential scanning calorimetry (DSC), polarised optical microscopy (POM), liquid-state and solid-state In-115 NMR spectroscopy, X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). Ionic liquids prepared using an excess of the organic chloride (chi(InCl3) 0.5) contained indium(III) chloride powder suspended in a neutral tetrachloroindate ionic liquid.

Continuous flow hydroformylation using supported ionic liquid phase catalysts with carbon dioxide as a carrier.

A supported ionic liquid phase (SILP) catalyst prepared from [PrMIM][Ph2P(3-C6H4SO3)] (PrMIM = 1-propyl-3-methylimidazolium), [Rh(CO)(2)(acac)] (acacH = 2,4-pentanedione) [OctMIM]NTf2 (OctMIM = 1-n-octyl-3-methylimidazolium, Tf = CF3SO2) and microporous silica has been used for the continuous flow hydroformylation of 1-octene in the presence of compressed CO2. Statistical experimental design was used to show that the reaction rate is neither much affected by the film thickness (IL loading) nor by the syngas: substrate ratio. However, a factor-dependent interaction between the syngas: substrate ratio and film thickness on the reaction rate was revealed. Increasing the substrate flow led to increased reaction rates but lower overall yields. One of the most important parameters proved to be the phase behaviour of the mobile phase, which was studied by varying the reaction pressure. At low CO2 pressures or when N-2 was used instead of CO2 rates were low because of poor gas diffusion to the catalytic sites in the SILP. Furthermore, leaching of IL and Rh was high because the substrate is liquid and the IL had been designed to dissolve in it. As the CO2 pressure was increased, the reaction rate increased and the IL and Rh leaching were reduced, because an expanded liquid phase developed. Due to its lower viscosity the expanded liquid allows better transport of gases to the catalyst and is a poorer solvent for the IL and the catalyst because of its reduced polarity. Above 100 bar (close to the transition to a single phase at 106 bar), the rate of reaction dropped again with increasing pressure because the flowing phase becomes a better and better solvent for the alkene, reducing its partitioning into the IL film. Under optimised conditions, the catalyst was shown to be stable over at least 40 h of continuous catalysis with a steady state turnover frequency (TOF, mol product (mol Rh)(-1)) of 500 h(-1) at low Rh leaching (0.2 ppm). The selectivity of the catalyst was not much affected by the variation of process parameters. The linear: branched (1:b) ratios were ca. 3, similar to that obtained using the very same catalyst in conventional organic solvents.

Entrapping homogeneous catalysts by sol-gel methods: the bottom-up synthesis of catalysts that recycle and cascade

Perspective and front cover article: Homogeneous catalysts entrapped in silica matrices, including ionic liquid containing 'ionogels', exhibit high selectivity, unexpected activity and excellent recyclability.

Diastereoselective assembly of pentanuclear circular helicates

Reaction of a ligand which contains two N-donor and O-donor tridentate domains separated by a 1,3-phenylene spacer unit with Zn2+ ions results in a pentanuclear circular helicate [Zn5(L)5]10+ and this structure persists in both the solid and solution state. The formation of this high nuclearity species is governed by unfavourable steric interactions between the phenyl units which destabilize the simple linear helicate. Incorporation of enantiopure units within the ligand strand controls the diastereoselectivity with up to 80% d.e.

Platinum(II) phosphine and orotate complexes with aminopyridine co-ligands, and their molecular recognition via hydrogen bonding

The new complexes [Pt(dppp)(py)(2)][OTf](2), 1, [Pt(dppp)(2-ap)(2)][OTf](2), 2, [(dppp)Pt(mu -OH){mu -NH(C5H3N)NH2}Pt(dppp)][OTf](2), 3 (py=pyridine, 2-ap=2-aminopyridine, NH(C5H3N)NH2=2,6-diaminopyridine anion, dppp = 1,3-bis(diphenylphosphino)propane, OTf=O3SCF3) have been prepared via reactions between [Pt(dppp)(OTf)(2)] and pyridine, 2-aminopyridine or 2,6-diaminopyridine (2,6-dap) respectively. The amines exhibit a range of co-ordination modes. Pyridine and 2-aminopyridine co-ordinate to platinum through endo-nitrogen atoms in complexes 1 and 2, the latter existing as a pair of rotomers due to the steric hindrance introduced by the 2-substituent. However, 2,6-diaminopyridine co-ordinates to platinum through the exo-nitrogen of one amino group, to give the unusual mu -amido complex 3. Reaction of the known orotate chelate complex [Pt(PEt3)(2)(N,O-HL)] [HL=orotate, the dianion of 2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid (orotic acid)] with 2,6-dap gave [Pt(PEt3)(2)(2,6-dap)(N-HL)] 4, which contains an unconventional monodentate orotate ligand. In this co-ordination mode the orotate retains an ADA hydrogen bonding site and was found to co-crystallise with 2,6-dap via complementary ADA:DAD triple hydrogen bonds to give [Pt(PEt3)(2)(N-HL)(2,6-dap)].2,6-dap, 5. Complex 5 exhibits a helical chain structure of associated [1+1] adducts in the solid state.

Synthesis and characterisation of new platinum-acetylide complexes containing diimine ligands

A new class of platinum-bipyridyl compounds has been synthesized by the dehydrohalogenative reaction of [4,4'-bis(tert-butyl)-2,2'-bipyridyl]platinum dichloride [PtCl2((t)Bu(2)bipy)] 1 with terminal alkynes HC=CR, in the presence of copper(I) iodide and diisopropylamine. The products [Pt(C=CR)(2)((t)Bu(2)bipy)] (R=C6H4NO2-p 2, C6H5 3, C6H4CH3-p 4 or SiMe3 5), have been characterised by spectroscopic and analytical methods, and a single crystal molecular structure determination has been carried out on 4. Extended Huckel molecular orbital calculations have also been carried out, and the results are used to help rationalise the voltammetric, EPR and spectroelectrochemical properties of the new compounds. These show that compounds 3, 4 and 5 undergo a one-electron bipyridyl based redox process, but that 2 has an unresolved two-electron process located on the nitro groups.

Orotate complexes of rhodium(I) and iridium(I): effect of coligand, counter ion, and solvent of crystallisation on association via complementary hydrogen bonding

The new complexes [NEt3H][M(HL)(cod)] (M = Rh 1 or Ir 2; H3L = 2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid, erotic acid; cod = cycloocta-1,5-diene) have been prepared by the reaction between [M2Cl2(cod)(2)] and erotic acid in dichloromethane in the presence of Ag2O and NEt3. They crystallise as dichloromethane adducts 1 . CH2Cl2 and 2 . CH2Cl2 from dichloromethane-hexane solutions. These isomorphous structures contain doubly hydrogen-bonded dimers, with additional hydrogen bonding to NEt3H+ cations and bridging CH2Cl2 molecules to form tapes. The use of (NBu4OH)-O-n instead of NEt3 gave the related complex [NBu4n][Rh(HL)(cod)] 1' which has an innocent cation not capable of forming strong hydrogen bonds and in contrast to 1 exists as discrete doubly hydrogen-bonded dimers. Complex 1' cocrystallises with 2,6-diaminopyridine (dap) via complementary triple hydrogen bonds to give [NBu4n][Rh(HL)(cod)]. dap . CH2Cl2 3. Complex 3 exhibits an extended sheet structure of associated [2 + 2] units, with layers of NBu4n, cations separating the sheets. These structural data together with those reported previously for platinum orotate complexes suggest that the steric requirements of the other ligands co-ordinated to the metal are important in influencing their hydrogen-bonding abilities. The solvent of crystallisation, the hydrogen-bonding propensity of the coligand and the nature of the counter ion also determine the type of association in the solid state.

Raman spectroelectrochemical studies and crystal structure of a binuclear copper(I) complex with a bridging diimine ligand

Raman spectroelectrochemical and X-ray crystallographic studies have been made for the binuclear copper(I) complex, [(Ph(3)P)(2)Cu(dpq)Cu(PPh(3))(2)][BF4](2), where dpq is the bridging ligand 2,3-di(2-pyridyl)quinoxaline. The X-ray data show that the pyridine rings are twisted out of plane with respect to the quinoxaline ring which is itself non-planar. The UV/VIS spectra of the metal-to-ligand charge-transfer excited state and those of the electrochemically reduced complex are similar. The resonance-Raman spectrum of the latter species exhibits little change in the frequency of the pyridinylquinoxaline inter-ring C-C bond stretching mode, compared to the ground electronic state. This suggests minimum change in the inter-ring C-C bond order in the electrochemically or charge-transfer generated radical anion. Semiempirical molecular-orbital calculations on both the neutral dpq and radical anion show two near-degenerate lowest unoccupied orbitals in the neutral species. One is strongly bonding across the inter-ring C-C bond while the other is almost nun-bonding. The Raman data suggest that it is this latter orbital which is populated in the transient and electrochemical experiments.