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A proxy-based high-throughput experimental approach was used to explore the stability and activity of Co-based Fischer-Tropsch Synthesis catalysts with different promoters on a variety of supports. The protocol is based on XRD estimation of the active phase polymorph, particle size and ratio of crystalline phases of Co to support. Sequential sample libraries enabled exploration of four Co loadings with five different promoters on six support materials. Catalysts stable to aging in syngas, i.e. displaying minimal change of particle size or active phase concentration, were evaluated under industrial conditions. This procedure identified SiC as a support that confers catalyst stability and that a combination of Ru and Hf promotes the stabilisation of hcp Co. Unsupported bulk samples of Co with appropriate amounts of Ru and Hf revealed that the formation of hcp Co is independent of the support. The hcp Co-containing catalyst afforded the highest catalytic activity and C5+ selectivity amongst the samples tested in this study, confirming the effectiveness of the proxy-based high-throughput method.

Sasol Ltd., the University of Glasgow and the EPSRC (grant numbers EP/P504937/1 and EP/P505534/1) are thanked for the provision of postgraduate studentships (RW and ALD). The Royal Society is thanked for the provision of an Industrial Fellowship (PBW). In order to examine fundamental processes connected with the use of an unpromoted iron based Fischer–Tropsch synthesis (FTS) catalyst, model studies examining the temporal formation of hydrocarbonaceous species that form over the catalyst are undertaken using a combination of temperature-programmed oxidation, powder X-ray diffraction, Raman scattering, transmission electron microscopy and inelastic neutron scattering (INS). Catalyst samples were exposed to ambient pressure CO hydrogenation at 623 K for defined periods of time-on-stream (3, 6, 12 and 24 h) prior to analysis. INS reveals a progressive retention of hydrogenous species that is associated with the evolution of a hydrocarbonaceous overlayer, as evidenced by the presence of sp2 and sp3 hybridized C–H vibrational modes. Correlations between the formation of aliphatic and olefinic/aromatic moieties with post-reaction characterization leads to the proposal of a number of chemical transformations that, collectively, define the conditioning phase of the catalyst under the specified set of reaction conditions. A comparison between the inelastic neutron scattering spectra of the 24 h sample with that of an iron catalyst extracted from a commercial grade Fischer–Tropsch reactor validates the relevance of the experimental approach adopted. Publisher PDF

A proxy-based high-throughput experimental approach was used to explore the stability and activity of Co-based Fischer Tropsch Synthesis catalysts with different promoters on various supports. The protocol is based on the estimation by XRD of active phase, Co, particle size and relative amounts of crystalline phases, Co to support. Sequential libraries samples enabled exploration of four Co loadings with five different promoters on six support materials. Catalysts stable to aging in syngas, displaying minimal change of particle size or relative area, were evaluated for their activity under industrial conditions. This procedure identified SiC as support for stable catalysts and a combination of Ru and Hf to promote the formation hcp Co. Unsupported bulk samples of Co with appropriate amounts of Ru and Hf revealed that the formation of hcp Co is independent of the support. The hcp Co containing catalyst presented the highest catalytic activity and C5+ selectivity amongst the samples tested in this study confirming the effectiveness of the proxy-based high-throughput method.

A series of tert-butyl-substituted pincer ligands based on 1,3-diaminobenzene and 3-aminophenol scaffolds, tBu4PXCYP (1e, X = Y = NH; 1f, X = NH; Y = O) and the corresponding iridium hydridochloro complexes (tBu4PXCYP)IrHCl (2e, X = Y = NH; 2f, X = NH; Y = O) were prepared with moderate yields and high purity and were fully characterized by 1H and 31P NMR spectroscopy. Unsymmetrical hybrid pincer ligands R2PNCOPtBu2 (1g, R = isopropyl; 1h, R = cyclohexyl) were prepared conveniently in high yield via a one-pot procedure by judiciously choosing reaction conditions and base; the corresponding iridium hydrido chloro complexes iPr2PNCOPtBu2IrHCl (2g) and Cy2PNCOPtBu2IrHCl (2h) were synthesized by the reaction of [IrCl(COE)2]2 with ligands. X-ray crystallography reveals that these iridium pincer complexes adopt similar square-pyramidal geometries and exhibit strong intermolecular hydrogen bonding between the NH linker and chloride ions of the adjacent iridium complex in the solid state. 1H NMR chemical shifts o...

The presence of traces of sulfur dioxide (i.e. 1–10 ppmV) alongside residual methane emissions induces the rapid deactivation of typical methane abatement catalysts. As a result, sulfur-induced poisoning is the main challenge faced by after-treatment technologies for residual methane abatement. The aim of this study was to synthesise a series of cobalt and molybdenum catalysts and assess their performance under realistic after-treatment conditions. The series of catalysts was characterised by BET, XRD, XPS, TPR, TGA under air flow, SEM, EDX and in situ DRIFTS. In addition, the performance of Co100 supported on an alumina hollow fibre was assessed under similar reaction conditions and characterised by SEM and EDX. It was found that the catalytic activity of the series of cobalt and molybdenum catalysts decreased in the following order: Co100 > Co80Mo20 > Co60Mo40. In addition, it was discovered that the other two catalysts (i.e. Co25Mo75 and Mo100) were inactive at 450 °C due to the lack of highly active Co3+ species. Among the active catalysts, Co100 and Co80Mo20 experienced an initial activation followed by a gradual deactivation whereas Co60Mo40 experienced a 1 h interval with stable methane conversion levels in between the activation and deactivation. The delay in poisoning of the active cobalt (II,III) oxide phase of Co60Mo40 was attributed to the sulfur sink-properties of the cobalt molybdenum oxide present in this catalyst (i.e. 44 wt%). Finally, Co100 supported on an alumina hollow fibre achieved the highest methane conversion per unit mass of catalyst and its performance was stable for a duration of 2.5 h. The high activity was attributed to the large surface area provided by the geometry of the support while the higher resistance to sulfur poisoning was credited to the sulfur sink-properties of the alumina, which delayed the poisoning of the active phase.

Sasol Ltd., the University of Glasgow and the EPSRC (grant numbers EP/P504937/1 and EP/P505534/1) are thanked for the provision of postgraduate studentships (RW and ALD). The STFC Rutherford Appleton Laboratory is thanked for access to neutron beam facilities. The Royal Society is thanked for the provision of an Industrial Fellowship (PBW). Fischer-Tropsch synthesis (FTS) is commonly viewed as an alternative approach to the production of diesel fuels via sources independent of crude oil. The adaptability of the FTS process allows for the selective production of shorter chain C2 to C6 hydrocarbons and has the potential to be a legitimate source of useable chemical feedstocks with high value to the chemical manufacturing industry. Interestingly, although recognised as a poison in most catalytic systems, small amounts of sulfur in iron-based FTS catalysts has been demonstrated to promote catalyst reducibility and activity towards shorter chain hydrocarbons. However, it is not known what impact sulfur has on the formation of hydrocarbonaceous surface species that have been proposed to play a pivotal role in the mediation of reactants during iron FTS. Here we apply ambient pressure CO hydrogenation at 623 K on a selection of sulfur promoted iron FTS catalysts to investigate the effect of sulfur content on hydrocarbonaceous species formation. For the first time, we report the application of inelastic neutron scattering to quantify the presence of hydrocarbonaceous species under the presence of sulfur promotion. In combination with temperature programmed oxidation, X-ray diffraction, and Raman spectroscopy, we observe how low sulfur loadings (

A range of iridium complexes, Ir(η3-C3H5)(CO)(PR2R')2 (1a-1e) [where 1a, PR2R' = PPh3, 1b P(p-tol)3, 1c PMePh2, 1d PMe2Ph and 1e PMe3] were synthesized and their reactivity as stoichiometric hydroformylation precursors studied. Para-hydrogen assisted NMR spectroscopy detected the following intermediates: Ir(H)2(η3-C3H5)(CO)(PR2R') (2a-e), Ir(H)2(η1-C3H5)(CO)(PR2R')2 (4d-e), Ir(H)2(η1-C3H5)(CO)2(PR2R') (10a-e), Ir(H)2(CO-C3H5)(CO)2(PR2R') (11a-c), Ir(H)2(CO-C3H7)(CO)2(PR2R') (12a-c) and Ir(H)2(CO-C3H5)(CO)(PR2R')2 (13d-e). Some of these species exist as two geometric isomers according to their multinuclear NMR characteristics. The NMR studies suggest a role for the following 16 electron species in these reactions: Ir(η3-C3H5)(CO)(PR2R'), Ir(η1-C3H5)(CO)(PR2R')2, Ir(η1-C3H5)(CO)2(PR2R'), Ir(CO-C3H5)(CO)2(PR2R'), Ir(CO-C3H7)(CO)2(PR2R') and Ir(CO-C3H5)(CO)(PR2R')2. Their role is linked to several 18 electron species in order to confirm the route by which hydroformylation and hydrogenation proceeds.

A series of iron and chromium-based oxides were used as catalysts for the total oxidation of residual methane under realistic after-treatment conditions. This study operated with sulfur dioxide, steam and methane concentrations similar to those typically found in natural gas turbines and natural gas-powered vehicle exhausts (around 4.6 ppmV of sulfur dioxide and 10%vol of steam alongside 312 ppmV of methane balanced in air). The catalysts were synthesised using the citrate sol-gel method and characterised by BET, XRD, TPR, in situ UV–vis, in situ DRIFTS, SEM, EDX, TEM and TGA under flowing air. The performance of the catalysts was tested at atmospheric pressure and operating temperatures between 450 °C and 550 °C using three different reactant mixtures: i) 366 ppmV of methane balanced in air, ii) 347 ppmV of methane and 5.1 ppmV of sulfur dioxide balanced in air, iii) 312 ppmV of methane, 4.6 ppmV of sulfur dioxide and 10%vol steam balanced in air. This study revealed that the iron:chromium ratio has a profound impact on the performance of the catalysts. The XRD characterisation revealed that the iron and chromium-based oxides are solid solutions of hematite and eskolaite. Furthermore, the iron oxide-rich catalysts (60%mol to 80%mol iron content) contain an additional phase, which was identified as a metastable FeCr2O4 mixed oxide with spinel structure. In terms of catalytic activity, resistance to sulfur poisoning and sensitivity towards steam inhibition, these two catalysts were superior to pure iron oxide and comparable to pure chromium oxide. Under dry conditions, these two catalysts achieved higher methane conversion levels than pure chromium oxide, suggesting that the metastable FeCr2O4 spinel gives rise to improved catalytic performance. Finally, this study has proven that the sulfur resistance characteristic of chromium oxide is maintained in iron and chromium-based oxides with a chromium oxide loading as low as 20%mol, resulting in similarly effective catalysts with a lower cost, a reduced environmental impact and a considerable reduction in the health hazards associated with the exposure to chromium.

Hexagonal close packed dumbbell-shaped cobalt nanoparticles (Co 0 -hcp) have been fabricated by the polyol method. The thermal stability of these Co 0 -hcp nanoparticles has been studied under Fischer-Tropsch Synthesis (FTS) relevant environments such as H 2 and H 2 /CO by using SiO 2 /SiN x TEM grids which allowed the structural changes of individual particles to be followed after each off line treatment. The TEM analyses demonstrated that the Co 0 -hcp nanodumbbells are very stable when thermally treated in H 2 at 250 °C for 9 h followed by H 2 /CO at 230 °C, 16 bar for 5 h. These studies indicate that the hcp phase of Co is retained after FTS. Furthermore, subjecting the cobalt nanodumbbells to regeneration conditions such as reduction followed by oxidation led to hollow nanodumbbells with a polycrystalline cobalt oxide (Co 3 O 4 ) shell (so-called Kirkendall effect) which disintegrated to smaller face centered cubic metallic cobalt (Co 0 -fcc) particles after further reduction.

The effect of a hydrogen pre-treatment step on an iron based Fischer–Tropsch catalyst applied to the CO hydrogenation reaction at 623 and 723 K has been investigated by inelastic neutron scattering (INS). The catalyst cannot support methane production over a 6 h period of reaction at 623 K but it is active at 723 K. The INS spectrum indicates the presence of a predominantly aliphatic hydrocarbonaceous overlayer for the post-reaction 623 K sample, whereas the spectrum for the 723 K sample is assigned to an overlayer comprising partially hydrogenated polycyclic aromatic compounds. The hydrocarbonaceous overlayer associated with the active phase of the catalyst is modified by the hydrogen pre-treatment step. The INS spectra are interpreted with reference to microreactor studies, powder X-ray diffraction, temperature-programmed oxidation and transmission electron microscopy. The hydrogen pre-treatment stage favours the formation of amorphous carbon and is deemed not to convey any advantage with respect to CO hydrogenation activity.

A Sc NHC complex readily activates three equivalents of CO2 showing ‘Frustrated Lewis Pair’ type reactivity with each metal–carbene bond, but whilst CS2 is also activated by the labile carbenes, no metal involvement is observed.\ud Graphical abstract: Activation of carbon dioxide and carbon disulfide by a scandium N-heterocyclic carbene complex

Direct conversion of methane to methanol (DMTM) has become a particularly attractive route for the functionalisation of natural gas. Here the proven capability of copper-exchanged ZSM-5 zeolites to carry out DMTM at mild conditions has been extended by also demonstrating its capability to perform repeated reactions in a concept known as cycling. A series of five copper-exchanged ZSM-5 zeolites with different Si:Al ratio were prepared via aqueous ion exchange. The materials characterisation was carried out using a combination of transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption isotherms at −196 °C (BET and BJH methods), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and in-situ ultraviolet-visible spectroscopy (UV–vis) techniques. Under mild isothermal conditions (air activation; T = 200 °C; P = 1 atm), methanol productions of 2.8 ± 0.1 μmol·gcat−1, 26.6 ± 0.1 μmol·gcat−1, 12.5 ± 0.1 μmol·gcat−1, 10.8 ± 0.1 μmol·gcat−1 and 3.2 ± 0.1 μmol·gcat−1 were achieved for copper-exchanged ZSM-5 containing 20:1, 30:1, 50:1, 80:1, and 200-400:1 Si:Al ratio, respectively. Comparing the results of cycling Cu-ZSM-5 (Si:Al = 200-400:1) with those obtained for Cu-ZSM-5 (Si:Al = 30:1) has led to the conclusion that hydrophobicity plays a decisive role in the capability to cycle, with materials containing a higher Si:Al being better suited to cycling. A total of five repeated cycles were achieved using Cu-ZSM-5 (Si:Al = 200-400:1). The methanol production was higher, the lower the Si:Al ratio with an optimal Si:Al = 30:1. However, TEM analysis suggests that precipitation of copper nanoparticles on the catalyst support structure could account for the reduced activity found within the material containing the lowest Si:Al. in situ UV-vis spectroscopy characterisation of the copper-exchanged ZSM-5 zeolite materials under similar DMTM reaction conditions suggested that active copper complexes were being created and then destroyed during the DMTM reaction. A speculative discussion of the copper complexes present within these materials has also been provided.

Inelastic neutron scattering (INS) has been used to obtain the vibrational spectrum of a technical-grade iron-based Fischer–Tropsch catalyst that has been taken from an industrial large-scale unit operation. Whereas previous reports on iron Fischer–Tropsch catalysts highlight the presence of retained carbonaceous species, the INS spectra reveal the additional presence of partially hydrogenated aromatic molecules.

The synthesis and full characterization of the unprecedented open-shell Cr(II) benzyl organometallic complexes [Cr(NHC)2(benzyl)2] (2) and [Cr(NHC*)(benzyl)2] (3) (NHC = N,N′-diisopropylimidazol-2-ylidene; NHC* = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) from [Cr(benzyl)3(THF)3] and [CrCl2(THF)2]/[Mg(benzyl)2], respectively, uncovered unusually acute angles (93° in 2 and 76° in 3) at the sp3 benzylic C of the coordinated benzyl ligands. Detailed theoretical analyses (DFT and CASPT2) of the four- and three-coordinate Cr(II) species were performed to elucidate the physical origin of the benzyl bending and led to the recognition of a noncovalent, intramolecular polarization-induced metal–arene (PIMA) interaction as being responsible for it. The energetic contribution from a single PIMA interaction is estimated to be ca. 50 kJ/mol. A comparison with the origin of the angular distortions in the d0 [Zr(benzyl)4] complex will also be presented. Sharing the common origin of an induced-dipole charge densi...

Scandium trichloride complexes with tridentate N(3)- and S(2)N-donor ligands (L(3)) have been synthesised and characterised by IR, (1)H, (13)C{(1)H} and (45)Sc NMR spectroscopy, microanalysis, and solid state and solution XAFS spectroscopy. Catalytic testing of a subset of these complexes with ethene has been undertaken in chlorobenzene with MMAO-3A and PMAO-IP at 60 °C and 40 bar ethene, giving low activity ethene polymerisation. The reactions of these complexes with MeLi and AlMe(3) were studied by (1)H, (13)C{(1)H}, (27)Al and (45)Sc NMR spectroscopy and in situ via Sc K-edge XAFS spectroscopy. Three or four mol. equivalents of MeLi react with [ScCl(3)(Me(3)-tacn)] in THF solution to form [ScMe(3)(Me(3)-tacn)] cleanly, while complexes of type [ScCl(3)(R-SNS)] {R-SNS = HN(CH(2)CH(2)SC(10)H(21))(2)} form two different species proposed to be [ScMe(3)(R-SN(Li)S)] and [ScMe(2)(R-SN(-)S)]. In contrast, in situ(45)Sc NMR and Sc K-edge XAFS spectroscopic studies of the reaction of [ScCl(3)(Me(3)-tacn)] with 10 mol. equivalents of AlMe(3) strongly suggest that alkylation at the Sc(III) centre does not occur, instead retaining the Cl(3)N(3) coordination environment and most likely forming Sc-Cl-AlMe(3) bridging interactions. Similar studies on [ScCl(3)(decyl-SNS)] with 10 mol. equivalents of AlMe(3) are also consistent with this, indicating that alkylation at the Sc centre does not occur except in the presence of co-catalyst [Ph(3)C][Al{OC(CF(3))(3)}(4)] and the α-alkene, hex-1-ene.

The ready construction of 24 stereochemically and functionally diverse carbohydrate ligand structures from a core D-glucosamine scaffold has allowed the evaluation of broad ranging structure activity relationships in ligand accelerated zincate additions to aldehydes, with variations in deltadeltaG+/+(R-S) of up to 5650 J mol(-1) that create opposing senses of asymmetric induction and that are consistent with models based on several ligand X-ray structures and molecular mechanics analysis. Factorial analysis of enantioselectivity using key dihedral angles and steric volume on N-2 also highlight the potential for the use of factorial design in ligand construction.

The electrocatalytic reduction of CO2 at carbon-supported Au-Pd core–shell nanoparticles is investigated systematically as a function of the Pd shell thickness. Liquid- and gas-phase products were determined by off-line 1H NMR spectroscopy and on-line electrochemical mass spectrometry. Our results uncover the relationship between the nature of the products generated and the Pd shell thickness. CO and H2 are the only products generated at 1 nm thick shells, whereas shells of 5 and 10 nm produced HCOO−, CH4 and C2H6. The concentration of HCOO− detected in the electrolyte was dependent on the applied potential and reached a maximum Faradaic efficiency of 27 % at −0.5 V versus the reversible hydrogen electrode for 10 nm thick shells. We conclude that collisions between absorbed hydrogen at relaxed Pd lattices and strongly bound “CO-like” intermediates promote the complete hydrogenation to C1 and C2 alkanes without the generation of other products, such as alcohols and aldehydes.

We report a facile biomimetic sol-gel synthesis using the sponge phase formed by the lipid monoolein as a structure-directing template, resulting in high phase purity, mesoporous dysprosium- and gadolinium titanates. The stability of monoolein in a 1,4-butanediol and water mixture complements the use of a simple sol-gel metal oxide synthesis route. By judicious control of the lipid/solvent concentration, the sponge phase of monoolein can be directly realised in the pyrochlore material, leading to a porous metal oxide network with an average pore diameter of 10 nm.

The chromium(III) complexes of the type L1CrXY (L1 = 1-(2,6-diisopropylphenyl)-3-[β-(4,7-dimethylindenyl)ethyl]-imidazol-2-ylidene, X, Y = Cl, 2a-Cl; X = Cl, Y = Me, 2a-Me; X = Cl, Y = Ph, 2a-Ph; X, Y = benzyl, 2a-Bz) and L2CrCl2 (L2 = 1-(2,6-diisopropylphenyl)-3-[γ-(4,7-dimethylindenyl)propyl]-imidazol-2-ylidene, 2b-Cl) have been prepared and characterized by analytical and diffraction methods. The salts [L1CrCl(THF)]+[BArF4]− and [L2CrCl(THF)]+[BArF4]− (ArF = 3,5-bis(trifluoromethyl)phenyl) were also characterized, having been obtained by abstraction of chloride, or indirectly a methyl, from 2a-Cl or 2a-Me, and 2b-Cl, by NaBArF4, respectively. Reaction of 2a-Bz with 1 equiv of [H(Et2O)2][BArF4] in THF gave the thermally unstable salt [L1Cr(Bz)(THF)]+[BArF4], [2a-Bz]+[BArF4], which was also characterized crystallographically. The chromium(II) analogue L1CrCl, 3a, was prepared from CrCl2 and L1K, but on prolonged standing in THF, it converted to the dimeric complex 4a. The complexes 2a-Cl, 2b-Cl, 2b-Me, a...

Our novel and facile synthesis of ruthenium nanostars opens the door to the shape control of previously inaccessible sophisticated and monodisperse ruthenium nanomaterials. The metallic state and hexagonal close-packed (hcp) structure of the Ru nanostars, which are approximately 15 nm across, were determined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). These materials can also act as seeds for the first preparation of ruthenium nanourchins. In addition, we have shown that they are as catalysts for the activation of CO and C═C bonds, since Fischer–Tropsch and solvent-free hydrogenation reactivities were observed on these unsupported materials.

Oxidative halogenation with trityl chloride provides convenient access to CeIV and UIV chloroamides [M(N{SiMe3}2)3Cl] and their N-heterocyclic carbene derivatives, [M(L)(N-{SiMe3}2)2Cl] (L= OCMe2CH2(CNCH2CH2NDipp) Dipp=2,6-iPr2C6H3). Computational analysis of the bonding in these and a fluoro analogue, [U(L)(N{SiMe3}2)2F], provides new information on the covalency in this relative rare oxidation state for molecular cerium complexes. Computational studies reveal increased Mayer bond orders in the actinide carbene bond compared with the lanthanide carbene bond, and natural and atoms-in-molecules analyses suggest greater overall ionicity in the cerium complexes than in the uranium analogues.

The synthesis of four new bulky bidentate phosphines that possess both tert-butyl and trifluoromethylphenyl substituents is described. Symmetric ligands were readily obtained by alkylation of phosphidoboranes of the type Li[P(BH(3))(tBu)(Ar)] with dihaloalkanes. Non-symmetric ligands were prepared from a new stable precursor, tBu(2)P(BH(3))(CH(2))(3)Br, that should prove useful for other ligand syntheses. Palladium(II) complexes of the four new ligands were prepared and were characterised by spectroscopic methods, microanalysis and X-ray crystallography. The new [PdCl(2)(L)] complexes were evaluated as catalysts for the hydroxycarbonylation of styrene and found to give unprecedented regioselectivity and yields for a diphosphine-based catalyst. A study on promoter effects reveals that the presence of acid and chloride is necessary to achieve such selectivities. It has been proposed in the literature that such conditions result in a new pathway in which styrene is converted into 2-phenethyl chloride, with the latter being the real substrate in the reaction. However, a deuterium labelling study seems to rule out this mechanism, at least under the conditions used herein.

Synthetic, structural, and catalytic studies of a series of molybdenum complexes with the tridentate “SNS” ligands bis(decylthioethyl)amine and bis(ethylthioethyl)amine are reported. Complexes with a range of molybdenum oxidation states {(0), (III), and (IV)} have been accessed synthetically in high yields from readily synthesized starting materials. The formation of an unexpected dimeric molybdenum(I) structure is also reported. Where possible, the complexes have been converted to salts of the weakly coordinating tetrakis(perfluoro-tert-butoxy)aluminate anion. The complexes have been screened for ethylene oligomerization activity with a number of aluminum cocatalysts.

Dimethylindenyl-functionalized N-heterocyclic carbene complexes of titanium(IV), titanium(III), zirconium(IV), and vanadium(III) were prepared from potassium indenylcarbenes by salt elimination reactions. X-ray diffraction studies revealed that in the complexes the ligand adopts a bidentate coordination mode. Alkanolysis of a dimethylindene-functionalized imidazolium salt with Y(CH2SiMe3)3(THF)2 gave rise to a dimeric yttrium bromo alkyl in which the ligand adopts a bidentate coodination mode. Aminolysis of the fluorene-functionalized imidazolium salts with {[Cr(N(SiMe3)2)2(THF)2} led to chromium(II) complexes in which the ligand adopts a monodentate binding mode via the N-heterocyclic carbene end with dangling fluorene groups.

The trimerization and tetramerization of ethylene to 1-hexene and 1-octene with a Cr/PNP/AlEt3 catalyst system, in combination with a variety of cocatalysts, has been investigated. The cocatalysts B(C6F5)3 (1), Al(OC6F5)3 (2), [(Et2O)2H][Al(OC6F5)4] (3), [Ph3C][Ta(OC6F5)6] (4), (Et2O)Al{OCH(C6F5)2}3 (5), (Et2O)Al{OC(CF3)3}3 (6), [Ph3C][Al{OC(CF3)3}4] (7), [Ph3C][AlF{OC(CF3)3}3] (8), [Ph3C][{(F3C)3CO}3Al−F−Al{OC(CF3)3}3] (9), and [Ph3C][CB11H6Br6] (10) have been evaluated. The relative selectivity to 1-hexene and 1-octene obtained shows a strong dependence on the nature of the cocatalyst, and a range of selectivities from

Various [Cr(CO)4(P∩P)]+ complexes have been synthesized and tested for the tetramerization of ethylene to give principally 1-octene. The effect of the anion has been investigated, and it has been found that for successful catalysis an extremely weakly coordinating anion is required. This study shows that when [Al(OC(CF3)3)4]- is employed as the anion, along with triethylaluminum and PNPiPr as the coordinated diphosphine, the system is active for the tetramerization of ethylene. This is the first example of CrI being used as a catalyst precursor for selective tetramerization and gives evidence toward the catalytic cycle acting through a CrI → CrIII cationic mechanism.

Chromium-based ethylene tri- and tetramerization catalysts have been evaluated with a combination of trialkylaluminium and borate cocatalyst activation. A remarkable effect on activity and selectivity has been observed and studied, and a cocatalyst-induced degradation pathway has been identified.

The phoban-indenylidene complex is a robust catalyst for self-metathesis and ethenolysis reactions of methyl oleate. The phoban-indenylidene catalyst was characterized by X-ray analysis, NMR and microanalysis and was used in various self-metathesis and ethenolysis of methyl oleate, giving rise to significantly higher end of run conversions compared to Grubbs 1st generation catalyst. These complexes are more stable and active than commercial Grubbs 1st generation catalyst, can be accessed from simple precursors and should give rise to more economical metathesis processes.

Selected PNP and SNS ethylene trimerization ligands have been coordinated to CrII and CrIII, and further reactions of these complexes have been studied. The ligands are easily deprotonated to affor...

The performance of certain olefin metathesis reactions catalyzed by Grubbs catalysts has been enhanced by the simple addition of phenol. Addition of phenol to self-metathesis reactions catalyzed by 1 produced very small quantities of unwanted byproducts and allowed for room-temperature metathesis at high substrate:catalyst loadings. The efficiency of cross-metathesis reactions between methyl acrylate and 1-decene catalyzed by 2 was also significantly increased by addition of p-cresol to the reaction mixture. Mechanistic studies, including NMR spectroscopy and DFT calculations, established that phenol is playing a number of positive roles in the active metathesis cycle, including altering the relative rates of phosphine loss and rebinding, activating the carbene carbon for reaction with olefinic substrate, and hemilabile stabilization of the key 14-electron intermediate species.

New ruthenium carbene complexes 5 and 6, containing a rigid bicyclic phosphine moiety, have been prepared, and the structure of 5 has been unambiguously established by single-crystal X-ray diffraction studies. These ruthenium-based complexes show excellent stability to air and moisture, can be recycled by chromatography, and are available from simple precursors. They are efficient catalysts for various metathesis reactions, particularly for applications where high selectivity is required.

The sequence of reaction steps and the role of each reactant, required for the transformation of the Pd(0) precursor [Pd(dtbpx)(dba)] [dtbpx = 1,2-(CH2PBut2)2C6H4; dba = trans,trans-(PhCHCH)2CO], 1, into [Pd(dtbpx)H(MeOH)]+, 2a, the active Pd(II)-hydride catalyst for the methoxycarbonylation of ethene to methylpropanoate, have been delineated using a combination of spectroscopic and crystallographic methods. The preparation and characterisation of a variety of related complexes are described including some unusual examples involving bidentate sulfonate complexes and mono-cationic and neutral palladium hydride complexes. X-Ray crystal structures have been determined for [Pd(dtbpx)(η2-O2)], 3, [Pd(dtbpx)(η2-BQ)] (BQ = benzoquinone), 4, [Pd(dcpx)(dbaH)]+ [dcpx = 1,2-(CH2PCy2)2C6H4], 7, and [Pd(dtbpx)(η2-MeSO3)]+, 9b.

A detailed spectroscopic study has allowed the solution structure and dynamic properties of all the intermediates in the Pd-catalyzed methoxycarbonylation of ethene to be established. [Pd(L−L)H(solv)]+ 1 (L−L = 1,2-(CH2PBut2)2C6H4; solv = MeOH, 1a; PrnOH, 1b; THF, 1c; EtCN, 1d) is static, and the two inequivalent P atoms do not become equivalent through solvent exchange over all the temperatures studied. 2, contains a strong β-agostic C−H interaction which is remarkably stable and is not displaced even in strongly coordinating solvents such as EtCN. Cα and Cβ of the ethyl group in 2 become equivalent via a stereospecific interchange involving [Pd(L−L)H(η2-C2H4)]+ without making the two P atoms equivalent; at higher temperatures these two inequivalent P atoms do become equivalent probably via a T-shaped intermediate. For [Pd(L−L)(C(O)Et)(solv)]+, 6, there is no β-agostic C−H interaction and multiple 13C-labeling of the C(O)Et group shows that the inequivalent P atoms become equivalent via movement of the i...

Reaction of ethene with CO in CH3OD in the presence of a catalyst prepared in situ from [Pd(DBPMB)(DBA)] (DBPMB = 1,2-bis[(di-tert-butyl)phosphinomethyl]benzene, DBA = dibenzylideneacetone) and methanesulfonic acid under conditions of good gas mixing gives a 1 ∶ 1 mixture of CH2DCH2CO2Me and CH3CHDCO2Me with no H incorporated into the CH3OD. If the gas mixing is less efficient, the methyl propanoate has 0–5 D atoms incorporated in the ethyl group, CH3OD exchanges to give increasing amounts of CH3OH throughout the reaction and there is a slight increase in the less deuteriated products with reaction time. Significant D incorporation into unreacted ethene is also observed. These results are interpreted in terms of a hydride mechanism with the rates of the individual steps under conditions of good mixing being: reversible H migration to coordinated ethene > CO coordination ≫ C2H4 exchange > H/D exchange.

A simple coordination complex of uranium(III), a uranium tris(amide), can selectively couple gaseous CO to the linear ynediolate [OCCO]2- dianion, at room temperature and pressure, regardless of the reagent stoichiometry. This product exhibits further reactivity upon warming in the form of the addition of a C-H bond of a methyl group across the C≡C triple bond, this second carbon-carbon bond forming reaction generating a functionalised enediolate dianion.

The reactivity of a series of organometallic rare earth and actinide complexes with hemilabile NHC-ligands towards substrates with acidic C-H and N-H bonds is described. The synthesis, characterisation and X-ray structures of the new heteroleptic mono- and bis(NHC) cyclopentadienyl complexes LnCp2(L) 1 (Ln = Sc, Y, Ce; L = alkoxy-tethered carbene [OCMe2CH2(1-C{NCHCHNiPr})]), LnCp(L)2 (Ln = Y) 2, and the homoleptic tetrakis(NHC) complex Th(L)4 4 are described. The reactivity of these complexes, and of the homoleptic complexes Ln(L)3 (Ln = Sc 3, Ce), with E-H substrates is described, where EH = pyrrole C4H4NH, indole C8H6NH, diphenylacetone Ph2CC(O)Me, terminal alkynes RC[triple bond, length as m-dash]CH (R = Me3Si, Ph), and cyclopentadiene C5H6. Complex 1-Y heterolytically cleaves and adds pyrrole and indole N-H across the metal carbene bond, whereas 1-Ce does not, although 3 and 4 form H-bonded adducts. Complexes 1-Y and 1-Sc form adducts with CpH without cleaving the acidic C-H bond, 1-Ce cleaves the Cp-H bond, but 2 reacts to form the very rare H+-[C5H5]--H+ motif. Complex 1-Ce cleaves alkyne C-H bonds but the products rearrange upon formation, while complex 1-Y cleaves the C-H bond in diphenylacetone forming a product which rearranges to the Y-O bonded enolate product.

The C4-bridged diphosphines cis- and trans-1,2-bis(diphenylphosphinomethyl)cyclohexane (cis, 1a; trans, 1b) and endo,endo-2,3-bis(diphenylphosphinomethyl)norbornane and exo,endo-2,3-bis(diphenylphosphinomethyl)norbornane (endo,endo, 1c; exo,endo, 1d) and their corresponding palladium complexes [(P−P)PdCl2] (2a−d), [(P−P)Pd(OAc)2] (3a−d), and [(P−P)PdMeCl] (P−P = 1a, 4a; P−P = 1c, 4c) have been prepared and characterized. Single-crystal X-ray analysis of 2a reveals that 1a forms a seven-membered chelate ring with the cis-disubstituted cyclohexyl ring in the expected chair conformation. Variable-temperature 31P{1H} NMR studies of 2a have revealed a dynamic process that interchanges stereoisomers via conformational changes in the six-membered ring, often characteristic of cis-disubstituted cyclohexane derivatives. The free energy of activation associated with this exchange has been determined (ΔG⧧ = 48 kJ mol-1, 2a). Variable-temperature 31P{1H} and 31P NOESY NMR studies have shown that 4a exist as an interc...

The fused tricyclic dialkyl(phenyl)phosphine, 1,1,6,6-tetramethylphosphajulolidine 11, has been synthesised on a large scale with a view to verifying a computationally derived theory of ligand influence upon the catalytic alkoxycarbonylation of propyne.

Analysis of the phosphorus containing by-products from the catalytic methoxycarbonylation of ethene using a palladium triphenylphosphine complex with a combination of High Performance Liquid Chromatography (HPLC) and Mass Spectrometry (MS) indicated increasing levels of phosphonium salts through the course of the reaction, major ones being methyltriphenylphosphonium, ethyltriphenylphosphonium and 3-oxopentyltriphenylphosphonium (CH3CH2C(O)CH2CH2PPh3) cations, isolated as the sulfonate salts. The latter are shown to be produced by metal mediated pathways and believed to be indicative of the operation of the hydride mechanism.

The zerovalent complexes Pd(Ph2Ppy)31 and Pd(Ph2Ppy)2(dba) 2, where Ph2Ppy is diphenyl-2-pyridylphosphine and dba = trans,trans-dibenzylideneacetone, have been synthesized and characterised. Reactions of 1 with alkynes have been studied and the dimethyl acetylenedicarboxylate complex Pd(Ph2Ppy)2(η2-DMAD) 3, where DMAD is dimethyl acetylenedicarboxylate, isolated and structurally characterised. The complexes trans-Pd(Ph2Ppy)2(PhC[double bond, length half m-dash]CH2)X, X = CF3CO2−4 or Cl−5, and trans-Pd(Ph2Ppy)2{CO(CH3)C[double bond, length half m-dash]CH2}Cl 6 result from oxidative addition of phenylacetylene/CF3CO2H, phenylacetylene/Et3NHCl and methacryloyl chloride respectively to 1, and the crystal structure of 4 is presented. The alkenyl ligand is bound to palladium through the α carbon in 4. Insertions into the M–C bond of the vinyl complexes have been studied. No isolable insertion product is obtained with carbon monoxide although the complex is active for the catalytic alkoxycarbonylation of phenylacetylene to 2-phenylpropenoate. Propadiene inserts into the Pd–C bond in 4 to give the cationic π-allyl complex [Pd(Ph2Ppy)2{η3-C3H4C(Ph)[double bond, length half m-dash]CH2}][CF3CO2] 7. The complex Pd(Ph2Ppy)3 is found to catalyse the vinylation of Ph2Ppy to the corresponding 2-propenylphosphonium trifluoromethanesulfonate.

A series of phosphorus−nitrogen−phosphorus (PNP) ligands of the type R−N(CH2CH2PPh2)2 (R = C(O)(C6H4OMe-p), tBu, Ph, C6H4OMe-p) have been prepared. Their coordination chemistry to palladium(II) and palladium(0) complexes was examined using a combination of X-ray crystallography, NMR, and electrochemical techniques. The palladium(0) complexes undergo reactions with aryl iodides to give the palladium(II) complexes [Pd(Ar){R−N(CH2CH2PPh2)2}]+I-, where the rate of oxidative addition was found to be dependent on the nature of the aryl group, as well as the substitution on nitrogen.

The alkoxycarbonyl complexes Pd(Ph2Ppy)2(CO2R)(OAc) where Ph2Ppy is 2-pyridyldiphenylphosphine and R = Me 1, Et 2, i-Pr 3 have been prepared from Pd(OAc)2 and Ph2Ppy in ethanol solution under an atmosphere of CO. Increasing the CO pressure favours the formation of palladium carbonyl species. In the presence of 2 mol equivalents of CF3CO2H, the complex Pd(Ph2Ppy)2(CO2CH3)(CF3CO2) 4 is isolated from methanol. Pd(Ph2Ppy)2(CO2CH3)Cl 5 has been obtained by the reaction of Pd(Ph2Ppy)2Cl2 with NaOCH3 in the presence of CO. 1 and 5 have been crystallographicaly characterised as trans isomers, a geometry confirmed for all the complexes by 13C NMR. The reactivity of the complexes toward alkynes and propadiene has been investigated and the π-allyl complex [Pd(Ph2Ppy)2{η3-C3H4C(CH3)[double bond, length half m-dash]CH2}][O2CCF3] 8 isolated and structurally characterised.

The disproportionation of dicobalt octacarbonyl induced by the free carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and the X-ray characterization of the cyclohexane solvate of the resulting cobalt carbonyl N-heterocyclic carbene salt, [Co(CO)3(IMes)2]+[Co(CO)4] -·1/4C6H12, is reported. The crystal structure represents the first example of a [Co(CO)3(L)2][Co(CO)4] disproportionate salt reported to date.

The stoichiometric reaction of diphenyl-2-pyridylphosphine (Ph2PC5H4N-2) and palladium(II) acetate afforded the palladium(I) dimer [Pd2(µ-Ph2PC5H4N)2(OAc)2] 1. Attempts to isolate the monomer, [Pd(µ-Ph2PC5H4N)2(OAc)2], from 2∶1 stoichiometry reactions (Ph2PC5H4N∶Pd), resulted only in the isolation of 1. When >3 mole equivalents of Ph2PC5H4N were used the zerovalent palladium complex [Pd(Ph2PC5H4N)3] was isolated. Other palladium(I) dimers with carboxylic or sulfonic anionic ligands have been prepared by a metathesis reaction of the co-ordinated acetates. The complexes 1 and [Pd2(µ-Ph2PC5H4N)2(O2CCF3)2] 2 have been structurally characterised as head-to-tail dimers. The mononuclear complex [Pd(Ph2PC5H4N)2(O2CCF3)2] has been obtained by reaction of Ph2C5H4N with [Pd(CH3CN)2(O2CCF3)2]. Complex 1 reacts with dimethyl acetylenedicarboxylate to give [Pd2(µ-Ph2PC5H4N)2(OAc)2(µ-MeO2CCCCO2Me)], while attempts to isolate an A-frame carbonyl complex were unsuccessful.

Palladium chloro complexes reacted with 9-phenyl-9-phosphabicyclononanes (PPBN) and 1-phenylphospholane and gave trans-chlorobis(phosphine)palladium(II) complexes, 1-phenylphospholane also gave rise to a chloro-bridged dimer. With palladium acetate, the two isomers of PPBN (9-phenyl-9-phosphabicyclo-[3.3.1]nonane and-[4.2.1]nonane, 3,3,1-PPBN and 4,2,1-PPBN respectively) formed trans bis(phosphine) complexes exclusively whereas 1-phenylphospholane formed the cis-bis(phosphine) complex; examples of both trans and cis complexes have been structurally characterised. The acetate groups were readily replaced by sulfonic and phosphonic acids to give sulfonato and phosphonato complexes respectively. Reduction of the acetato–4,2,1-PPBN complex to [Pd 0 (4,2,1-PPBN) 3 ] occurred in alcoholic media readily, however the isomeric 3,3,1-PPBN complex was considerably more resistant to reduction. Abstraction of halide from both dichloro–PPBN complexes by Ag(O 3 SCF 3 ) in ethanol resulted in the formation of phosphonium salts.

Morphologically similar cobalt oxide nanoparticles (Co3O4) of four different sizes (3 nm, 6 nm, 11 nm and 29 nm) with narrow size distribution were prepared by subtle variation of synthesis conditions. These nanoparticles were used as model materials to understand the structural and morphological changes that occur to cobalt oxide during sequential reduction, oxidation and further re-reduction process as a function of the initial size of cobalt oxide. On reduction, spherical cobalt nanoparticles were obtained independent of the original size of cobalt oxide. In contrast, subsequent oxidation of the metal particles led to solid spheres, hollow spheres or core–shell structures depending on the size of the initial metal particle. Further re-reduction of the oxidized structures was also observed to be size dependent. The hollow oxide shells formed by the large particles (29 nm) fragmented into smaller particles on reduction, while the hollow shells of the medium sized particles (11 nm) did not re-disperse on further reduction. Similarly, no re-dispersion was observed in the case of the small particles (6 nm). This model study provides useful insights into the size dependent behavior of metal/metal oxide particles during oxidation/reduction. This has important implications in petrochemical industry where cobalt is used as a catalyst in the Fischer–Tropsch process.

The reactions of f-block silylamido N-heterocyclic carbene (NHC) complexes ([M(L)(N{SiMe3}2)2], M = Y, Ce, and U, L = bidentate alkoxy-tethered NHC ligand) with CO and CO2 have been studied and compared to each other, to those of selected [M(L)2 (N{SiMe3}2)] complexes, and to those of [M(N{SiMe3}2)3] to identify the effect of the labile NHC group on the small molecule activation chemistry. The small molecules COS and N2CPh2 have also been studied.

A new family of N,N'-bis-(2,6-diisopropylphenyl)-(2,6-diisopropylphenyl-imidazolium)-acetamidines have been developed as NHC proligands and ligands that are functionalised with neutral amidine and anionic amidinato moieties. On coordination they adopt diverse binding modes, depending on the nature of the metal and the reaction conditions. In the Ag, K and Cr complexes reported in this paper, monodentate κ(1)(NHC), bimetallic bridging-(κ(1)-NHC-κ(1)-amidinato) and bidentate (κ(1)-NHC-κ(1)-amidinato) binding modes were observed, respectively. Two of the novel Cr complexes, in the presence of activators, were tested as catalysts for the polymerisation of ethylene showing low activity.

This tutorial review highlights the most promising methods for the preparation of well-defined copper metal and oxide nanocrystals. These methodologies could be applied to other metals. We present the main synthetic strategies and associated mechanisms to control monodispersity, size, morphology and structure of metal and oxide nanomaterials which can adopt spherical, polyhedral, cubic, rod, wire, plate shapes and possibly hollow structures. We also consider the scale-up of the production of these nanocrystals, which is crucial for a wide range of potential applications such as catalysis, photovoltaics, electronics, optics and electrocatalysis.