Using para hydrogen induced polarization to study steps in the hydroformylation reaction.

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.

Examining the temporal behavior of the hydrocarbonaceous overlayer on an iron based Fischer-Tropsch catalyst.

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.

The application of inelastic neutron scattering to explore the significance of a magnetic transition in an iron based Fischer-Tropsch catalyst that is active for the hydrogenation of CO.

An iron based Fischer-Tropsch synthesis catalyst is evaluated using CO hydrogenation at ambient pressure as a test reaction and is characterised by a combination of inelastic neutron scattering (INS), powder X-ray diffraction, temperature-programmed oxidation, Raman scattering, and transmission electron microscopy. The INS spectrum of the as-prepared bulk iron oxide pre-catalyst (hematite, α-Fe2O3) is distinguished by a relatively intense band at 810 cm(-1), which has previously been tentatively assigned as a magnon (spinon) feature. An analysis of the neutron scattering intensity of this band as a function of momentum transfer unambiguously confirms this assignment. Post-reaction, the spinon feature disappears and the INS spectrum is characterised by the presence of a hydrocarbonaceous overlayer. A role for the application of INS in magnetic characterisation of iron based FTS catalysts is briefly considered.

Homo- and heteroleptic alkoxycarbene f-element complexes and their reactivity towards acidic N-H and C-H bonds.

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{NCHCHN(i)Pr})]), LnCp(L)2 (Ln = Y) , 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≡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.

Activation of carbon dioxide and carbon disulfide by a scandium N-heterocyclic carbene complex.

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.

One-step synthesis and shape-control of CuPd nanowire networks.

An effective one-step method has been developed to synthesize CuPd bimetallic nanowire networks. Investigation of the growth process revealed that the nanowires were formed by attachment of spherical particles and strongly influenced by interactions between surface ligands and metals. The morphology of CuPd nanoparticles is tuned via changing the molecular weight of polyvinylpyrrolidone (PVP) and solvents. The versatility of this method was further demonstrated by preparation of AgPd nanowires. An electrochemical study of CuPd nanowire networks shows morphology dependent activity in oxygen reduction reaction (ORR), which is comparable to that of platinum.

Size dependent reduction-oxidation-reduction behaviour of cobalt oxide nanocrystals.

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.

Sc(III) complexes with neutral N3- and SNS-donor ligands--a spectroscopic study of the activation of ethene polymerisation catalysts.

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.

Carbon monoxide and carbon dioxide insertion chemistry of f-block N-heterocyclic carbene complexes.

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

Amidine- and amidinate-functionalised N-heterocyclic carbene complexes of silver and chromium.

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.

Application of molybdenum bis(imido) complexes in ethylene dimerisation catalysis.

In combination with EtAlCl(2) (Mo : Al = 1 : 15) the imido complexes [MoCl(2)(NR)(NR')(dme)] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (1); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (3); R = R' = Bu(t) (4); dme = 1,2-dimethoxyethane) and [Mo(NHBu(t))(2)(NR)(2)] (R = 2,6-Pr(i)(2)-C(6)H(3) (5); R = Bu(t) (6)) each show moderate TON, activity, and selectivity for the catalytic dimerisation of ethylene, which is influenced by the nature of the imido substituents. In contrast, the productivity of [MoCl(2)(NPh)(2)(dme)] (2) is low and polymerisation is favoured over dimerisation. Catalysis initiated by complexes 1-4 in combination with MeAlCl(2) (Mo : Al = 1 : 15) exhibits a significantly lower productivity. Reaction of complex 5 with EtAlCl(2) (2 equiv.) gives rise to a mixture of products, while addition of MeAlCl(2) affords [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)]. Treatment of 6 with RAlCl(2) (2 equiv.) (R = Me, Et) yields [Mo({µ-N-Bu(t)}AlCl(2))(2)] (7) in both cases. Imido derivatives 1 and 3 react with Me(3)Al and MeAlCl(2) to form the bimetallic complexes [MoMe(2)(N{R}AlMe(2){µ-Cl})(NR')] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (8); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (10)) and [MoMe(2)(N{R}AlCl(2){µ-Cl})(NR')] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (9); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (11)), respectively. Exposure of complex 8 to five equivalents of thf or PMe(3) affords the adducts [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)(L)] (L = thf (12); L = PMe(3) (13)), while reaction with NEt(3) (5 equiv.) yields [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)]. The molecular structures of complexes 5, 9 and 11 have been determined.

Scalable strategies for the synthesis of well-defined copper metal and oxide nanocrystals.

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.

Carbon-silicon and carbon-carbon bond formation by elimination reactions at metal N-heterocyclic carbene complexes.

Two functional groups can be delivered at once to organo-rare earth complexes, (L)MR(2) and (L)(2)MR (M = Sc, Y; L = ({1-C(NDippCH(2)CH(2)N)}CH(2)CMe(2)O), Dipp = 2,6-(i)Pr(2)-C(6)H(3); R = CH(2)SiMe(3), CH(2)CMe(3)), via the addition of E-X across the metal-carbene bond to form a zwitterionic imidazolinium-metal complex, (L(E))MR(2)X, where L(E) = {1-EC(NDippCH(2)CH(2)N)}CH(2)CMe(2)O, E is a p-block functional group such as SiR(3), PR(2), or SnR(3), and X is a halide. The "ate" complex (L(Li))ScR(3) is readily accessible and is best described as a Li carbene adduct, ({1-Li(THF)C(NDippCH(2)CH(2)N)}CH(2)CMe(2)O)Sc(CH(2)SiMe(3))(3), since structural characterization shows the alkoxide ligand bridging the two metals and the carbene Li-bound with the shortest yet recorded Li-C bond distance. This can be converted via lithium halide-eliminating salt metathesis reactions to alkylated or silylated imidazolinium derivatives, (L(E))ScR(3) (E = SiMe(3) or CPh(3)). All the E-functionalized imidazolinium complexes spontaneously eliminate functionalized hydrocarbyl compounds upon warming to room temperature or slightly above, forming new organic products ER, i.e., forming C-Si, C-P, and C-Sn bonds, and re-forming the inorganic metal carbene (L)MR(X) or (L)(2)MX complex, respectively. Warming the tris(alkyl) complexes (L(E))MR(3) forms organic products arising from C-C or C-Si bond formation, which appears to proceed via the same elimination route. Treatment of (L)(2)Sc(CH(2)SiMe(3)) with iodopentafluorobenzene results in the "reverse sense" addition, which upon thermolysis forms the metal aryl complex (L)(2)Sc(C(6)F(5)) and releases the iodoalkane Me(3)SiCH(2)I, again facilitated by the reversible functionalization of the N-heterocyclic carbene group in these tethered systems.

Covalency in Ce(IV) and U(IV) halide and N-heterocyclic carbene bonds.

Oxidative halogenation with trityl chloride provides convenient access to Ce(IV) and U(IV) chloroamides [M(N{SiMe(3)}(2))(3)Cl] and their N-heterocyclic carbene derivatives, [M(L)(N{SiMe(3)}(2))(2)Cl] (L = OCMe(2)CH(2)(CNCH(2)CH(2)NDipp) Dipp = 2,6-iPr(2)C(6)H(3)). Computational analysis of the bonding in these and a fluoro analogue, [U(L)(N{SiMe(3)}(2))(2)F], 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.

Lanthanide/actinide differentiation with sterically encumbered N-heterocyclic carbene ligands.

A study is reported on the relative stability of trivalent bis(ligand) complexes of the form [M(L(R))(2)N''] for trivalent group 3, lanthanide and actinide cations, using the sterically demanding N-heterocyclic carbene ligand L(R) = [OCMe(2)CH(2){CNCH(2)CH(2)NR}] (R = (i)Pr L(P), Mes L(M), Dipp L(D); N'' = N(SiMe(3))(2)). For the small Y(III) cation (r(6-coord) = 1.040 A) and the smallest L(R), R = (i)Pr, mono, bis, and tris(L(P)) complexes can be made; [Y(L(P))(2)N''] and [Y(L(P))(3)] have been characterised. For the larger ligands, L(M) and L(D), only the mono(L(R)) complexes [Y(L(M))N''(2)] and [Y(L(D))N''(2)] can be made. For the larger Ce(III) (r(6-coord) = 1.15 A), mono(L(R)) and bis(L(R)) complexes [Ce(L(M))N''(2)], [Ce(L(D))N''(2)], [Ce(L(M))(2)N''], and [Ce(L(D))(2)N''] can be made; structural characterisation of the latter two confirm the high degree of steric congestion. The new complex [U(L(M))N''(2)] has also been isolated. Despite the very similar radii of Ce(III) and U(III) (r(6-coord) = 1.165 A), the complexes [U(L(R))(2)N''] cannot be isolated; a surprising display of the difference between the 4f and 5f metal series. However, the six-coordinate, bis(ligand) U(IV) complexes can readily be isolated if smaller ancillary ligands are used; [U(L(M))(2)I(2)] and [U(L(D))(2)I(2)] have been fully, including structurally, characterised.

Exploring the reactivity of tungsten bis(imido) dimethyl complexes with methyl aluminium reagents: implications for ethylene dimerization.

The reaction of [WCl2(NAr)2(DME)] (1) with excess Me3Al affords the dimethyl complex [WMe2(N{Ar}AlMe2{mu-Cl})(NAr)] (2), which on treatment with THF or MeAlCl2 yields [WMe2(NAr)2(THF)] (3) and [WMe2(N{Ar}AlMe(Cl){mu-Cl})(NAr)] (5), respectively. Complex 3 is unstable in solution dissociating to form [WMe2(NAr)2] (4) that may be isolated as an adduct with PMe3, [WMe2(NAr)2(PMe3)] (6). While complex 2 is inert towards ethylene, complex 3 reacts rapidly to afford a mixture of methane and but-1-ene (1:4). Neither complex 2 nor 3 react with propylene. Reaction of 3 with a C2H4/C2D4 (1:1) affords a mixture of isotopomers that is consistent with complete isotopic scrambling. The structures of complexes 1, 2, and 3 have been determined by X-ray diffraction.

Addition-elimination reactions across the M-C bond of metal N-heterocyclic carbenes.

Silyl, phosphinyl, stannyl, and boryl reagents can be added across the neutral metal-carbon dative bond in d(0) f-block metal N-heterocyclic carbene complexes in a reversible manner, allowing additional functional groups to be incorporated into redox-inactive organo-f-block compounds.

Palladium(II) complexes of new bulky bidentate phosphanes: active and highly regioselective catalysts for the hydroxycarbonylation of styrene.

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.

Coordination chemistry of 2,6-dixylyl-4-phenylphosphabarrelene with selected transition metals.

The 2,6-dixylyl-4-phenylphosphabarrelene has been synthesised from the parent phosphinine and its properties as a ligand explored through the preparation and characterisation of the complexes W(CO)(5)(L), Re(CO)(4)(L)Cl, (eta(6)-cymene)RuCl(2)(L), [(eta(5)-Me(3)SiC(5)H(4))Fe(CO)(2)(L)]PF(6), Rh(1,5-COD)(L)Cl, Ir(1,5-COD)(L)Cl, and cis-Pt(L)(2)Cl(2), where L = 4-phenyl-2,10-bis-(2,4-dimethylphenyl)-4H-1,4-ethenophospholine ((x)PB), cymene = 4-isopropyltoluene, eta(5)-Me(3)SiC(5)H(4) = trimethylsilylcyclopentadienyl and 1,5-COD = 1,5-cyclooctadiene. The new complexes were characterised by spectroscopic and analytical techniques and, for [(eta(5)-Me(3)SiC(5)H(4))Fe(CO)(2)(L)]PF(6) and Ru(eta(6)-cymene)(L)Cl(2), by single-crystal X-ray structure determination. The coordination properties of the phosphabarrelene have been established and compared with analogous complexes of triarylphosphines and triarylphosphites. Most spectroscopic and structural indicators suggest that the phosphabarrelene has coordination behaviour similar to that of simple triarylphosphines such as PPh(3).