Ferracyclic carbonyl complexes as anti-inflammatory agents.

Reaction of Fe(CO)Br with 2-aminopyridine and 2-aminonapthalene yields ferracyclic iron(ii) complexes bearing two CO ligands. Irradiation with visible light releases these two CO molecules. Substitution of a halide in the parent complexes by thioglucose provides significantly enhanced water solublity and raises the quantum yield for CO release by around five times.

Organoimido-Polyoxometalate Nonlinear Optical Chromophores: A Structural, Spectroscopic, and Computational Study.

Ten organoimido polyoxometalate (POM)-based chromophores have been synthesized and studied by hyper-Rayleigh scattering (HRS), Stark and Resonance Raman spectroscopies, and density functional theory (DFT) calculations. HRS β values for chromophores with resonance electron donors are significant (up to 139 × 10 esu, ∼5 times greater than that of the DAS cation), but systems with no donor, or the -NO acceptor show no activity, in some cases, despite large DFT-predicted β-values. In active systems with short (phenyl) π-bridges, β values comfortably exceed that of the purely organic structural analogue N,N-dimethyl-4-nitroaniline (DMPNA), and intrinsic β-values, β/N (where N is the number of bridge π-electrons) thus appear to break empirical performance limits (β/N vs λ) for planar organic systems.

Muonium Chemistry at Diiron Subsite Analogues of [FeFe]-Hydrogenase.

The chemistry of metal hydrides is implicated in a range of catalytic processes at metal centers. Gaining insight into the formation of such sites by protonation and/or electronation is therefore of significant value in fully exploiting the potential of such systems. Here, we show that the muonium radical (Mu ), used as a low isotopic mass analogue of hydrogen, can be exploited to probe the early stages of hydride formation at metal centers.

Encapsulating Subsite Analogues of the [FeFe]-Hydrogenases in Micelles Enables Direct Water Interactions.

Encapsulation of subsite analogues of the [FeFe]-hydrogenase enzymes in supramolecular structures has been shown to dramatically increase their catalytic ability, but the molecular basis for this enhancement remains unclear. We report the results of experiments employing infrared absorption, ultrafast infrared pump-probe, and 2D-IR spectroscopy to investigate the molecular environment of Fe2(pdt)(CO)6 (pdt: propanedithiolate) [1] encapsulated in the dispersed alkane phase of a heptane-dodecyltrimethylammonium bromide-water microemulsion. It is demonstrated that 1 is partitioned between two molecular environments, one that closely resembles bulk heptane solution and a second that features direct hydrogen-bonding interactions with water molecules that penetrate the surfactant shell.

PhotoCORMs: CO release moves into the visible.

The potential of carbon monoxide to act as a therapeutic agent is now well-established. Controlled delivery of CO is best achieved using 'CORMs': molecules which release known amounts of carbon monoxide in response to a stimulus. Metal carbonyl complexes will release CO if irradiated with ultraviolet light, but it is only in the past five years that development of true 'photoCORMs' has been explored.

EPR detection and characterisation of a paramagnetic Mo(iii) dihydride intermediate involved in electrocatalytic hydrogen evolution.

EPR spectroscopy and theoretical data show that the slow heterogeneous electron-transfer kinetics associated with the reduction of an 18-electron Mo(IV) acetato dihydride are a consequence of an η(2)-η(1) rearrangement of the carboxylate ligand which gives a unique paramagnetic 17-electron Mo(III) dihydride.

Detection of Transient Intermediates Generated from Subsite Analogues of [FeFe] Hydrogenases.

This article reviews the application of transient techniques in the elucidation of electron, proton, and photon chemistry related to the catalytic subsite of [FeFe] hydrogenase from the perspective of research in this area carried out at the UEA and Strathclyde laboratories. The detection of mixed-valence states, bridging CO intermediates, paramagnetic hydrides, and coordinatively unsaturated species has both informed understanding of biological catalysis and stimulated the search for stable analogues of key structural motifs likely involved in turnover states.

Gold(III)-CO and gold(III)-CO2 complexes and their role in the water-gas shift reaction.

The water-gas shift (WGS) reaction is an important process for the generation of hydrogen. Heterogeneous gold catalysts exhibit good WGS activity, but the nature of the active site, the oxidation state, and competing reaction mechanisms are very much matters of debate. Homogeneous gold WGS systems that could shed light on the mechanism are conspicuous by their absence: gold(I)-CO is inactive and gold(III)-CO complexes were unknown.

An element through the looking glass: exploring the Au-C, Au-H and Au-O energy landscape.

Gold, the archetypal "noble metal", used to be considered of little interest in catalysis. It is now clear that this was a misconception, and a multitude of gold-catalysed transformations has been reported. However, one consequence of the long-held view of gold as inert metal is that its organometallic chemistry contains many "unknowns", and catalytic cycles devised to explain gold's reactivity draw largely on analogies with other transition metals.

Zinc calixarene complexes for the ring opening polymerization of cyclic esters.

Reaction of Zn(C6F5)2·toluene (two equivalents) with 1,3-dipropoxy-p-tert-butyl-calix[4]arene (L(1)H2) led to the isolation of the complex [{Zn(C6F5)}2L(1)] (1), whilst similar use of Zn(Me)2 resulted in the known complex [{Zn(Me)}2L(1)] (2). Treatment of L(1)H2 with in situ prepared Zn{N(SiMe3)2}2 in refluxing toluene led to the isolation of the compound [(Na)ZnN(SiMe3)2L(1)] (3). The stepwise reaction of L(1)H2 and sodium hydride, followed by ZnCl2 and finally NaN(SiMe3)2 yielded the compound [Zn{N(SiMe3)2}2L(1)] (4).

Tri- and tetra-dentate imine vanadyl complexes: synthesis, structure and ethylene polymerization/ring opening polymerization capability.

Reaction of the ligand 2,4-tert-butyl-6-[(2-methylquinolin-8-ylimino)methyl]phenol (L(1)H) with [VOCl3] in the presence of triethylamine afforded the complex [VOCl2L(1)] (1), whereas use of [VO(OnPr)3] led to the isolation of [VO2L(1)] (2) or [VO2L(1)]·2/3MeCN (2·2/3MeCN). Reaction of 2-((2-(1H-benzo[d]imidazol-2-yl)quinolin-8-ylimino)methyl)-4,6-R(1),R(2)-phenols (R(1) = R(2) = (t)Bu; L(2)H), (R(1) = R(2) = Me; L(3)H) or (R(1) = Me, R(2) = Ad; L(4)H) with [VO(OnPr)3] afforded complexes of the type [L(2-4)VO] (where L(2) = 3, L(3) = 4, L(4) = 5). The molecular structures of 1 to 3 are reported; the metal centre adopts a distorted octahedral, trigonal bipyramidal or square-based pyramidal geometry respectively.

Electronic control of the protonation rates of Fe-Fe bonds.

Protonation at metal-metal bonds is of fundamental interest in the context of the function of the active sites of hydrogenases and nitrogenases. In diiron dithiolate complexes bearing carbonyl and electron-donating ligands, the metal-metal bond is the highest occupied molecular orbital (HOMO) with a "bent" geometry. Here we show that the experimentally measured rates of protonation (kH) of this bond and the energy of the HOMO as measured by the oxidation potential of the complexes (E1/2(ox)) correlate in a linear free energy relationship: ln kH = ((F(c - βE1/2(ox)))/(RT)), where c is a constant and β is the dimensionless Brønsted coefficient.

[FeFe] hydrogenase: protonation of {2Fe3S} systems and formation of super-reduced hydride states.

The synthesis and crystallographic characterization of a complex possessing a well-defined {2Fe3S(μ-H)} core gives access to a paramagnetic bridging hydride with retention of the core geometry. Chemistry of this 35-electron species within the confines of a thin-layer FTIR spectro-electrochemistry cell provides evidence for a unprecedented super-reduced Fe(I)(μ-H)Fe(I) intermediate.

Vanadyl complexes bearing bi-dentate phenoxyimine ligands: synthesis, structural studies and ethylene polymerization capability.

Reaction of [VO(OnPr)3] with the Schiff bases 3,5-(tBu)2-2-OH-C6H2CH(N(x-OR-C6H4)) (R = Me; x = 2, L(1)H; x = 3, L(2)H; x = 4, L(3)H; R = Et (L(4)H), CF3 (L(5)H), Ph (L(6)H)) or 4-methyl-3-(R)-2-(OH)-C6H4C[double bond, length as m-dash]N(2'-(2''-(OR1)C6H4)C6H4) (R = adamantyl, R(1) = Ph (L(7)H) or R = C(Me)2Ph, R(1) = Ph (L(8)H)) afforded the bis(chelate) vanadium(iv) complexes [VO(L(n))2] (n = 1 (1·2MeCN); n = 2 (2); n = 3 (3·2MeCN); n = 4 (4); n = 5 (5); n = 6 (6); n = 6, (7·1.5MeCN); n = 7, (8); n = 8, (9)); in the case of L(6)H, the oxo-bridged vanadium(v) complexes [VO(μ-O)(L(6))]2 (10) was also isolated. By contrast, interaction of 4-methyl-3-(R)-2-(OH)-C6H4C[double bond, length as m-dash]N(2'-(2''-(OR1)C6H4)C6H4) (R = adamantyl, R(1) = Me (L(9)H); R = tBu, R(1) = Me (L(10)H); R = C(Me)2Ph, R(1) = Me (L(11)H)) with [VO(OnPr)3] led to the isolation of the dinuclear complexes [VO(μ-OH)(μ-OnPr)(L(n))]2 (n = 9, (·4MeCN); 10, (12); 11, (13)), respectively.

Electrochemistry of Au(II) and Au(III) pincer complexes: determination of the Au(II)-Au(II) bond energy.

The bond energy of the unsupported Au-Au bond in the Au(ii) dimer [(C(∧)N(∧)C)Au]2 and the difference between Au(III)-OH and Au(III)-H bond enthalpies have been determined experimentally by electrochemical methods, with Au-OH and Au-H complexes showing unexpected differences in their reduction pathways, supported by DFT modelling.

Gold peroxide complexes and the conversion of hydroperoxides into gold hydrides by successive oxygen-transfer reactions.

Gold catalysts are widely studied in chemical and electrochemical oxidation processes. Computational modelling has suggested the participation of Au-OO-Au, Au-OOH or Au-OH surface species, attached to gold in various oxidation states. However, no structural information was available as isolable gold peroxo and hydroperoxo compounds were unknown.

Ferracyclic carbamoyl complexes related to the active site of [Fe]-hydrogenase.

The active site of the [Fe]-hydrogenase features an iron(II) centre bearing cis carbonyl groups and a chelating pyridine-acyl ligand. Reproducing these unusual features in synthetic models is an intriguing challenge, which will allow both better understanding of the enzymatic system and more fundamental insight into the coordination modes of iron. By using the carbamoyl group as a surrogate for acyl, we have been able to synthesize a range of ferracyclic complexes.

Encapsulating [FeFe]-hydrogenase model compounds in peptide hydrogels dramatically modifies stability and photochemistry.

A [FeFe]-hydrogenase model compound (µ-S(CH(2))(3)S)Fe(2)(CO)(4)(PMe(3))(2) [1] has been encapsulated in a low molecular weight (LMW) hydrogelator (Fmoc-Leu-Leu). Linear infrared absorption spectroscopy, gel melting and ultrafast time-resolved infrared spectroscopy experiments reveal significant contrasts in chemical environment and photochemistry between the encapsulated molecules and solution phase systems. Specifically, the gel provides a more rigid hydrogen bonding environment, which restricts isomerisation following photolysis while imparting significant increases in stability relative to a similarly aqueous solution.

Towards alternatives to anodic water oxidation: basket-handle thiolate Fe(III) porphyrins for electrocatalytic hydrocarbon oxidation.

Selective electrocatalytic oxidation of hydrocarbons to alcohols, epoxides or other (higher value) oxygenates should in principal present a useful complementary anodic half-cell reaction to cathodic generation of fuels from water or CO(2) viz. an alternative to oxygen evolution. A series of new basket-handle thiolate Fe(III) porphyrins have been synthesised and shown to mediate anodic oxidation of hydrocarbons, specifically adamantane hydroxylation and cyclooctene epoxidation.

Solar fuels: visible-light-driven generation of dihydrogen at p-type silicon electrocatalysed by molybdenum hydrides.

We show that a robust molybdenum hydride system can sustain photoelectrocatalysis of a hydrogen evolution reaction at boron-doped, hydrogen-terminated, p-type silicon. The photovoltage for the system is about 600-650 mV and the current densities, which can be sustained at the photocathode in non-catalytic and catalytic regimes, are similar to those at a photoinert vitreous carbon electrode. The kinetics of electrocatalysed hydrogen evolution at the photocathode are also very similar to those measured at vitreous carbon-evidently visible light does not significantly perturb the catalytic mechanism.

Tris[3,6-di-tert-butyl-1-(isoquinolin-1-yl)naphthalen-2-olato-κ2N,O]aluminium(III) toluene sesquisolvate.

The central Al(III) atom of the title compound, [Al(C(27)H(28)NO)(3)]·1.5C(7)H(8), has octahedral geometry in which the three N atoms are arranged in a meridional fashion. One of the toluene solvent molecules is located on a general position, while the second is disordered around a centre of inversion.

Synthesis and structure of amido- and imido(pentafluorophenyl)borane zirconocene and hafnocene complexes: N-H and B-H activation.

Treatment of Me(2)S·B(C(6)F(5))(n) H(3-n) (n=1 or 2) with ammonia yields the corresponding adducts. H(3)N·B(C(6)F(5))H(2) dimerises in the solid state through N-H···H-B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH(2)B(C(6)F(5))(n)H(3-n)].

Solution-phase photochemistry of a [FeFe]hydrogenase model compound: evidence of photoinduced isomerisation.

The solution-phase photochemistry of the [FeFe] hydrogenase subsite model (μ-S(CH(2))(3)S)Fe(2)(CO)(4)(PMe(3))(2) has been studied using ultrafast time-resolved infrared spectroscopy supported by density functional theory calculations. In three different solvents, n-heptane, methanol, and acetonitrile, relaxation of the tricarbonyl intermediate formed by UV photolysis of a carbonyl ligand leads to geminate recombination with a bias towards a thermodynamically less stable isomeric form, suggesting that facile interconversion of the ligand groups at the Fe center is possible in the unsaturated species. In a polar or hydrogen bonding solvent, this process competes with solvent substitution leading to the formation of stable solvent adduct species.

Cellular uptake of a fluorescent vanadyl sulfonylcalix[4]arene.

Vanadyl bearing calix[4]arene ligands have undergone evaluation against several cell lines, and show varying degrees of toxicity. For vanadyl complexed to a sulfonylcalix[4]arene, monitoring of the strong blue fluorescence revealed slow uptake kinetics. The complex is exclusively found in the cytoplasm of the cells and uptake is not due to active endocytotic mechanisms.