Publications by authors named "Graeme Hogarth"

38 Publications

Dithiocarbamate Complexes as Single Source Precursors to Nanoscale Binary, Ternary and Quaternary Metal Sulfides.

Chem Rev 2021 Apr 13. Epub 2021 Apr 13.

Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, U.K.

Nanodimensional metal sulfides are a developing class of low-cost materials with potential applications in areas as wide-ranging as energy storage, electrocatalysis, and imaging. An attractive synthetic strategy, which allows careful control over stoichiometry, is the single source precursor (SSP) approach in which well-defined molecular species containing preformed metal-sulfur bonds are heated to decomposition, either in the vapor or solution phase, resulting in facile loss of organics and formation of nanodimensional metal sulfides. By careful control of the precursor, the decomposition environment and addition of surfactants, this approach affords a range of nanocrystalline materials from a library of precursors. Dithiocarbamates (DTCs) are monoanionic chelating ligands that have been known for over a century and find applications in agriculture, medicine, and materials science. They are easily prepared from nontoxic secondary and primary amines and form stable complexes with all elements. Since pioneering work in the late 1980s, the use of DTC complexes as SSPs to a wide range of binary, ternary, and multinary sulfides has been extensively documented. This review maps these developments, from the formation of thin films, often comprised of embedded nanocrystals, to quantum dots coated with organic ligands or shelled by other metal sulfides that show high photoluminescence quantum yields, and a range of other nanomaterials in which both the phase and morphology of the nanocrystals can be engineered, allowing fine-tuning of technologically important physical properties, thus opening up a myriad of potential applications.
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http://dx.doi.org/10.1021/acs.chemrev.0c01183DOI Listing
April 2021

Two new monofunctional platinum(II) dithiocarbamate complexes: -type axial protection, equatorial-axial conformational isomerism, and anticancer and DNA binding studies.

Dalton Trans 2020 Nov;49(43):15385-15396

University of Hawaii at Hilo, The Daniel K. Inouye College of Pharmacy, USA.

The syntheses of two platinum(ii) dithiocarbamate complexes (1 and 2) that show quinoplatin- and phenanthriplatin-type axial protection of the Pt-plane are described. The Pt-plane of complex 2 is axially more protected than that of complex 1. Furthermore, both complexes adopt two different stereochemical conformations in the solid state (based on single-crystal X-ray structures) owing to the structurally flexible piperazine backbone; i.e., C-e,e-Anti (1) and C-e,a-Syn (2), where "C" stands for the chair configuration, "e" and "a" stand for the equatorial and axial positions and "Anti" (opposite side) and "Syn" (same side) represent the relative orientations in space of the terminal substituents on the piperazine ring. In complex 2, the C-e,a-Syn conformation may provide additional steric hindrance to the Pt-plane. Despite the lower lipophilicity of 2 as compared to that of 1, the in vitro anticancer action against selected cancer cell lines is better for the former revealing the superior role of the axial protection over lipophilicity in modulating anticancer activity. The activity against the cancer promoting protein NF-κB signifies that the mode of cancer cell death may be the result of hindering the activity of NF-κB in the initiation of apoptosis. The apoptotic mode of cell death has been established earlier in a study using Annexin V-FITC. Finally, DNA binding studies revealed that the complex-DNA adduct formation is spontaneous and the mode of interaction is non-intercalative (electrostatic/covalent).
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http://dx.doi.org/10.1039/d0dt03018jDOI Listing
November 2020

Electrocatalytic proton-reduction behaviour of telluride-capped triiron clusters: tuning of overpotentials and stabilization of redox states relative to lighter chalcogenide analogues.

Dalton Trans 2020 Jun;49(21):7133-7143

Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK.

Reaction of [Fe3(CO)9(μ3-Te)2] (1) with the corresponding phosphine has been used to prepare the phosphine-substituted tellurium-capped triiron clusters [Fe3(CO)9(μ3-Te)2(PPh3)] (2), [Fe3(CO)8(μ3-Te)2(PPh3)] (3) and [Fe3(CO)7(μ3-Te)2(μ-R2PXPR2)] (X = CH2, R = Ph (4), Cy (5); X = NPri, R = Ph (6)). The directly related cluster [Fe3(CO)7(μ3-CO)(μ3-Te)(μ-dppm)] (7) was isolated from the reaction of [Fe3(CO)10(μ-Ph2PCH2PPh2)] with elemental tellurium. The electrochemistry of these new clusters has been probed by cyclic voltammetry, and selected complexes have been tested as proton reduction catalysts. Each 50-electron dicapped cluster exhibits two reductive processes; the first has good chemical reversibility in all cases but the reversibility of the second is dependent upon the nature of the supporting ligands. For the parent cluster 1 and the diphosphine derivatives 4-5 this second reduction is reversible, but for the PPh3 complex 3 it is irreversible, possibly as a result of CO or phosphine loss. The nature of the reduced products of 1 has been probed by DFT calculations. Upon addition of one electron, an elongation of one of the Fe-Te bonding interactions is found, while the addition of the second electron affords an open-shell triplet which is more stable by 8.8 kcal mol-1 than the closed-shell singlet dianion and has two elongated Fe-Te bonds. The phosphine-substituted clusters also exhibit oxidation chemistry but with poor reversibility in all cases. Since the reduction potentials for the tellurium-capped clusters occur at more positive potentials than for the sulfur and selenium analogues, and the redox processes also show better reversibility than for the S/Se analogues, the tellurium-capped clusters 1 and 3-5 have been examined as proton reduction catalysts. In the presence of p-toluenesulfonic acid (TsOH) or trifluoroacetic acid (TFA), these clusters reduce protons to H2 at both their first and second reduction potentials. Electron uptake at the second reduction potential is far greater than the first, suggesting that the open-shell triplet dianions are efficient catalysts. As expected, the catalytic overpotential increases upon successive phosphine substitution but so does the current response. A mechanistic scheme that takes the roles of the supporting ligands on the preferred route(s) to H2 production and release into account is presented.
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http://dx.doi.org/10.1039/d0dt00556hDOI Listing
June 2020

Phosphine-promoted ring-opening of benzisothiazolinate ligands at a nickel(ii) centre: a convenient synthesis of Ni(ii)-thiolate complexes.

Dalton Trans 2019 Apr;48(17):5520-5522

Department of Chemistry, College of Science, University of Tikrit, Tikrit, Iraq.

Phosphines react with the benzisothiazolinate (bit) paddlewheel dimer, [Ni2(μ-bit)4·2H2O], resulting in sulfur-nitrogen bond scission and a series of unexpected transformations leading to novel Ni(ii) complexes containing 2-cyanophenylthiolate and related thiolate ligands.
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http://dx.doi.org/10.1039/c9dt00953aDOI Listing
April 2019

Models of the iron-only hydrogenase enzyme: structure, electrochemistry and catalytic activity of Fe(CO)(μ-dithiolate)(μ,κ,κ-triphos).

Dalton Trans 2019 May;48(18):6174-6190

Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.

A series of diiron bis(2-diphenylphosphinoethyl)phenylphosphine (triphos) complexes Fe2(CO)3(μ-dithiolate)(μ,κ1,κ2-triphos) (1-4) [dithiolate = 1 pdt; 2 edt; 3 adt (R = Bz), 4 (SMe)2] have been prepared and investigated as biomimics of the diiron site of [FeFe]-hydrogenases. The triphos ligand bridges the diiron vector whilst also chelating to one iron and 1-3 exist as a mixture of basal-basal-apical (bba) and basal-basal-basal (bbb) isomers which differ in the mode of chelation. In solution the bba and bbb forms do not interconvert on the NMR time scale, but the bba isomers are fluxional, and at low temperature four forms of 1bba are seen as the conformations for the pdt ring and triphos methylene groups are frozen. Crystallographic studies have established bba (pdt) and bbb (adt) ground state conformations and in both there is a significant deviation away from the expected eclipsed conformation (Lap-Fe-Fe-Lap torsion angle 0°) by 49.4 and 24.9° respectively, suggesting that introduction of triphos leads to significant strain and DFT calculations have been used to understand the relative energies of isomers. The electron rich nature of the diiron centre in 1-4 would suggest rapid protonation, but while bridging hydride complexes such as [Fe2(CO)3(μ-pdt)(μ,κ1,κ2-triphos)(μ-H)][BF4] (1H+) can be formed the process is slow. This behavior is likely a result of the high energy barrier in forming the initial (not observed) terminal hydride which requires a significant conformational change in triphos coordination. CV studies show that all starting compounds oxidize at low potentials and the addition of [Cp2Fe][PF6] to 1 affords [Fe2(CO)3(μ-pdt)(μ,κ1,κ2-triphos)][PF6] (1+) which has been characterised by IR spectroscopy. DFT studies suggest a ground state for 1+ with a partially rotated Fe(CO)2P moiety that yields a weak semi-bridging carbonyl with the adjacent Fe(CO)P2 group. No reduction peaks are seen for 1-4 within the solvent window but 1H+ undergoes reduction at -1.7 V. All complexes act as proton-reduction catalysts in the presence of HBF4·Et2O. For 1, three separate processes are observed and their dependence on acid concentration has been probed, and a mechanistic scheme is proposed based on formation via a CECE process of 1(μ-H)H which can either slowly release H2 or undergo further reduction. Relative contributions of the three processes to the total current were found to be highly dependent upon the background electrolyte, being attributed to their relative abilities to facilitate proton transfer processes. While 2 and 4 show similar proton reduction behaviour, the adt complex 3 is quite different being attributed to facile protonation of nitrogen which is followed by addition of a second proton at the diiron centre.
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http://dx.doi.org/10.1039/c9dt00700hDOI Listing
May 2019

Chemistry, pharmacology, and cellular uptake mechanisms of thiometallate sulfide donors.

Br J Pharmacol 2020 02 23;177(4):745-756. Epub 2019 May 23.

Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK.

Background And Purpose: A clinical need exists for targeted, safe, and effective sulfide donors. We recently reported that ammonium tetrathiomolybdate (ATTM) belongs to a new class of sulfide-releasing drugs. Here, we investigated the cellular uptake mechanisms of this drug class compared to sodium hydrosulfide (NaHS) and the effects of a thiometallate tungsten congener of ATTM, ammonium tetrathiotungstate (ATTT).

Experimental Approach: In vitro H S release was determined by headspace gas sampling of vials containing dissolved thiometallates. Thiometallate and NaHS bioactivity was assessed by spectrophotometry-derived sulfhaemoglobin formation. Cellular uptake dependence on the anion exchange protein (AE)-1 was investigated in human red blood cells. ATTM/glutathione interactions were assessed by LC-MS/MS. Rodent pharmacokinetic and pharmacodynamic studies focused on haemodynamics and inhibition of aerobic respiration.

Key Results: ATTM and ATTT both exhibit temperature-, pH-, and thiol-dependence of sulfide release. ATTM/glutathione interactions revealed the generation of inorganic and organic persulfides and polysulfides. ATTM showed greater ex vivo and in vivo bioactivity over ATTT, notwithstanding similar pharmacokinetic profiles. Cellular uptake mechanisms of the two drug classes are distinct; thiometallates show dependence on AE-1, while hydrosulfide itself was unaffected by inhibition of this pathway.

Conclusions And Implications: The cellular uptake of thiometallates relies upon a plasma membrane ion channel. This advances our pharmacological knowledge of this drug class, and further supports their utility as cell-targeted sulfide donor therapies. Our results indicate that, as a more stable form, ATTT is better suited as a copper chelator. ATTM, a superior sulfide donor, may additionally participate in intracellular redox recycling.

Linked Articles: This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.
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http://dx.doi.org/10.1111/bph.14670DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7024710PMC
February 2020

Hydrogenase biomimics containing redox-active ligands: Fe(CO)(μ-edt)(κ-bpcd) with electron-acceptor 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) as a potential [Fe-S] surrogate.

Dalton Trans 2019 May;48(18):6051-6060

Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK.

[FeFe]-hydrogenases contain strongly electronically coupled diiron [2Fe]H and tetrairon [Fe4-S4]H clusters, and thus much recent effort has focused on the chemistry of diiron-dithiolate biomimics with appended redox-active ligands. Here we report on the synthesis and electrocatalytic activity of Fe2(CO)4(μ-edt)(κ2-bpcd) (2) in which the electron-acceptor 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) acts as a surrogate of the [Fe4-S4]H sub-cluster. The complex is prepared in low yield but has been fully characterised, including a crystallographic study which shows that the diphosphine adopts a basal-apical coordination geometry in the solid state. Cyclic voltammetry shows that 2 undergoes four reduction events with DFT studies confirming that the first reduction is localised on the low-lying π* system of the diphosphine ligand. The addition of the second electron furnishes a triplet dianion that exhibits spin density distributed over the diphosphine and diiron subunits. Protonation at the Fe-Fe bond of the triplet dianion furnishes the corresponding bridging hydride as the thermodynamically favoured species that contains a reduced bpcd ligand. Complex 2 functions as a catalyst for proton-reduction at its second reduction potential, in contrast to the related 2,3-bis(diphenylphosphino)maleic anhydride (bma) complex, Fe2(CO)4(μ-pdt)(κ2-bma) (1), which shows similar electrochemical behaviour but is not catalytically active. The difference in chemical behaviour is attributed to greater stability of the 4-cyclopenten-1,3-dione platform in 2 as compared to the maleic anhydride ring of the bma ligand in 1 following the uptake of the second electron. Thus protonation of the Fe-Fe bond in the 22- affords a species which is stable enough to undergo a further reduction-protonation event, unlike the bma ligand whose maleic anhydride ring undergoes deleterious C-O bond scission upon protonation or reaction with adventitious moisture. DFT studies, however, suggest that electron-transfer from the diphosphine to the diiron centre is not significant, probably due to their poor redox levelling. Thus, while the diphosphine is readily reduced, the added electron is apparently not utilised in proton-reduction and hence cannot truly be considered as an [Fe4-S4]H surrogate.
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http://dx.doi.org/10.1039/c8dt04906hDOI Listing
May 2019

Insight into the Nature of Iron Sulfide Surfaces During the Electrochemical Hydrogen Evolution and CO Reduction Reactions.

ACS Appl Mater Interfaces 2018 Sep 11;10(38):32078-32085. Epub 2018 Sep 11.

Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , U.K.

Greigite and other iron sulfides are potential, cheap, earth-abundant electrocatalysts for the hydrogen evolution reaction (HER), yet little is known about the underlying surface chemistry. Structural and chemical changes to a greigite (FeS)-modified electrode were determined at -0.6 V versus standard hydrogen electrode (SHE) at pH 7, under conditions of the HER. In situ X-ray absorption spectroscopy was employed at the Fe K-edge to show that iron-sulfur linkages were replaced by iron-oxygen units under these conditions. The resulting material was determined as 60% greigite and 40% iron hydroxide (goethite) with a proposed core-shell structure. A large increase in pH at the electrode surface (to pH 12) is caused by the generation of OH as a product of the HER. Under these conditions, iron sulfide materials are thermodynamically unstable with respect to the hydroxide. In situ infrared spectroscopy of the solution near the electrode interface confirmed changes in the phosphate ion speciation consistent with a change in pH from 7 to 12 when -0.6 V versus SHE is applied. Saturation of the solution with CO resulted in the inhibition of the hydroxide formation, potentially due to surface adsorption of HCO. This study shows that the true nature of the greigite electrode under conditions of the HER is a core-shell greigite-hydroxide material and emphasizes the importance of in situ investigation of the catalyst under operation to develop true and accurate mechanistic models.
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http://dx.doi.org/10.1021/acsami.8b08612DOI Listing
September 2018

Mixed-valence dimolybdenum complexes containing hard oxo and soft carbonyl ligands: synthesis, structure, and electrochemistry of Mo(O)(CO)(μ-κ-S(CH)S)(κ-diphosphine).

Dalton Trans 2018 Jul;47(30):10102-10112

Department of Chemistry, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh.

Mixed-valence dimolybdenum complexes Mo2(O)(CO)2{μ-κ2-S(CH2)nS}2(κ2-Ph2P(CH2)mPPh2) (n = 2, 3; m = 1, 2) (1-4) have been synthesized from one-pot reactions of fac-Mo(CO)3(NCMe)3 and dithiols, HS(CH2)nSH, in the presence of diphosphines. The dimolybdenum framework is supported by two thiolate bridges, with one molybdenum carrying a terminal oxo ligand and the second two carbonyls. The dppm (m = 1) products exist as a pair of diastereomers differing in the relative orientation of the two carbonyls (cis and trans) at the Mo(CO)2(dppm) center, while dppe (m = 2) complexes are found solely as the trans isomers. Small amounts of Mo(CO){κ3-S(CH2CH2S)2}(κ2-dppe) (5) also result from the reaction using HS(CH2)2SH and dppe. The bonding in isomers of 1-4 has been computationally explored by DFT calculations, trans diastereomers being computed to be more stable than the corresponding pair of cis diastereomers for all. The calculations confirm the existence of Mo[triple bond, length as m-dash]O and Mo-Mo bond orders and suggest that the new dimeric compounds are best viewed as Mo(v)-Mo(i) mixed-valence systems. The electrochemical properties of 1 have been investigated by CV and show a reversible one-electron reduction associated with the Mo(v) centre, while two closely spaced irreversible oxidation waves are tentatively assigned to oxidation of the Mo(i) centre of the two isomers as supported by DFT calculations.
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http://dx.doi.org/10.1039/c8dt02231cDOI Listing
July 2018

Induction of Necroptosis in Cancer Stem Cells using a Nickel(II)-Dithiocarbamate Phenanthroline Complex.

Chemistry 2017 Jul 27;23(40):9674-9682. Epub 2017 Jun 27.

Department of Chemistry, King's College London, London, SE1 1DB, UK.

The cytotoxic properties of a series of nickel(II)-dithiocarbamate phenanthroline complexes is reported. The complexes 1-6 kill bulk cancer cells and cancer stem cells (CSCs) with micromolar potency. Two of the complexes, 2 and 6, kill twice as many breast cancer stem cell (CSC)-enriched HMLER-shEcad cells as compared to breast CSC-depleted HMLER cells. Complex 2 inhibits mammosphere formation to a similar extent as salinomycin (a CSC-specific toxin). Detailed mechanistic studies suggest that 2 induces CSC death by necroptosis, a programmed form of necrosis. Specifically, 2 triggers MLKL phosphorylation, oligomerization, and translocation to the cell membrane. Additionally, 2 induces necrosome-mediated propidium iodide (PI) uptake and mitochondrial membrane depolarisation, as well as morphological changes consistent with necroptotosis. Strikingly, 2 does not evoke necroptosis by intracellular reactive oxygen species (ROS) production or poly(ADP) ribose polymerase (PARP-1) activation.
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http://dx.doi.org/10.1002/chem.201701837DOI Listing
July 2017

Phase control during the synthesis of nickel sulfide nanoparticles from dithiocarbamate precursors.

Nanoscale 2016 Jun 13;8(21):11067-75. Epub 2016 May 13.

Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.

Square-planar nickel bis(dithiocarbamate) complexes, [Ni(S2CNR2)2], have been prepared and utilised as single source precursors to nanoparticulate nickel sulfides. While they are stable in the solid-state to around 300 °C, heating in oleylamine at 230 °C, 5 mM solutions afford pure α-NiS, where the outcome is independent of the substituents. DFT calculations show an electronic effect rather than steric hindrance influences the resulting particle size. Decomposition of the iso-butyl derivative, [Ni(S2CN(i)Bu2)2], has been studied in detail. There is a temperature-dependence of the phase of the nickel sulfide formed. At low temperatures (150 °C), pure α-NiS is formed. Upon raising the temperature, increasing amounts of β-NiS are produced and at 280 °C this is formed in pure form. A range of concentrations (from 5-50 mM) was also investigated at 180 °C and while in all cases pure α-NiS was formed, particle sizes varied significantly. Thus at low concentrations average particle sizes were ca. 100 nm, but at higher concentrations they increased to ca. 150 nm. The addition of two equivalents of tetra-iso-butyl thiuram disulfide, ((i)Bu2NCS2)2, to the decomposition mixture was found to influence the material formed. At 230 °C and above, α-NiS was generated, in contrast to the results found without added thiuram disulfide, suggesting that addition of ((i)Bu2NCS2)2 stabilises the metastable α-NiS phase. At low temperatures (150-180 °C) and concentrations (5 mM), mixtures of α-NiS and Ni3S4, result. A growing proportion of Ni3S4 is noted upon increasing precursor concentration to 10 mM. At 20 mM a metastable phase of nickel sulfide, NiS2 is formed and as the concentration is increased, α-NiS appears alongside NiS2. Reasons for these variations are discussed.
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http://dx.doi.org/10.1039/c6nr00053cDOI Listing
June 2016

Formation of ortho-cyano-aminothiophenolate ligands with versatile binding modes via facile carbon-sulfur bond cleavage of 2-aminobenzothiazoles at mercury(II) centres.

Dalton Trans 2015 Aug;44(32):14217-9

Department of Chemistry, College of Science, University of Tikrit, Tikrit, Iraq.

Addition of 2-aminobenzothiazole and substituted derivatives to mercuric acetate in warm ethanol leads to the high yield formation of [Hg{SC6H3XN(C[triple bond, length as m-dash]N)}]n resulting from loss of hydrogen and sulfur-carbon bond cleavage. Addition of phosphines affords a series of complexes in which the new ortho-cyano-aminothiophenolate ligands adopt three different binding modes.
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http://dx.doi.org/10.1039/c5dt02080hDOI Listing
August 2015

Multimetallic complexes based on a diphosphine-dithiocarbamate "Janus" ligand.

Inorg Chem 2015 May 16;54(9):4222-30. Epub 2015 Apr 16.

†Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, U.K.

The HCl salt of the aminodiphosphine ligand HN(CH2CH2PPh2)2 reacts with [M(CO)4(pip)2] (M = Mo, W; pip = piperidine) to yield [M{κ(2)-HN(CH2CH2PPh2)2}(CO)4]. The molybdenum analogue readily loses a carbonyl ligand to form [Mo{κ(3)-HN(CH2CH2PPh2)2}(CO)3], which was structurally characterized. The same ligand backbone is used to form the new bifunctional ligand, KS2CN(CH2CH2PPh2)2, which reacts with nickel and cobalt precursors to yield [Ni{S2CN(CH2CH2PPh2)2}2] and [Co{S2CN(CH2CH2PPh2)2}3]. Addition of [AuCl(tht)] (tht = tetrahydrothiophene) to [Ni{S2CN(CH2CH2PPh2)2}2] leads to formation of the pentametallic complex, [Ni{S2CN(CH2CH2PPh2AuCl)2}2]. In contrast, addition of [PdCl2(py)2] (py = pyridine) to [Ni{S2CN(CH2CH2PPh2)2}2] does not lead to a trimetallic complex but instead yields the transmetalated cyclic compound [Pd{S2CN(CH2CH2PPh2)2}]2, which was structurally characterized. The same product is obtained directly from [PdCl2(py)2] and KS2CN(CH2CH2PPh2)2. In contrast, the same reaction with [PtCl2(NCPh)2] yields the oligomer, [Pt{S2CN(CH2CH2PPh2)2}]n. Reaction of KS2CN(CH2CH2PPh2)2 with cis-[RuCl2(dppm)2] provides [Ru{S2CN(CH2CH2PPh2)2}(dppm)2](+), which reacts with [AuCl(tht)] to yield [Ru{S2CN(CH2CH2PPh2AuCl)2}(dppm)2](+). Addition of [M(CO)4(pip)2] (M = Mo, W) to the same precursor leads to formation of the bimetallic compounds [(dppm)2Ru{S2CN(CH2CH2PPh2)2}M(CO)4](+), while treatment with [ReCl(CO)5] yields [(dppm)2Ru{S2CN(CH2CH2PPh2)2}ReCl(CO)3](+). Reaction of KS2CN(CH2CH2PPh2)2 with [Os(CH═CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole) provides [Os(CH═CHC6H4Me-4){S2CN(CH2CH2PPh2)2}(CO)(PPh3)2], but reaction with the analogous ruthenium precursor fails to yield a clean product.
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http://dx.doi.org/10.1021/ic5028527DOI Listing
May 2015

Copper catalysed amidation of aryl halides through chelation assistance.

Chem Commun (Camb) 2015 Mar;51(23):4834-7

Bioorganic & Biophysical Chemistry Laboratory, Linnaeus University Centre for Biomaterials Chemistry, Linnæus University, SE-391 82 Kalmar, Sweden.

A copper mediated C-N bond formation for the amidation of aryl halides using 8-aminoquinoline has been developed. This strategy provides efficient access to amides bearing two contiguous heterocyclic moieties and does not require the presence of additional ligands.
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http://dx.doi.org/10.1039/c4cc09940kDOI Listing
March 2015

Electrocatalytic proton reduction catalysed by the low-valent tetrairon-oxo cluster [Fe4(CO)10(κ(2)-dppn)(μ4-O)](2-) [dppn = 1,1'-bis(diphenylphosphino)naphthalene].

Dalton Trans 2015 Mar;44(11):5160-9

Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK.

The 62-electron oxo-capped tetrairon butterfly cluster, Fe4(CO)10(κ(2)-dppn)(μ4-O) (1) {dppn = 1,8-bis(diphenylphosphino)naphthalene}, undergoes reversible one-electron oxidation and reduction events to generate the 61- and 63-electron radicals [Fe4(CO)10(κ(2)-dppn)(μ4-O)](+) (1+) and [Fe4(CO)10(κ(2)-dppn)(μ4-O)](-) (1-) respectively. Addition of a second electron affords the 64-electron cluster [Fe4(CO)10(κ(2)-dppn)(μ4-O)](2-) (1(2-)) which has more limited stability but is stable within the time frame of the electrochemical experiment. While 1 and 1(-1) are inactive as proton reduction catalysts, dianionic 1(2-) is active for the formation of hydrogen from both CHCl2CO2H and CF3CO2H. This occurs via two separate mechanistic cycles branching at the mono-protonated species [Fe4(CO)10(κ(2)-dppn)(μ4-O)H](-) (1H-) resulting from the rapid protonation of 1(2-). This intermediate then undergoes competing protonation and reduction events leading to EECC and ECEC catalytic cycles respectively with 1- being pivotal to both. In order to understand the nature of [Fe4(CO)10(κ(2)-dppn)(μ4-O)](2-) (1(2-)) and its protonated products density functional theory (DFT) calculations have been employed. Theoretical calculations reveal that the cluster core remains intact in 1(2-), but the two consecutive one-electron reductions lead to an expansion of one of the trigonal-pyramids of this trigonal-bipyramidal cluster. The two-electron reduced cluster 1(2-) protonates at dppn-bound iron, accompanied by a wingtip-hinge iron-iron bond scission, and then reacts with a second proton to evolve hydrogen.
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http://dx.doi.org/10.1039/c4dt03323jDOI Listing
March 2015

Single-step co-deposition of nanostructured tungsten oxide supported gold nanoparticles using a gold-phosphine cluster complex as the gold precursor.

Sci Technol Adv Mater 2014 Dec 9;15(6):065004. Epub 2014 Dec 9.

Department of Chemistry, University College London, 20 Gordon Street, WC1H 0AJ London, UK.

The use of a molecular gold organometallic cluster in chemical vapour deposition is reported, and it is utilized, together with a tungsten oxide precursor, for the single-step co-deposition of (nanostructured) tungsten oxide supported gold nanoparticles (NPs). The deposited gold-NP and tungsten oxide supported gold-NP are highly active catalysts for benzyl alcohol oxidation; both show higher activity than SiO supported gold-NP synthesized via a solution-phase method, and tungsten oxide supported gold-NP show excellent selectivity for conversion to benzaldehyde.
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http://dx.doi.org/10.1088/1468-6996/15/6/065004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090393PMC
December 2014

Combining anti-cancer drugs with artificial sweeteners: synthesis and anti-cancer activity of saccharinate (sac) and thiosaccharinate (tsac) complexes cis-[Pt(sac)2(NH3)2] and cis-[Pt(tsac)2(NH3)2].

J Inorg Biochem 2014 Dec 1;141:55-57. Epub 2014 Aug 1.

Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK; Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK. Electronic address:

The new platinum(II) complexes cis-[Pt(sac)2(NH3)2] (sac=saccharinate) and cis-[Pt(tsac)2(NH3)2] (tsac=thiosaccharinate) have been prepared, the X-ray crystal structure of cis-[Pt(sac)2(NH3)2] x H2O reveals that both saccharinate anions are N-bound in a cis-arrangement being inequivalent in both the solid-state and in solution at room temperature. Preliminary anti-cancer activity has been assessed against A549 human alveolar type-II like cell lines with the thiosaccharinate complex showing good activity.
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http://dx.doi.org/10.1016/j.jinorgbio.2014.07.017DOI Listing
December 2014

Bioinspired Hydrogenase Models: The Mixed-Valence Triiron Complex [Fe(CO)(μ-edt)] and Phosphine Derivatives [Fe(CO) (PPh) (μ-edt)] ( = 1, 2) and [Fe(CO)(κ-diphosphine)(μ-edt)] as Proton Reduction Catalysts.

Organometallics 2014 Mar 5;33(6):1356-1366. Epub 2014 Mar 5.

Department of Chemistry, University College London , 20 Gordon Street, London WC1H 0AJ, U.K. ; Department of Chemistry, King's College London , Britannia House, 7 Trinity Street, London SE1 1DB, U.K.

The mixed-valence triiron complexes [Fe(CO) (PPh) (μ-edt)] ( = 0-2; edt = SCHCHS) and [Fe(CO)(κ-diphosphine)(μ-edt)] (diphosphine = dppv, dppe, dppb, dppn) have been prepared and structurally characterized. All adopt an arrangement of the dithiolate bridges, and PPh substitution occurs at the apical positions of the outer iron atoms, while the diphosphine complexes exist only in the dibasal form in both the solid state and solution. The carbonyl on the central iron atom is semibridging, and this leads to a rotated structure between the bridged diiron center. IR studies reveal that all complexes are inert to protonation by HBF·EtO, but addition of acid to the pentacarbonyl complexes results in one-electron oxidation to yield the moderately stable cations [Fe(CO)(PPh)(μ-edt)] and [Fe(CO)(κ-diphosphine)(μ-edt)], species which also result upon oxidation by [CpFe][PF]. The electrochemistry of the formally Fe(I)-Fe(II)-Fe(I) complexes has been investigated. Each undergoes a quasi-reversible oxidation, the potential of which is sensitive to phosphine substitution, generally occurring between 0.15 and 0.50 V, although [Fe(CO)(PPh)(μ-edt)] is oxidized at -0.05 V. Reduction of all complexes is irreversible and is again sensitive to phosphine substitution, varying between -1.47 V for [Fe(CO)(μ-edt)] and around -1.7 V for phosphine-substituted complexes. In their one-electron-reduced states, all complexes are catalysts for the reduction of protons to hydrogen, the catalytic overpotential being increased upon successive phosphine substitution. In comparison to the diiron complex [Fe(CO)(μ-edt)], [Fe(CO)(μ-edt)] catalyzes proton reduction at 0.36 V less negative potentials. Electronic structure calculations have been carried out in order to fully elucidate the nature of the oxidation and reduction processes. In all complexes, the HOMO comprises an iron-iron bonding orbital localized between the two iron atoms not ligated by the semibridging carbonyl, while the LUMO is highly delocalized in nature and is antibonding between both pairs of iron atoms but also contains an antibonding dithiolate interaction.
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http://dx.doi.org/10.1021/om400691qDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3985925PMC
March 2014

Ring-closing metathesis and nanoparticle formation based on diallyldithiocarbamate complexes of gold(I): synthetic, structural, and computational studies.

Inorg Chem 2014 Mar 10;53(5):2404-16. Epub 2014 Feb 10.

Department of Chemistry, Imperial College London, South Kensington Campus , London SW7 2AZ, U.K.

The gold(I) complexes [Au{S2CN(CH2CH═CH2)2}(L)] [L = PPh3, PCy3, PMe3, CN(t)Bu, IDip] are prepared from KS2CN(CH2CH═CH2)2 and [(L)AuCl]. The compounds [L2(AuCl)2] (L2 = dppa, dppf) yield [(L2){AuS2CN(CH2CH═CH2)2}2], while the cyclic complex [(dppm){Au2S2CN(CH2CH═CH2)2}]OTf is obtained from [dppm(AuCl)2] and AgOTf followed by KS2CN(CH2CH═CH2)2. The compound [Au2{S2CN(CH2CH═CH2)2}2] is prepared from [(tht)AuCl] (tht = tetrahydrothiophene) and the diallyldithiocarbamate ligand. This product ring-closes with [Ru(═CHPh)Cl2(SIMes)(PCy3)] to yield [Au2(S2CNC4H6)2], whereas ring-closing of [Au{S2CN(CH2CH═CH2)2}(PR3)] fails. Warming [Au2{S2CN(CH2CH═CH2)2}2] results in formation of gold nanoparticles with diallydithiocarbamate surface units, while heating [Au2(S2CNC4H6)2] with NaBH4 results in nanoparticles with 3-pyrroline dithiocarbamate surface units. Larger nanoparticles with the same surface units are prepared by citrate reduction of HAuCl4 followed by addition of the dithiocarbamate. The diallydithiocarbamate-functionalized nanoparticles undergo ring-closing metathesis using [Ru(═CHC6H4O(i)Pr-2)Cl2(SIMes)]. The interaction between the dithiocarbamate units and the gold surface is explored using computational methods to reveal no need for a countercation. Preliminary calculations indicate that the Au-S interactions are substantially different from those established in theoretical and experimental studies on thiolate-coated nanoparticles. Structural studies are reported for [Au{S2CN(CH2CH═CH2)2}(PPh3)] and [Au2{S2CN(CH2CH═CH2)2}2]. In the latter, exceptionally short intermolecular aurophilic interactions are observed.
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http://dx.doi.org/10.1021/ic402048aDOI Listing
March 2014

Copper-doped CdSe/ZnS quantum dots: controllable photoactivated copper(I) cation storage and release vectors for catalysis.

Angew Chem Int Ed Engl 2014 Feb 27;53(6):1598-601. Epub 2013 Dec 27.

Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ (UK).

The first photoactivated doped quantum dot vector for metal-ion release has been developed. A facile method for doping copper(I) cations within ZnS quantum dot shells was achieved through the use of metal-dithiocarbamates, with Cu(+) ions elucidated by X-ray photoelectron spectroscopy. Photoexcitation of the quantum dots has been shown to release Cu(+) ions, which was employed as an effective catalyst for the Huisgen [3+2] cycloaddition reaction. The relationship between the extent of doping, catalytic activity, and the fluorescence quenching was also explored.
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http://dx.doi.org/10.1002/anie.201308778DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4138996PMC
February 2014

Hydrogenase biomimetics: Fe2(CO)4(μ-dppf)(μ-pdt) (dppf = 1,1'-bis(diphenylphosphino)ferrocene) both a proton-reduction and hydrogen oxidation catalyst.

Chem Commun (Camb) 2014 Jan;50(8):945-7

Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.

Fe2(CO)4(μ-dppf)(μ-pdt) catalyses the conversion of protons and electrons into hydrogen and also the reverse reaction thus mimicing both types of binuclear hydrogenase enzymes.
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http://dx.doi.org/10.1039/c3cc46456cDOI Listing
January 2014

Models of the iron-only hydrogenase: a comparison of chelate and bridge isomers of Fe2(CO)4{Ph2PN(R)PPh2}(μ-pdt) as proton-reduction catalysts.

Dalton Trans 2013 May;42(19):6775-92

Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.

Reactions of Fe2(CO)6(μ-pdt) (pdt = SCH2CH2CH2S) with aminodiphosphines Ph2PN(R)PPh2 (R = allyl, (i)Pr, (i)Bu, p-tolyl, H) have been carried out under different conditions. At room temperature in MeCN with added Me3NO·2H2O, dibasal chelate complexes Fe2(CO)4{κ(2)-Ph2PN(R)PPh2}(μ-pdt) are formed, while in refluxing toluene bridge isomers Fe2(CO)4{μ-Ph2PN(R)PPh2}(μ-pdt) are the major products. Separate studies have shown that chelate complexes convert to the bridge isomers at higher temperatures. Two pairs of bridge and chelate isomers (R = allyl, (i)Pr) have been crystallographically characterised together with Fe2(CO)4{μ-Ph2PN(H)PPh2}(μ-pdt). Chelate complexes adopt the dibasal diphosphine arrangement in the solid state and exhibit very small P-Fe-P bite-angles, while the bridge complexes adopt the expected cisoid dibasal geometry. Density functional calculations have been carried out on the chelate and bridge isomers of the model compound Fe2(CO)4{Ph2PN(Me)PPh2}(μ-pdt) and reveal that the bridge isomer is thermodynamically favourable relative to the chelate isomers that are isoenergetic. The HOMO in each of the three isomers exhibits significant metal-metal bonding character, supporting a site-specific protonation of the iron-iron bond upon treatment with acid. Addition of HBF4·Et2O to the Fe2(CO)4{κ(2)-Ph2PN(allyl)PPh2}(μ-pdt) results in the clean formation of the corresponding dibasal hydride complex [Fe2(CO)4{κ(2)-Ph2PN(allyl)PPh2}(μ-H)(μ-pdt)][BF4], with spectroscopic measurements revealing the intermediate formation of a basal-apical isomer. A crystallographic study reveals that there are only very small metric changes upon protonation. In contrast, the bridge isomers react more slowly to form unstable species that cannot be isolated. Electrochemical and electrocatalysis studies have been carried out on the isomers of Fe2(CO)4{Ph2PN(allyl)PPh2}(μ-pdt). Electron accession is predicted to occur at an orbital that is anti-bonding with respect to the two metal centres based on the DFT calculations. The LUMO in the isomeric model compounds is similar in nature and is best described as an antibonding Fe-Fe interaction that contains differing amounts of aryl π* contributions from the ancillary PNP ligand. The proton reduction catalysis observed under electrochemical conditions at ca. -1.55 V is discussed as a function of the initial isomer and a mechanism that involves an initial protonation step involving the iron-iron bond. The measured CV currents were higher at this potential for the chelating complex, indicating faster turnover. Digital simulations showed that the faster rate of catalysis of the chelating complex can be traced to its greater propensity for protonation. This supports the theory that asymmetric distribution of electron density along the iron-iron bond leads to faster catalysis for models of the Fe-Fe hydrogenase active site.
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http://dx.doi.org/10.1039/c3dt50147gDOI Listing
May 2013

Metal-dithiocarbamate complexes: chemistry and biological activity.

Authors:
Graeme Hogarth

Mini Rev Med Chem 2012 Oct;12(12):1202-15

Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.

Dithiocarbamates are highly versatile mono-anionic chelating ligands which form stable complexes with all the transition elements and also the majority of main group, lanthanide and actinide elements. They are easily prepared from primary or secondary amines and depending upon the nature of the cation can show good solubility in water or organic solvents. They are related to the thiuram disulfides by a one-electron redox process (followed by dimerisation via sulfur-sulfur bond formation) which is easily carried out upon addition of iodide or ferric salts. Dithiocarbamates are lipophilic and generally bind to metals in a symmetrical chelate fashion but examples of other coordination modes are known, the monodentate and anisobidentate modes being most prevalent. They are planar sterically non-demanding ligands which can be electronically tuned by judicious choice of substituents. They stabilize metals in a wide range of oxidation states, this being attributed to the existence of soft dithiocarbamate and hard thioureide resonance forms, the latter formally resulting from delocalization of the nitrogen lone pair onto the sulfurs, and consequently their complexes tend to have a rich electrochemistry. Tetraethyl thiuramdisulfide (disulfiram or antabuse) has been used as a drug since the 1950s but it is only recently that dithiocarbamate complexes have been explored within the medicinal domain. Over the past two decades anti-cancer activity has been noted for gold and copper complexes, technetium and copper complexes have been used in PET-imaging, dithiocarbamates have been used to treat acute cadmium poisoning and copper complexes also have been investigated as SOD inhibitors.
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http://dx.doi.org/10.2174/138955712802762095DOI Listing
October 2012

The effects of ligand variation on enantioselective hydrogenation catalysed by RuH2(diphosphine)(diamine) complexes.

Dalton Trans 2012 Feb 14;41(6):1867-77. Epub 2011 Dec 14.

Department of Chemistry, University College London, 20 Gordon Street, London, United Kingdom WC1H 0AJ.

Density functional theory calculations have been used to investigate the hydrogenation of acetophenone (ACP) catalysed by the RuH(2)(diphosphine)(diamine) complexes with emphasis on the effect of the structure of the diphosphine and diamine ligands on the enantioselectivity. The computed reaction coordinate diagrams of RuH(2)(diphosphine)[(S,S)-DPEN] catalysed reactions with different (S)-diphosphine ligands (XylBINAP, TolBINAP, and BINAP) show that the presence of two methyl groups in the meta position is critical to obtaining a high difference in activation energy for the reaction pathways associated with the (R)- and (S)-alcohols, and consequently high enantioselectivity. The effect of the diamine structure while keeping the TolBINAP and XylBINAP fixed has also been analysed. To enhance the enantioselectivity of the TolBINAP system, the addition of two methyl groups and the removal of a phenyl group of the diamine (DMAPEN) offer the necessary steric interactions. We conclude by reporting a correlation between the enantiomeric excess and the difference in the computed activation energies of the two most favourable (S) and (R) reaction pathways, which shows that the computational procedure adopted could be used to predict the enantiomeric excess of ketone hydrogenation reactions catalysed by the Noyori-type catalysts, and assist in the choice of ligand when optimising the enantiomeric excess.
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http://dx.doi.org/10.1039/c1dt11244aDOI Listing
February 2012

Bio-inspired hydrogenase models: mixed-valence triion complexes as proton reduction catalysts.

Chem Commun (Camb) 2011 Oct 13;47(40):11222-4. Epub 2011 Sep 13.

Department of Chemistry, Jahangirnager University, Savar, Dhaka-1342, Bangladesh.

Mixed-valence triiron complexes Fe(3)(CO)(7-x)(PPh(3))(x)(μ-edt)(2) (x = 0-2) have been prepared and are shown to act as proton reduction catalysts. Catalysis takes place via an ECEC mechanism with a reduced overpotential of ca. 0.45 V for Fe(3)(CO)(7)(μ-edt)(2) as compared to the corresponding diiron complex.
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http://dx.doi.org/10.1039/c1cc13249kDOI Listing
October 2011

Multimetallic complexes of group 10 and 11 metals based on polydentate dithiocarbamate ligands.

Dalton Trans 2011 Jun 9;40(22):5852-64. Epub 2011 Mar 9.

Department of Chemistry, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK.

The ligands KS(2)CN(Bz)CH(2)CH(2)N(Bz)CS(2)K (K(2)L(1)), N(CH(2)CH(2)N(Me)CS(2)Na)(3) (Na(3)L(2)), and the new chelates {(CH(2)CH(2))NCS(2)Na}(3) (Na(3)L(3)) and {CH(2)CH(2)N(CS(2)Na)CH(2)CH(2)CH(2)NCS(2)Na}(2) (Na(4)L(4)), react with the gold(I) complexes [ClAu(PR(3))] (R = Me, Ph, Cy) and [ClAu(IDip)] to yield di-, tri-and tetragold compounds. Larger metal units can also be coordinated by the longer, flexible linker, K(2)L(1). Thus two equivalents of cis-[PtCl(2)(PEt(3))(2)] react with K(2)L(1) in the presence of NH(4)PF(6) to yield the bimetallic complex [L(1){Pt(PEt(3))(2)}(2)](PF(6))(2). The compounds [NiCl(2)(dppp)] and [MCl(2)(dppf)] (M = Ni, Pd, Pt; dppp = 1,3-bis(diphenylphosphino)propane, dppf = 1,1'-bis(diphenylphosphino)ferrocene) also yield the dications, [L(1){Ni(dppp)}(2)](2+) and [L(1){Ni(dppf)}(2)](2+) in an analogous fashion. In the same manner, reaction between [(L'(2))(AuCl)(2)] (L'(2) = dppm, dppf; dppm = bis(diphenylphosphino)methane) and KS(2)CN(Bz)CH(2)CH(2)N(Bz)CS(2)K yield [L(1){Au(2)(L'(2))}(2)]. The molecular structures of [L(1){M(dppf)}(2)](PF(6))(2) (M = Ni, Pd) and [L(1){Au(PR(3))}(2)] (R = Me, Ph) are reported.
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http://dx.doi.org/10.1039/c0dt01745kDOI Listing
June 2011

trans-Fe(II)(H)2(diphosphine)(diamine) complexes as alternative catalysts for the asymmetric hydrogenation of ketones? A DFT study.

Dalton Trans 2011 Jan 23;40(2):402-12. Epub 2010 Nov 23.

Kathleen Lonsdale Building, Department of Chemistry, University College London, Gower Street, London, United Kingdom WC1E 6BT.

New insights into the structural, electronic and catalytic properties of Fe complexes are provided by a density functional theory study of model as well as real [Fe(II)(H)(2)(diphosphine)(diamine)] systems. Calculations conducted using several different functionals on the trans- and cis-isomers of [Fe(II)(H)(2)(S-xylbinap)(S,S-dpen)] complexes show that, as with the [Ru(II)(H)(2)(diphosphine)(diamine)] complexes, the trans-[Fe(II)(H)(2)(diphosphine)(diamine)] complex is the more stable isomer. Analysis of the spin states of the trans-[Fe(II)(H)(2)(diphosphine)(diamine)] complexes also shows that the singlet state is significantly more stable than the triplet and the quintet, as with the [Ru(II)(H)(2)(diphosphine)(diamine)] complexes. Calculations of the catalytic cycle for the hydrogenation of ketones using two model trans-[M(II)(H)(2)(PH(3))(2)(en)] catalysts, where M = Ru and Fe, show that the mechanism of reaction as well as the activation energies are very similar, in particular: (i) the ketone/alcohol hydrogen transfer reaction occurs through the metal-ligand bifunctional mechanism, with energy barriers of 3.4 and 3.2 kcal mol(-1) for the Ru- and Fe-catalysed reactions, respectively; (ii) the heterolytic splitting of H(2) across the M[partial double bond, bottom dashed]N bond for the regeneration of the Ru and Fe catalysts has an activation barrier of 13.8 and 12.8 kcal mol(-1), respectively, and is expected to be the rate determining step for both catalytic systems. The reduction of acetophenone by trans-[M(II)(H)(2)(S-xylbinap)(S,S-dpen)] complexes along two competitive reaction pathways, shows that the intermediates for the Fe catalytic system are similar to those responsible for the high enantioselectivity of (R)-alcohol in those proposed trans-[Ru(II)(H)(2)(S-xylbinap)(S,S-dpen)] catalysed acetophenone hydrogenation reaction. Thus the high enantiomeric excess in the hydrogenation of acetophenone could, in principle, be achieved using Fe catalysts.
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http://dx.doi.org/10.1039/c0dt00820fDOI Listing
January 2011

Cluster chemistry in the Noughties: new developments and their relationship to nanoparticles.

Dalton Trans 2010 Jul 15;39(27):6153-74. Epub 2010 Jun 15.

Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.

Over the past decade, the chemistry of low-valent transition metal clusters has again come to the fore, primarily as a result of the development of nanochemistry and the realization that large clusters are on the cusp of the nano-domain. This perspective focuses on these recent developments in low-valent transition metal cluster chemistry, specifically looking at cluster-nanoparticles, the use of small and medium sized clusters as nanoparticle precursors, the development of clusters as homogeneous catalysts and hydrogen uptake and storage systems, together with fundamental discoveries relating to novel transformations that can take place within the cluster framework.
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http://dx.doi.org/10.1039/c000514bDOI Listing
July 2010

The functionalisation of ruthenium(II) and osmium(II) alkenyl complexes with amine- and alkoxy-terminated dithiocarbamates.

Dalton Trans 2010 May 11;39(17):4080-9. Epub 2010 Mar 11.

Department of Chemistry, Imperial College London, South Kensington Campus, London, UK SW7 2AZ.

The complex cis-[RuCl(2)(dppm)(2)] reacts with the amine-terminated dithiocarbamates KS(2)CN(CH(2)CH(2)NEt(2))(2) and KS(2)CN(CH(2)CH(2)CH(2)NMe(2))(2) to form the compounds [Ru{S(2)CN(CH(2)CH(2)NEt(2))(2)}(dppm)(2)](+) and [Ru{S(2)CN(CH(2)CH(2)CH(2)NMe(2))(2)}(dppm)(2)](+), respectively. The methoxy-terminated dithiocarbamate compound [Ru{S(2)CN(CH(2)CH(2)OMe)(2)}(dppm)(2)](+) was also prepared from the same precursor using KS(2)CN(CH(2)CH(2)OMe)(2). The alkenyl complexes [RuRCl(CO)(BTD)(PPh(3))(2)] (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, CH=CHCPh(2)OH), [Ru(C(C[triple bond]CBu(t))=CHBu(t))Cl(CO)(PPh(3))(2)] and [Os(CH=CHC(6)H(4)Me-4)Cl(CO)(BTD)(PPh(3))(2)] also react cleanly with KS(2)CN(CH(2)CH(2)CH(2)NMe(2))(2) and KS(2)CN(CH(2)CH(2)NEt(2))(2) to yield [MR{S(2)CN(CH(2)CH(2)CH(2)NMe(2))(2)}(CO)(PPh(3))(2)] and [MR{S(2)CN(CH(2)CH(2)NEt(2))(2)}(CO)(PPh(3))(2)], respectively. In a similar fashion, the compounds [RuR{S(2)CN(CH(2)CH(2)OMe(2))(2)}(CO)(PPh(3))(2)] (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C[triple bond]CBu(t))=CHBu(t)) were also prepared. Treatment of [Ru(CH=CHBu(t)){S(2)CN(CH(2)CH(2)CH(2)NMe(2))(2)}(CO)(PPh(3))(2)] and [Ru{S(2)CN(CH(2)CH(2)NEt(2))(2)}(dppm)(2)](+) with trifluoroacetic acid affords the ammonium complexes [Ru(CH=CHBu(t)){S(2)CN(CH(2)CH(2)CH(2)NHMe(2))(2)}(CO)(PPh(3))(2)](2+) and [Ru{S(2)CN(CH(2)CH(2)NHEt(2))(2)}(dppm)(2)](2+), while the same reagent generates the tricationic vinylcarbene complex [Ru(=CHCH=CPh(2)){S(2)CN(CH(2)CH(2)CH(2)NHMe(2))(2)}(CO)(PPh(3))(2)](3+) through loss of water from [Ru(CH=CHCPh(2)OH){S(2)CN(CH(2)CH(2)CH(2)NMe(2))(2)}(CO)(PPh(3))(2)]. The structures of [Ru{S(2)CN(CH(2)CH(2)OMe)(2)}(dppm)(2)]PF(6) and [Ru(CH=CHC(6)H(4)Me-4){S(2)CN(CH(2)CH(2)OMe)(2)}(CO)(PPh(3))(2)] were determined crystallographically.
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http://dx.doi.org/10.1039/b925536bDOI Listing
May 2010

Multimetallic arrays: symmetrical bi-, tri- and tetrametallic complexes based on the group 10 metals and the functionalisation of gold nanoparticles with nickel-phosphine surface units.

Dalton Trans 2009 May 13(19):3688-97. Epub 2009 Mar 13.

Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, UK OX1 3TA.

Homobimetallic complexes of nickel, palladium and platinum, [(L2M)2(S2CNC4H8NCS2)]2+, are formed on reaction of the piperazine bis(dithiocarbamate) linker, KS2CNC4H8NCS2K, with [MCl2L2] (M=Ni, L2=dppe, dppf; M=Pd, L2=dppf; M=Pt, L=PEt3, PMePh2, PPh3, L2=dppf). [{Pd(C,N-C6H4CH2NMe2)}2(S2CNC4H8NCS2)] can be obtained in the same way. On reaction of [MCl2L2] (M=Pd, Pt) with the zwitterion S2CNC4H8NH2, a symmetrisation process occurs to yield a mixture of the complexes [M(S2CNC4H8NH2)L2]2+ and [(L2M)2(S2CNC4H8NCS2)]2+. However, the monometallic complexes [L2Ni(S2CNC4H8NH2)]2+ (L2=dppe, dppf) and [(L2Ni)2(S2CNC4H8NCS2)]2+ can be prepared without ready symmetrisation. Starting from the previously reported [(dppm)Ru(S2CNC4H8NH2)]2+, the heterotrimetallic products [(dppm)Ru(S2CNC4H8NCS2)M(dppf)]2+ (M=Pd, Pt) can be prepared without symmetrisation occurring. The crystal structures of five complexes are reported. The metalla-dithiocarbamate complexes [L2Ni(S2CNC4H8NCS2)] (L2=dppe, dppf) were used to functionalise the surface of gold nanoparticles by the displacement of a citrate shell to yield NiAu and FeNiAu materials.
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http://dx.doi.org/10.1039/b821947hDOI Listing
May 2009