Bis Gold Research Articles

Structure-activity relationship of anticancer and antiplasmodial gold bis(dithiolene) complexes.

Monoanionic gold bis(dithiolene) complexes were recently shown to display activity against ovarian cancer cells, Gram-positive bacteria, Candida strains and the rodent malaria parasite, P. berghei. To date, only monoanionic gold(III) bis(dithiolene) complexes with a thiazoline backbone substituted with small alkyl chains have been evaluated for biomedical applications. We now analyzed the influence of the length and the hydrophobicity vs. hydrophilicity of these complexes' alkyl chain on their anticancer and antiplasmodial properties. Isomer analogues of these monoanionic gold(III) bis(dithiolene) complexes, this time with a thiazole backbone, were also investigated in order to assess the influence of the nature of the heterocyclic ligand on their overall chemical and biological properties. In this report we present the total synthesis of four novel monoanionic gold(III) bis(dithiolene) complexes with a long alkyl chain and a polyoxygenated (PEG) chain aiming to improve their solubility and biological properties. Our results showed that the complexes with a PEG chain showed promising anticancer and antiplasmodial activities beside improved solubility, a key parameter in drug discovery and development.

Mixed-ligand, radical, gold bis(dithiolene) complexes: from single-component conductors to controllable NIR-II absorbers.

Neutral radical bis(dithiolene) gold complexes [Au(dt)2]˙ are known to exhibit a strong absorption in the 1400-2000 nm NIR absorption range. Here, we demonstrate that the NIR signature of mixed-ligand bis(dithiolene) gold complexes [Au(dtA)(dtD)]˙ associating two different dithiolene, dtA and dtD, is found at higher energy, out of the range of the homoleptic analogs [Au(dtA)2]˙ and [Au(dtD)2]˙, in the looked-after NIR-II 1000-1400 nm absorption range. An efficient synthetic approach towards precursor mixed-ligand monoanionic gold bis(dithiolene) complexes [Au(dtA)(dtD)]-1 is reported. Using this strategy, no symmetrical complexes are formed and, upon electrocrystallization, no scrambling was observed in solution, allowing for the isolation of radical gold bis(dithiolene) complex such as [Au(bdt)(Et-thiazdt)]˙ (bdt: benzene-1,2-dithiolate; Et-thiazdt: N-ethyl-thiazoline-2-thione-3,4-dithiolate), which behaves as a single-component conductor. It is shown from theoretical calculations that the spin polarization induced by electron repulsions leads to a strong localization of the spin-orbitals, and provides a sound basis to understand, (i) the different ligand-based oxidation potentials, (ii) the NIR optical absorption at notably higher energies and (iii) the larger potential difference of the two redox processes than in the parent symmetric complexes. The solid-state properties of the radical complex [Au(bdt)(Et-thiazdt)]˙ are the consequence of a strongly 1D electronic structure with weakly dimerized chains and electronic localization favoring a semiconducting behavior, stable under pressures up to 18.2 GPa. Altogether, the versatility of the preparation method of [Au(dtA)(dtD)]-1 salts opens the route for a wide library of different mixed-ligand radical complexes [Au(dtA)(dtD)]˙ with simultaneously an adaptable absorption in the NIR-II range and the rich structural chemistry of single-component conductors.

Influence of bulky groups in single-component conductors based on neutral radical gold bis(dithiolene) complexes

Influence of bulky groups in single-component conductors based on neutral radical gold bis(dithiolene) complexes

Mixed-valence gold bis(diselenolene) complex turning metallic under pressure

A rare mixed-valence gold bis(diselenolene) complex, exhibiting charge order between cis and trans isomers stabilized by C–H⋯S interactions, turns metallic under high pressure (>10 GPa)

A radical mixed-ligand gold bis(dithiolene) complex.

A mixed-ligand bis(dithiolene) gold complex is isolated from scrambling reaction of two neutral radical symmetric complexes. Its asymmetric character translates into specific structural and electronic properties including larger electrochemical and optical band gaps than those of both precursors.

Monolithic Nanoporous Gold Foams with Catalytic Activity for Chemical Vapor Deposition Growth of Carbon Nanostructures

While bulk gold is generally considered to be a catalytically inactive material, nanostructured forms of gold can in fact be highly catalytically active. However, few methods exist for preparing high-purity macroscopic forms of catalytically active gold. In this work, we describe the synthesis of catalytically active macroscopic nanoporous gold foams via combustion synthesis of gold bis(tetrazolato)amine complexes. The resulting metallically pure porous gold nanoarchitectures exhibit bulk densities of <0.1 g/cm3 and Brunauer-Emmett-Teller (BET) surface areas as high as 10.9 m2/g, making them among the lowest-density and highest-surface-area monolithic forms of gold produced to date. Thanks to the presence of a highly nanostructured gold surface, such gold nanofoams have also been found to be highly catalytically active toward thermal chemical vapor deposition (CVD) growth of carbon nanotubes, providing a novel method for direct synthesis of carbon nanostructures on macroscopic gold substrates. In contrast, analogous copper nanofoams were found to be catalytically inactive toward the growth of graphitic nanostructures under the same synthesis conditions, highlighting the unusually high catalytic propensity of this form factor of gold. The combustion synthesis process described herein represents a never-wet approach for directly synthesizing macroscopic catalytically active gold. Unlike sol-gel and dealloying approaches, combustion synthesis eliminates the time-consuming diffusion-mediated steps associated with previous methods and offers multiple degrees of freedom for tuning morphology, electrical conductivity, and mechanical properties.

Stable Metallic State of a Neutral-Radical Single-Component Conductor at Ambient Pressure.

Molecular metals have been essentially obtained with tetrathiafulvalene (TTF)-based precursors, either with multicomponent ionic materials or, in a few instances, with single-component systems. In that respect, gold bis(dithiolene) complexes, in their neutral radical state, provide a prototype platform toward such single-component conductors. Herein we report the first single-component molecular metal under ambient pressure derived from such Au complexes without any TTF backbone. This complex exhibits a conductivity of 750 S·cm-1 at 300 K up to 3800 S·cm-1 at 4 K. First-principles electronic structure calculations show that the striking stability of the metallic state finds its origin in sizable internal electron transfer from the SOMO-1 to the SOMO of the complex as well as in substantial interstack and interlayer interactions.

Subtle Steric Differences Impact the Structural and Conducting Properties of Radical Gold Bis(dithiolene) Complexes.

Among single component molecular conductors, neutral radical gold dithiolene complexes [(R-thiazdt)2 Au]. derived from the N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate (R-thiazdt) ligand provide an extensive series of conducting, non-dimerized, half-filled band systems. Analogues of the known R=isopropyl (iPr) derivative were investigated here with R=NMe2 , cyclopropyl (cPr) and n-propyl (nPr), aiming at rationalizing the different solid state structures adopted by these compounds despite very closely related substituents on the heterocyclic nitrogen atom. An original crisscross organization within dimerized chains is observed with R=NMe2 , differing however from the analogous iPr derivative by a 180° rotation of the heterocyclic nitrogen substituent. On the other hand, the cyclopropyl and n-propyl substituents lead to robust, uniform, non-dimerized chains with a strongly 1 D electronic structure and a formal half-filled electronic structure. The semiconducting behaviour of these two radical complexes is characteristic of a Mott insulator, whose sensitivity to external pressure has been evaluated up to 2.5 GPa.

Efficient Synthesis of One‐ and Two‐Dimensional Multimetallic Gold–Bis(dithiolene) Complexes

Multimetallic complexes having π‐conjugated dithiolate ligands have recently received attention because of their unique solid‐state properties. Reported herein are efficient and versatile routes for the synthesis of structurally well‐defined multimetallic gold–bis(dithiolene) complexes. A dichlorogold(III) complex having a benzene‐1,2‐dithiolate ligand was prepared as a key terminal unit. A one‐dimensional dimetallic gold complex was synthesized in good yield by using benzene‐1,2,4,5‐tetrathiolate as a bridging ligand. Furthermore, by using benzenehexathiolate as a bridging ligand, this strategy was applied to the synthesis of a two‐dimensional trimetallic complex with a starburst structure. The solid‐state structures of the anionic complexes were unambiguously confirmed by X‐ray diffraction analyses.

Localization versus Delocalization in Chiral Single Component Conductors of Gold Bis(dithiolene) Complexes.

The first examples of chiral single component conductors are reported. Both (S,S) and (R,R) enantiomers of 5,6-dimethyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (dm-dddt) ligand have been used to prepare anionic metal bis(dithiolene) complexes formulated as ([(n-Bu)4N][M(dm-dddt)2] (M = Au, Ni), which are isostructural according to single crystal X-ray analysis. Single crystal transport measurements indicate semiconducting behavior for the anionic radical Ni complexes, with low room temperature conductivity values and high activation energies. Electrocrystallization experiments provided neutral [M(dm-dddt)2] (M = Au, Ni) complexes. The neutral radical gold compounds show intermolecular S···S interactions in the solid state giving rise to layers interconnected through weak C-H···S hydrogen bonds. The most peculiar structural feature concerns a dissymmetry between the two dithiolene moieties, while the nickel counterpart is symmetric. Single crystal resistivity measurements show thermally activated behavior for the open-shell gold complexes, with room temperature conductivity values of 0.02-0.04 S·cm(-1) and activation energies strongly influenced by hydrostatic pressure. A thorough theoretical study on nickel anion radical and gold neutral radical bis(dithiolene) complexes applied to the chiral complexes [M(dm-dddt)2] (M = Au, Ni(-)) and to a series of previously reported compounds addressed the issue of symmetry versus asymmetry from an electronic coupling perspective between the two dithiolene ligands. It results that neutral gold complexes with dithiolene ligands without extended delocalization are Class II mixed-valent compounds in the Robin and Day classification, presenting an inherent tendency toward asymmetric structures, which can be however modulated by the intermolecular organization in the solid state.

Chiral, radical, gold bis(dithiolene) complexes

Chiral gold(iii) dithiolene complexes are investigated for further oxidation to the neutral radical species, as potential single component conductors.

Dimeric Gold Bis(carbene) Complexes by Transmetalation in Water

Due to its cost, environmental benefits, and safety advantages, water has become more and more important as a solvent for catalytic reactions and constitutes the best environment for biomedical applications. Therefore, water-soluble and water-stable metal complexes containing strong σ-donor ligands such as N-heterocyclic carbenes (NHCs) are of great interest in modern coordination chemistry. In this paper we present the successful preparation of two new dinuclear gold(I)–bis(NHC) complexes in water, by applying the Ag–NHC transfer route. This green synthetic strategy is valuable for gold(I) compounds involving N-functionalized neutral and dianionic bis(NHC) ligands. These two water-soluble compounds were analyzed by spectroscopic methods and by X-ray diffraction. Furthermore, ab initio and DFT calculations on the corresponding dinuclear gold complexes illustrate the important influence of the electrostatic environment of the dinuclear entity on the aurophilic interactions and help to understand the molecular arrangement presented in this paper.

Gold(I)‐Catalyzed Tandem Alkoxylation/Lactonization of γ‐Hydroxy‐α,β‐Acetylenic Esters

AbstractThe formation of 4‐alkoxy‐2(5H)‐furanones was achieved via tandem alkoxylation/lactonization of γ‐hydroxy‐α,β‐acetylenic esters catalyzed by 2 mol% of [2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine]gold bis(trifluoromethanesulfonyl)imidate [Au(IPr)(NTf2)]. The economic and simple procedure was applied to a series of various secondary propargylic alcohols allowing for yields of desired product of up to 95%. In addition, tertiary propargylic alcohols bearing mostly cyclic substituents were converted into the corresponding spiro derivatives. Both primary and secondary alcohols reacted with propargylic alcohols at moderate temperatures (65–80 °C) in either neat reactions or using 1,2‐dichloroethane as a reaction medium allowing for yields of 23–95%. In contrast to [Au(IPr)(NTf2)], reactions with cationic complexes such as [2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine](acetonitrile)gold tetrafluoroborate [Au(IPr)(CH3CN)][BF4] or (μ‐hydroxy)bis{[2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine]gold} tetrafluoroborate or bis(trifluoromethanesulfonyl)imidate – [{Au(IPr)}2(μ‐OH)][X] (X=BF4, NTf2) – mostly stop after the alkoxylation. Analysis of the intermediate proved the exclusive formation of the E‐isomer which allows for the subsequent lactonization.

Dimensionality of coordination polymers decided by the type of hybridization of the central carbon atom of the solvent molecule that coordinates to an alkali metal cation: from discrete to 3D networks based on a gold(iii) bis(dithiolene) complex

The solvent coordination with sodium metal ions leads to the formation of coordination polymers from discrete to 3D networks based on a gold bis(dithiolene) complex {[AuIII(btdt)2]−} (btdt = 2,1,3-benzenethiadiazole-5,6-dithilolate); all these complexes show great discrepancy in dimensionality of the self assembled coordinated networks due to the effect of solvents, which we have explained in terms of the difference in geometry of the hybridized orbitals of the central carbon attached to the coordinating atom (N or O in the present study).

A Single-Component Molecular Metal Based on a Thiazole Dithiolate Gold Complex

A single component molecular conductor has been isolated from electrocrystallization of the monoanionic gold bis(dithiolene) complex based on the N-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate (Et-thiazdt) ligand. The crystal structure of the system exhibits layers built from parallel uniform one-dimensional stacks of the planar molecule. At room temperature and ambient pressure the system is semiconducting (0.33 S x cm(-1)) with a small activation energy. However, the single crystal conductivity is strongly pressure dependent reaching 1000 S x cm(-1) at 21 kbar. At 13 kbar there is a crossover between semiconducting and metallic regimes. Thus, the present system is the first well characterized single-component molecular metal without TTF dithiolate ligands. First-principles DFT calculations show that the ground state is antiferromagnetic with a very small band gap. A simulation of the effect of pressure on the electronic structure provides a rationale for the observed variations of the conductivity and gives insight on how to further stabilize the metallic state of the system.

A new view on gold speciation in sulfur-bearing hydrothermal fluids from in situ X-ray absorption spectroscopy and quantum-chemical modeling

Despite the common belief that Au I complexes with hydrogen sulfide ligands (H 2S/HS −) are the major carriers of gold in natural hydrothermal fluids, their identity, structure and stability are still subjects of debate. Here we present the first in situ measurement, using X-ray absorption fine structure (XAFS) spectroscopy, of the stability and structure of aqueous Au I–S complexes at temperatures and pressures ( T–P) typical of natural sulfur-rich ore-forming fluids. The solubility of native gold and the local atomic structure around the dissolved metal in S–NaOH–Na 2SO 4–H 2SO 4 aqueous solutions were characterized at temperatures 200–450 °C and pressures 300–600 bar using an X-ray cell that allows simultaneous measurement of the absolute concentration of the absorbing atom (Au) and its local atomic environment in the fluid phase. Structural and solubility data obtained from XAFS spectra, combined with quantum-chemical calculations of species geometries, show that gold bis(hydrogensulfide) Au(HS) 2 − is the dominant Au species in neutral-to-basic solutions (5.5 ⩽ pH ⩽ 8.5; H 2O–S–NaOH) over a wide range of sulfur concentrations (0.2 < ΣS < 3.6 mol/kg), in agreement with previous solubility studies. Our results provide the first direct determination of this species structure, in which two sulfur atoms are in a linear geometry around Au I at an average distance of 2.29 ± 0.01 Å. At acidic conditions (1.5 ⩽ pH ⩽ 5.0; H 2O–S–Na 2SO 4–H 2SO 4), the Au atomic environment determined by XAFS is similar to that in neutral solutions. These findings, together with measured high Au solubilities, are inconsistent with the predominance of the gold hydrogensulfide Au(HS) 0 complex suggested by recent solubility studies. Our spectroscopic data and quantum-chemical calculations imply the formation of species composed of linear S–Au–S moieties, like the neutral [H 2S–Au–SH] complex. This species may account for the elevated Au solubilities in acidic fluids and vapors with H 2S concentrations higher than 0.1–0.2 mol/kg. However, because of the complex sulfur speciation in acidic solutions that involves sulfite, thiosulfate and polysulfide species, the formation of Au I complexes with these ligands (e.g., AuHS(SO 2) 0, Au(HS 2O 3) 2 −, Au(HS n ) 2 −) cannot be ruled out. The existence of such species may significantly enhance Au transport by high T–P acidic ore-forming fluids and vapors, responsible for the formation of a major part of the gold resources on Earth.

Cycloisomerization of (arene)chromium complexes with enyne by gold(I) catalyst for axially chiral biaryls

Planar chiral arene chromium complexes with enyne bond gave stereoselectively axial biaryl chromium complexes by gold(I) catalyzed cycloisomerization in good yields. Arene chromium complexes with enyne bonds were treated with triphenylphosphine gold bis(trifluoromethanesulfonyl)imidate in methylene chloride to give anti-biaryl monochromium complexes without formation of stereoisomers.

Coordination complexes of the hydroxymethylphosphine FcCH 2P(CH 2OH) 2 [Fc=( η5-C 5H 5)Fe( η5-C 5H 4)] and the X-ray crystal structure of the cationic gold bis(phosphine) complex [Au{FcCH 2P(CH 2OH) 2} 2]Cl

Platinum(II) and palladium(II) complexes MCl 2L 2 and the gold(I) complex [AuL 2]Cl of the air-stable ferrocene-derived hydroxymethylphosphine FcCH 2P(CH 2OH) 2 (L) have been synthesised by ligand substitution reactions, and the η 6- p-cymene ruthenium(II) complex RuCl 2( η 6-C 10H 14)L has been synthesised by a chloride bridge-splitting reaction of the dimer [RuCl 2( η 6-C 10H 14)] 2. The cationic gold complex has been the subject of a single-crystal X-ray diffraction study, which shows the presence of the expected linearly coordinated bis(phosphine)gold cation, hydrogen-bonded to the chloride counterion and a lattice water molecule.

The first example of a gold bis(diphenylphosphino)methane cationic dimer with a bridging iodide. The X-ray crystal structures of (μ-I)[Au(dppm)] 2[I] and [Au(dppm)Br] 2

(μ-I)[Au(dppm)] 2 [I] cristallise dans le systeme orthorhombique avec le groupe d'espace P2 1 2 1 2 1 . [Au(dppm)Br] 2 cristallise dans le systeme triclinique avec le groupe d'espace P1. Affinement de la structure jusqu'a 0,0425 et 0,0535 respectivement

Bis(diphenylmethylphosphine)gold(I) hexafluorophosphate

Bis(diphenylmethylphosphine)gold(I) hexafluorophosphate