AuIII Complexes Research Articles

In Vivo Gold Complex Catalysis within Live Mice

AbstractMetal complex catalysis within biological systems is largely limited to cell and bacterial systems. In this work, a glycoalbumin–AuIII complex was designed and developed that enables organ‐specific, localized propargyl ester amidation with nearby proteins within live mice. The targeted reactivity can be imaged through the use of Cy7.5‐ and TAMRA‐linked propargyl ester based fluorescent probes. This targeting system could enable the exploitation of other metal catalysis strategies for biomedical and clinical applications.

Rationally Designed Blue Triplet Emitting Gold(III) Complexes Based on a Phenylpyridine-Derived Framework.

A series of blue-emitting phosphorescent mono-cyclometalated AuIII complexes have been successfully synthesized. Tailoring the substitutions on the phenylpyridine (ppy) ligand scaffold with electron-withdrawing fluorine groups on the phenyl ring to achieve stabilization of the HOMO and an electron-donating dimethylamino group on the pyridine ring to destabilize the LUMO resulted in a large energy gap and bestowed on the gold(III) complexes high-energy emission and high quantum efficiencies. The results of cyclic voltammetry studies suggested a predominantly redox event localized on the cyclometalated ligand. Thermogravimetric analysis of selected complexes revealed a high stability up to 280 °C, thus the complexes are suitable for device fabrication through vacuum-deposition. Photophysical investigations performed on all the derivatives revealed phosphorescence emission in neat solid, solution, doped in poly(methyl methacrylate) (PMMA) films at room temperature as well as in rigidified glass media (2-MeTHF) at 77 K. A high photoluminescent quantum efficiency of 28 % was obtained for a complex in PMMA, the highest quantum yield reported for a blue-emitting gold(III) complex.

Stable AuIII complexes with four N-heterocyclic carbene groups can be prepared in high yield directly from KAuCl4.

Gold(iii) N-heterocyclic carbene (NHC) complexes of form [Au(NHC)4Cl2]Cl were synthesized by reaction of KAuCl4 with bis- and tetrakis(imidazolium) salts in the presence of a mild base. Treatment of these complexes with KPF6 afforded four-coordinate AuIII complexes of form [Au(NHC)4](PF6)3. X-Ray crystallography showed the [AuIII(NHC)4]3+ cations in the hexafluorophosphate salts to have a square planar Au(NHC)4 moiety [AuCNHC 2.024(4)-2.082(7) Å]. In the [AuIII(NHC)4Cl2]+ cations in the chloride salts, coordination about Au was tetragonally-distorted octahedral, the axial Au-Cl bonds being substantially longer [AuCl 3.148(2)-3.693(1) Å] than the equatorial Au-CNHC bonds [AuC 2.024(4)-2.082(7) Å]. NMR and conductance studies suggested that the structures of the complexes seen in the solid state persisted in DMSO solution, except in one case where a chlorido ligand dissociated from [AuIII(NHC)4Cl2]+ to form [AuIII(NHC)4Cl]2+. The AuIII(NHC)4 unit was surprisingly robust. An AuIII complex was found to undergo H/D exchange reactions in D2O solution at 100 °C with no signs of decomposition detectable by 1H NMR spectroscopy. 1H NMR studies showed that various complexes containing AuIII(NHC)4 moieties underwent little or no decomposition when heated at 120 °C in DMSO-d6 for extended periods.

Visible-Light-Promoted AuI to AuIII Oxidation in Triazol-5-ylidene Complexes.

Reaction of triazolium precursors [MIC(CH2 )n - H+ ]I- (n=1-3) with potassium hexamethyldisilazane (KHMDS) and AuCl(SMe2 ) generates the gold(I) complexes of the type MIC(CH2 )n ⋅AuI. Visible light exposure of the latter complexes promotes a spontaneous disproportionation process rendering gold(III) complexes of the type [{MIC(CH2 )n }2 ⋅AuI2 ]+ I- . Both the AuI and AuIII complex series were tested in the catalytic hydrohydrazination of terminal alkynes using hydrazine as nitrogen source.

Well‐Defined Dinuclear Gold Complexes for Preorganization‐Induced Selective Dual Gold Catalysis

AbstractThe synthesis, reactivity, and potential of well‐defined dinuclear gold complexes as precursors for dual gold catalysis are explored. Using the preorganizing abilities of the ditopic PNHPiPr (LH) ligand, dinuclear AuI–AuI complex 1 and mixed‐valent AuI–AuIII complex 2 provide access to structurally characterized chlorido‐bridged cationic species 3 and 4 upon halide abstraction. For 2, this transformation involves unprecedented two‐electron oxidation of the redox‐active ligand, generating a highly rigidified environment for the Au2 core. Facile reaction with phenylacetylene affords the σ,π‐activated phenylacetylide complex 5. When applied in the dual gold heterocycloaddition of a urea‐functionalized alkyne, well‐defined precatalyst 3 provides high regioselectivities for the anti‐Markovnikov product, even at low catalyst loadings, and outperforms common mononuclear AuI systems. This proof‐of‐concept demonstrates the benefit of preorganization of two gold centers to enforce selective non‐classical σ,π‐activation with bifunctional substrates.

Synthesis and thermal properties of salts comprising cationic bis(oxazoline)-AuIII complexes and fluorinated anions

Salts comprising cationic bis(oxazoline) (box)-AuIII complexes and fluorinated anions were synthesized and their thermal properties were investigated. Cations that contain box ligands with butyl substituents (butyl-box) were used with either achiral-(R,S) ([1]+) or chiral-(S,S) ([2]+) configurations. [1][Tf2N] (Tf2N−=bis(trifluoromethanesulfonyl)amide) is a solid that can also be classified as an ionic liquid (Tm=62°C, Tg=−11°C). [1]X and [2]X (X=SbF6− and BF4−) exhibit melting points higher than 100°C, where [1]X exhibits a higher melting point than [2]X. A salt with an ethyl-box ligand ([3][SbF6]) exhibits no melting up to its decomposition temperature of 267°C. Crystal structure determination revealed that the achiral cation in [1][BF4] has a bent structure. The potential utility of [1][Tf2N] for catalysis was demonstrated by the catalytic formation of an acetal from an alkyne.

A macromolecular cyclometalated gold(iii) amphiphile displays long-lived emissive excited state in water: self-assembly and in vitro photo-toxicity.

We report an amphiphilic macromolecule containing a cyclometalated gold(iii) complex that self-assembles into nano-sized micelles and also displays a long-lived emissive triplet excited state with a lifetime of 84 μs in degassed water. This amphiphilic AuIII complex exhibits good biocompatibility and activity towards in vitro photo-toxicity, as well as enhanced permeability and retention effects in vivo.

Spectroscopic Elaboration and Structural Characterizations of New Fe(III), Pd(II), and Au(III) Ampicillin Complexes: Metal-Antibiotic Ligational Behaviors

Two modes of complexation were resulted upon the chemical interactions of ampicillin (amp) antibiotic drug with iron(III), palladium(II), and gold(III) metal ions in 50/50 % of methanol/distilled water mixed solvent. The chemical formulas of FeIII, PdII, and AuIII complexes are [Fe2(amp)(Cl)5(H2O)3].3H2O, [Pd(amp)2].2H2O and [Au2(amp)(Cl)4].Cl.2H2O. These complexes were characterized using elemental analyses, molar conductivity, (infrared,1H-NMR, UV-vis.) spectra, effective magnetic moment in Bohr magnetons, thermal analysis (TG), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), as well as transmitting electron microscopy (TEM). The binuclear complexes of FeIII and AuIII ions are coordinated toward the oxygen of carbonyl amide and nitrogen of –NH2 groups and oxygens of carbonyl β-lactam ring and deprotonated of the −COOH group, while the mononuclear complex of PdII ions coordinated through oxygens of β-lactam and carboxylate groups. Magnetic susceptibilities of the solid samples indicated that the PdII and AuIII complexes have a diamagnetic form but the FeIII complex has a paramagnetic nature with octahedral ligational statement. The antibacterial and antifungal activities of the respected complexes were tested against some kind of bacteria and fungi strains if comparable with the ampicillin free drug. In vitro cytotoxicity assays of the gold(III) complex were determined against the human colon carcinoma (HCT-116) and human hepatocellular carcinoma (HepG-2) tumor cell lines.

ChemInform Abstract: Regioselectivity in the Au‐Catalyzed Hydration and Hydroalkoxylation of Alkynes

AbstractReview: [51 refs.

Cationic Gold(III) Alkyl Complexes: Generation, Trapping, and Insertion of Norbornene

AbstractMigratory insertion of alkenes into gold–carbon bonds, a fundamental yet unprecedented organometallic transformation, has been investigated from a discrete (P,C) cyclometalated gold(III) dimethyl complex. Methide abstraction by B(C6F5)3 is shown to generate a highly reactive cationic AuIII complex that evolves spontaneously by C6F5 transfer from boron. In the presence of norbornene, migratory insertion into the AuC bond proceeds readily. The resulting norbornyl complex is efficiently trapped with pyridines or chloride to give stable four‐coordinate adducts.

Water-soluble luminescent cyclometalated gold(III) complexes with cis-chelating bis(N-heterocyclic carbene) ligands: synthesis and photophysical properties.

A new class of cyclometalated Au(III) complexes containing various bidentate C-deprotonated C^N and cis-chelating bis(N-heterocyclic carbene) (bis-NHC) ligands has been synthesized and characterized. These are the first examples of Au(III) complexes supported by cis-chelating bis-NHC ligands. [Au(C^N)(bis-NHC)] complexes display emission in solutions under degassed condition at room temperature with emission maxima (λmax ) at 498-633 nm and emission quantum yields of up to 10.1 %. The emissions are assigned to triplet intraligand (IL) π→π* transitions of C^N ligands. The Au(III) complex containing a C^N (C-deprotonated naphthalene-substituted quinoline) ligand with extended π-conjugation exhibits prompt fluorescence and phosphorescence of comparable intensity with λmax at 454 and 611 nm respectively. With sulfonate-functionalized bis-NHC ligand, four water-soluble luminescent Au(III) complexes, including those displaying both fluorescence and phosphorescence, were prepared. They show similar photophysical properties in water when compared with their counterparts in acetonitrile. The long phosphorescence lifetime of the water-soluble AuIII complex with C-deprotonated naphthalene-substituted quinoline ligand renders it to function as ratiometric sensor for oxygen. Inhibitory activity of one of these water-soluble Au(III) complexes towards deubiquitinase (DUB) UCHL3 has been investigated; this complex also displayed a significant inhibitory activity with IC50 value of 0.15 μM.

Deconstructing Selectivity in the Gold-Promoted Cyclization of Alkynyl Benzothioamides to Six-Membered Mesoionic Carbene or Acyclic Carbene Complexes

We demonstrate that the experimentally observed switch in selectivity from 5-exo-dig to 6-endo-dig cyclization of an alkynyl substrate, promoted by AuI and AuIII complexes, is connected to a switch from thermodynamic to kinetic reaction control. The AuIII center pushes alkyne coordination toward a single Au–C(alkyne) σ-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom.

Synthesis, Characterization and Luminescence of Gold Complexes Bearing an NHC Ligand Based on the Imidazo[1,5‐a]quinolinol Scaffold

AbstractWe report on the synthesis and characterization of an NHC ligand based on the imidazo[1,5‐a]quinolinol scaffold. The benzyl‐protected NHC precursor was used for the preparation of the corresponding AgI, AuI and AuIII complexes. The molecular structures of the AuI and AuIII halide complexes determined by single‐crystal X‐ray diffraction reveal considerable distortion of the rigid NHC moiety due to steric repulsion between the gold and oxygen atoms. At ambient temperature, the complexes are weakly fluorescent from an intraligand excited state, whereas at 77 K the emission spectra are dominated by intraligand phosphorescence.

Gold(III) Complexes Containing N‐Heterocyclic Carbene Ligands: Thiol “Switch‐on” Fluorescent Probes and Anti‐Cancer Agents

Illuminating results: Activation of non-emissive [AuIII(N N N)(NHC)]+ complexes (such as 1) through reduction by intracellular glutathione gives active AuI–NHC complexes, which show promising anti-cancer properties, accompanied by release of the highly fluorescent ligand. The high fluorescence “switch-on” efficiency makes these AuIII complexes excellent probes for cellular thiol detection.

NHC Gold(III) Triflimidate Complexes

Substitution of a trans chloride ligand in the N-heterocyclic carbene (NHC) AuIII complexes (NHC)AuCl3 in the presence of AgNTf2 yields a new family of (NHC)AuCl2(NTf2) complexes. They display a moderate stability in solution but are stable once crystallized. These new organogold(III) complexes could be fully characterized by NMR, IR, and single crystal X-ray diffraction. They exhibit in 13C{1H} NMR an unusually upfield-shifted resonance associated with the carbene center.

One-Pot Radiolytic Synthesis of Gold Nanorods and Their Optical Properties

A novel one-pot synthesis method to prepare gold nanorods of different aspect ratios using radiolysis is presented. The gold nanorods are synthesized by radiolytic reduction of AuIII complexes in a micellar solution formed by a mixture of cationic surfactants (cetyltrimethylammonium bromide and tetraoctylammonium bromide) and in the presence of acetone and silver ions. The mechanisms of reduction of gold complexes and formation of the nanorods are discussed. The nanorods can be trapped in a poly(vinyl alcohol) gel formed under irradiation. The UV−visible absorption spectra of nanorod solutions are compared with calculations performed by using the discrete dipole approximation method, underlying the effect of the rod aspect ratio distribution.

Theoretical Study of Metallophilic Interactions and Excited States of Heterobimetallic d10−d8 Complexes with Bridging Ligands: The Tuning of Electronic Spectroscopy

A series of heterobimetallic d10−d8 complexes, [AuIM′(R1)2(R2)2] (M′ = PtII, AuIII; R1 = CN−, C≡CH−; R2 = PH2CH2PH2, CH2PH2CH2−), were explored using ab initio methods and time-dependent density functional theory (TD-DFT). In the ground states, d10−d8 distances were calculated at 2.88−3.00 Å with associated vibrational frequencies of 102−114 cm−1 by the MP2 method; energies of metallophilic interactions were estimated to be in the range 11.0−18.2 and 7.03−9.14 kcal/mol at the MP2 and CCSD levels, respectively. With the reference complex [AuIPtII(CN)2(PH2CH2PH2)2]+ (1), the variation of the d8 heterometal (M′), the coordination environment of the d8 metal (R1), and the bridging ligand (R2) changes the electronic structures and thus further tunes the electronic spectroscopy of these complexes. The known experimental absorption spectra were well reproduced by the present TD-DFT calculations. Upon excitation, UMP2 revealed the metal−metal interactions in their triplet excited states were strengthened. The corresponding phosphorescent emissions were attributed to the combination of metal-centered (MC) transition, metal-to-metal charge transfer (MM′CT), and ligand-to-metal charge transfer (LMCT). The MC and MM′CT transitions are responsible for the excited metal−metal contraction. The contraction in the AuI−AuIII complex is larger than that in corresponding AuI−PtII complex due to greater participation of MM′CT transitions.

Synthesis of a New Tetrakis(2‐pyridinyl)pyrazine Complex of Gold(III) and Its Computational, Spectroscopic and Electrochemical Characterization

AbstractThe cationic dinuclear (hydroxo)AuIII complex [Au2(OH)2(tppz)]Cl4 [tppz = 2,3,5,6‐tetrakis(2‐pyridinyl)pyrazine] was prepared by allowing the ligand tppz to react with K[AuCl4]·2H2O in refluxing methanol. Its NMR and IR spectra support the formation of a symmetric hydroxo derivative instead of the expected chloro complex. DFT B3PW91 calculations were performed with various basis sets to give better insights into the properties of the prepared complex and to compare it with the known derivative [Au(OH)(terpy)]2+ (terpy = 2,2′:6′,2″‐terpyridine). The electrochemical behaviour of [Au2(OH)2(tppz)]Cl4 was investigated by cyclic voltammetry and it was found that two main irreversible reduction processes occurred. In particular, a four‐electron process, leading to the formation of gold(I) complex species in solution, and a two‐electron process affording metallic gold were observed. The electronicity involved in the two processes was verified by macroelectrolysis at controlled potential. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Perylene salts of unsymmetrical nickel and gold dithiolene complexes with 3 ? 2 stoichiometry: conformational polymorphism and strong antiferromagnetic interactions

The square-planar AuIII complex of the unsymmetrical tfadt dithiolate ligand (tfadt: 2-(trifluoromethyl)acrylonitrile-1,2-dithiolate) is found to exhibit conformational polymorphism in its n-Bu4N+ salt, as both cis and trans isomers were found to crystallize separately in the same crystallization batch. Electrocrystallization of perylene in the presence of the diamagnetic [n-Bu4N][Au(tfadt)2] or the paramagnetic (S = 1/2) [n-Bu4N][Ni(tfadt)2] nickel analog affords isostructural salts with an unusual 3 ∶ 2 stoichiometry, that is [Per]3[M(tfadt)2]2 (M = Au, Ni), with an alternation of dicationic [Per]32+ perylene triads and dianionic [M(tfadt)2]22− dithiolene complex dyads within one-dimensional chains. These salts are characterized by strong antiferromagnetic interactions within perylene triads and [Ni(tfadt)2]22− dyads and an essentially diamagnetic behaviour.

A highly active catalyst for CO oxidation at 298 K: mononuclear Auiii complexes anchored to La2O3 nanoparticles

Mononuclear La2O3-supported AuIII complexes synthesised from AuIII(CH3)2(C5H7O2) and characterised by X-ray absorption spectroscopy are highly active, stable CO oxidation catalysts at room temperature, demonstrating the importance of the support in stabilizing catalytically active gold species, which need not include zerovalent gold for high activity.