Deactivation of Cationic CuI and AuI Catalysts for A3 Coupling by CH2Cl2: Mechanistic Implications of the Formation of Neutral CuI and AuI Chlorides

Care should be exercised when using CH₂Cl₂ as a solvent for reactions in which amines are a reagent, since undesirable deactivation of cationic copper(I) and gold(I) catalysts to form the corresponding inactive neutral chloride complexes [LMCl] (M=Cu or Au) can occur as a result of the generation of hydrogen chloride in the medium. Cu^I and Au^I deactivation has been proved for the Mannich three‐component coupling reaction. A series of Cu^I and Au^I complexes with potential mechanistic implications were isolated and characterized by X‐ray crystallography.     

Alkyne/Alkene/Allene‐Induced Disproportionation of Cationic Gold(I) Catalyst

The first detailed experimental study of the deactivation of cationic gold was conducted, and the influence of each component in the reaction system (substrate, counterion, solvent) on the decay process was examined. It was found that a substrate (alkyne/allene/alkene)‐induced disproportionation of gold(I) may play a key role in the decay process. Our mechanism is supported by kinetic, XPS, voltammetry studies, and high‐resolution ESI‐MS data.     

Quenching and blinking of fluorescence of a single dye molecule bound to gold nanoparticles

A fluorescein derivative (SAMSA) bound to gold nanoparticles of different diameters is investigated by time-resolved fluorescence at the single molecule level in a wide dynamic range, from nanosecond to second time scale. The significant decrease of both SAMSA excited state lifetime and fluorescence quantum yield observed upon binding to gold nanoparticles can be essentially traced back to an increase of the nonradiative deactivation rate, probably due to energy transfer, that depends on the nanoparticle size. A slow single molecule fluorescence blinking, in the ms time scale, has a marked dependence on the excitation intensity both under single and under two photon excitation. The blinking dynamics is limited by a low probability nonlinear excitation to a high energy state from which a transition to a dark state occurs. The results point out a strong coupling between the vibro-electronic configuration of the dye and the plasmonic features of the metal nanoparticles that provide dye radiationless deactivation channels on a wide dynamic range.     

Correlation between photophysical parameters and gold-gold distances in gold(I) (4-pyridyl)ethynyl complexes

The systematic analysis of the luminescence of a series of alkynyl gold derivatives with general formulas [(diphos)(AuC≡Cpy)(2)] (diphosphane =2,2'-bis(diphenylphosphanyl)propane or dppip (1), bis(diphenylphosphanyl)acetylene or dppa (2), 1,2-bis(diphenylphosphanyl)ethane or dppe (3) and 1,4-bis(diphenylphosphanyl)butane or dppb, (4), has shown a straightforward correlation between the Au(I)···Au(I) distance and the emission quantum yields and decaytimes. The analysis of the decaytimes, quantum yields and thus, the corresponding calculated rate constants demonstrated the existence of a correlation between Au(I)···Au(I) distance and the radiative rate constant for the deactivation of the emissive triplet states. It was concluded that the increased emission of these compounds results from the increase in spin-orbit coupling that favors the spin forbidden transition to the singlet ground state.     

Cyclometalated Gold(III)-Hydride Complexes Exhibit Visible Light-Induced Thiol Reactivity and Act as Potent Photo-Activated Anti-Cancer Agents

The specific gold-sulfur binding interaction renders gold complexes as promising anti-cancer agents that can potentially overcome cisplatin resistance; while their unbiased binding towards non-tumoral off-target thiol-proteins has posed a big hurdle to clinical application. Herein we report that cyclometalated gold(III) complexes bearing hydride ligands are highly stable towards thiols in the dark but can efficiently dissociate the auxiliary hydride moiety and generate a gold-thiol adduct when excited with visible light. In consequence, the photo-activated gold(III) complexes potently inhibited thioredoxin reductase in association with up to >400-fold increment of photocytotoxicity (vs. dark condition) without deactivation by serum albumin and along with strong anti-angiogenesis activity in zebrafish embryos. Importantly, the gold(III)-hydride complexes could be activated by two-photon laser irradiation at the phototherapeutic window as effectively as blue-light irradiation.     

Gold(I)-catalyzed intramolecular acetylenic Schmidt reaction

Substituted pyrroles were prepared by a gold(I)-catalyzed acetylenic Schmidt reaction of homopropargyl azides. The reaction allows for regiospecific substitution at each position of the pyrrole ring under mild conditions. A mechanism in which azides serve as nucleophiles toward gold(I)-activated alkynes with subsequent gold(I)-aided expulsion of dinitrogen is proposed.     

Cyclometalated Gold(III)‐Hydride Complexes Exhibit Visible Light‐Induced Thiol Reactivity and Act as Potent Photo‐Activated Anti‐Cancer Agents

The specific gold‐sulfur binding interaction renders gold complexes as promising anti‐cancer agents that can potentially overcome cisplatin resistance; while their unbiased binding towards non‐tumoral off‐target thiol‐proteins has posed a big hurdle to clinical application. Herein we report that cyclometalated gold(III) complexes bearing hydride ligands are highly stable towards thiols in the dark but can efficiently dissociate the auxiliary hydride moiety and generate a gold‐thiol adduct when excited with visible light. In consequence, the photo‐activated gold(III) complexes potently inhibited thioredoxin reductase in association with up to >400‐fold increment of photocytotoxicity (vs. dark condition) without deactivation by serum albumin and along with strong anti‐angiogenesis activity in zebrafish embryos. Importantly, the gold(III)‐hydride complexes could be activated by two‐photon laser irradiation at the phototherapeutic window as effectively as blue‐light irradiation.     

A luminescent supermolecule with gold(I) quinoline-8-thiolate: crystal structure,spectroscopic and photophysical properties

The trinuclear complex [(8-QNS)(2)Au(AuPPh(3))(2)].BF(4) (8-QNS = quinoline-8-thiolate), with intramolecular gold(I)...gold(I) distances of 3.0952(4) and 3.0526(3) A, is aggregated to form a novel hexanuclear supermolecule, ([(8-QNS)2(Au(AuPPh3)2])2.(BF4)2, via a close intermolecular gold(I)...gold(I) contact of 3.1135(3) A. The beautiful hexanuclear supermolecule has an inversion center, and the six metal centers can be viewed as roughly coplanar. Six gold(I) ions are embedded in an ellipse and surrounded by 4 quinoline and 12 phenyl rings. The title compound shows interesting spectroscopic and luminescence properties dependent on the solvent polarity; i.e., it emits at ca. 440 and 636 nm in CH(2)Cl(2) and only at ca. 450 nm in CH(3)CN. The long-lived emission at ca. 636 nm (16.2 micros) in CH(2)Cl(2) is quenched by polar solvents such as CH(3)CN and CH(3)OH with quenching constants as 1.00 x 10(5) and 3.03 x 10(4) s(-1) M(-1), respectively, which is suggested to be related to the presence or absence of gold(I)...gold(I) interactions due to scrambling of the [AuPPh(3)]+ units, isolobal to H+.     

Gold(I)‐Catalyzed Addition of Silylacetylenes to Acylsilanes: Synthesis of Indanones by C?H Functionalization through a Gold(I) Carbenoid

A gold(I)‐catalyzed synthesis of indanones from trimethylsilylacetylenes and acylsilanes is presented. The reaction is initiated through a synergistic acylsilane activation–gold acetylide formation and involves consecutive alkyne σ‐gold(I) addition, π‐activation, and 1,2‐migration of a silyl group. Studies performed on the reaction mechanism allowed to establish the nature of the silyl migrating group and invoke the participation of a gold(I) carbenoid intermediate. The reaction is completed by a gold(I) C H functionalization step.     

Gold(I)‐Catalyzed Addition of Silylacetylenes to Acylsilanes: Synthesis of Indanones by CH Functionalization through a Gold(I) Carbenoid

A gold(I)‐catalyzed synthesis of indanones from trimethylsilylacetylenes and acylsilanes is presented. The reaction is initiated through a synergistic acylsilane activation–gold acetylide formation and involves consecutive alkyne σ‐gold(I) addition, π‐activation, and 1,2‐migration of a silyl group. Studies performed on the reaction mechanism allowed to establish the nature of the silyl migrating group and invoke the participation of a gold(I) carbenoid intermediate. The reaction is completed by a gold(I) C? H functionalization step.     

纳米金催化剂的存放失活

 采用共沉淀法制备了2.5%Au/ZnO催化剂,并用扫描隧道显微镜、 X射线衍射、 X射线光电子能谱和热重研究了纳米金催化剂在空气中存放失活的机理. 结果表明,纳米金催化剂在空气中存放失活是部分可逆的. 纳米金催化剂的存放失活有两方面原因: 一是纳米金粒子的长大,导致不可逆失活; 二是碳酸盐在催化剂表面的累积,这种失活可以通过高温焙烧来恢复,是可逆的.     

Gold(I) and silver(I) complexes containing a tripodal tetraphosphine ligand: influence of the halogen and stoichiometry on the properties. The X-ray crystal structure of two gold(I) dimeric aggregates

Complexes of the type [Au2(micro-PP3)2]X2 [X=Cl (), Br (), I ()], [Ag2(micro-PP3)2](NO3)2 (), Ag(PP3)Cl (), M3(micro-PP3)X3 [M=Au, X=Cl (), Br (), I (); M=Ag, X=NO3 ()] and Au4(micro-PP3)X4 [X=Cl (), Br (), I ()] have been prepared by interaction between gold(I) or silver(I) salts and the ligand tris[2-(diphenylphosphino)ethyl]phosphine (PP3) in the appropriate molar ratio. Microanalysis, mass spectrometry, IR and NMR spectroscopies and conductivity measurements were used for characterization. and are ionic dinuclear species containing four-coordinate gold(i) and four/three coordinate silver(i), respectively. Solutions of behave as mixtures of complexes in a 2:1 [Au2(micro-PP3)X2; X=Cl(), Br(), I()] and 4:1 () metal to ligand ratio. and react with free PP(3) in solution to generate the ionic compounds and , respectively. Complexes and , with four linear PAuX fragments per molecule, were shown by X-ray diffraction to consist of dimeric aggregates via close intermolecular gold(I)gold(I) contacts of 3.270 A () and 3.184 A (). The resultant octanuclear systems have an inversion center with two symmetry-related gold(I) atoms being totally out of the aurophilic area and represent a new form of aggregation compared to that found in other halo complexes of gold(I) containing polyphosphines. The luminescence properties of the ligand and complexes, in the solid state, have been studied. Most of the gold systems display intense luminescent emission at room and low temperature. The influence of the halogen on the aurophilic contacts of compounds with a 4:1 metal to ligand ratio results in different photophysical properties, while and are luminescent complex is nonemissive. The luminescence increases with increasing the phosphine/metal ratio affording for complexes , without aurophilic contacts, the stronger emissions. Silver complexes and are nonemissive at room temperature and show weaker emissions than gold(I) species at 77 K.     

Gold(I)-catalyzed stereoselective olefin cyclopropanation

A triphenylphosphinegold(I)-catalyzed cyclopropanation of olefins using propargyl esters as gold(I)-carbene precursors is reported. This reaction provided the basis for the use of a DTBM-SEGPHOS gold(I) complex as a catalyst in the enantioselective (up to 94% ee) preparation of vinyl cyclopropanes with high cis-selectivity.     

Cytotoxic gold(I)-bearing dendrimers from alkyne precursors

A series of four dendrimers end-functionalized with gold(I) has been prepared from alkyne-terminated precursors and (tricyclohexylphosphine)gold(I) azide. Isolated yields range from 84-89%, based on gold. The first-generation dendrimer is cytotoxic toward 3T3 mouse fibroblast cells. Apoptosis ensues within 6 h of treatment with gold(I).     

Determinants for Tight and Selective Binding of a Medicinal Dicarbene Gold(I) Complex to a Telomeric DNA G‐Quadruplex: a Joint ESI MS and XRD Investigation

The dicarbene gold(I) complex [Au(9‐methylcaffein‐8‐ylidene)₂]BF₄ is an exceptional organometallic compound of profound interest as a prospective anticancer agent. This gold(I) complex was previously reported to be highly cytotoxic toward various cancer cell lines in vitro and behaves as a selective G‐quadruplex stabilizer. Interactions of the gold complex with various telomeric DNA models have been analyzed by a combined ESI MS and X‐ray diffraction (XRD) approach. ESI MS measurements confirmed formation of stable adducts between the intact gold(I) complex and Tel 23 DNA sequence. The crystal structure of the adduct formed between [Au(9‐methylcaffein‐8‐ylidene)₂]⁺ and Tel 23 DNA G‐quadruplex was solved. Tel 23 maintains a characteristic propeller conformation while binding three gold(I) dicarbene moieties at two distinct sites. Stacking interactions appear to drive noncovalent binding of the gold(I) complex. The structural basis for tight gold(I) complex/G‐quadruplex recognition and its selectivity are described.     

氮杂环卡宾双核金络合物催化的胺芳基化反应

联萘胺出发合成了氮杂环卡宾双核和单核金络合物, 通过X射线的单晶衍射确定了它们的结构, 并将其应用于催化胺芳基化反应中, 以高达95%的收率得到吡咯烷类化合物. 综合上述实验结果, 发现氮杂环卡宾双核金络合物4b中存在着Au(I)-Au(I)间相互弱作用力, 而且这种弱相互作用可能对该催化反应起重要的作用, 以高收率得到吡咯烷类化合物.     

Synthesis, structural characterization, and theoretical studies of gold(I) and gold(I)-gold(III) thiolate complexes: quenching of gold(I) thiolate luminescence

The gold(I) thiolate complexes [Au(2-SC6H4NH2)(PPh3)] (1), [PPN][Au(2-SC6H4NH2)2] (2) (PPN = PPh3=N=PPh3), and [{Au(2-SC6H4NH2)}2(mu-dppm)] (3) (dppm = PPh2CH2PPh2) have been prepared by reaction of acetylacetonato gold(I) precursors with 2-aminobenzenethiol in the appropriate molar ratio. All products are intensely photoluminescent at 77 K. The molecular structure of the dinuclear derivative 3 displays a gold-gold intramolecular contact of 3.1346(4) A. Further reaction with the organometallic gold(III) complex [Au(C6F5)3(tht)] affords dinuclear or tetranuclear mixed gold(I)-gold(III) derivatives with a thiolate bridge, namely, [(AuPPh3){Au(C6F5)3}(mu2-2-SC6H4NH2)] (4) and [(C6F5)3Au(mu2-2-SC6H4NH2)(AudppmAu)(mu2-2-SC(6)H4NH2)Au(C6F5)3] (5). X-ray diffraction studies of the latter show a shortening of the intramolecular gold(I)-gold(I) contact [2.9353(7) or 2.9332(7) A for a second independent molecule], and short gold(I)-gold(III) distances of 3.2812(7) and 3.3822(7) A [or 3.2923(7) and 3.4052(7) A] are also displayed. Despite the gold-gold interactions, the mixed derivatives are nonemissive compounds. Therefore, the complexes were studied by DFT methods. The HOMOs and LUMOs for gold(I) derivatives 1 and 3 are mainly centered on the thiolate and phosphine (or the second thiolate for complex 2), respectively, with some gold contributions, whereas the LUMO for derivative 4 is more centered on the gold(III) fragment. TD-DFT results show a good agreement with the experimental UV-vis absorption and excitation spectra. The excitations can be assigned as a S --> Au-P charge transfer with some mixture of LLCT for derivative 1, an LLCT mixed with ILCT for derivative 2, and a S --> Au...Au-P charge transfer with LLCT and MC for derivative 3. An LMCT (thiolate --> Au(III) mixed with thiolate --> Au-P) excitation was found for derivative 4. The differing nature of the excited states [participation of the gold(III) fragment and the small contribution of sulfur] is proposed to be responsible for quenching the luminescence.     

Reactions of Cationic Gold(I) with Allenoates: Synthesis of Stable Organogold(I) Complexes and Mechanistic Investigations on Gold‐Catalyzed Cyclizations

The reaction of allenoates with cationic gold(I)—generated in situ from a phosphine gold chloride and a silver salt—formed unusual, room temperature stable vinyl gold(I) lactones under very mild conditions. The scope and limitations for the synthesis of this novel organogold complex was investigated. DFT calculations on the highest occupied molecular orbitals (HOMOs) of allenoates and the natural bond orbital (NBO) charge densities provided an explanation for the limitations. A plausible mechanism for its formation was proposed based on in situ ¹H and ³¹P NMR spectroscopic analyses. Controlled experiments for the cleavage of the gold–carbon bond by electrophiles indicated that this vinyl gold(I) complex is the likely intermediate in the gold‐catalyzed reaction of carbon–carbon multiple bonds.     

A complex of gold(I) benzenethiolate with isocyanide: synthesis and crystal and molecular structures

2,6-Dimethylphenyl isocyanide forms complexes with gold( I) chloride (complex 4) and gold(I) benzenethiolate (complex 5) but forms no stable complexes with gold alkanethiolates. A reaction of complex 5 with tetramethylthiuram disulfide yields gold(I) dimethyldithiocar-bamate. Stable gold(III) derivatives cannot be obtained in such a way. Shortened intermolecular Au...Au contacts in complexes 4 and 5 (X-ray diffraction) suggest the presence of “aurophilic” interactions in them.     

Gold(I)‐Catalyzed Diazo Coupling: Strategy towards Alkene Formation and Tandem Benzannulation

A gold(I)‐catalyzed cross‐coupling of diazo compounds to afford tetrasubstituted alkenes has been developed by taking advantage of a trivial electronic difference between two diazo substrates. A N‐heterocyclic‐carbene‐derived gold complex is the most effective catalyst for this transformation. Based on this new strategy, a gold(I)‐initiated benzannulation has been achieved through a tandem reaction involving a diazo cross‐coupling, 6π electrocyclization, and oxidative aromatization.