Dinuclear Au Research Articles

Anthracene derived dinuclear gold(I) diacetylide complexes: Synthesis, photophysical properties and supramolecular interactions

New anthracene derived dinuclear Au(I)-diacetylide complex (1) has been synthesized in which two Au(I) units are attached at 9,10- positions of ethynyl anthracene moiety. 1 exhibits rare non-covalent intermolecular Au⋯HC interactions, leading to the formation of a supramolecular 2D-network. Further, to understand the effect of CCAuPPh3 units at different position, complexes (2) and (3) were synthesized, where CCAuPPh3 units are attached to 2,6- and 1,8- positions of anthracene, respectively. The absorption and emission spectra of 1–3 have been studied and surprisingly 1 was found to be highly fluorescent with high quantum yield compared to 2 and 3, this may be due to more perturbation of Au(I) on π system. Complexes 1–3 have been characterized by elemental analysis, NMR and Mass spectroscopy and authenticated by their single-crystal X-ray structures.

Aurophilicity in Action: Fine-Tuning the Gold(I)-Gold(I) Distance in the Excited State To Modulate the Emission in a Series of Dinuclear Homoleptic Gold(I)-NHC Complexes.

The solution-state emission profiles of a series of dinuclear Au(I) complexes 4-6 of the general formula Au2(NHC-(CH2)n-NHC)2Br2, where NHC = N-benzylbenzimidazol-2-ylidene and n = 1-3, were found to be markedly different from each other and dependent on the presence of excess bromide. The addition of excess bromide to the solutions of 4 and 6 leads to red shifts of ca. 60 nm, and in the case of 5, which is nonemissive when neat, green luminescence emerges. A detailed computational study undertaken to rationalize the observed behavior revealed the determining role aurophilicity plays in the photophysics of these compounds, and the formation of exciplexes between the complex cations and solvent molecules or counterions was demonstrated to significantly decrease the Au-Au distance in the triplet excited state. A direct dependence of the emission wavelength on the strength of the intracationic aurophilic contact allows for a controlled manipulation of the emission energy by varying the linker length of a diNHC ligand and by judicial choice of counterions or solvent. Such unique stimuli-responsive solution-state behavior is of interest to prospective applications in medical diagnostics, bioimaging, and sensing. In the solid, the investigated complexes are intensely phosphorescent and, notably, 5 and 6 exhibit reversible luminescent mechanochromism arising from amorphization accompanied by the loss of co-crystallized methanol molecules. The mechano-responsive properties are also likely to be related to changes in bromide coordination and the ensuing alterations of intramolecular aurophilic interactions. Somewhat surprisingly, the photophysics of NHC ligand precursors 2 and 3 is related to the formation of ground-state associates with bromide counterions through hydrogen bonding, whereas 1 does not appear to bind its counterions.

Metal–Metal Interactions in Heterobimetallic Complexes with Dinucleating Redox‐Active Ligands

AbstractThe tuning of metal–metal interactions in multinuclear assemblies is a challenge. Selective P coordination of a redox‐active PNO ligand to AuI followed by homoleptic metalation of the NO pocket with NiII affords a unique trinuclear Au–Ni–Au complex. This species features two antiferromagnetically coupled ligand‐centered radicals and a double intramolecular d8–d10 interaction, as supported by spectroscopic, single‐crystal X‐ray diffraction, and computational data. A corresponding cationic dinuclear Au–Ni analogue with a stronger d8–d10 interaction is also reported. Although both heterobimetallic structures display rich electrochemistry, only the trinuclear Au–Ni–Au complex facilitates electrocatalytic C−X bond activation of alkyl halides in its doubly reduced state. Hence, the presence of a redox‐active ligand framework, an available coordination site at gold, and the nature of the nickel–gold interaction appear to be essential for this reactivity.

“Host–guest” binding of a luminescent dinuclear Au(i) complex based on cyclic diphosphine with organic substrates as a reason for luminescence tuneability

A dinuclear Au(i) complex with cyclic diphosphine is a versatile platform for different luminescence responses to nucleophilic and electrophilic molecules in solutions.

Synthesis, structural characterization and biological evaluation of dinuclear gold(iii) complexes with aromatic nitrogen-containing ligands: antimicrobial activity in relation to the complex nuclearity

Dinuclear Au(iii) complexes with N-heterocycles have been synthesized and biologically evaluated.

Dinuclear Au(i) N-heterocyclic carbene complexes derived from unsymmetrical azolium cyclophane salts: potential probes for live cell imaging applications.

We have synthesized a new series of azolium cyclophanes and used them as precursors of inherently luminescent dinuclear Au(i)-N-heterocyclic carbene (NHC) complexes. The azolium cyclophanes contained two azolium groups (either imidazolium or benzimidazolium), an o-xylyl group, and an alkyl linker chain (either C2, C3 or C4). All of the azolium cyclophanes were characterised by X-ray diffraction studies and VT NMR studies, and all were fluxional in solution on the NMR timescale. The C3- and C4-linked azolium cyclophanes served as precursors of Au2L2(2+) complexes (L is a cyclophane bis(NHC) ligand). Due to the unsymmetrical nature of the azolium cyclophanes, the Au2L2(2+) complexes each existed as cis and trans isomers. X-ray diffraction studies showed that the Au2L2(2+) complexes had short intramolecular AuAu distances, in the range 2.9-3.3 Å, suggestive of an aurophilic attraction, presumably as a consequence of the geometrical constraints imposed by the cyclophane bis(NHC) ligands. The complexes having the shortest AuAu distances (i.e., those based on C3-linked cyclophanes) exhibited intense luminescence in solution. The uptake of one of the dinuclear Au-NHC complexes by tumorigenic cells, and its subsequent distribution and toxicity in the cells, was monitored by luminescence microscopy over 6 h and proliferation measurements, respectively.

Stepwise isolation of an unprecedented silylene supported dinuclear gold(i) cation with aurophilic interaction.

The silylene (PhC(NtBu)2SiN(PPh2)(2,6-iPr2-C6H3)) (2) was prepared from the previously reported (PhC(NtBu)2SiCl) salt elimination method. The reaction of 2 with AuCl(SMe2) afforded [(PhC(NtBu)2SiN(PPh2)(2,6-iPr2-C6H3))AuCl] (3). Note here that only Si(ii) is coordinated to Au(i), while P(iii) remains uncoordinated. The higher negative value of the electrostatic potential (ESP) at the Si-centre (-28.8 kcal mol(-1)) as compared to that at the P-centre (-15.3 kcal mol(-1)) justifies this observation. Furthermore, the chloride abstraction from 3 by AgSbF6 led to the formation of a dinuclear Au(i) cationic complex, [PhC(NtBu)2Si(2,6-iPr2-C6H3NPPh2)(Au)]2[SbF6]2 (4), which displays an intra-molecular Au...Au interaction of 2.865 Å.

Synthesis, Characterization, and Luminescence Studies of Gold(I) Complexes with PNP- and PNB-Based Ligand Systems.

The synthesis, X-ray crystal structures, and spectroscopic studies of a series of PPh2N(2,6-iPr2C6H3)PPh2 (PNP) and PPh2N(2,6-iPr2C6H3)BCy2 (PNB; Cy = cyclohexyl) based gold(I) complexes are presented herein. The gold(I) chloride complexes 2 and 6 were treated with AgSbF6 to yield the corresponding dimeric dinuclear Au(I) cation (3) and dimeric mononuclear Au(I) cation (7) with PNP and PNB systems, respectively. The molecular structure of 3 revealed the presence of a strong intramolecular aurophilic interaction with a Au···Au bond distance of 2.7944(19) Å, one of the shortest aurophilic interactions known in the literature. However, complex 7 displays no aurophilic interaction. The reaction of 3 with diphenyl disulfide was performed, which led to a multinuclear tetragold(I) complex (4), keeping the aurophilic interaction intact. The effect of an aurophilic interaction is also illustrated through the study of the luminescent properties of these gold(I) complexes. Complexes 3 and 4 exhibit luminescence in solution as well as in the solid state, whereas the other gold(I) complexes remain nonluminescent.

Controlling intermolecular aurophilicity in emissive dinuclear Au(I) materials and their luminescent response to ammonia vapour.

The concept that hydrogen bonding cations can reduce the coulombic repulsion inherent to anionic gold species and thereby trigger aurophilicity is realized with three new photoluminescent compounds of the form [Q]2[Au2(i-mnt)2] (i-mnt = (CN)2C[double bond, length as m-dash]CS2(2-), Q = 3,5-dimethylpyrazolium, piperidinium). These compounds illustrate unprecedented supramolecular aurophilicity between the anions, the emission of which is significantly red-shifted compared to zero-dimensional analogues, a direct result of the aurophilic network. The piperidinium salt exhibits a vapochromic/luminescent response to ammonia, inducing a change in colour of the reflectance and emission from red to yellow. These results demonstrate the ability to rationally control the formation of supramolecular metallophilic networks via the incorporation of hydrogen bonding cations.

Reactivity of Mononuclear and Dinuclear Gold(I) Amidinate Complexes with CS2 and CsBr3

To probe the reactivity of gold-nitrogen bonds, we have examined the insertion chemistry with carbon disulfide (CS2) as well as oxidation with cesium tribromide (CsBr3) with Au(I) amidinate complexes. The reaction of Ph3PAuCl with Na[(2,6-Me2C6H3N)2C(H)] yields the mononuclear, two-coordinate gold(I) complex, Ph3PAu[κ1-(2,6-Me2C6H3N)2C(H)], 1. The reactivity of 1 with CS2 produced the mononuclear Au(I) compound, Ph3PAu{κ1-S2C[(2,6-Me2C6H3N)2C(H)]}, 2. In the case of CsBr3 the previously reported dinuclear Au(I) complex, Au[(2,6-Me2C6H3N)2C(H)]2, 3, was isolated with formation of Ph3PBr2. We also compared the reactivity of CS2 and CsBr3 with 3. Carbon disulfide insertion with 3 produces a dimeric product, Aun[CS2(2,6-Me2C6H3NC(H)=NC6H3Me2)]n, 4, featuring a dinuclear core with linking aurophilic interactions, making it appear polymeric in the solid state. When CsBr3 is reacted with 3 the Au(II,II) product is obtained, Au2[(2,6-Me2C6H3N)2C(H)]2(Br)2, 5.

Dinuclear gold(i) dithio- and diselenophosph(in)ate complexes forming mononuclear gold(iii) oxidative addition complexes and reversible chemical reductive elimination products

Dinuclear gold(i) dithio- and diselenophosph(in)ate complexes were prepared to serve as precursors for subsequent oxidative addition (OA) chemistry following reaction with mild oxidant iodine, I2. The new OA products circumvented the formation of the expected dinuclear Au(ii) complexes, but instead formed novel chelating mononuclear square-planar gold(iii) products of the type [AuI2{E2PR2}] (R = (CH2)2Ph; E = S, 2; E = Se, 3) and [AuI2{Se2P(OR)2}] (R = Et, 4; (i)Pr, 5) directly. We further demonstrate that this process is chemically reversible as all the Au(iii) complexes undergo chemical reductive elimination to the starting dinuclear Au(i) complexes in the presence of SnI2 as determined by (119)Sn and (31)P NMR. The complexes (2-5) were all prepared from the reaction between I2 and the corresponding dinuclear gold(i) precursor material. All new complexes were characterized by (1)H, (31)P, (77)Se (for E = Se) NMR, infrared spectroscopy, elemental analysis and single crystal X-ray diffraction.

Bromide ion binding by a dinuclear gold(i) N-heterocyclic carbene complex: a spectrofluorescence and X-ray absorption spectroscopic study

Fluorescence and X-ray absorption spectroscopy were used to investigate the anion binding properties of a luminescent, dinuclear Au(I) N-heterocyclic carbene (NHC) complex ([1](2+)) with a short Au(I)···Au(I) contact. The addition of Br(-) ions to a DMSO solution of [1](PF(6))(2) caused a red-shift in the fluorescence emission band from 396 nm to 496 nm. Similarly, the addition of Br(-) ions to [1](PF(6))(2) caused a decrease in the energy of the Au L(3)-edge in the X-ray absorption spectrum, consistent with the formation of an association complex between the cation [1](2+) and Br(-) ions. Solution-based structural studies of the association complex were carried out using extended X-ray absorption fine structure (EXAFS) modelling of the Au(I)···Au(I) core of the cation. These studies indicate that the association complex results from Au(I)···Br(-) interactions, with the Br(-) ions occupying two partially occupied sites at ~2.9 and 3.9 Å from the Au(I) atoms.

Alkali-metal-mediated zincation (AMMZn) meets N-heterocyclic carbene (NHC) chemistry: Zn–H exchange reactions and structural authentication of a dinuclear Au(i) complex with a NHC anion

Merging two evolving areas in synthesis, namely cooperative bimetallics and N-heterocyclic carbenes (NHCs), this study reports the isolation of the first intermediates of alkali-metal-mediated zincation (AMMZn) of a free NHC and a Zn–NHC complex using sodium zincate [(TMEDA)NaZn(TMP)(tBu)2] (1) as a metallating reagent. The structural authentication of (THF)3Na[:C{[N(2,6-iPr2C6H3)]2CHCZn(tBu2)}] (2) and [Na(THF)6]+[tBu2Zn:C{[N(2,6-iPr2C6H3)]2CHCZn(tBu2)}]− (4), resulting from the reactions of 1 with unsaturated free NHC IPr (IPr = 1,3-bis(2,6-di-isopropylphenylimidazole-2-ylidene) and NHC complex ZntBu2IPr (3) respectively demonstrates that in both cases, this mixed-metal approach can easily facilitate the selective C4 zincation of the unsaturated backbone of the NHC ligand. Furthermore, the generation of anionic NHC fragments enables dual coordination through their normal (C2) and abnormal (C4) positions to the bimetallic system, stabilising the kinetic AMMZn intermediates which normally go undetected and provides new mechanistic insights in to how these mixed-metal reagents operate. In stark contrast to this bimetallic approach when NHC-complex 3 is reacted with a more conventional single-metal base such as tBuLi, the deprotonation of the coordinated carbene is inhibited, favouring instead, co-complexation to give NHC-stabilised [IPr·LiZntBu3] (5). Showing the potential of 2 to act as a transfer agent of its anionic NHC unit to transition metal complexes, this intermediate reacts with two molar equivalents of [ClAu(PPh3)] to afford the novel digold species [ClAu:C{[N(2,6-iPr2C6H3)]2CHCAu(PPh3)}] (6) resulting from an unprecedented double transmetallation reaction which involves the simultaneous exchange of both cationic (Na+) and neutral (ZntBu2) entities on the NHC framework.

A hexanuclear gold(i) metallatriangle derived from a chiral dithiophosphate: synthesis, structure, luminescence and oxidative bromination reactivity

We report the synthesis, structure, luminescence and reactivity of a 27-membered gold(I) metallatriangle containing three separate dinuclear gold(I) units self-assembled from a chiral tetradentate dianionic dithiophosphate ligand. The hexanuclear complex luminesces in the solid-state (λmax = 488 nm) at 298 K. Additionally, the Au(I) complex forms an unexpected dinuclear Au(III) oxidative addition product upon reaction with Br2.

Solvent-Independent Electrode Potentials of Solids Undergoing Insertion Electrochemical Reactions: Part II. Experimental Data for Alkynyl–diphosphine Dinuclear Au(I) Complexes Undergoing Electron Exchange Coupled to Anion Exchange

A method is presented to obtain solvent-independent redox potential systems using solid-state electrochemistry of alkynyl–diphosphine dinuclear Au(I) complexes (AuC2R)2PPh2C6H4PPh2 (L1, R = Fc; L2, R = C6H4Fc) containing ferrocenyl units. These compounds exhibit a well-defined, essentially reversible solid-state oxidation in contact with different electrolytes based on ferrocenyl-centered oxidation processes involving anion insertion. Midpeak potentials appear to be essentially solvent-independent upon referring it to the bis(η-biphenyl)chromium(I)/bis(biphenyl)chromium(0) couple. Theoretical modeling of diffusion processes allows us to combine voltammetric and chronoamperometric data to determine equilibrium potentials that are strictly solvent-independent. Data for water, MeOH, EtOH, MeCN, DMS, DMF, and NM are provided.

Intramolecular d10–d10 interactions in neutral, dinuclear Au(I) complexes supported by amino-thiazoline- and -thiazole-based P,N-phosphine ligands

Abstract The ligands N-(diphenylphosphino)-thiazoline-2-amine (1), N-(diphenylphosphino)thiazol-2-amine (2) and N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine 3, readily reacted with [AuCl(THT)] in dichloromethane to form the linearly coordinated complexes [AuCl(1-κP)] (5), [AuCl(2-κP)] (6) and [AuCl(3-κP)] (7), respectively. Facile deprotonation with t-BuOK or Na2CO3 of 5–7 afforded the stable, neutral dinuclear complexes [AuCl(1—H-κP,κN)]2 (8), [AuCl(2—H-κP,κN)]2 (9) and [AuCl(3—H-κP,κN)]2 (10), respectively. The crystal structures of the mononuclear complexes 5, 6 and 7 and of the dinuclear complexes 8, 9 and 10 have been determined by X-ray diffraction. The latter represent rare examples of neutral complexes supported by bridging P,N-ligands which display intramolecular Au(I)···Au(I) d10–d10 interactions, in the range 2.8592(4)–2.8831(4) A.

Determination of Individual Gibbs Energies of Anion Transfer and Excess Gibbs Energies Using an Electrochemical Method Based on Insertion Electrochemistry of Solid Compounds

A method is presented to determine, individually and with minimal extra-thermodynamic assumptions, the Gibbs energy for anion transfer between two solvents using solid state electrochemistry of alkynyldiphosphine dinuclear Au(I) complexes (AuC2R)2PPh2C6H4PPh2 (L1, R = Fc; L2, R = C6H4Fc) and the heterometallic Au(I)–Cu(I) [{Au3Cu2(C2R)6}Au3(PPh2C6H4PPh2)3](PF6)2 (L3, R = Fc; L4, R = C6H4Fc) cluster complexes containing ferrocenyl units. These compounds exhibit a well-defined, essentially reversible solid-state oxidation in contact with different electrolytes, based on ferrocenyl-centered oxidation processes involving anion insertion. Voltammetric data can be used for a direct measurement of the free energy of ion transfer from one solvent to another using midpeak potentials in solutions of suitable salts in each one of the solvents separately or mixtures of the solvents. Excess Gibbs energy of solvation in solvent mixtures can also be directly measured using this procedure. Solvation data for different common inorganic oxoanions in water, MeOH, and MeCN and water–MeOH and water–MeCN mixtures are provided.

Estimation of free energies of anion transfer from solid-state electrochemistry of alkynyl-based Au(I) dinuclear and Au(I)–Cu(I) cluster complexes containing ferrocenyl groups

A method is presented to determine the free energy for anion transfer between two solvents. This is based on solid-state electrochemistry of alkynyl-based dinuclear Au(I) complexes (AuC 2R) 2PPh 2C 6H 4PPh 2 ( L1: R = Fc; L2: R = C 6H 4Fc) and heterometallic Au(I) –Cu(I) [{Au 3Cu 2 (C 2R) 6}Au 3(PPh 2C 6H 4PPh 2) 3](PF 6) 2 ( L3: R = Fc; L4: R = C 6H 4Fc) complexes. These compounds exhibit a reversible ferrocenyl-centred solid-state oxidation processes involving anion insertion in contact with aqueous, MeOH and MeCN electrolytes. Voltammetric data can be used for a direct measurement of the free energy of ion transfer using midpeak potentials in solutions of suitable salts in the solvents separately or in mixtures of the solvents.

Design and Synthesis of Calixarene‐Based Bis‐alkynyl‐Bridged Dinuclear AuI Isonitrile Complexes as Luminescent Ion Probes by the Modulation of Au⋅⋅⋅Au Interactions

Two calixarene-based bis-alkynyl-bridged Au(I) isonitrile complexes with two different crown ether pendants, [{calix[4]arene-(OCH(2)CONH-C(6)H(4)C[triple bond]C)(2)}{Au(CNR)}(2)] (R=benzo[15]crown-5 (1); R=benzo[18]crown-6 (2)), together with their related crown-free analogue 3 (R=C(6)H(3)(OMe)(2)-3,4) and a mononuclear gold(I) complex 4 with benzo[15]crown-5 pendant, have been designed and synthesized, and their photophysical properties have been studied. The X-ray structure of the ligand, calix[4]arene-(OCH(2)CONH-C(6)H(4)C[triple bond]CH)(2) has been determined. The cation-binding properties of these complexes with various metal ions have been studied using UV/Vis, emission, (1)H NMR, and ESI-MS techniques, and DFT calculations. A new low-energy emission band associated with AuAu interaction could be switched on upon formation of the metal ion-bound adduct in a sandwich fashion.

Dinuclear gold(III) pyrazolato complexes – Synthesis, structural characterization and transformation to their trinuclear gold(I) and gold(I/III) analogues

The reaction of AuCl 3py with Na(pz∗) (pz∗ = pyrazolato, or substituted pyrazolato anion) yields stable dinuclear [ cis-Au IIICl 2(μ-pz∗)] 2 complexes. In the presence of a base, the latter undergo reduction with concomitant transformation of the dinuclear Au 2 III -structure to trinuclear Au 2 III Au I, Au III Au 2 I (containing trans Au IIICl 2-centres) and Au 3 I species.