Two-coordinate Gold Research Articles

Two-Coordinate Gold(I) Complex with Rotational Freedom: A Platform Integrating Thermally Activated Delayed Fluorescence, Polymorphism, and Linearly Polarized Luminescence.

Two-coordinate coinage metal complexes have been exploited for various applications. Herein, a new donor-metal-acceptor (D-M-A) complex PZI-Au-TOT, using bulky pyrazine-fused N-heterocyclic carbene (PZI) and trioxytriphenylamine (TOT) ligands, was synthesized. PZI-Au-TOT displays decent thermally activated delayed fluorescence (TADF) with a quantum yield of 93 % in doped film. The crystals of PZI-Au-TOT show simultaneous TADF, polymorphism, and linearly polarized luminescence (LPL). The polymorph-dependent emission properties with widely varied peaks from 560 to 655 nm are attributed to different packing modes in terms of isolated monomers, discrete π-π stacked dimers or dimer PLUS. Two well-defined microcrystals of PZI-Au-TOT exhibit linearly polarized thermally activated delayed fluorescence with a degree of polarization up to 0.64. This work demonstrates that the molecular rotational flexibility of D-M-A type complexes endows an integration of multiple functions into one complex through manipulation of supramolecular aggregation. This type of complexes is expected to serve as a versatile platform for the fabrication of crystal materials for advanced photonic applications.

Homobimetallic Au(I)-Au(I) and Heterotrimetallic Au(I)-Fe(II)-Au(I) Complexes with Dialkyldithiophosphates and Phosphine Ligands: Structural Characterization, DFT Analysis, and Tyrosinase Inhibitory and Biological Effects.

The role of bridging and terminal ligand electronic and steric properties on the structure and antiproliferative activity of two-coordinated gold(I) complexes was investigated on seven novel binuclear and trinuclear gold(I) complexes synthesized by the reaction of either Au2(dppm)Cl2, Au2(dppe)Cl2, or Au2(dppf)Cl2 with potassium diisopropyldithiophosphate, K[(S-OiPr)2], potassium dicyclohexyldithiophosphate, K[(S-OCy)2], or sodium bis(methimazolyl)borate, Na(S-Mt)2, which afforded air-stable gold(I) complexes. In 1-7, the gold(I) centers adopt a two-coordinated linear geometry and are structurally similar. However, their structural features and antiproliferative properties highly depend upon subtle ligand substituent changes. All complexes were validated by 1H, 13C{1H}, 31P NMR, and IR spectroscopy. The solid-state structures of 1, 2, 3, 6, and 7 were confirmed using single-crystal X-ray diffraction. A density functional theory geometry optimization calculation was used to extract further structural and electronic information. To investigate the possible cytotoxicities of 2, 3, and 7, in vitro cellular tests were carried out on the human cancerous breast cell line MCF-7. 2 and 7 show promising cytotoxicity.

Synthesis, structural characterization and in vitro anticancer screening of several gold(I) thiolate, dithiocarbonate and dithiocarbamate complexes

The crystal and molecular structures of four (triphenylphosphine)-gold(I) complexes synthesized from chloro(triphenylphosphine)-gold(I) and the thiols 5-methyl-1,3,4-oxadiazole-2-thiol and 5-methyl-1,3,4-thiadiazole-2-thiol, the dithiocarbonate potassium O-isopropyldithiocarbonate and the dithiocarbamate sodium dibenzyldithiocarbamate have been determined. (5-methyl-1,3,4-oxadiazole-2-thiolato)-triphenylphosphine-gold(I) (1), (5-methyl-1,3,4-thiadiazole-2-thiolato)-triphenylphosphine-gold(I) (2), (O-isopropyldithiocarbonato-S)-triphenylphosphine-gold(I) (3) and (N,N-dibenzyldithiocarbamato-S)-triphenylphosphine-gold(I) (4) all exhibit a nearly linear two-coordinate gold(I) metal center. The structures of the two thiolate complexes contain similar AuSC angles of 100.86(10)° in (1) and 99.51(13)° in (2), but different AuSCO/S torsional angles of 36.9(3)° and −15.0(3)°, respectively, highlighting a 3.227(2) Å intramolecular gold-oxygen contact in (1) and a 3.2635(11) Å intramolecular gold-sulfur contact in (2), the Au●●●S distance being less than the sum of the Van der Waals radii. The packing in (1) features a 4.234(1) Å intermolecular Au●●●S contact while (2) features a very long 4.8408(3) Å gold–gold contact. In the structure of the dithiocarbonate (3) the AuSC bond angle of 102.49(14)° is meaningfully larger than the corresponding angle in the structure of the dithiocarbamate (4), with an AuSC angle of 98.0(2)°, highlighting an even shorter intramolecular gold-sulfur contact in (4) of 3.0120(18) Å which is significantly less than the sum of the Van der Waals radii. The structure of (4) is accompanied by nearly planar AuSCS torsional angle of −3.6(4)° and no intramolecular Au●●●S or Au●●●Au contacts, while in the dithiocarbonate (3) the AuSCS torsional angle of 175.1(3)° reveals the absence of an intramolecular gold-sulfur contact, instead featuring an intramolecular gold-oxygen interaction. Each product was characterized through X-ray crystallography, 1H, 13C and 31P NMR, elemental analysis, IR and MS. In collaboration with the National Institutes of Health (NIH) Developmental Therapeutics Programs (DTP), the complexes have been evaluated for cytotoxic activity against the National Cancer Institute 60 human tumor cell lines screen (NCI-60). The complexes exhibited mild cytotoxicity similar to other known gold(I) phosphine and thiolate complexes.

Conformational Engineering of Two-Coordinate Gold(I) Complexes: Regulation of Excited-State Dynamics for Efficient Delayed Fluorescence.

Carbene-Au-amide (CMA) type complexes, in which the amide and carbene ligands act as an electron donor (D) and acceptor (A), respectively, can exhibit strong delayed fluorescence (DF) from a ligand to ligand charge transfer (LLCT) excited state. Although the coplanar donor-acceptor (D-A) conformation has been suggested to be a crucial factor favoring radiative decay of the charge-transfer excited state, the geometric structural factor underpinning the excited-state mechanism of CMA complexes remains an open question. We herein develop a new class of carbene-Au-carbazolate complexes by introducing large aromatic substituents onto the carbazolate ligand, the presence of which are conceived to restrict the rotation of the Au-N bond and thus confine a twisted D-A conformation in both ground and excited states. A highly twisted D-A orientation is found for the complexes in their crystal structures. Photophysical studies reveal that the twisted conformation induces a decrease in the gap (ΔEST) between the lowest singlet excited state (S1) and the triplet manifold (T1) and thus a faster reverse intersystem crossing (RISC) from T1 to S1 at the expense of oscillator strength for an S1 radiative transition. In comparison with the coplanar analogue, the twisted complexes exhibit comparable or improved DF with quantum yields of up to 94% and short emission lifetimes down to sub-microseconds. The tuning of excited-state dynamics has been well interpreted by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, which unveil much faster RISC rates for twisted complexes. Solution-processed organic light-emitting diodes (OLEDs) based on the new CMA complexes show promising performances with almost negligible efficiency rolloff at a brightness of 1000 cd m-2. This work implies that neither a coplanar ground-state D-A conformation nor a dynamic rotation of the M-N bond is the key to the realization of efficient DF for CMA complexes.

Tetranuclear Au2Cu2 Clusters with Butterfly- and Planar-Shaped Metal Cores: Strong Rigidochromism Induced by Jahn-Teller Distortion in Two-Coordinated Gold(I) Centers.

Two tetranuclear Au2Cu2 cluster complexes [Au2Cu2(μ-(PPh2)2py)2(μ-OH)](PF6)3, 2, and [Au2Cu2Cl2(μ-(PPh2)2 py)2](OTf)2, 4, have been prepared by the reactions of precursor complexes [Au2(μ-(PPh2)2py)2](OTf)2, 1, and [Cu2(μ-(PPh2)2py)2(μ-SMe2)(OTf)2], 3, with [Cu(NCCH3)4]PF6 and AuCl(SMe2), respectively. The crystal structures of complexes 2 and 4 were determined by X-ray crystallography, indicating a butterfly-shaped Au2Cu2 metal core for 2 and a planar-shaped Au2Cu2 metal core for 4. In complex 2, the Cu atoms occupy the edge-sharing bond, while in complex 4, alternating Au and Cu atoms occupy the tetragon vertices. The optical properties of the complexes were investigated by experimental and computational methods. Although complex 2 displayed a luminescence vapochromic behavior in the presence several volatile organic compounds, complex 4 indicated only an distinguishable change in its emission color when it was exposed to vapor of hydrogen-bond donor solvents. The calculations showed that 2 undergoes an unsymmetrical distortion in its two-coordinated gold(I) centers upon excitation to the first triplet excited state. This distortion induces a large Stokes shift and a strong rigidochromism behavior that is unprecedented for two-coordinated gold(I) complexes.

Changing the gold standard

Gold — long presumed to be an inert metal — has been increasingly shaking this image over the past couple of decades, mostly through electrophilic behaviour. Now, a two-coordinate gold complex has been shown to exhibit nucleophilic reactivity, with the insertion of CO2 into its polarized Auδ−–Alδ+ bond.

A nucleophilic gold complex.

Solid-state auride salts featuring the negatively charged Au- ion are known to be stable in the presence of alkali metal counterions. While such electron-rich species might be expected to be nucleophilic (in the same manner as I-, for example), their instability in solution means that this has not been verified experimentally. Here we report a two-coordinate gold complex (NON)AlAuPtBu3 (where NON is the chelating tridentate ligand 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) that features a strongly polarized bond, Auδ--Alδ+. This is synthesized by reaction of the potassium aluminyl compound [K{Al(NON)}]2 with tBu3PAuI. Computational studies of the complex, including quantum theory of atoms in molecules charge analysis, imply a charge at gold (-0.82) that is in line with the relative electronegativities of the two metals (Au: 2.54; Al: 1.61 on the Pauling scale). Consistently, the complex is found to act as a nucleophilic source of gold, reacting with diisopropylcarbodiimide and CO2 to give the Au-C bonded insertion products (NON)Al(X2C)AuPtBu3 (X = NiPr, 4; X = O, 5).

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.

Formation and structure of two luminescent salts of [Au(SCSN3)2]- obtained through the [2 + 3] cyclization of carbon disulfide and azide ion.

The colorless, two-coordinate gold(i) complex, [(H2O)3Na][Au(SCSN3)2], has been synthesized through the [2 + 3] cyclic reaction of carbon disulfide and sodium azide in the presence of the labile complex (tht)AuCl. Metathesis of [(H2O)3Na][Au(SCSN3)2], with tetra(phenyl)arsonium chloride produced colorless needles of (Ph4As)[Au(SCSN3)2]. The structure of [(H2O)3Na][Au(SCSN3)2] involves linear gold coordination by two exocyclic sulfur atoms of the 1,2,3,4-thiatriazole-5-thiolate anions. These two-coordinate anions self-associate to form extended, zig-zag chains that are connected by aurophilic bonding with Au∙∙∙Au distances of 3.2653(3) Å and 3.3090(3) Å. Remarkably, the individual S-Au-S units that are connected though aurophilic interactions are eclipsed. The structure of (Ph4As)[Au(SCSN3)2] also contains linear, two-coordinate gold ions with bonding to the 1,2,3,4-thiatriazole-5-thiolate anionic ligands through the exocyclic sulfur atoms. However, in this salt, the anions self-associate through AuAu bonds (Au∙∙∙Au distance of 3.2007(3) Å) to form simple dimers, which also have an eclipsed arrangement of the ligands. Electronic structure calculations strongly suggest that the staggered geometry for the [(Au(SCSN3))2](+) dimer is energetically favored relative to the eclipsed geometry. However, attractive π-stacking interactions appear to promote the observed eclipsed arrangement of the ligands.

Cationic, Two‐Coordinate Gold π Complexes

Cationic, two-coordinate gold π complexes that contain a phosphine or N-heterocyclic supporting ligand have attracted considerable attention recently owing to the potential relevance of these species as intermediates in the gold-catalyzed functionalization of C-C multiple bonds. Although neutral two-coordinate gold π complexes have been known for over 40 years, examples of the cationic two-coordinate gold(I) π complexes germane to catalysis remained undocumented prior to 2006. This situation has changed dramatically in recent years and well-defined examples of two-coordinate, cationic gold π complexes containing alkene, alkyne, diene, allene, and enol ether ligands have been documented. This Minireview highlights this recent work with a focus on the structure, bonding, and ligand exchange behavior of these complexes.

Azido, Triazolyl, and Alkynyl Complexes of Gold(I): Syntheses, Structures, and Ligand Effects

Gold(I) triazolyl complexes are prepared in [3 + 2] cycloaddition reactions of (tertiary phosphine)gold(I) azides with terminal alkynes. Seven such triazolyl complexes, not previously prepared, are described. Reducible functional groups are accommodated. In addition, two new (N-heterocyclic carbene)gold(I) azides and two new gold(I) alkynyls are described. Eight complexes are crystallographically authenticated; aurophilic interactions appear in one structure only. The packing diagrams of gold(I) triazolyls all show intermolecular hydrogen bonding between N-1 of one molecule and N-3 of a neighbor. This hydrogen bonding permeates the crystal lattice. Density-functional theory calculations of (triphenylphosphine)gold(I) triazolyls and the corresponding alkynyls indicate that the triazolyl is a stronger trans-influencer than is the alkynyl, but the alkynyl is more electron-releasing. These results suggest that trans-influences in two-coordinate gold(I) complexes can be more than a simple matter of ligand donicity.

Correction to Syntheses, X-ray Crystal Structures, and Solution Behavior of Cationic, Two-Coordinate Gold(I) η2-Diene Complexes

Correction to Syntheses, X-ray Crystal Structures, and Solution Behavior of Cationic, Two-Coordinate Gold(I) η²-Diene Complexes

Cationic Gold Carbonyl Complex on a Phosphine Support

A cationic gold carbonyl complex has been synthesized and characterized using several techniques including X-ray crystallography. [(Mes(3)P)Au(CO)][SbF(6)] (Mes = 2,4,6-Me(3)C(6)H(2)) has a linear, two-coordinate gold atom. This compound displays the CO stretching frequency at 2185 cm(-1). The (13)C NMR signal of the gold-bound (13)CO appears as a doublet centered at δ 182.6 ((2)J(C,P) = 115 Hz). A computational study shows that the Au-CO bond consists of electrostatic attraction, Au ← CO donation, and significant Au → CO π-back-bonding components. Polarization of the CO bond caused by the electrostatic effect of the cationic gold center is mainly responsible for the large blue shift in the CO stretching frequency.

Isolable, gold carbonyl complexes supported by N-heterocyclic carbenes

Cationic gold carbonyl complexes supported by N-heterocyclic carbene ligands, SIDipp and IDipp, have been synthesized. [(SIDipp)Au(CO)][SbF(6)] has a linear, two-coordinate gold center. [(SIDipp)Au(CO)][SbF(6)] and [(IDipp)Au(CO)][SbF(6)] display ̃ν(CO) values at 2197 and 2193 cm(-1), respectively. Computational studies on [(SIMe)Au(CO)](+) indicate the presence of a strong Au(I)-CO bond.

(Ferrocenylthiophosphonato-κS)(triphenylphosphane-κP)gold(I) dichloromethane monosolvate

In the title compound, [AuFe(C5H5)(C5H5O2PS)(C18H15P)]·CH2Cl2, the two-coordinate gold(I) atom shows a slightly distorted linear arrangement, with a P—Au—S bond angle of 176.81 (6)°. The difference in P=O and P—O(H) bond lengths, which are 1.503 (6) and 1.541 (5) Å, respectively, implies there is apparently no delocalization between the P—O bonds, and the proton appears to be localized on one O atom only. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds link dinuclear mol­ecules into chains propagated in the [010] direction. The dichloro­methane solvent mol­ecule was disordered between two positions in a 0.63 (3):0.37 (3) ratio.

Synthesis and equilibrium binding studies of cationic, two-coordinate gold(I) π-alkyne complexes

Reaction of a 1:1 mixture of (L)AuCl [L = P( t-Bu) 2 o-biphenyl or IPr] and AgSbF 6 with internal alkynes led to isolation of the corresponding cationic, two-coordinate gold π-alkyne complexes in ≥ 90% yield. Equilibrium binding studies show that the binding affinities of alkynes to gold(I) are strongly affected by the electron density of the alkyne and to a lesser extent on the steric bulk of the alkyne. These substituent effects on alkyne binding affinity are greater than are the differences between the inherent binding affinities of alkynes and alkenes to gold(I).

Solid-State and Dynamic Solution Behavior of a Cationic, Two-Coordinate Gold(I) π-Allene Complex

The cationic gold π-allene complex {[P(t-Bu)2o-biphenyl]Au[η2-H2C═C═C(CH3)2]}+SbF6− was isolated in 98% yield from reaction of 3-methyl-1,2-butadiene with a mixture of [P(t-Bu)2o-biphenyl]AuCl and AgSbF6 and was characterized by X-ray crystallography and variable-temperature NMR spectroscopy. These studies revealed preferential binding of gold to the less substituted C═C bond of the allene in both the solid state and solution and also revealed fluxional behavior consistent with π-face exchange of the allene ligand via an η1-C2 allene intermediate or transition state.

Two polymorphs of chlorido(cyclohexyldiphenylphosphine)gold(I).

The title compound, [AuCl(C(18)H(21)P)], a monomeric two-coordinate gold(I) complex, has been characterized at 100 K as two distinct monoclinic polymorphs, one from a single crystal, (Is), and one from a pseudo-merohedrally twinned crystal, (It). The molecular structures in the two monoclinic [P2(1)/n for (Is) and P2(1)/c for (It)] polymorphs are similar; however, the packing arrangements in the two lattices differ considerably. The structure of (It) is pseudo-merohedrally twinned by a twofold rotation about the a* axis.

Syntheses, X-ray Crystal Structures, and Solution Behavior of Monomeric, Cationic, Two-Coordinate Gold(I) π-Alkene Complexes

Treatment of a suspension of (IPr)AuCl [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine] and AgSbF(6) (1:1) with isobutylene at room temperature for 12 h led to isolation of [(NHC)Au(eta(2)-H(2)C=CMe(2))](+) SbF(6)(-) (1a) in 98% yield, which was characterized by spectroscopy and X-ray crystallography. A number of cationic gold pi-alkene complexes were isolated employing a procedure similar to that used to isolate 1a, two of which were analyzed by X-ray crystallography. Spectroscopy, X-ray crystallography, and alkene binding studies were in accord with a gold-(pi-alkene) interaction dominated by sigma-donation from the alkene to gold.

Syntheses and X-ray crystal structures of cationic, two-coordinate gold(i) π-alkene complexes that contain a sterically hindered o-biphenylphosphine ligand

A number of cationic gold pi-alkene complexes of the form {[P(t-Bu)(2)o-biphenyl]Au(pi-alkene)}(+)SbF(6)(-) were isolated and three were analyzed by X-ray crystallography.