Aurophilic Interactions Research Articles

Dicyanoaurate-based heterobimetallic uranyl coordination polymers.

The first series of uranyl ([UO2]2+)-dicyanoaurate coordination polymers and molecular complexes has been synthesized. Reactions of [A][Au(CN)2] (A = [nBu4N]+ or [(Ph3P)2N]+ ([PPN])) and uranyl nitrate in alcoholic solvents in ambient light led to [A]2[(UO2)2(μ-η2:η2-O2)(NO3)2(μ-Au(CN)2)2], which incorporates peroxo ligands into a one-dimensional ladder topology with alternating aurophilic and peroxo rungs. Conducting the reaction with non-alcoholic solvents formed two polymorphs of a one-dimensional chain, [PPN][UO2(NO3)2Au(CN)2], from acetone, and a molecular analogue, [PPN]2[UO2(NO3)2(Au(CN)2)2], from acetonitrile, none of which exhibited aurophilic interactions. The addition of 2,2'-bipyridine to the initial reaction resulted in [UO2(bipy)(MeO)(MeOH)]2[(μ-Au(CN)2)(Au(CN)2)], a one-dimensional structure which propagates via a series of linear aurophilic bonds with pendant uranyl complexes; methanol and methoxy ligands provide additional connections through hydrogen bonding. The addition of 5,5'-dimethyl-2,2'-bipyridine using solvothermal conditions resulted in the one-dimensional ladder [UO2(Me2bipy)Au(CN)2]2[(μ-OH)2], generated through aurophilic bonds and hydroxide ligands. The incorporation of 2,2':6',2''-terpyridine (terpy) using solvothermal conditions resulted in [[UO2(terpy)]2(μ-NO3)(μ-O)][Au(CN)2], a molecular salt with no aurophilic interactions. Emission spectra attributable to aurophilic interactions are observed in [nBu4N]2[(UO2)2(μ-η2:η2-O2)(NO3)2(μ-Au(CN)2)2], while all others only show emission typical of the uranyl cation.

Synthesis, structure and cytotoxicity of cyclic (alkyl)(amino) carbene and acyclic carbene complexes of group 11 metals.

A series of complexes of cyclic (alkyl)(amino)carbene (CAAC) complexes of copper, silver and gold have been investigated for their antiproliferative properties. A second series of acyclic carbene (ACC) complexes of gold(i) were prepared by nucleophilic attack on isocyanide complexes by amines and amino esters, to give (ACC)AuCl, [(ACC)Au(PTA)]+ (PTA = triazaphosphaadamantane), as well as mixed-carbene compounds [(CAAC)Au(ACC)]+. Representative complexes were characterised by X-ray diffraction which confirmed the mononuclear linear structures without close intermolecular contacts or aurophilic interactions. The redox properties of these complexes have been determined. The compounds were tested against a panel of human cancer cell lines including leukemia (HL 60), breast adenocarcinoma cells (MCF-7) and human lung adenocarcinoma epithelial cell lines (A549), which show varying degrees of cisplatin resistance. The pro-ligand iminium salts and the PTA complexes were non-toxic. By contrast, the CAAC complexes show high cytotoxicity, with IC50 values in the sub-micromolar to ∼100 nanomolar range, even against cisplatin-insensitive MCF-7 and A549 cells. Cationic bis-carbene complexes [(Me2CAAC)2M]+ (6-8, M = Cu, Ag and Au) proved particularly effective. The mechanism of cell growth control by these complexes remains to be established, although possible modes of action such as inhibition of thioredoxin reductase (TrxR), which is a common pathway for gold NHC compounds, or the formation of reactive oxygen species (ROS) through redox processes, could be ruled out as primary pathways.

Coordination chemistry of phosphinocarbynes: phosphorus vs. carbyne site selectivity.

The phosphinocarbyne complex [W([triple bond, length as m-dash]CPPh2)(CO)2(Tp*)] (1: Tp* = hydrotris(dimethylpyrazolyl)borate) coordinates transition metal fragments via the phosphine to form bimetallic species [W{[triple bond, length as m-dash]CPPh2RhCl2(Cp*)}(CO)2(Tp*)] (2) and [W([triple bond, length as m-dash]CPPh2AuCl)(CO)2(Tp*)] (3). Appropriately tailored sterics allow for complexation of a second equivalent of AuCl to afford the trimetallic complex [W{η2-C(AuCl)PPh2AuCl}(CO)2(Tp*)] (4), containing an Au-W-C dimetallacyclopropene connectivity. Similarly, AuCl binds to the carbyne linkage in [W{[triple bond, length as m-dash]CP([double bond, length as m-dash]S)Ph2}(CO)2(Tp*)], yielding [W{η2-C(AuCl)P([double bond, length as m-dash]S)Ph2}(CO)2(Tp*)] (5). In the case of auration of the ditungsten species [W2(μ-C2PPh)(CO)4(Tp*)2] (6), variation in the stoichiometry leads to trimetallic [W2(μ-C2PPhAuCl)(CO)4(Tp*)2] (7) and pentametallic [W2{μ-(η2-CAuCl)2PPhAuCl}(CO)4(Tp*)2] (8) complexes, via a proposed tetrametallic intermediate [W2{μ-(η2-CAuCl)2PPh}(CO)4(Tp*)2], the site selectivity being dictated by aurophilic interactions.

Control of aurophilic interaction: conformations and electronic structures of one-dimensional supramolecular architectures.

Gold(i) chloride complexes with the diarsenic ligands cis-1,4-dihydro-1,4-diarsinines (cis-DHDAs) were synthesized. X-ray diffraction revealed that they formed one-dimensional polymeric structures through aurophilic interactions. Their higher-ordered structures are controlled by the ligand structure; methyl- and t-butyl substituted ligands offered transoid-transoid and transoid-cisoid conformations, respectively. Density functional theory (DFT) calculations indicated that the electronic structure of the aurophilic network was highly dependent on the conformations. This is the first study on the relationship between the chain conformation and 5d-orbital structures of gold complexes.

Charge transfer-induced assembly of a gold nanocomposite mediated by N-methylfulleropyrrolidine: excitation energy transfer from Rhodamine B

A pH controlled functionalized fullerene-C60-gold NP composite self-assembles via electrostatic as well as aurophilic interactions and acts as an excitation energy acceptor from fluorescent Rhodamine B (3.79 × 6.5 inch).

Photoluminescence of self-assembled Ag(i) and Au(i) N-heterocyclic carbene complexes. Interplay the aurophilic, hydrogen bonding and hydrophobic interactions

The incorporation of a 2-hydroxyl group at the long alkyl chain of NHC increases the hydrogen bonding interactions and thus induces the liquid crystal phase formation for the tetra nuclear Ag–NHC complex.

Intensely luminescent gold(i) phosphinopyridyl clusters: visualization of unsupported aurophilic interactions in solution

Gold(i) phosphinopyridyl clusters [Au9(PNC)6](BF4)3 (1) and [Au11(PNC)6(PPh3)2](BF4)5 (2) (PNC = 2-diphenylphosphinopyridyl monoion) are assembled. In contrast to the green luminescence of 1, 2 is brightly orange emissive in CH2Cl2, which shows the presence of unsupported AuI-AuI interactions in solution. Besides, 1 and 2 can selectively light up the mitochondria of living cells.

A highly luminescent octanuclear gold(i) carbide cluster.

The ligand [{Me3SiC[triple bond, length as m-dash]CC(NDipp)2}Li(thf)3] (Dipp = 2,6-diisopropylphenyl) was used for salt metathesis reactions with [AuCl(tht)] (tht = tetrahydrothiophene) to obtain the dinuclear alkyne functionalized bisamidinate [{Me3SiC[triple bond, length as m-dash]CC(NDipp)2}2Au2]. This compound serves as a building block for the polynuclear carbide bridged gold(i) amidinate complex [Au8{μ3-(η1:η2-C[triple bond, length as m-dash]C)}2(Me3SiC[triple bond, length as m-dash]CC(NDipp)2)4(tht)2], which is the first gold(i) complex with a μ3-η1:η2 carbide coordination. Both gold(i) compounds show distinct aurophilic interactions and are remarkably stable at ambient conditions. Photophysical investigations revealed intense luminescence with notable high quantum yields both in the solid state and in solution.

ChemInform Abstract: Aurophilicity in Gold(I) Catalysis: For Better or Worse?

AbstractReview: 208 refs.

Mono- and Digold(I) Complexes with Mesoionic Carbenes: Structural Characterization and Use in Catalytic Silver-Free Oxazoline Formation

Triazolylidenes are a prominent class of mesoionic carbenes that have found use as supporting ligands in homogeneous catalysis in recent years. We present here the syntheses of three new mononuclear gold(I) chlorido and two new dinuclear gold(I) chlorido complexes. The ligands in the aforementioned complexes are derived from either the corresponding monotriazolium or the bitriazolium salts. All complexes have been characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction studies. Structural characterization delivers a delocalized bonding situation within the triazolylidene ligands and a linear coordination at the gold(I) centers. The gold(I) centers in all cases are bound to one triazolylidene-C donor and a chlorido ligand. Additionally, for the digold(I) complexes large Au–Au distances were observed, ruling out the existence of aurophilic interactions in these digold complexes in the solid state. All of the gold(I) complexes were tested as (pre)catalysts fo...

Gold(I) Complexes of Ferrocenyl Polyphosphines: Aurophilic Gold Chloride Formation and Phosphine-Concerted Shuttling of a Dinuclear [ClAu···AuCl] Fragment.

A smart steric control of the metallocene backbone in bis- and poly(phosphino)ferrocene ligands favors intramolecular aurophilic interactions between [AuCl] fragments in polynuclear gold(I) complexes. We synthesized and characterized by multinuclear NMR and X-ray diffraction analysis mono-, di-, and polynuclear gold complexes of constrained ferrocenyl diphosphines, which bear either bulky tert-butyl groups or more flexible siloxane substituents at the cyclopentadienyl rings. The complexes meso-1,1'-bis(diphenylphosphino)-3,3'-di-tert-butylferrocene (4-m), rac-1,1'-bis[bis(5-methyl-2-furyl)phosphino]-3,3'-di-tert-butylferrocene (5-r), and rac-1,1'-bis(diphenylphosphino)-3,3'-bis[(tri-iso-propylsilyl)oxy]ferrocene (6-r) were used to form dinuclear gold complexes. Coordination of tert-butylated ferrocenyl phosphines generated aurophilic interactions in the corresponding dinuclear gold complexes, contrary to gold(I) complexes reported with 1,1'-bis(diphenylphosphino)ferrocene. The structurally related tetraphosphine 1,1',2,2'-tetrakis(diphenylphosphino)-4,4'-di-tert-butylferrocene (11) also gave access to mononuclear, dinuclear, and the original trinuclear gold chloride aurophilic complexes in which 14e- to 16e- gold centers coexist. In such complexes, nonbonded ("through-space") 31P-31P' nuclear spin couplings were evidenced by high-resolution NMR. In these interactions nuclear spin information is transferred between the lone-pair electron of an uncoordinated phosphorus P and a phosphorus P' that is involved in a σ covalent bond Au-P'. The dinuclear aurophilic complex displayed a concerted shuttling of its [ClAu···AuCl] fragment between the four phosphorus donors of the tetraphosphine ligand. Thus, an aurophilic Au···Au bond, which is assumed to be a weak energy interaction, can be conserved within a dynamic shuttling process at high temperature involving an intramolecular coordination-decoordination process of digold(I) at phosphorus atoms.

Diphosphine-bridged digold(I) compounds: Structural and computational studies on the aurophilic interaction in Au2Cl2(μ-bpcd) and Au2Cl2(μ-bmi)

The reaction of AuCl(tht) with the diphosphine donors 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and 2,3-bis(diphenylphosphino)-N-phenylmaleimide (bmi) in a 2:1 stoichiometry affords the diphosphine-bridged digold(I) complexes Au2Cl2(bpcd) (1) and Au2Cl2(bmi) (2), respectively. 1 and 2 have been isolated and characterized in solution by IR and NMR spectroscopy (1H and 31P), and the solid-state structures established by X-ray crystallography. The X-Au-Au-X (X = Cl, P) atoms in both Au2 dimers exhibit a gauche-type (staggered) interaction based on a torsion angle of −54° for 1 (X = Cl) and −70° for 2 (X = Cl, mean angle for the two independent molecules). Each Au2 product displays a weak aurophilic interaction based on a Au-Au internuclear distance on the order of 2.9 Å. The bonding in 1 and 2 has been investigated by electronic structure calculations and the composition of the HOMO and LUMO levels determined in the case of 2. The potential energy surface for the interconversion of 2 to an alternative staggered conformation has been computed, and this transformation takes place through an eclipsed transition structure. The preference for a structure that contains a staggered orientation of Cl-Au-Au-Cl and P-Au-Au-Cl atoms is discussed.

Observation of a re-entrant phase transition in the molecular complex tris(μ2-3,5-diiso-propyl-1,2,4-triazolato-κ2N1:N2)trigold(I) under high pressure.

We report a molecular crystal that exhibits four successive phase transitions under hydro-static pressure, driven by aurophilic interactions, with the ground-state structure re-emerging at high pressure. The effect of pressure on two polytypes of tris(μ2-3,5-diiso-propyl-1,2,4-triazolato-κ2N1:N2)trigold(I) (denoted Form-I and Form-II) has been analysed using luminescence spectroscopy, single-crystal X-ray diffraction and first-principles computation. A unique phase behaviour was observed in Form-I, with a complex sequence of phase transitions between 1 and 3.5 GPa. The ambient C2/c mother cell transforms to a P21/n phase above 1 GPa, followed by a P21/a phase above 2 GPa and a large-volume C2/c supercell at 2.70 GPa, with the previously observed P21/n phase then reappearing at higher pressure. The observation of crystallographically identical low- and high-pressure P21/n phases makes this a rare example of a re-entrant phase transformation. The phase behaviour has been characterized using detailed crystallographic theory and modelling, and rationalized in terms of molecular structural distortions. The dramatic changes in conformation are correlated with shifts of the luminescence maxima, from a band maximum at 14040 cm-1 at 2.40 GPa, decreasing steeply to 13550 cm-1 at 3 GPa. A similar study of Form-II displays more conventional crystallographic behaviour, indicating that the complex behaviour observed in Form-I is likely to be a direct consequence of the differences in crystal packing between the two polytypes.

Intermolecular Aurophilic versus Intramolecular Au⋅⋅⋅N Secondary Interactions in Two‐Coordinate Gold(I) Selenolate Complexes

AbstractA series of gold(I) selenolates viz., [Au(Sepy‐2)(PPh3)] (1), [Au(Sepy‐4)(PPh3)] (2) (py=pyridyl), [Au(Sepyz‐2)(PPh3)] (3) (pyz=pyrazinyl), [Au(Sepym‐2)(PPh3)] (4) (pym=pyrimidyl) and [Au{Sepym(Me2‐4,6)‐2}(PPh3)] (5) {pym‐2‐(Me2‐4,6)=4,6‐dimethyl‐2‐pyrimidyl} have been synthesized and structurally characterized. The gold atom acquires a two‐coordinate linear geometry with Au−Se distance of ∼ 2.41 Å. The existence of aurophilic interactions are determined by the nature of substituent on selenium. It was observed that the complexes derived from selenolate ligand with pyridyl moiety (one hetero‐N atom in the ring) could exhibit aurophilicity; whereas, the complexes derived from ligands containing pyrazinyl and pyrimidyl moieties (two hetero‐N atoms) are devoid of such interaction but show secondary Au⋅⋅⋅N interaction. The complex [Au(Sepy‐4)(PPh3)] shows polymorphism and the two polymorphs differ in the relative orientations of linear molecules. There are competing secondary intramolecular Au⋅⋅⋅N interaction which plays crucial role on intermolecular aurophilic interaction and overall structure. Theoretical calculations at DFT and MP2 levels have been carried out to rationalize the experimental findings.

Metallophilic interactions in polymeric group 11 thiols

Three polymeric group 11 transition metal polymers featuring metallophilic interactions were obtained directly via self-assembly of metal ions and 4-pyridinethiol ligands. In the cationic [Cu2(S-pyH)4]n2+ with [ZnCl4]n2− counterion (1) and in the neutral [Ag(S-py) (S-pyH)]n (2) 4-pyridinethiol (S-pyH) and its deprotonated form (S-py) are coordinated through the sulfur atom. Both ligands are acting as bridging ligands linking the metal centers together. In the solid state, the gold(I) polymer [Au(S-pyH)2]Cl (3) consists of the repeating cationic [Au(S-pyH)2]+ units held together by aurophilic interactions. Compound 1 is a zig-zag chain, whereas the metal chains in the structures of 2 and 3 are linear. The protonation level of the thiol ligand had an impact on the crystallization of polymers. Both nature of the metal center and reaction conditions affected the polymerization. QTAIM analysis confirmed direct metal-metal contacts only in polymers 1 and 3. In polymer 2, no theoretical evidence of argentophilic contacts was obtained even though the Ag⋅⋅⋅Ag distance was found to be less than sum of the Bondi's van der Waals radius of silver.

Emissive Heterobimetallic Copper(I) Dicyanoaurate-Based Coordination Polymers.

Five new CuI /[Au(CN)2 ]- -based coordination polymer materials-Cu(py)2 [Au(CN)2 ] (1), Cu(PPh3 )(MeCN)[Au(CN)2 ]⋅MeCN (2 a), Cu(PPh3 )(MeCN)[Au(CN)2 ] (2 b), Cu3 (THT)4 [Au(CN)2 ]3 (3 a) and Cu(THT)[Au(CN)2 ] (3 b)-were prepared and characterized in terms of their structural and photoluminescence properties, and thermal stability (py=pyridine, THT=tetrahydrothiophene). While 1 and 2 a/2 b adopted one-dimensional zig-zag chain structures with no Au⋅⋅⋅Au (aurophilic) bonding, 3 a and 3 b exhibited much more complex three-dimensional frameworks featuring numerous aurophilic interactions; bridging THT units formed either eight-membered Cu4 S4 rings (3 a) or helical (Cu/S)n chains (3 b). When these materials are excited using a broad-band UV source (365 nm), they each emit light of a distinct colour (except for 2 a): light green for 1, pale blue for 2 b, deep blue for 3 a, and violet for 3 b (λmax =506 nm (1), 464 nm (2 b), 457 nm (3 a) and 404 nm (3 b)). The emission band in 1, 2 b and 3 b was assigned to CuI /ligand/CN- -based MLCT transitions, while the emission band of 3 a appears to be influenced by the presence of the aurophilic interactions in the structure. Materials 1 and 3 a lose their bound pyridine and THT, respectively, at 110 and 95 °C, respectively, indicating their potential utility as sensory materials.

Synthesis and Structural Characterization of Mono‐ and Bimetallic Rhodium(I), Iridium(I) and Gold(I) Methanide and Methandiide Complexes from 2‐Quinolyl‐Linked (Thiophosphoranyl)methane

The synthesis and structural characterization of RhI, IrI and AuI metal complexes derived from 2‐quinolyl‐linked (thiophosphoranyl)methane CH2(iPr2P=S)(C9H6N‐2) (A) are reported. Metathesis reactions of 2‐quinolyl‐thiophosphinoyl potassium complex [K{CH(iPr2P‐S)(C9H6N‐2)}]n (1) with 1 equiv. of [MCl(COD)]2 (M = Rh, Ir; COD = cycloocta‐1,5‐diene) afforded monomeric 2‐quinolyl‐thiophosphinoyl‐rhodium(I) and iridium(I) complex [M(COD){CH(iPr2P=S)(C9H6N‐2)}] {M = Rh (2), Ir (3)}, respectively. Upon treatment of 1 with 2 equiv. of [MCl(COD)]2 (M = Ir, Rh), bimetallic complexes [M(COD){CH(iPr2P=S)(C9H6N‐2)(M(COD)Cl)}] {M = Rh (4), Ir (5)} were obtained. The reaction of 1 with [AuCl(PPh3)] afforded a geminal dinuclear gold(I) methandiide complex [{Au(PPh3)}2{C(iPr2P‐S)(C9H6N‐2)}] (6), featuring an aurophilic interaction. Meanwhile, the metathesis reaction of 1 with 1 equiv. of gold(I) complex [AuCl(IPrNHC)] {IPrNHC = C[N(2,6‐iPr2C6H3)CH]2} afforded a monomeric two‐coordinate monoaurated product, 2‐quinolyl‐thiophosphinoyl‐gold(I) N‐heterocyclic carbene complex [Au(IPrNHC){CH(iPr2P‐S)(C9H6N‐2)}] (7). The structures of 3–7 have been determined by X‐ray crystallography and the UV/Vis absorption properties of 2–6 have also been studied.

Demetalation of copper undecaarylcorroles: Molecular structures of a free-base undecaarylisocorrole and a gold undecaarylcorrole

Copper undecaarylcorroles were found to undergo acid-induced demetalation with unusual ease under both reductive and nonreductive conditions. The resulting free-base undecaarylcorroles were found to be rather reactive, readily photooxygenating to yield 5/10-hydroxyisocorroles and open-chain tetrapyrroles. The use of nonreductive conditions led to 50-75% yields of undecaarylisocorroles, a new class of sterically hindered ligands, of which one proved amenable to single-crystal X-ray structural analysis. In one case, interaction of an undecaarylisocorrole with gold(III) acetate resulted in aromatization of the macrocycle and a gold undecaarylcorrole. The Au complex exhibited Au-N distances of 1.941(3)–1.965(3) Å, and no significant nonbonded interactions involving the gold. The significant solubility of this complex in organic solvents, compared with the relative insolubility of gold β-octabromo-meso-triarylcorroles, appears to be related to the lack of aurophilic and metallophilic interactions.

Steric effects and aurophilic interactions in crystals of Au2(μ-1,2-bis(diphenylphosphino)ethane)X2 and Au2(μ-1,2-bis(dicyclohexylphosphino)ethane)X2 (X = Cl, Br, I)

Crystals in the isostructural series Au2(μ-dppe)X2 (dppe is 1,2-bis(diphenylphosphino)ethane, X=Cl, Br, I) form centrosymmetric, dimeric structures with two short Au⋯Au contacts between the component molecules. We found no evidence for a second polymorph for any member of the Au2(μ-dppe)X2 series, although two polymorphs were observed previously for the related Au2(Ph2As(CH2)2AsPh2)X2 series. Crystals of Au2(μ-dcpe)X2 (where dcpe is 1,2-bis(dicyclohexylphosphino)ethane) show structures that differ appreciably from those of Au2(μ-dppe)X2. The bulky cyclohexyl substituents appear to be playing a major role in eliminating the formation of polymeric or dimeric structures. Au2(μ-dcpe)Cl2 has a monomeric structure without aurophilic interactions. In contrast, Au2(μ-dcpe)Br2 and Au2(μ-dcpe)I2 have similar structures with intramolecular aurophilic interactions. Au2(μ-dcpe)I2 displays a form of aggregation-induced emission. It displays a red-pink luminescence in crystalline form but is non-emissive in solution.

A Screening Approach for the Discovery of Mechanochromic Gold(I) Isocyanide Complexes with Crystal-to-Crystal Phase Transitions.

Mechanoinduced phase transitions of emissive organic crystalline materials have received much attention. Although a variety of such luminescent mechanochromic compounds have been reported, it is challenging to develop mechanochromic compounds with crystal-to-crystal phase transitions in which precise structural information about molecular arrangements can be obtained. Here, we report a screening approach to explore mechanochromic compounds exhibiting a crystal-to-crystal phase transition. We prepared 48 para-substituted (R(1)) phenyl[para-substituted (R(2)) phenyl isocyanide]gold(I) complexes designated R(1)-R(2) (six R(1) and eight R(2) substituents) and then performed three-step screening experiments. The first screening step was selection of emissive complexes under UV light, which gave 37 emissive R(1)-R(2) complexes. The second screening step involved evaluation of the mechanochromic properties by emission spectroscopy. Twenty-eight complexes were found to be mechanochromic. The third screening step involved preparation of single crystals, reprecipitated powders, and ground powders of the 28 mechanochromic R(1)-R(2) complexes. The changes in the powder diffraction patterns of these complexes induced by mechanical stimulation were investigated. Two compounds exhibited a crystal-to-crystal phase transition upon mechanical stimulation, including the previously reported H-H complex. Single crystals of the as-prepared and ground forms of the newly discovered CF3-CN complex were obtained. Density functional theory calculations indicated that the mechanoinduced red-shifted emission of CF3-CN is caused by formation of aurophilic interactions. Comparison of the crystal structures of CF3-CN with those of the other complexes suggests that the weaker intermolecular interactions in the as-prepared form are an important structural factor for the observed mechanoinduced crystal-to-crystal phase transition.