Amine-amide equilibrium in gold(III) complexes and a gold(III)-gold(I) aurophilic bond

The ligands HN(CH2-2-C5H4N)2, BPMA, and PhCH2N(CH2-2-C5H4N)2, BBPMA, react with Na[AuCl4] to give the cationic complexes [AuCl(BPMA-H)]+ and [AuCl(BBPMA)]2+, respectively. The amido complex [AuCl(BPMA-H)]+ undergoes easy inversion at the amido nitrogen atom and can be reversibly protonated by triflic acid to give [AuCl(BPMA)]2+. The complex [AuCl(BBPMA)]2+ is easily decomposed in aqueous solution by cleavage of a carbon-nitrogen bond or, in dilute HCl solution, by protonation of the ligand to give [BBPMAH2]Cl[AuCl4] The complexes [BBPMAH2]Cl[AuCl4] and [BBPMAH2]Cl[AuCl2] can be formed by direct reaction of BBPMA with H[AuCl4]. Unusual forms of gold(III)...gold(III) and gold(III)...gold(I) aurophilic bonding are observed in the salts [AuCl(BPMA-H)][PF6] and [AuCl(BPMA-H)][AuCl2], respectively. The first comparison of the structures of gold(III) amine and amido complexes, in the cations [AuCl(BPMA-H)]+ and [AuCl(BPMA)]2+, indicates that there is little ppi-dpi bonding in the amido-gold bond and that the amide exerts a stronger trans influence than the amine group.     

Synthesis of luminescent gold(I) and gold(III) complexes with a triphosphine ligand

We have synthesized and characterized a series of trinuclear gold(I) complexes [(AuX)(3)(mu-triphos)] (triphos = bis(2-diphenylphosphinoethyl)phenylphosphine; X = Cl 1, Br 2, I 3, C(6)F(5) 4) and di- and trinuclear gold(III) complexes [[Au(C(6)F(5))(3)](n)(mu-triphos)] (n = 2 (5), 3 (6)). The crystal structure of 6 [[Au(C(6)F(5))(3)](3)(mu-triphos)] has been determined by X-ray diffraction studies, which show the triphosphine in a conformation resulting in very long gold-gold distances, probably associated with the steric requirements of the tris(pentafluorophenyl)gold(III) units. Complex 6 crystallizes in the triclinic space group P(-1) with a = 12.7746(16) A, b = 18.560(2) A, c = 21.750(3) A, alpha = 98.215(3) degrees, beta = 101.666(3) degrees, gamma = 96.640(3) degrees, and Z = 2. Chloride substitutions in complex 1 afford trinuclear gold(I) complexes [(AuX)(3)(mu-triphos)] (X = Fmes (1,3,5-tris(trifluoromethyl)phenyl) 7, p-SC(6)H(4)Me 8, SCN 9) and [Au(3)Cl(3)(-)(n)()(S(2)CNR(2))(n)(mu-triphos)] (R = Me, n = 3 (10), 2 (12), 1 (14); R = CH(2)Ph, n = 3 (11), 2 (13), 1 (15)). The luminescence properties of these complexes in the solid state have been studied; at low temperature most of them are luminescent, including the gold(III) derivative 6, with the intensity and the emission maxima being clearly influenced by the nature and the number of the ligands bonded to the gold centers.     

The first acetimine gold(I) and gold(III) complexes and the first acetonine complexes

Ketimino(phosphino)gold(I) complexes of the type [Au[NR=C(Me)R']L]X (X = ClO4, R = H, L = PPh3, R'=Me (la), Et (2a); L=PAr3 (Ar=C6H4OMe-4), R'=Me (1b), Et (2b); L=PPh3, R=R'=Me (3); X= CF3SO3 (OTf), L=PPh3, R=R'=Me (3'); R=Ar, R'=Me (4)) have been prepared from [Au(acac)L] (acac = acetyl acetonate) and ammonium salts [RNH3]X dissolved in the appropriate ketone MeC(O)R'. Complexes [Au(NH=CMe2)2]X (X = C1O4 (6), OTf (6')) were obtained from solutions of [Au(NH3)2]X in acetone. The reaction of 6 with PPN[AuCl2] or with PhICl2 gave [AuCl(NH=CMe2)] (7) or [AuCI2(NH=CMe2)2]ClO4 (8), respectively. Complex 7 was oxidized with PhICl2 to give [AuCl3(NH=CMe2)] (9). The reaction of [AuCl(tht)] (tht = tetrahydrothiophene), NaClO4, and ammonia in acetone gave [Au(acetonine)2]ClO4 (10) (acetonine = 2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine) which reacted with PPh3 or with PPN[AuCl2] to give [Au(PPh3)(acetonine)]ClO4 (11) or [AuCl(acetonine)] (12), respectively. Complex 11 reacts with [Au(PPh3)(Me2CO)]ClO4 to give [(AuPPh3)2(mu-acetonine)](ClO4)2 (13). The reaction of AgClO4 with acetonine gave [Ag(acetonine)(OClO3)] (14). The crystal structures of [Au(NH2Ar)(PPh3)]OTf (5), 6' and 10 have been determined.     

Spatially-directed oxidation of gold nanoparticles by Au(III)-CTAB complexes

Gold nanoparticles are readily oxidized by Au(III) in the presence of cetyl-trimethylammonium bromide (CTAB). Oxidation occurs preferentially at surface sites with higher curvature. Conversely, oxidation with cyanide ions in the absence of CTAB leads to uniform oxidation over the whole surface. Examples of the spatially directed oxidation are provided using large, irregular spheres, nanocubes, and nanorods. We conclude that the mechanism of oxidation depends on whether the oxidant is attached to CTAB micelles. It is postulated that the CTAB micelles approach the nanoparticles preferentially at the tips, leading to spatially directed oxidation.     

Therapeutic applications of gold complexes: lipophilic gold(III) cations and gold(I) complexes for anti-cancer treatment

Gold and its complexes have long been known to display unique biological and medicinal properties. Extensive cell-based (in vitro) and animal (in vivo) studies have revealed the potent anti-cancer activities of diverse classes of gold(I) and gold(III) complexes. Most of the reported anti-cancer active gold complexes are highly cytotoxic and unstable under physiological conditions, which hamper their development to be launched clinically. Several clinical reports showed that lipophilic organic cations are promising anti-cancer drug candidates targeting to mitochondria. Through metal-ligand coordination, gold(I) and gold(III) ions can form stable lipophilic cations containing organic ligands having tunable lipophilicity and diverse functionalities. The present highlight summarizes the recent development of lipophilic gold(III) cations and gold(I) complexes with promising anti-cancer activities.     

Synthesis and solution- and solid-state characterization of gold(I) rings with short Au...Au interactions. Spontaneous resolution of a gold(I) complex

We report the synthesis and solution- and solid-state characterization of gold(I) rings with short 1,9-transannular Au...Au interactions. The 9- and 16-membered gold(I) rings were prepared by reacting 9,9-dimethyl-4,5-bis(diphenylphosphino)-xanthene and (Me2S)AuCl in the presence of AgNO3 in the molar ratio of 1:0.5:1 and 1:1:1, respectively. X-ray crystallographic measurements in conjunction with solution X-ray diffraction and NMR methods have been used to determine the structure of gold(I) rings, and we also gained insight into the dynamics. The nine-membered gold(I) ring is chiral, and the crystal contains only one of the two enantiomers, either right- or left-handed. To the best of our knowledge this represents the first example of crystallization-induced spontaneous resolution of a binuclear gold(I) cycle. The 16-membered ring with 1,9-transannular Au...Au interaction is in a figure-eight conformation.     

An ab initio study on luminescent properties and aurophilic attraction of binuclear gold(I) complexes with phosphinothioether ligands

Electronic structures and spectroscopic properties of the binuclear head-to-tail [Au(2)(PH(2)CH(2)SH)(2)](2+) (1) complex were investigated by ab initio calculations. The solvent effect of the complex in the acetonitrile solution was taken into account by the weakly solvated [Au(2)(PH(2)CH(2)SH)(2)](2+).(MeCN)(2) (2) moiety in the calculations. The ground-state geometries of 1 and 2 were fully optimized by the MP2 method, while their excited-state structures were optimized by the CIS method. Aurophilic attraction apparently exists between the two Au(I) atoms in the ground state and is strongly enhanced in the excited state. A high-energy phosphorescent emission was calculated at 337 nm for 1 in the absence of the interactions with solvent molecules and/or counteranion in solid state; however the lowest-energy emission of 2 was obtained at 614 nm with the nature of (3)A(u)(s(sigma)) --> (1)A(g)(d(sigma)) (metal-centered, MC) transition. The coordination of acetonitrile to the gold atom in solution results in a dramatic red shift of emission wavelength. The investigations on the head-to-tail [Au(2)(PH(2)CH(2)SCH(3))(2)](2+) (5) and [Au(2)(PH(2)CH(2)SCH(3))(2)](2+).(MeCN)(2) (6) moieties indicate that the CH(3) substituent on the S atom causes blue shifts of emission wavelength for 5 and 6 with respect to 1 and 2. By comparison between Au(I) thioether 1 and head-to-tail Au(I) thiolate [Au(2)(PH(2)CH(2)S)(2)] (7), it is concluded that the S-->Au dative bonding results in evidently different transition characteristics from the S-Au covalent bonding in the Au(I) thioether/thiolate complexes.     

Supramolecular assembly of trimeric gold(I) pyrazolates through aurophilic attractions

The supramolecular architecture of trinuclear gold(I) pyrazolato aggregates is held together by intermolecular aurophilic attractions, sterically governed by the substituents on the pyrazole rings. A two-dimensional network of [Au(mu-pz)]3 complexes, 1 (pz = pyrazolato anion, C3H3N2-), and a large intricate aggregate of 16 [Au(mu-4-Me-pz)]3 complexes in 2 have been determined crystallographically. Under UV irradiation at ambient temperature, solid samples of 1 and 2 luminesce with lambda max = 626 and 631 cm-1, respectively, attributed to intermolecular Au...Au aurophilic contacts.     

Solvent-assisted spontaneous resolution of a 16-membered ring containing gold(I) showing short Au...Au aurophilic interaction and a figure-eight conformation

The achiral 4,6-bis(diphenylphosphino) phenoxazine (nixantphos) ligand was used to synthesize a gold(I) complex, [Au2(nixantphos)2](NO3)2, containing a 16-membered [Au2(nixantphos)2](+2) cationic ring in a chiral figure-eight conformation. The single crystal X-ray diffraction analysis of [Au2(nixantphos)2](NO3)2.3MeOH.H2O (1) and [Au2(nixantphos)2](NO3)2.4MeCN (2) revealed a solvent-assisted spontaneous resolution of the [Au2(nixantphos)2](NO3)2 complex. By changing the nature of the solvent, homochiral hydrogen bonded helices (1) and heterochiral hydrogen bonded monomers (2) were obtained. Multinuclear NMR spectroscopy showed the evidence of chemical exchange phenomenon related to the interconversion of the enantiomeric skeletons of the 16-membered macrocycle in solution. The existence of the Au...Au aurophilic interaction was confirmed by the analysis of the spin-system in the (31)P NMR spectrum.     

某些Au(III)、Au(I)配离子在溶液中扩散的研究

用毛细管色谱在25℃测定了AuCl4、[Au(SO3)2]、[Au(CSN2H4)2]、[Au(CN)2]等配位体离子在HCl溶液中的扩散系数及AuCl4阴离子的扩散活化能, 并与文献中其它配阴离子的D值比较, 认为扩散离子的质量和所载电荷可能是决定配阴离子扩散系数的主要因素.     

A G-octamer scaffold via self-assembly of a guanosine-based Au(I) isonitrile complex for Au(I)-Au(I) interaction

A guanosine-based Au(I) isonitrile complex was demonstrated to serve as the reliable scaffold via self-assembly, wherein the quartet and octamer were formed in the absence and presence of a potassium ion, respectively, exhibiting a switchable emission based on Au(I)-Au(I) interaction.     

Kinetics and mechanism of interactions of some monofunctional Au(III) complexes with sulphur nucleophiles

Kinetics of the substitution reactions between monofunctional Au(III) complexes, [Au(dien)Cl]²⁺, [Au(bpma)Cl]²⁺ and [Au(terpy)Cl]²⁺ (dien?=?3-azapentane-1,5-diamine, bpma?=?di-(2-picolyl) amine, terpy?=?2,2′;6′,2″-terpyridine), and biologically relevant sulphur ligands, namely glutathione (GSH), l-methionine (l-Met) and l-cysteine (l-Cys), were studied in 0.1 M HCl (pH?=?1.0). The reactions were followed under pseudo-first-order conditions as a function of ligand concentration and temperature using stopped-flow spectrophotometry. The [Au(terpy)Cl]²⁺ complex proved to be more reactive than the [Au(bpma)Cl]²⁺ and [Au(dien)Cl]²⁺ complexes. The reactivities of the nucleophiles follow the same order for all three complexes, viz. l-Met?>?GSH?>?l-Cys. Values of the activation parameters of the reactions support an associative substitution mechanism. In order to confirm that these monofunctional Au(III) complexes undergo a single substitution process in strongly acidic medium, the reaction between [Au(terpy)Cl]²⁺ and l-Met was studied by HPLC. At pH?=?1.0, only one reaction product was detected.     

Au(I) and Au(III) complexes of a sterically bulky benzimidazole-derived N-heterocyclic carbene

The reaction of [AuCl(SMe₂)] with in situ generated [AgCl(ⁱPr₂-bimy)] (ⁱPr₂-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene), which in turn was obtained by the reaction of Ag₂O with 1,3-diisopropylbenzimidazolium bromide (ⁱPr₂-bimyH⁺Br⁻, A), afforded the monocarbene Au(I) complex [AuCl(ⁱPr₂-bimy)] (1). Subsequent reaction of 1 and the ligand precursor ⁱPr₂-bimyH⁺BF₄⁻, (B) in acetone in the presence of K₂CO₃ yielded the bis(carbene) complex [Au(ⁱPr₂-bimy)₂]BF₄ (2) as a white powder in 80% yield. The oxidative addition of elemental iodine to complex 2 gave the bis(carbene) Au(III) complex trans-[AuI₂(ⁱPr₂-bimy)₂]BF₄ (3) as an orange-red powder in 92% yield. All complexes 1-3 have been fully characterized by multinuclear NMR spectroscopies, ESI mass spectrometry, elemental analysis, and X-ray single crystal diffraction. Complexes 1 and 2 adopt a linear geometry around metal centers as expected for d¹⁰ metals. The geometry around the Au(III) metal center in 3 is essentially square-planar with two carbene ligands in trans-position to each other. Complex 3 shows absorption and photoluminescence properties owing to a ligand to metal charge transfer.     

Stable gold(III) complexes with thiosemicarbazone derivatives

Novel thiosemicarbazonato complexes of gold(III) have been prepared from reactions of [Au(damp-C1,N)Cl2(damp- = 2-(N,N-dimethylaminomethyl)phenyl) or [NBu4][AuCl4] with 2-pyridineformamide thiosemicarbazones (HL). The thiosemicarbazones deprotonate and coordinate as mononegative, tridentate NNS ligands to gold to give [Au(Hdamp-C1)(L)]Cl2 or [AuCl(L)]Cl complexes. The organometallic damp- ligand is protonated during the reactions and the Au-N bond is cleaved. The [AuCl(L)]+ cations represent the first gold(III) complexes with thiourea derivatives which are not stabilised by an additional organometallic ligand. Reactions of [NBu4][AuX4](X = Cl, Br) with diphenylthiocarbazone (dithizone) result in reduction of the metal and the formation of gold(I) complexes of the composition [AuX(SCN4-3,4-Ph2)] where SCN4-3,4-Ph2 is 3,4-diphenyltetrazole thione which is formed from cyclisation of dithizone.     

Luminescent cyclometalated gold(III) complexes

Many luminescent gold(I) compounds are known, but in the vast majority of gold(III) complexes reported until recently, room temperature emission in fluid solution does not occur. As for other d(8) and d(6) metals, the key to obtaining gold(III) compounds with favorable luminescence properties seems to be the use of cyclometalating ligands that ensure very strong ligand fields. Recent progress in this emerging research field is discussed, and where appropriate, comparison to isoelectronic platinum(II) complexes and their photophysical properties is made.     

Morphology of gold nanoparticles synthesized by filamentous cyanobacteria from gold(I)-thiosulfate and gold(III)--chloride complexes

Plectonema boryanum UTEX 485, a filamentous cyanobacterium, has been reacted with aqueous Au(S(2)O(3))(2)(3)(-) and AuCl(4)(-) solutions ( approximately 400-550 mg/L Au) at 25-100 degrees C for up to 1 month and at 200 degrees C for 1 day. The interaction of cyanobacteria with aqueous Au(S(2)O(3))(2)(3)(-) promoted the precipitation of cubic (100) gold nanoparticles (<10-25 nm) at membrane vesicles and admixed with gold sulfide within cells and encrusted on the cyanobacteria, whereas reaction with AuCl(4)(-) resulted in the precipitation of octahedral (111) gold platelets ( approximately 1-10 microm) in solutions and nanoparticles of gold (<10 nm) within bacterial cells. Functional groups imaged by negative ion TOF-SIMS on (111) faces of the octahedral platelets were predominantly Cl and CN, with smaller amounts of C(2)H and CNO.     

Intermolecular interactions in polymorphs of trinuclear gold(I) complexes: insight into the solvoluminescence of Au(I)3(MeN=COMe)3

The trinuclear complex, Au(I)3(MeN=COMe)3, which displays a number of remarkable properties including solvoluminescence, has been found to crystallize as three polymorphs. The new triclinic and monoclinic polymorphs crystallized as colorless blocks, whereas the original hexagonal polymorph formed colorless needles. These polymorphs differ in the manner in which the nearly planar molecules pack and in the nature of the aurophilic interactions between them. Each of the three polymorphs of Au(I)3(MeN=COMe)3 shows a distinctive emission spectrum, but only the original hexagonal polymorph shows the low-energy emission that is responsible for its solvoluminescence. Colorless Au(I)3(n-PentN=COMe)3 crystallized from diethyl ether as needles of an orthorhombic polymorph and blocks of a triclinic polymorph. These polymorphs differ in the orientation of the n-Pent substituents, in the orientation of the trimers with respect to one another, and in the nature of the aurophilic interactions between the molecules. Only the triclinic polymorph of Au(I)3(n-PentN=COMe)3 shows luminescence at room temperature, but it is not solvoluminescent. Colorless Au(I)3(i-PrN=COMe)3 has also been prepared and crystallographically characterized. The isopropyl groups protrude out of the plane of the nine-membered ring and prevent self-association. The closest Au...Au contact between molecules is 6.417 A. Crystalline Au(I)3(i-PrN=COMe)3 is not luminescent at room temperature.     

Gold(I) and gold(III) ortho-nitrophenyl complexes. Crystal and molecular structure of ortho-nitrophenyltriphenylarsinegold(I)

The reaction between [Au(o-C₆H₄NO₂)Cl]⁻ and tetrahydrothiophene (tht) in the presence of NaClO₄ give a solution (probably containing [Au(o-C₆H₄NO₂)(tht)]) that can be used to prepare neutral [Au(o-C₆H₄NO₂)L_n] (L = AsPh₃, n = 1; L = SbPh₃, n = 2; L = 1,10-phenanthroline, n = 1) or anionic [Au(o-C₆H₄-NO₂(CN)]⁻ complexes. Treatment of [Au(o-C₆H₄NO₂)(PPh₃)] with chlorine or PhICl₂ gives trans- or cis-[Au(o-C₆H₄NO₂)Cl₂(PPh₃)]. Isomerizations occur when the cis-isomer is treated with concentrated solutions of chlorine or when the trans-isomer is heated.An X-ray diffraction study of [Au(o-C₆H₄NO₂)(AsPh₃)] has revealed an almost linear coordination around the gold atom (AsAuC mean value 177(2)°). The AuO distance is too long (mean value 2.80(3) Å) for intramolecular coordination.