Alfredo Burini

Reactions of C-imidazolyllithium derivatives with Group Ib compounds: Tris[μ-(1-alkylimidazolato-N3,C2)]tri-gold(I) and -silver(I). Crystal structure of bis(1-benzylimidazolin-2-yliden)gold(I) chloride

Abstract Upon reaction of LMX (M  Au, X  Cl, L  PPh3 or Me2S; M  Ag, X  NO3, L  Me2S) with 1-R-2-lithiumimidazole the lithium is replaced by a noble metal to give the species (1-R-2-M-imidazole)n (M  Au, R  methyl or benzyl, n = 3; M  Ag, R = benzyl). From Me2SCuBr the compound bis(1-R-imidazol-2-yl) was obtained (R = methyl or benzyl). The unexpected formation during work up of [Au( CN(CH 2 Ph)CHCHN H)2]Cl, a carbene derivative, was confirmed by an X-ray crystal structural study which showed the presence of two independent molecules where CAuC is 175.2(4) or 176.6(4)°, average AuC is 2.027(7) A, and there is an Au ··· Au interaction at 3.2630(5) A.

Luminescent Chains Formed from Neutral, Triangular Gold Complexes Sandwiching TlI and AgI. Structures of {Ag([Au(μ-C2,N3-bzim)]3)2}BF4·CH2Cl2, {Tl([Au(μ-C2,N3-bzim)]3)2}PF6·0.5THF (bzim = 1-Benzylimidazolate), and {Tl([Au(μ-C(OEt)═NC6H4CH3)]3)2}PF6·THF, with MAu6 (M = Ag+, Tl+) Cluster Cores

It has been found that several trinuclear complexes of AuI interact with silver and thallium salts to intercalate Ag+ and Tl+ cations, thereby forming chains. The resulting sandwich clusters center the cations between the planar trinuclear moieties producing structures in which six AuI atoms interact with each cation in a distorted trigonal prismatic coordination. The resultant (B3AB3B3AB3)∞ pattern of metal atoms also shows short (∼3.0 Å) aurophilic interactions between BAB molecular centers. These compounds display a strong visible luminescence, under UV excitation, which is sensitive to temperature and the metal ion interacting with the gold. X-ray crystal structures are reported for Ag([Au(μ-C2,N3-bzim)]3)2BF4·CH2Cl2 (P [Formula: see text] , Z = 2, a = 14.4505(1)Å; b = 15.098(2)Å; c = 15.957(1)Å; α = 106.189(3)°; β = 103.551(5)°; γ = 101.310(5)°); Tl([Au(μ-C2,N3-bzim)]3)2PF6·0.5C4H8O (P [Formula: see text] , Z = 2, a = 15.2093(1)Å; b =15.3931(4)Å; c = 16.1599(4)Å; α = 106.018(1)°; β = 101.585(2)°; γ=102.068(2)°); and Tl([Au(μ-C(OEt)═NC6H4CH3)]3)2PF6·C4H8O (P2(1)/n, Z = 4, a = 16.4136(3)Å; b = 27.6277(4)Å; c = 16.7182(1)Å; β = 105.644(1)°). Each compound shows that the intercalated cation, Ag+ or Tl+, coordinates to a distorted trigonal prism of six AuI atoms. The counteranions reside well apart from the cations between the cluster chains.

CYCLIC TRINUCLEAR GOLD(I) COMPOUNDS: SYNTHESIS, STRUCTURES AND SUPRAMOLECULAR ACID-BASE π-STACKS

Trinuclear 9-membered rings can be formed by gold(I) ions with exobidentate C,N or N,N monoanionic ligands. They are generally slightly irregular and puckered unless the metallocycle is imposed by intramolecular crystallographic symmetry. Gold-gold intramolecular interactions are always present and the complexes exhibit a roughly D3h symmetry. Crystal structures of these trinuclear complexes show individual complexes, dimers supramolecular columnar packing or more complex supramolecular aggregates. Dimers and supramolecular structures are held together by aurophilic intermolecular gold-gold interactions. Bulky substituents on the ligands can prevent intermolecular metal-metal interactions or the formation of supramolecular architectures. It is well established that the Au(I) center in many linear 2-coordinate Au(I) complexes displays electrophilic tendencies in reaction chemistry while also often accepting electron donors to expand the coordination. Trinuclear Au(I) pyrazolates, carbeniates and benzylimidazolates are well known and undergo electron loss through oxidative addition forming first Au(I,III) mixed valence species and ultimately (with the carbeniates, TR(carb), the benzylimidazolates, TR(bzim) and the chlorinated pyrazolate TR(Cl-pz) trinuclear Au(III) species. Surprisingly, these Au(I) carbeniates and benzylimidazolates also are excellent bases for the metals cations Tl(I) and Ag(I). The acidic, neutral [Hg(C6F4)3]3 interacts with TR(carb) and TR(bzim) as seen by X-ray solid state and solution NMR measurements. Recently it has been shown that the neutral pi acids C6F6 and TCNQ also form stacked pi-acid, pi-base solid state products with TR(carb) and TR(bzim). The TR(bzim) and TR(carb) products are luminescent as solids but C6F6 intercalation quenches the luminescence of the p-tol, ethoxy TR(carb), which is a dimer in the solid state. It is interesting that pi-acid, pi-base stacking can involve either a ABAB pattern or an ABBABBA pattern of the molecules, where B is base, TR(carb) or TR(bzim). The B units are aurophilically bonded to each other by two Au…Au linkages. DFT calculations demonstrate that the basicity of the BB dimer is increased relative to the molecular species.

Sulfonate- or carboxylate-functionalized N-heterocyclic bis-carbene ligands and related water soluble silver complexes

New N-heterocyclic carbene ligand precursors {H(2)C(HTz(R))(2)} and {H(2)C(HIm(R))(2)} (HTz = 1,2,4-triazole; HIm = imidazole; R = PrSO(3) or EtCOO) were obtained starting from the compounds bis(1,2,4-triazol-1-yl)methane and bis(imidazol-1-yl)methane. The related silver(i) carbene complexes were prepared in degassed water solution by treatment of the triazolium or imidazolium species with Ag(2)O, resulting in well-characterized and water soluble bimetallic complexes of general formula {Na(2)[H(2)C(Tz(R))(2)](2)Ag(2)} and {Na(2)[H(2)C(Im(R))(2)](2)Ag(2)}. In these metallacycles every silver atom is coordinated to two triazolin- or imidazolin-2-ylidene rings, belonging to two different dicarbene units.

Reactions of (tertiary phosphine)gold(I) substituted imidazoles or pyrazolones with acidic reagents: protonation, zole displacement, and adduct formation. Crystal structure determination of the adduct 1-methyl-2-(cyclohexylphosphinegoldthiolato)imidazole · 2benzimidazole

Abstract Imidazole (QH) or pyrazolone (Q′H2) in QAuL or (LAu)2Q′ (where L is a tertiary phosphine) is displaced by some acidic reagents HZ, where HZ = terminal acetylene, imide, thiol, dithio acid, or HI, to give ZAuL. If Z− is not a soft ligand an adduct between the ragents is obtained, and this is formulated as a protonated species, e.g. [LAuQH]+Z− (HZ = picric acid). In other cases the adduct is LAuZ · HQ (rather than LAuQ · HZ or a protonated species), in which the displaced QH is hydrogen-bonded to the product, as shown by the crystal structure of the adduct 1-methyl-2(cyclohexylphosphinegoldthiolato)imidazole sd 2benzimidazole. In this species gold(I) is two-coordinated (PAuS 172.0(1)), with AuP and AuS 2.292(3) and 2.331(3) A, respectively; the first benzimidazole is hydrogen-bonded to N(3) of the imidazole, and the second benzimidazole to the N(3) of the first, the inter-diazole N⋯HN distance being 2.81 and 2.86(1) A, respectively.

Reactions of symmetric C-imidazolylgold(I) leading to Au1 carbene complexes or mixed valence or AuIII imidazolyl derivatives. Crystal structure of [1-benzyl-3-(carboethoxy)imidazolin-2-yliden]chlorogold(I)

Reaction of trimeric 1-benzyl-2-gold(I)-imidazole, Au3im3 (im  [μ-(N1-benzyl)imidazolato-N3,C2]) with XY reagents gives either gold(I) mononuclear carbene derivatives, XAuCNRCHCHNY (Y−X = Et-I or EtO(O)CCl) or trinuclear mixed valence or gold(III) compounds. The gold(III) complexes, [(X)(Y)Au]3im3, are formed by addition of X–Y (benzoyl or p-tosyl chloride) or by reaction with thionyl chloride. With iodine and with Me3SiI, Au3im3I2 and Au3im3I4, respectively, are formed. The crystal structure of ClAuCN(CH2Ph)CHCHNCOOEt has been determined.

Dinuclear gold(I) and silver(I) derivatives with bridging phosphines containing an imidazole ring; X-ray crystal structure of (1-benzyl-2-imidazolyl)diphenylphosphinegold(I)chloride.

Abstract (1-Benzyl-2-imidazolyl)diphenylphosphine [(BzIm)Ph 2 P] can act as a monodentate or bidentate ligand to afford mononuclear (BzIm)Ph 2 PAuCl ( I ) or dinuclear [μ-(BzIm)Ph 2 PAu] 2 2+ 2X − (X = PF 6 − , BF 4 − or NO 3 − ) ( IIa,b,c ) derivatives of gold(I). Analogous dinuclear silver(I) derivatives were obtained reacting the ligand [(BzIm)Ph 2 P] with AgX salts (X = NO 3 − , BF 4 − ) ( IIIa,b ). In solution the silver complexes show a fluxional behaviour, and two conformers were observed by 31 P NMR spectroscopy. The structure of compound I was established by X-ray crystallography (monoclinic, space group C2/c, a = 18.068(2), b = 16.576(2), c = 15.391(2) A , β = 117.2(2)°, Z = 8) . The short intermolecular Au⋯Au distance of 3.03(2) A indicates a metal-metal interaction. The 197 Au Mossbauer parameters of compounds I and IIa are consistent with IR, NMR and crystallographic data.

Synthesis and characterization of azolate gold(I) phosphane complexes as thioredoxin reductase inhibiting antitumor agents

Following an increasing interest in the gold drug therapy field, nine new neutral azolate gold(I) phosphane compounds have been synthesized and tested as anticancer agents. The azolate ligands used in this study are pyrazolates and imidazolates substituted with deactivating groups such as trifluoromethyl, nitro or chloride moieties, whereas the phosphane co-ligand is the triphenylphosphane or the more hydrophilic TPA (TPA = 1,3,5-triazaphosphaadamantane). The studied gold(I) complexes are: (3,5-bis-trifluoromethyl-1H-pyrazolate-1-yl)-triphenylphosphane-gold(I) (1), (3,5-dinitro-1H-pyrazolate-1-yl)-triphenylphosphane-gold(I) (2), (4-nitro-1H-pyrazolate-1-yl)-triphenylphosphane-gold(I) (5), (4,5-dichloro-1H-imidazolate-1-yl)-triphenylphosphane-gold(I) (7), with the related TPA complexes (3), (4), (6) and (8) and (1-benzyl-4,5-di-chloro-2H-imidazolate-2-yl)-triphenylphosphane-gold(I) (9). The presence of deactivating groups on the azole rings improves the solubility of these complexes in polar media. Compounds 1-8 contain the N-Au-P environment, whilst compound 9 is the only one to contain a C-Au-P environment. Crystal structures for compounds 1 and 2 have been obtained and discussed. Interestingly, the newly synthesized gold(I) compounds were found to possess a pronounced cytotoxic activity on several human cancer cells, some of which were endowed with cis-platin or multidrug resistance. In particular, among azolate gold(I) complexes, 1 and 2 proved to be the most promising derivatives eliciting an antiproliferative effect up to 70 times higher than cis-platin. Mechanistic experiments indicated that the inhibition of thioredoxin reductase (TrxR) might be involved in the pharmacodynamic behavior of these gold species.

A 197Au mössbauer study of reaction products of trimeric 1-benzyl-2-gold(I)-imidazole leading to AuI carbene or AuI imidazoline complexes and trinuclear AuIII imidazolyl derivatives. X-Ray crystal structure of [{(μ-1-benzylimidazolato-N3,C2)Au}3I2]

Reactions of the trinuclear [Au3Rim3] compound (Rim = [μ-1-benzylimidazolato-N3,C2] with several reagents capable of oxidative addition have been investigated by 197Au Mossbauer spectroscopy. The reaction products are either AuI carbene mononuclear and binuclear complexes or trinuclear AuIII and mixed-valence compounds. The X-ray crystal structure of the mixed-valence complex [AuIIIAuI2Rim3I2] has been determined. Two two-coordinate AuI centres show average AuC and AuN distances of 2.02(3) and 2.04(2) A and average CAuN angles of 175.0(1.2)°, whereas the four-coordinate AuIII centre gives AuC and AuN 1.96(4) and 1.91(3) A with the CAuN angle 170.5(1.6)°, and AuI average distances 2.598(3) A, with an IAuI angle 175.8(1)°. The AuAu intramolecular distances [Au(1) ⋯ Au(2) 3.432(3), Au(1) ⋯ Au(3) 3.508(3), Au(2) ⋯ Au(3) 3.464(3) A] indicate a weak metal-metal interaction.

Reactions of trimeric 1-benzyl-2-gold(I)imidazole leading to AuI carbene complexes. Crystal structure of [1-benzyl-3-benzoyl-imidazolin-2-yliden]chlorogold(I)☆

Abstract The crystal structure determination of a compound previously described as tris-[{μ-(N1-benzyl)imidazolato-N3,C2}(chloro)benzoylgold(III)], which turned out to be a gold(I) mononuclear carbene derivative, has led to a reconsideration of the reactions of [Au3 (im3 = μ-(N1-benzyl)imidazolato-N3,C2) with reagents X–Y. The mononuclear or trinuclear nature of other Au imidazolyl derivatives is discussed and the compounds obtained by reaction with X–Y = ClCOOEt, IEt or Cl-p-tosyl and chlorobenzoyl appear to be mononuclear, whereas those obtained by reaction with Me3SiI, SOCl2 or I2 appear to be trinuclear mixed valence or gold(III) compounds.