Exploring Ligand Effects on Structure, Bonding, and Photolytic Hydride Transfer of Cationic Gold(I) Bridging Hydride Complexes of Molybdocene and Tungstenocene.

A diverse family of heterobimetallic bridging hydride adducts of the type [LAu(µ-H)2MCp2][X] (L = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene, IPr; 1,3-bis(1-adamantyl)imidazole-2-ylidene, IAd; 1,3-bis(2,6-di-iso-propylphenyl)-5,5-dimethyl-4,6-diketopyrimidinyl-2-ylidene, DippDAC; triphenylphosphine, PPh3; 2-di-tert-butylphosphino-2',4',6'-triisopropylbiphenyl, tBuXPhos; X = SbF6-, BF4- or TfO-) was synthesized by reacting group VI metallocene dihydrides Cp2MH2 (Cp = cyclopentadienyl anion; M = Mo, W) with cationic gold(I) complexes [LAu(NCMe)][X]. Trimetallic [L'Au2(µ-H)2WCp2][X]2 and tetrametallic [L'Au2{(µ-H)2WCp2}2] [X]2 complexes (L' = rac-2,2'-bis(diphenylphosphino)-1,1'-binaphthalene or bis(diphenylphosphinomethane)) were obtained by reacting digold [L'{Au(NCMe)}2][X]2 with Cp2WH2 in a 1:1 and a 1:2 stoichiometry. Accessing such a broad structural diversity allowed us to pinpoint roles played by the ancillary ligands and group VI metals on the bonding properties of this family of bridging hydrides. In particular, a clear effect of the ligand on the interaction energy and electronic structure was observed, with important implications on photolytic reactivity. UV or visible light irradiation, indeed, leads to the selective cleavage of the heterobimetallic Au(µ-H)2M arrangement and formation of molecular gold hydrides. The photolysis was found to be chromoselective (wavelength-dependent), which can be ascribed to different charge redistributions upon excitation to the first (Kasha's reactivity) and higher (anti-Kasha's reactivity) excited states.

Luminescent Au(III)-M(I) (M = Cu, Ag) Aggregates Based on Dicyclometalated Bis(alkynyl) Gold Anions†.

The syntheses and structures of a series of complexes based on the C∧C-chelated Au(III) unit (C∧C = 4,4'-bis(t-butyl) 2,2'-biphenyl-1,1'-diyl) are reported, namely, [{(C∧C)Au(C≡CtBu)2}2M2], (C∧C)Au(C≡CR)(C≡NXyl), and [{(C∧C)Au(C≡CR)2}{M(C≡NXyl)}] (M = Ag, Cu; R = tBu, C6H4tBu-4, C6H4OMe-4; Xyl = 3,5-Me2C6H3). The X-ray structures reveal a broad range of dispositions determined by the different coordination modes of Ag(I) or Cu(I). The complexes are bright photoemitters in the solid state and in poly(methyl methacrylate) (PMMA) films. The photoluminescence is dominated by 3IL(C∧C) transitions, with indirect effects from the rest of the molecules, as supported by theoretical calculations. This work opens up the possibility of accessing Au(III) carbon-rich anions to construct photoluminescent aggregates.

An expedient copper-catalysed asymmetric synthesis of γ-lactones and γ-lactams. Application to the synthesis of lucidulactone A.

The parent Josiphos ligand gave excellent ee values (95-99%) and good yields (60-97%) in the copper-catalysed asymmetric conjugate reduction of ß-aryl α,ß-unsaturated lactones and lactams with PMHS. The substrates were obtained from stereospecific copper-catalysed addition of arylboronic acids to alkynoates followed by deprotection and cyclisation. The acyclic lactam precursors also underwent reduction with good ee values (83-85%) and yields (79-95%). Application of this asymmetric reduction methodology included the synthesis of natural product lucidulactone A.

Synthesis, Mechanism Elucidation and Biological Insights of Tellurium(IV)-Containing Heterocycles.

Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te-O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te-O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center-containing compounds. Antileishmanial assays against Leishmania amazonensis promastigotes disclosed 1,2λ4 -oxatellurane LQ50 (IC50 =4.1±1.0; SI=12), 1,2λ4 -oxatellurolane LQ04 (IC50 =7.0±1.3; SI=7) and 1,2λ4 -benzoxatellurole LQ56 (IC50 =5.7±0.3; SI=6) as more powerful and more selective compounds than the reference, being up to four times more active. A stability study supported by 125 Te NMR analyses showed that these heterocycles do not suffer structural modifications in aqueous-organic media or at temperatures up to 65 °C.

Seven-Coordinate Tb3+ Complexes with 90% Quantum Yields: High-Performance Examples of Combined Singlet- and Triplet-to-Tb3+ Energy-Transfer Pathways.

Seven-coordinate, pentagonal-bipyramidal (PBP) complexes [Ln(bbpen)Cl] and [Ln(bbppn)Cl], in which Ln = Tb3+ (products I and II), Eu3+ (III and IV), and Gd3+ (V and VI), with bbpen2- = N,N'-bis(2-oxidobenzyl)-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and bbppn2- = N,N'-bis(2-oxidobenzyl)-N,N'-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by single-crystal X-ray diffraction analysis, alternating-current magnetic susceptibility measurements, and photoluminescence (steady-state and time-resolved) spectroscopy. Under a static magnetic field of 0.1 T, the Tb3+ complexes I and II revealed single-ion-magnet behavior. Also, upon excitation at 320 nm at 300 K, I and II presented very high absolute emission quantum yields (0.90 ± 0.09 and 0.92 ± 0.09, respectively), while the corresponding Eu3+ complexes III and IV showed no photoluminescence. Detailed theoretical calculations on the intramolecular energy-transfer rates for the Tb3+ products indicated that both singlet and triplet ligand excited states contribute efficiently to the overall emission performance. The expressive quantum yields, QLnL, measured for I and II in the solid state and a dichloromethane solution depend on the excitation wavelength, being higher at 320 nm. Such a dependence was rationalized by computing the intersystem crossing rates (WISC) and singlet fluorescence lifetimes (τS) related to the population dynamics of the S1 and T1 levels. Thin films of product II showed high air stability and photostability upon continuous UV illumination, which allowed their use as downshifting layers in a green light-emitting device (LED). The prototypes presented a luminous efficacy comparable with those found in commercial LED coatings, without requiring encapsulation or dispersion of II in host matrixes. The results indicate that the PBP environment determined by the ethylenediamine (en)-based ligands investigated in this work favors the outstanding optical properties in Tb3+ complexes. This work presents a comprehensive structural, chemical, and spectroscopic characterization of two Tb3+ complexes of mixed-donor, en-based ligands, focusing on their outstanding optical properties. They constitute good molecular examples in which both triplet and singlet excited states provide energy to the Tb3+ ion and lead to high values of QLnL.

Complementary Syntheses Giving Access to a Full Suite of Differentially Substituted Phthalocyanine-Porphyrin Hybrids.

Phthalocyanines and porphyrins are often the scaffolds of choice for use in widespread applications. Synthetic advances allow bespoke derivatives to be made, tailoring their properties. The selective synthesis of unsymmetrical systems, particularly phthalocyanines, has remained a significant unmet challenge. Porphyrin-phthalocyanine hybrids offer the potential to combine the favorable features of both parent structures, but again synthetic strategies are poorly developed. Here we demonstrate strategies that give straightforward, controlled access to differentially substituted meso-aryl-tetrabenzotriazaporphyrins by reaction between an aryl-aminoisoindolene (A) initiator and a complementary phthalonitrile (B). The choice of precursors and reaction conditions allows selective preparation of 1:3 Ar-ABBB and, uniquely, 2:2 Ar-ABBA functionalized hybrids.

Hydride Transfer to Gold: Yes or No? Exploring the Unexpected Versatility of Au⋠⋠⋠H-M Bonding in Heterobimetallic Dihydrides.

The potential for coordination and H-transfer from Cp2 MH2 (M=Zr, W) to gold(I) and gold(III) complexes was explored in a combined experimental and computational study. [(L)Au]+ cations react with Cp2 WH2 giving [(L)Au(κ2 -H2 WCp2 )]+ (L=IPr (1), cyclic (alkyl)(amino)carbene (2), PPh3 (3) and Dalphos-Me (4) [IPr=1,3-bis(diisopropylphenyl)imidazolylidene; Dalphos-Me=di(1-adamantyl)-2-(dimethylamino)phenyl-phosphine], while [Au(DMAP)2 ]+ (DMAP=p-dimethylaminopyridine) affords the C2 -symmetric [Au(κ-H2 WCp2 )2 ]+ (5). The Dalphos complex 4 can be protonated to give the bicationic adduct 4 H, showing AuI ⋅⋅⋅H+ -N hydrogen bonding. The gold(III) Lewis acid [(C^N-CH)Au(C6 F5 )(OEt2 )]+ binds Cp2 WH2 to give an Au-H-W σ-complex. By contrast, the pincer species [(C^N^C)Au]+ adds Cp2 WH2 by a purely dative W→Au bond, without Au⋅⋅⋅H interaction. The biphenylyl-based chelate [(C^C)Au]+ forms [(C^C)Au(µ-H)2 WCp2 ]+ , with two 2-electron-3-centre W-H⋅⋅⋅Au interactions and practically no Au-W donor acceptor contribution. In all these complexes, strong but polarized W-H bonds are maintained, without H-transfer to gold. On the other hand, the reactions of Cp2 ZrH2 with gold complexes led in all cases to rapid H-transfer and formation of gold hydrides. Relativistic DFT calculations were used to rationalize the striking reactivity and bonding differences in these heterobimetallic hydride complexes along with an analysis of their characteristic NMR parameters and UV/Vis absorption properties.

Straightforward and Controlled Synthesis of Porphyrin-Phthalocyanine-Porphyrin Heteroleptic Triple-Decker Assemblies.

A versatile and straightforward protocol is disclosed for controlled synthesis of complex lanthanide-bridged heteroleptic porphyrin-phthalocyanine triple-decker assemblies. Two porphyrins, linked by a flexible spacer chain of intermediate length, sequentially capture lanthanide ions and a phthalocyanine to efficiently form the triple-decker complex. The bridge directs assembly, but also controls the mobility of the central macrocycle and further imparts a fully eclipsed arrangement of all three rings.

Do Gold(III) Complexes Form Hydrogen Bonds? An Exploration of AuIII Dicarboranyl Chemistry.

The reaction of 1,1'-Li2 [(2,2'-C2 B10 H10 )2 ] with the cyclometallated gold(III) complex (C^N)AuCl2 afforded the first examples of gold(III) dicarboranyl complexes. The reactivity of these complexes is subject to the trans-influence exerted by the dicarboranyl ligand, which is substantially weaker than that of non-carboranyl anionic C-ligands. In line with this, displacement of coordinated pyridine by chloride is only possible under forcing conditions. While treatment of (C^N)Au{(2,2'-C2 B10 H10 )2 } (2) with triflic acid leads to Au-C rather than Au-N bond protonolysis, aqueous HBr cleaves the Au-N bond to give the pyridinium bromo complex 7. The trans-influence of a series of ligands including dicarboranyl and bis(dicarboranyl) was assessed by means of DFT calculations. The analysis demonstrated that it was not sufficient to rely exclusively on geometric descriptors (calculated or experimental) when attempting to rank ligands for their trans influence. Complex (C^N)Au(C2 B10 H11 )2 containing two non-chelating dicarboranyl ligands was prepared similar to 2. Its reaction with trifluoroacetic acid also leads to Au-N cleavage to give trans-(Hpy^C)Au(OAcF )(C2 B10 H11 )2 (8). In crystals of 8 the pyridinium N-H bond points towards the metal centre, while in 7 it is bent away. The possible contribution of gold(III)⋅⋅⋅H-N hydrogen bonding in these complexes was investigated by DFT calculations. The results show that, unlike the situation for platinum(II), there is no evidence for an energetically significant contribution by hydrogen bonding in the case of gold(III).

Stereoselective Synthesis of All Possible Phosferrox Ligand Diastereoisomers Displaying Three Elements of Chirality: Stereochemical Optimization for Asymmetric Catalysis.

All four possible diastereoisomers of phosphinoferrocenyloxazoline (Phosferrox type) ligands containing three elements of chirality were synthesized as single enantiomers. The Sc configured oxazoline moiety (R = Me, i-Pr) was used to control the generation of planar chirality by lithiation, with the alternative diastereoisomer formed by use of a deuterium blocking group. In each case subsequent addition of PhPCl2 followed by o-TolMgBr resulted in a single P-stereogenic diastereoisomer (Sc,Sp,Sphos and Sc,Rp,Rphos, respectively). The alternative diastereoisomers were formed selectively by addition of o-TolPCl2 followed by PhMgBr ((Sc,Sp,Rphos and Sc,Rp,Sphos, respectively). Preliminary application of these four ligand diastereoisomers, together with (Sc,Sp) and (Sc,Rp) Phosferrox (PPh2), to palladium catalyzed allylic alkylation of trans-1,3-diphenylallyl acetate revealed a stepwise increase/decrease in ee, with the configuration of the matched/matched diastereoisomer as Sc,Sp,Sphos (97% ee).

Planar chiral palladacycle precatalysts for asymmetric synthesis.

Chiral non-racemic palladacycles were employed as precatalysts for Pd(0) mediated asymmetric synthesis. Addition of HPAr2/base to a ferrocenyloxazoline planar chiral palladacycle resulted in ligand synthesis and palladium capture to give a bidentate Phosferrox/Pd(0) complex. A series of these complexes were generated in situ and applied successfully as catalysts for asymmetric allylic alkylation.

An Oxalate-Bridged Copper(II) Complex Combining Monodentate Benzoate, 2,2'-bipyridine and Aqua Ligands: Synthesis, Crystal Structure and Investigation of Magnetic Properties.

A dinuclear copper(II) complex of formula [{Cu(bipy)(bzt)(OH2)}2(µ-ox)] (1) (where bipy = 2,2'-bipyridine, bzt = benzoate and ox = oxalate) was synthesised and characterised by diffractometric (powder and single-crystal XRD) and thermogravimetric (TG/DTG) analyses, spectroscopic techniques (IR, Raman, electron paramagnetic resonance spectroscopy (EPR) and electronic spectroscopy), magnetic measurements and density functional theory (DFT) calculations. The analysis of the crystal structure revealed that the oxalate ligand is in bis(bidentate) coordination mode between two copper(II) centres. The other four positions of the coordination environment of the copper(II) ion are occupied by one water molecule, a bidentate bipy and a monodentate bzt ligand. An inversion centre located on the ox ligand generates the other half of the dinuclear complex. Intermolecular hydrogen bonds and π-π interactions are responsible for the organisation of the molecules in the solid state. Molar magnetic susceptibility and field dependence magnetisation studies evidenced a weak intramolecular-ferromagnetic interaction (J = +2.9 cm-1) between the metal ions. The sign and magnitude of the calculated J value by density functional theory (DFT) are in agreement with the experimental data.

Methyl Ester Functionalized Phenalenyl Arene- and Bipyridine-Ruthenium-Based Complexes for Electroactive Langmuir-Blodgett Films.

We report the synthesis of a new phenalenyl ligand, functionalized with a methyl ester electron withdrawing group, named 9-hydroxy-1-oxo-1 H-phenalen-5-methyl carboxylate (L), and the generated complexes [Ru(bpy)2L]PF6 and [(η6-C6H6)Ru(L)Cl]. Compounds were characterized by spectroscopic and X-ray diffraction methods, and their electrochemical behavior was investigated via cyclic voltammetry and UV-vis spectroelectrochemistry. The one-electron oxidized compounds have an unpaired electron located in the phenalenyl ring, as supported by theoretical calculations (DFT) and EPR results. Langmuir-Blodgett (LB) films deposited by [Ru(bpy)2L]2+/3+ species mixed with stearic acid are electroactive, showing a quasi-reversible wave with E1/2Film1 = 0.74 V and E1/2Film2 = 0.81, which are promising systems that allow access to immobilized open-shell species in the film.

Promoting a Significant Increase in the Photoluminescence Quantum Yield of Terbium(III) Complexes by Ligand Modification.

Two discrete mononuclear complexes, [Tb(bbpen)(NO3)] (I) and [Tb(bbppn)(NO3)] (II), for which H2bbpen = N,N'-bis(2-hydroxybenzyl)-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and H2bbppn = N,N'-bis(2-hydroxylbenzyl)-N,N'-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates II from I and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of H2bbppn is described here for the first time, while that of complex II has been redetermined in the monoclinic C2 space group in light of new diffraction data. In II, selective crystallization leads to spontaneous resolution of enantiomeric molecules in different crystals. Absolute emission quantum yields (ϕ) and luminescence excited-state lifetimes (at room temperature and 11 K) were measured for both complexes. Despite their similar molecular structures, I and II exhibit remarkably different ϕ values of 21 ± 2% and 67 ± 7%, respectively, under UV excitation at room temperature. Results of quantum-mechanical (DFT and TD-DFT) calculations and experimental PL measurements also performed for H2bbpen and H2bbppn confirmed that both ligands are suitable to work as "antennas" for TbIII. Considering the 5D4 lifetime profiles and the significantly higher absolute quantum yield of II, it appears that thermally active nonradiative pathways present in I are minimized in II due to differences in the conformation of the ethylenediamine bridge.

Thermally Stable Gold(III) Alkene and Alkyne Complexes: Synthesis, Structures, and Assessment of the trans-Influence on Gold-Ligand Bond Enthalpies.

The reaction of [C^C)Au(OEt2 )2 ]+ with 1,5-cyclooctadiene or norbornadiene affords the corresponding olefin complexes [(C^C)Au(COD)]SbF6 and [(C^C)Au(NBD)]SbF6 , which are thermally stable in solution and the solid state (C^C=4,4'-di-tert-butylbiphenyl-2,2'-diyl). The crystal structures of these complexes have been determined. By contrast, dienones such as dibenzylideneacetone are O- rather than C=C-bonded. The reactions of (C^C)Au(OAcF )(L) (L=PMe3 or CNxyl) with B(C6 F5 )3 in the presence of bis(1-adamantyl)acetylene give the mixed-ligand alkyne complexes [(C^C)Au(AdC≡CAd)(L)]+ , the first complexes of their type in gold chemistry. In the presence of an excess of acetylene these compounds are thermally stable in solution and as solids. The bonding of n- and π-donor ligands to AuIII fragments and the effect of the trans influence exerted by N- and C-donors was explored with the aid of DFT calculations. Results show that the Au-L bond enthalpies trans to anionic C are 35-60 % of the enthalpies trans to N, with strong π-acceptors being particularly affected. In comparison with [Me2 Au]+ , the [(C^C)Au]+ fragment is more polar and in bond enthalpy terms resembles Me2 Pt.

Fixing the Conformation of Calix[4]arenes: When Are Three Carbons Not Enough?

Calix[4]arenes are unique macrocycles that through judicious functionalisation at the lower rim can be either fixed in one of four conformations or remain conformationally flexible. Introduction of propynyl or propenyl groups unexpectedly provides a new possibility; a unidirectional conformational switch, with the 1,3-alternate and 1,2-alternate conformers switching to the partial cone conformation, whilst the cone conformation is unchanged, under standard experimental conditions. Using 1 H NMR kinetic studies, rates of switching have been shown to be dependent on the starting conformation, upper-rim substituent, where reduction in bulk enables faster switching, solvent and temperature with 1,2-alternate conformations switching fastest. Ab initio calculations (DFT) confirmed the relative stabilities of the conformations and point towards the partial cone conformer being the most stable of the four. The potential impact on synthesis through the "click" reaction has been investigated and found not to be significant.

Effects of Decavanadate Salts with Organic and Inorganic Cations on Escherichia coli, Giardia intestinalis, and Vero Cells.

Decavanadate salts with nicotinamide (3-pyridinecarboxamide, 3-pca) and isonicotinamide (4-pyridinecarboxamide, 4-pca) in both neutral and protonated forms, (3-Hpca)4[H2V10O28]·2H2O·2(3-pca) (complex I) and (4-Hpca)4[H2V10O28]·2(4-pca) (complex II), have been synthesized and characterized by vibrational spectroscopy (infrared and Raman), thermogravimetric analysis (TGA), 51V NMR, and single-crystal X-ray diffraction analysis. The effects of sodium decavanadate (henceforth called NaV10) and compounds I and II on Escherichia coli, Giardia intestinalis, and Vero (African green monkey epithelial kidney) cells were evaluated. Enhanced growth inhibitory activity against E. coli cultures was observed upon treatment with products I and II when compared to that with NaV10 (GI50 values of 2.8, 4.0, and 11 mmol L-1, respectively), as well as lower cell viability as measured by the intake of propidium iodide (PI). Exposure of Giardia trophozoites to NaV10 and II revealed reduction in trophozoite viability (GI50 values of ca. 10 µmol L-1) and affected the parasite adherence to both polystyrene culture tubes and a monolayer of Vero cells, even at low concentrations. A lesser effect on Giardia was shown for I. Furthermore, all three compounds were significantly less toxic to Vero cells than the reference drug, albendazole, employed in the treatment of giardiasis. Toxicity reports of oxidovanadium compounds toward Giardia are unprecedented and open a path to the development of new therapeutic agents.

A Rare Example of Four-Coordinate Nonoxido Vanadium(IV) Alkoxide in the Solid State: Structure, Spectroscopy, and Magnetization Dynamics.

The distorted tetrahedral [V(OAd)4] alkoxide (OAd = 1-adamantoxide, complex 1) is the first homoleptic, mononuclear vanadium(IV) alkoxide to be characterized in the solid state by X-ray diffraction analysis. The compound crystallizes in the cubic P4̅3 n space group with two highly disordered, crystallographically independent molecules in the asymmetric unit. Spin Hamiltonian parameters extracted from low temperature X- and Q-band electron paramagnetic resonance (EPR) experiments performed for polycrystalline samples of 1, both in the concentrated (bulk) form and diluted in the diamagnetic [Ti(OAd)4] analogue, reveal a fully axial system with g z < g x, g y and A z ≫ A x, A y. Complex 1 has also been characterized by alternate current susceptometry with varying temperature (3-30 K) and static magnetic field (up to 8.5 T), showing field-induced slow relaxation of the magnetization with relaxation times ranging from ca. 3 ms at 3 K to 0.02-0.03 ms at 30 K, in line with relevant results described recently for other potential molecular quantum bits. Pulsed EPR measurements, in turn, disclosed long coherence times of ca. 4 µs at temperatures lower than 40 K, despite the presence of the H-rich ligands. The slow spin relaxation in 1 is the first observed for a tetracoordinate nonoxido vanadium(IV) complex, and results are compared here to those generated by square-pyramidal VIV(O)2+ and trigonal prismatic V4+ with oxygen donor atom sets. Considering that the number of promising d1 complexes investigated in detail for slow magnetization dynamics is still small, the present work contributes to the establishment of possible structural/electronic correlations of interest to the field of quantum information processing.

Luminescent Gold(III) Thiolates: Supramolecular Interactions Trigger and Control Switchable Photoemissions from Bimolecular Excited States.

A new family of cyclometallated gold(III) thiolato complexes based on pyrazine-centred pincer ligands has been prepared, (C^Npz ^C)AuSR, where C^Npz ^C=2,6-bis(4-But C6 H4 )pyrazine dianion and R=Ph (1), C6 H4 tBu-4 (2), 2-pyridyl (3), 1-naphthyl (1-Np, 4), 2-Np (5), quinolinyl (Quin, 6), 4-methylcoumarinyl (Coum, 7) and 1-adamantyl (8). The complexes were isolated as yellow to red solids in high yields using mild synthetic conditions. The single-crystal X-ray structures revealed that the colour of the deep-red solids is associated with the formation of a particular type of short (3.2-3.3 Å) intermolecular pyrazine⋅⋅⋅pyrazine π-interactions. In some cases, yellow and red crystal polymorphs were formed; only the latter were emissive at room temperature. Combined NMR and UV/Vis techniques showed that the supramolecular π-stacking interactions persist in solution and give rise to intense deep-red photoluminescence. Monomeric molecules show vibronically structured green emissions at low temperature, assigned to ligand-based 3 IL(C^N^C) triplet emissions. By contrast, the unstructured red emissions correlate mainly with a 3 LLCT(SR→{(C^Npz ^C)2 }) charge transfer transition from the thiolate ligand to the π⋅⋅⋅π dimerized pyrazine. Unusually, the π-interactions can be influenced by sample treatment in solution, such that the emissions can switch reversibly from red to green. To our knowledge this is the first report of aggregation-enhanced emission in gold(III) chemistry.

Naphthoquinones of Sinningia reitzii and Anti-inflammatory/Antinociceptive Activities of 8-Hydroxydehydrodunnione.

Chemical investigation of the tubers of Sinningia reitzii led to the isolation of five new naphthoquinones, 8-hydroxydehydrodunnione (1), 7-hydroxydehydrodunnione (2), 5-hydroxy-6,7-dimethoxy-α-dunnione (3), 5-hydroxy-6,7-dimethoxydunniol (4), and 8-hydroxy-7-methoxy-2-O-methylstreptocarpone (5). Three known naphthoquinones, 7-hydroxy-α-dunnione, 8-hydroxydunnione, and 6,8-dihydroxy-7-methoxy-2-O-methyldunniol, were also identified. When tested for anti-inflammatory activity in a mouse model, compound 1 (50-500 pg/paw) reduced the edema induced by carrageenan in a dose-dependent fashion. The highest dose showed a similar inhibition to that observed for the positive control dexamethasone. At lower doses (5-10 pg/paw), 1 also dose dependently reduced the mechanical hyperalgesia induced by carrageenan. Compound 1 (15 pg/paw) abolished the mechanical hyperalgesia induced by prostaglandin E2 and dopamine, but not that induced by dibutyryl cyclic AMP. Dipyrone (320 µg/paw) completely abolished the hyperalgesia induced by these algogens. Additionally, compound 1 did not alter heat-induced nociception. These results suggest that this new naphthoquinone exhibits important anti-inflammatory and antinociceptive activities, which is dissimilar to that of most known analgesics.