Complexes of heterocyclic thionates Part 2: complexes of bridging ligands

Selective Reduction of Nitroarenes to Arylamines by the Cooperative Action of Methylhydrazine and a Tris(N-heterocyclic thioamidate) Cobalt(III) Complex

We report an efficient catalytic protocol that chemoselectively reduces nitroarenes to arylamines, by using methylhydrazine as a reducing agent in combination with the easily synthesized and robust catalyst tris(N-heterocyclic thioamidate) Co(III) complex [Co(κS,N-tfmp2S)₃], tfmp2S = 4-(trifluoromethyl)-pyrimidine-2-thiolate. A series of arylamines and heterocyclic amines were formed in excellent yields and chemoselectivity. High conversion yields of nitroarenes into the corresponding amines were observed by using polar protic solvents, such as MeOH and ⁱPrOH. Among several hydrogen donors that were examined, methylhydrazine demonstrated the best performance. Preliminary mechanistic investigations, supported by UV-vis and NMR spectroscopy, cyclic voltammetry, and high-resolution mass spectrometry, suggest a cooperative action of methylhydrazine and [Co(κS,N-tfmp2S)₃] via a coordination activation pathway that leads to the formation of a reduced cobalt species, responsible for the catalytic transformation. In general, the corresponding N-arylhydroxylamines were identified as the sole intermediates. Nevertheless, the corresponding nitrosoarenes can also be formed as intermediates, which, however, are rapidly transformed into the desired arylamines in the presence of methylhydrazine through a noncatalytic path. On the basis of the observed high chemoselectivity and yields, and the fast and clean reaction processes, the present catalytic system [Co(κS,N-tfmp2S)₃]/MeNHNH₂ shows promise for the efficient synthesis of aromatic amines that could find various industrial applications.

Dehydration of UO2Cl2·3H2O and Nd(NO3)3·6H2O with a Soft Donor Ligand and Comparison of Their Interactions through X-ray Diffraction and Theoretical Investigation

We investigated whether the relatively Lewis basic imidazole-2-thiones could be used to substitute water ligands bound to f-element cations and generate f-element soft donor complexes. Reactions of 1,3-diethylimidazole-2-thione (C₂C₂ImT) with Nd(NO₃)₃·6H₂O and UO₂Cl₂·3H₂O led to the isolation of the anhydrous thione complexes Nd(NO₃)₃(C₂C₂ImT)₃ and UO₂Cl₂(C₂C₂ImT)₂, characterized by single crystal X-ray diffraction. Differences in the strength of metal-thione interactions have been examined by means of the crystal structure analysis and density functional theory (DFT) calculations. The C₂C₂ImT ligands were found to be affected by both coordination and noncovalent interactions, making it impossible to deconvolute the effects of one from the other. Calculated partial atomic charges indicated greater ligand-to-metal charge transfer in the [UO₂]²⁺ complex, indicative of a stronger interaction. The reactivity of C₂C₂ImT demonstrates its usefulness in the preparation of f-element soft donor complexes from readily available hydrates that could be useful intermediates for promoting the coordination and studying the effects of soft donor anions.

UV and Resonance Raman Spectroscopic and Theoretical Studies on the Solvent-Dependent Ground and Excited-State Thione → Thiol Tautomerization of 4,6-Dimethyl-2-mercaptopyrimidine (DMMP)

The vibrational spectra of 4,6-dimethyl-2-mercaptopyrimidine (DMMP) in acetonitrile, methanol, and water were assigned by resonance Raman spectroscopy through a combination of Fourier-transform infrared spectroscopy (FT-IR), FT-Raman UV-vis spectroscopy, and density functional theoretical (DFT) calculations. The FT-Raman spectra show that the neat solid DMMP is formed as a dimer due to intermolecular hydrogen bonding. In methanol and water, however, the majority of the Raman spectra were assigned to the vibrational modes of DMMP(solvent) _n ( n = 1-4) clusters containing NH···O hydrogen bonds. The intermolecular NH···O hydrogen bond interactions, which are key constituents of the stable DMMP thione structure, revealed significant structural differences in acetonitrile, methanol, and water. In addition, UV-induced hydrogen transfer isomeric reactions between the thione and thiol forms of DMMP were detected in water and acetonitrile. DFT calculations indicate that the observed thione → thiol tautomerization should occur easily in lower excited states in acetonitrile and water.

Ring-to-Cage Structural Conversion via Template Effect in a Gold(I) Metallosupramolecular System

A unique example of a ring-to-cage structural conversion in a multinuclear gold(I) coordination system with d-penicillamine (d-H2 pen) is reported. The reaction of [Au2 Cl2 (dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) with d-H2 pen in a 1:1 ratio gave [Au4 (dppe)2 (d-pen)2 ] ([1]), in which two [Au2 (dppe)]2+ units are linked by two d-pen S atoms in a cyclic form so as to have two bidentate-N,O coordination arms. The subsequent reaction of [1] with Cu(OTf)2 afforded [Au4 Cu(dppe)2 (d-pen)2 ]2+ ([2]2+ ), in which a CuII ion is chelated by the two coordination arms in [1] to form an AuI4 CuII bicyclic metallocage. A similar reaction using Cu(NO3 )2 was accompanied by the ring expansion of [1] to [Au8 (dppe)4 (d-pen)4 ], leading to the production of [Au8 Cu2 (dppe)4 (d-pen)4 ]4+ ([3]4+ ). In [3]4+ , two CuII ions are each chelated by the two coordination arms to form an AuI8 CuII2 tricyclic metallocage, accommodating a nitrate ion. The use of Ni(NO3 )2 or Ni(OAc)2 instead of Cu(NO3 )2 commonly gave a tricyclic metallocage of [Au8 Ni2 (dppe)4 (d-pen)4 ]4+ ([4]4+ ), but a water molecule was accommodated inside the AuI8 NiII2 metallocage.

The influence of thiolate ligands on the luminescence properties of cycloplatinated(ii) complexes

Complexes [Pt(C^{^}N)(PPh₃)Cl] (C^{^}N = bzq (7,8-benzoquinolinyl, A) and ppy (2-phenylpyridinyl, B)) were reacted with various thiolate ligands to afford complexes [Pt(C^{^}N)(PPh₃)(κ¹-S-SR)], C^{^}N = bzq, R = SPh (thiophenolate, 1a); C^{^}N = ppy, R = SPh (1b); C^{^}N = bzq, R = Spy (pyridine-2-thiolate, 2a); C^{^}N = ppy, R = Spy (2b); C^{^}N = bzq, R = SpyN (pyrimidine-2-thiolate, 3a); C^{^}N = ppy, R = SpyN (3b). Complexes 1-3 were characterized by NMR spectroscopy, and the solid-state structures of 1a and 2a were determined by X-ray diffraction methods. Replacing a chloride ligand with electron-rich thiolates changes the lowest energy singlet and triplet excited states to the ones that feature charge transfer from the thiolate (mixed with some metal character) to the C^{^}N ligand, which was supported by TD-DFT calculations. All complexes are emissive at 298 K in the solid state except 2b and 3b, which are emissive only at 77 K having a less rigid structure compared to others. The emission of 1a and 1b originates from a low-energy excited state of d_Pt/π_SR → π*_C^N while 3a exhibits a ³LC/³MLCT transition. For 1a and 1b, the radiative rate and the quantum efficiency are higher in a rigid environment such as a solid compared to a polymer and solution. Decreasing the rigidity of the environment leads to a flexibility of rotation of the -SR around the axis of the Pt-S bond. So the geometry can be easily changed after radiation and the lowest lying triplet excited state would have the effective contribution of the dd* transition, which opens a nonradiative pathway at room temperature.

Crystal structure of 1-(4-fluorophenyl)-N-(5-((triphenylstannyl)thio)thiophen-2-yl)methanimine, C27H20FN3S2Sn

C27H20FN3S2Sn, monoclinic, P21/n (no. 14), a = 15.631(4) Å, b = 9.865(3) Å, c = 17.256(3) Å β = 108.335(11)°, V = 2525.8(10) Å3, Z = 4, R gt(F) = 0.0398, wR ref(F 2) = 0.0917, T = 298 K.

A uniquely fabricated Cu(ii)-metallacycle as a reusable highly sensitive dual-channel and practically functional metalloreceptor for Fe3+ and Ca2+ ions: an inorganic site of cation detection

Dimeric Cu(ii)-complex developed from disulfane ligand, serves as dual-channel metalloreceptor for Fe³⁺/Ca²⁺ and detection of Fe³⁺ in real water samples.

Synthesis, structures and antimicrobial activity of copper derivatives of N-substituted imidazolidine-2-thiones: unusual bio-activity against Staphylococcus epidermidis and Enterococcus faecalis

Synthesis and antimicrobial activity of copper(i) complexes with N-substituted imidazolidine-2-thiones is investigated.

Synthesis, structures, and ESI-mass studies of silver(I) derivatives of imidazolidine-2-thiones: Antimicrobial potential and biosafety evaluation

The basic objective of this investigation is to explore potential metallo-organic antimicrobial agents based on silver-heterocyclic-2-thiones. In this respect, a series of silver(I) halide complexes with imidazolidine-2-thiones (L-NR, R=H, Me, Et, Prⁿ, Buⁿ, Ph), namely, mononuclear [AgX(L-NR)(PPh₃)₂] (X, R: Cl, Bu, 1; Br, Ph, 7); [AgX(L-NR)₃] (Br, Bu, 5; Br, Prⁿ, 8) and halogen bridged dinuclear [Ag₂(μ-X)₂(L-NR)₂(PPh₃)₂] (Cl, Buⁿ, 2; Cl, Ph, 3; Cl, Prⁿ, 4; Br, Ph, 6) have been synthesized and characterized using modern techniques. The thio-ligands are terminally S-bonded in all the complexes. The in vitro antimicrobial potential and biosafety evaluation of the above complexes as well as that of previously reported analogous silver complexes has been studied against Gram positive bacteria, namely, Staphylococcus aureus (MTCC 740) and Methicillin resistant Staphylococcus aureus (MRSA), Gram negative bacteria Klebsiella pneumoniae (MTCC 109), Salmonella typhimurium (MTCC 98) and a yeast Candida albicans (MTCC 227). Most of the complexes tested have shown significant antimicrobial activity with low values of minimum inhibitory concentration (MIC). Significantly, the activity against MRSA is an important outcome of this investigation. Among complexes tested for their cytotoxicity using MTT [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide] assay, some complexes showed low cellular toxicity with high percent cell viability. A dinuclear complex [Ag₂(μ-Cl)₂(L-NPh)₂(PPh₃)₂] 3 with 93.3% cell viability emerges the most important candidate for further investigations.

Tris(2-mercaptoimidazolyl)hydroborato Cadmium Thiolate Complexes, [TmBut]CdSAr: Thiolate Exchange at Cadmium in a Sulfur-Rich Coordination Environment

A series of cadmium thiolate compounds that feature a sulfur-rich coordination environment, namely [TmBut]CdSAr, have been synthesized by the reactions of [TmBut]CdMe with ArSH (Ar = C6H4-4-F, C6H4-4-But, C6H4-4-OMe, and C6H4-3-OMe). In addition, the pyridine-2-thiolate and pyridine-2-selenolate derivatives, [TmBut]CdSPy and [TmBut]CdSePy have been obtained via the respective reactions of [TmBut]CdMe with pyridine-2-thione and pyridine-2-selone. The molecular structures of [TmBut]CdSAr and [TmBut]CdEPy (E = S or Se) have been determined by X-ray diffraction and demonstrate that, in each case, the [CdS4] motif is distorted tetrahedral and approaches a trigonal monopyramidal geometry in which the thiolate ligand adopts an equatorial position; [TmBut]CdSPy and [TmBut]CdSePy, however, exhibit an additional long-range interaction with the pyridyl nitrogen atoms. The ability of the thiolate ligands to participate in exchange was probed by 1H and 19F nuclear magnetic resonance (NMR) spectroscopic studies of the reactions of [TmBut]CdSC6H4-4-F with ArSH (Ar = C6H4-4-But or C6H4-4-OMe), which demonstrate that (i) exchange is facile and (ii) coordination of thiolate to cadmium is most favored for the p-fluorophenyl derivative. Furthermore, a two-dimensional EXSY experiment involving [TmBut]CdSC6H4-4-F and 4-fluorothiophenol demonstrates that degenerate thiolate ligand exchange is also facile on the NMR time scale.

Variable coordination and C–S bond cleavage activity of N-substituted imidazolidine-2-thiones towards copper: synthesis, spectroscopy, structures, ESI-mass and antimicrobial studies

N-substituted imidazoldine-2-thiones with copper(i) halides have shown variable nuclearity, C–S bond cleavage, antimicrobial activity and non-toxicity in some cases to living cells.

Reactivity of a half-lantern Pt2(ii,ii) complex with triphenylphosphine: selectivity in a protonation reaction

Reaction of PPh₃ with half-lantern complex [{Pt(ppy)(μ₂-Spy)}₂], 1, gave complex [Pt(ppy)(η¹-S-Spy)(PPh₃)], 2, as a result of platinum–nitrogen bonds dissociation. Complex 2 revealed anionic selectivity upon protonation reaction with acidic species.

Bismuth(iii)dichalcogenones as highly active catalysts in multiple C–C bond formation reactions

Thirteen new bismuth(iii) dichalcogenone derivatives with diversified structural motifs were successfully isolated and used as potential catalysts for the synthesis of triaryl- or triheteroarylmethanes.

Synthesis and structural characterization of monomeric mercury(ii) selenolate complexes derived from 2-phenylbenzamide ligands

The present work describes the synthesis and structural characterization of mercury selenolate complexes derived from 2-phenylbenzamide ligands and their isolation in monomeric form for the first time.

Facile access to zinc and cadmium selones: highly active catalysts for Barbier reactions in aqueous media

Zinc and cadmium imidazoline selone complexes were synthesized and demonstrated to be potential catalysts for Barbier coupling in aqueous alcohol media.

Zinc(II)-methimazole complexes: synthesis and reactivity

The tetrahedral S-coordinated complex [Zn(MeImHS)4](ClO4)2, synthesised from the reaction of [Zn(ClO4)2] with methimazole (1-methyl-3H-imidazole-2-thione, MeImHS), reacts with triethylamine to yield the homoleptic complex [Zn(MeImS)2] (MeImS = anion methimazole). ESI-MS and MAS (13)C-NMR experiments supported MeImS acting as a (N,S)-chelating ligand. The DFT-optimised structure of [Zn(MeImS)2] is also reported and the main bond lengths compared to those of related Zn-methimazole complexes. The complex [Zn(MeImS)2] reacts under mild conditions with methyl iodide and separates the novel complex [Zn(MeImSMe)2I2] (MeImSMe = S-methylmethimazole). X-ray diffraction analysis of the complex shows a ZnI2N2 core, with the methyl thioethers uncoordinated to zinc. Conversely, the reaction of [Zn(MeImS)2] with hydroiodic acid led to the formation of the complex [Zn(MeImHS)2I2] having a ZnI2S2 core with the neutral methimazole units S-coordinating the metal centre. The Zn-coordinated methimazole can markedly modify the coordination environment when changing from its thione to thionate form and vice versa. The study of the interaction of the drug methimazole with the complex [Zn(MeIm)4](2+) (MeIm = 1-methylimidazole) - as a model for Zn-enzymes containing a N4 donor set from histidine residues - shows that methimazole displaces only one of the coordinated MeIm molecules; the formation constant of the mixed complex [Zn(MeIm)3(MeImHS)](2+) was determined.

Hemilabile silver(i) complexes containing pyridyl chalcogenolate (S, Se) ligands and their utility as molecular precursors for silver chalcogenides

A series of silver triphenylphosphine complexes containing pyridyl chacogenolate (S, Se) ligands has been synthesized by employing [AgCl(PPh₃)₃] and [Ag₂(μ-Cl)₂(PPh₃)₄].

Chemistry of heterocyclic-2-thiones: in situ generated 1-(4,5-dihydro-3-alkyl-imidazolidin-2-yl)-3-alkyl-imidazolidine-2-thione and triiodide form novel mixed valent CuI–II/CuII complexes

Copper(i) iodide transforms N-n-butyl-imidazolidine-2-thione in air into 1-(4,5-dihydro-3-butyl-imidazolidin-2-yl)-3-butyl-imidazolidine-2-thione (L-NBuⁿ) which formed novel complex, [Cu(κ²-N,S-L-NBuⁿ)₂](I₃)₂.

C–H reductive elimination during the reaction of cycloplatinated(ii) complexes with pyridine-2-thione: kinetic follow up

Reactions of the cycloplatinated(ii) complexes [PtR(ppy)(SMe₂)], 1, where ppy = deprotonated 2-phenylpyridine and R = Me or p-MeC₆H₄, with pyridine-2-thione, C₅H₅SN, were studied by UV-vis and ¹H NMR spectroscopies and on the basis of the data a mechanism is proposed.

Heavier chalcogenone complexes of bismuth(iii)trihalides: potential catalysts for acylative cleavage of cyclic ethers

Heavier chalcogenone complexes of discrete mononuclear and dinuclear bismuth(iii)trihalides have been synthesized and used as potential catalyst in acylative cleavage of cyclic ethers.

DNA interaction and cytotoxic activities of square planar platinum(II) complexes with N, S-donor ligands

The platinum(II) complexes with N, S-donor ligands have been synthesized and characterized by physicochemical methods viz. elemental, electronic, FT-IR, (1)H NMR and LC-MS spectra. The binding mode and potency of the complexes with HS DNA (Herring Sperm) have been examined by absorption titration and viscosity measurement studies. The results revealed that complexes bind to HS DNA via covalent mode with the intrinsic binding constant (Kb) in the range 1.37-7.76×10(5)M(-1). Decrease in the relative viscosity of HS DNA also supports the covalent mode of binding. The DNA cleavage activity of synthesized complexes has been carried out by gel electrophoresis experiment using supercoiled form of pUC19 DNA; showing the unwinding of the negatively charged supercoiled DNA. Brine shrimp (Artemia Cysts) lethality bioassay technique has been applied for the determination of toxic property of synthesized complexes in terms of μM.

Reversible recrystallization process of copper and silver thioacetamide–halide coordination polymers and their basic building blocks

Three-dimensional [CuX(TAA)]_n (X = Br (1), I (2)) and bi-dimensional [AgX(TAA)]_n (X = Cl (3), Br (4)) coordination polymers have been isolated by the direct synthesis from copper(i) and silver(i) halides and thioacetamide (TAA).