Co(III) N,N′-diarylformamidine dithiocarbamate complexes: Synthesis,characterization, crystal structures and biological studies

Three symmetric N,N-diarylformamidine dithiocarbamates, N,N′-bis(2,6-dimethylphenyl)formamidine dithiocarbamate (DTL1), N,N′-bis(2,6-disopropylphenyl)formamidine dithiocarbamate (DTL2) and N,N′-dimesitylformamidine dithiocarbamate (DTL3), and three unsymmetric ones, N′-(2,6-dichlorophenyl-N-(2,6-dimethylphenyl)formamidine dithiocarbamate (DTL4), N′-(2,6-dichlorophenyl)-N-(2,6-diisopropylphenyl)formamidine dithiocarbamate (DTL5) and N′-(2,6-dichlorophenyl)-N-mesitylformamidine dithiocarbamate (DLT6), were reacted with chloridocobalt(III) in water to give Co-(DTL1)₃ ( 1 ), Co-(DTL2)₃ ( 2 ), Co-(DTL3)₃ ( 3 ), Co-(DTL4)₃ ( 4 ), Co-(DTL5)₃ ( 5 ) and Co-(DTL6)₃ ( 6 ). All the dithiocarbamates and complexes were characterized using ¹H NMR, ¹³C NMR, Fourier transform infrared, UV–visible and mass spectra and the purity confirmed by elemental analysis. In addition, crystal structures of complexes 1 , 2 , 4 and 5 were determined, confirming the formation of mononuclear species in which the Co(III) centers coordinated to six sulfur atoms from three dithiocarbamate ligands resulting in distorted octahedral geometries. All complexes showed moderate to good antibacterial activities against Gram-negative bacteria Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae and Pseudomonas aeruginosa even at low concentrations. None of the six were active against Gram-positive bacterium methicillin-resistant Staphylococcus aureus and only active against S. aureus at high concentrations. Complexes 5 and 6 were found to be more active than ciprofloxacin against S. typhimurium, E. coli, P. aeruginosa and K. pneumoniae and complexes with chloro-substituted ligands generally had enhanced activities. Antioxidant activities of the dithiocarbamate salts and their Co(III) complexes were also investigated using DPPH assay and the complexes were found to be more efficient. Complex 2 with an IC₅₀ value of 2.84 × 10⁻⁴ mM displayed the highest activity of all compounds tested, even outdoing ascorbic acid. The radical scavenging ability of the complexes followed the order 2 > 1 > ascorbic acid > 3 > 4 > 6 > 5 .     

Syntheses,Cytotoxicity and Properties of CO Releasing Molecules Containing Acetyl Salicylamide‐3‐pyridine

A series of CO‐releasing molecules [M(CO)₅L] (M=Cr, W, Mo, L=acetyl salicylamide 3‐pyridine, 1 – 3 ; L=N,N‐dimethyl‐4‐pyridine, 4 – 6 ; L=nicotinamide, 7 – 9 ; L=4‐CHO‐pyridine, 10 – 12 ) were synthesized. And in this paper, we have investigated mainly cytotoxicity and properties of the CO‐releasing molecules containing acetyl salicyamide‐3‐pyridine, namely complexes 1 – 3 . The stability of complexes 1 and 2 was evaluated by means of UV‐Vis spectroscopy and ¹H NMR spectra. The results indicate complexes 1 and 2 were stable in methanol and acidic aqueous solution, but unstable and decayed in basic media (pH 10.0). Among all the complexes, complex 2 was the slowest CO‐releaser, and its half‐life was 73.8 min. Complex 9 containing nicotinamide was the fastest CO‐releaser with half‐life only 6.5 min. In addition, cytotoxic effects of all the complexes on the proliferation of fibroblast line were assayed by MTT. Among all the complexes, the IC₅₀ of complex 1 was 6 µmol/L, revealing complex 1 possessed stronger antiproliferative activity than the control. Analysis by Flow cytometry revealed that complex 1 arrested Hela cells in S phase while complexes 2 and 8 arrested in G2/M phase. Cell apoptosis caused by the complexes mainly occurred in "Late apoptosis".     

Structurally Modelling the 2-His-1-Carboxylate Facial Triad with a Bulky N,N,O Phenolate Ligand

We present the synthesis and coordination chemistry of a bulky, tripodal N,N,O ligand, Im^Ph2NNO ^{t Bu} ( L ), designed to model the 2-His-1-carboxylate facial triad (2H1C) by means of two imidazole groups and an anionic 2,4-di-tert-butyl-subtituted phenolate. Reacting K-L with MCl₂ (M = Fe, Zn) affords the isostructural, tetrahedral non-heme complexes [Fe(L)(Cl)] ( 1 ) and [Zn(L)(Cl)] ( 2 ) in high yield. The tridentate N,N,O ligand coordination observed in their X-ray crystal structures remains intact and well-defined in MeCN and CH₂Cl₂ solution. Reacting 2 with NaSPh affords a tetrahedral zinc thiolate complex, [Zn(L)(SPh)] ( 4 ), that is relevant to isopenicillin N synthase (IPNS) biomimicry. Cyclic voltammetry studies demonstrate the ligand's redox non-innocence, where phenolate oxidation is the first electrochemical response observed in K-L , 2 and 4 . However, the first electrochemical oxidation in 1 is iron-centred, the assignment of which is supported by DFT calculations. Overall, Im^Ph2NNO ^{t Bu} provides access to well-defined mononuclear, monoligated, N,N,O-bound metal complexes, enabling more accurate structural modelling of the 2H1C to be achieved.     

Copper(I) halide complexes with a sterically hindered thiourea: synthesis and crystal structures of [Cu(dchtu)2Cl] and [Cu(dchtu)2Br] (dchtu = N,N ′-dicyclohexylthiourea)

Copper(I) complexes with a sterically hindered thiourea, [Cu(dchtu)₂X] (dchtu = N,N′-dicyclohexylthiourea; X=Cl 1, Br 2), were synthesized and their crystal structures were determined. Compounds 1 and 2 are isostructural orthorhombic, space group P2₁2₁2₁. Crystallographic data for 1 : a = 13.1711(13), b = 14.2610(19), c = 15.793(2) Å, V = 2966.4(6) ų, Z = 4. For 2 : a = 13.2628(13), b = 14.3410(19), c = 15.860(2) Å, V = 3016.5(6) ų, Z = 4. The stoichiometry of CuX complexes with thiourea is influenced by substituents on the nitrogens. Copper(I) halides only form bis-adducts with the sterically hindered dchtu ligand even with molar excesses of dchtu due to steric hinderance of the cyclohexyl substituents. In 1 and 2, the Cu(I) is trigonally coordinated by the sulfur atoms of two monodentate N,N′-dicyclohexylthiourea ligands and one halide. The structures of the complexes are stabilized by a system of intermolecular H-bonding.     

Three New Alkaloids from the Leaves of Uncaria rhynchophylla

Three new alkaloids, 2′‐O‐β‐D ‐glucopyranosyl‐11‐hydroxyvincoside lactam ( 1 ), 22‐O‐demethyl‐22‐O‐β‐D ‐glucopyranosylisocorynoxeine ( 2 ), and (4S)‐corynoxeine N‐oxide ( 3 ) were isolated from the leaves of Uncaria rhynchophylla, together with four known tetracyclic oxindole or indole alkaloids, isocorynoxeine N‐oxide ( 4 ), rhynchophylline N‐oxide ( 5 ), isorhynchophylline N‐oxide ( 6 ), and dihydrocorynantheine ( 7 ), and an indole alkaloid glycoside, strictosidine ( 8 ). The structures of 1 – 3 were elucidated by spectroscopic methods including UV, IR, ESI‐TOF‐MS, 1D‐ and 2D‐NMR, as well as CD experiments. The activity assay showed that 8 (IC₅₀=8.3 μM ) exhibited potent inhibitory activity on lipopolysaccharide(LPS)‐induced nitrogen monoxide (NO) release in N9 microglia cells. However, only weak inhibitory activities were observed for 1 – 7 (IC₅₀>100 μM for 1 – 6 or >30 μM for 7 ).     

Syntheses,Structures, and Magnetism of Trinuclear Zn2Ln Complexes with 2,6‐Dipicolinoylbis(N,N‐diethylthiourea)

The bifunctional ligand 2,6‐dipicolinoylbis(N,N‐diethylthiourea) (H₂L) readily reacts with mixtures of Zn(CH₃COO)₂ and LnCl₃ in MeOH at ambient temperature with formation of trinuclear heterobimetallic complexes [Zn₂Ln(L)₂(OAc)₃] ( 1a – 1f ) (Ln = Ce, Nd, Sm, Gd, Dy, Er). The X‐ray single‐crystal diffraction and structural studies of the complexes revealed their isostructural nature, in which two doubly‐charged ligands {L^2–} bind two Zn²⁺ ions with the terminal acylthiourea sites and one Ln³⁺ ion with the central 2,6‐pyridinedicarboxamide site. In the complexes, the coordination numbers of Ln^III and Zn^II ions are 9 and 5, respectively. Magnetic properties of the complexes were studied by temperature‐dependent dc magnetic measurements. The observed μ_eff values at room temperature are all closed to the calculated values. Fitting χ_M and M data of [Zn₂Gd(L)₂(OAc)₃] ( 1d ) shows a g_iso value of 1.94.     

Heteropentanuclear Oxalato‐Bridged nd–4f (n=4, 5) Metal Complexes with NO Ligand: Synthesis,Crystal Structures,Aqueous Stability and Antiproliferative Activity

A series of heteropentanuclear oxalate‐bridged Ru(NO)‐Ln (4d–4f) metal complexes of the general formula (nBu₄N)₅[Ln{RuCl₃(μ‐ox)(NO)}₄], where Ln=Y ( 2 ), Gd ( 3 ), Tb ( 4 ), Dy ( 5 ) and ox=oxalate anion, were obtained by treatment of (nBu₄N)₂[RuCl₃(ox)(NO)] ( 1 ) with the respective lanthanide salt in 4:1 molar ratio. The compounds were characterized by elemental analysis, IR spectroscopy, electrospray ionization (ESI) mass spectrometry, while 1 , 2 , and 5 were in addition analyzed by X‐ray crystallography, 1 by Ru K‐edge XAS and 1 and 2 by ¹³C NMR spectroscopy. X‐ray diffraction showed that in 2 and 5 four complex anions [RuCl₃(ox)(NO)]^2? are coordinated to Y^III and Dy^III, respectively, with formation of [Ln{RuCl₃(μ‐ox)(NO)}₄]^5? (Ln=Y, Dy). While Y^III is eight‐coordinate in 2 , Dy^III is nine‐coordinate in 5 , with an additional coordination of an EtOH molecule. The negative charge is counterbalanced by five nBu₄N⁺ ions present in the crystal structure. The stability of complexes 2 and 5 in aqueous medium was monitored by UV/Vis spectroscopy. The antiproliferative activity of ruthenium‐lanthanide complexes 2 – 5 were assayed in two human cancer cell lines (HeLa and A549) and in a noncancerous cell line (MRC‐5) and compared with those obtained for the previously reported Os(NO)‐Ln (5d–4f) analogues (nBu₄N)₅[Ln{OsCl₃(ox)(NO)}₄] (Ln=Y ( 6 ), Gd ( 7 ), Tb ( 8 ), Dy ( 9 )). Complexes 2 – 5 were found to be slightly more active than 1 in inhibiting the proliferation of HeLa and A549 cells, and significantly more cytotoxic than 5d–4f metal complexes 6 – 9 in terms of IC₅₀ values. The highest antiproliferative activity with IC₅₀ values of 20.0 and 22.4 μM was found for 4 in HeLa and A549 cell lines, respectively. These cytotoxicity results are in accord with the presented ICP‐MS data, indicating five‐ to eightfold greater accumulation of ruthenium versus osmium in human A549 cancer cells.     

Synthesis,spectral characterization,C?C coupling,oxidation reactions and antibacterial activities of new ruthenium(III) Schiff base complexes

A new series of hexa‐coordinated stable Ru(III) Schiff base complexes of the type [RuX(EPh₃)(L)] (where X = Cl/Br; E = P/As; L = tetradentate N₂O₂ donor Schiff ligands) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurement, FT‐IR, UV–vis, ¹³C{¹H}‐NMR, ESR spectra, electrochemical and powder X‐ray diffraction pattern studies. The selective oxidation of alcohols to their corresponding carbonyl compounds occurred in the presence of N‐methylmorpholin‐N‐oxide (NMO), H₂O₂ and O₂ atmosphere at ambient temperature as co‐oxidants and C? C coupling reactions. Further, these new Schiff base ligands and their Ru(III) complexes were also screened for their antibacterial activity against K. pneumoniae, Shigella sp., M. luteus, E. coli and S. typhi. Copyright © 2010 John Wiley & Sons, Ltd.     

Complexes of Some 3d-Metal Salts with N,N-Dimethylhydrazide of 4-Nitrobenzoic Acid

The [M(HL)₂(H₂O)₂]X₂ complexes were synthesized (M = Mn(II), Co(II), Ni(II), Cu(II), Zn; X = CH₃COO^–, Cl^–, BF₄ ^–) that incorporate bidentately coordinated molecules of N,N-dimethylhydrazide of 4-nitrobenzoic acid (HL). The latter molecules chelate the metal atom through the carbonyl O atom and the N atom of dimethylamino group. The square-planar complexes of Cu and Ni with deprotonated form of a ligand with composition ML₂ were also isolated. The synthesized complexes were studied by IR, electronic and EPR spectroscopies, and by cyclic voltammetry.     

Novel Octahedral Bis[2‐(1‐aziridinyl)ethanol‐κ2N,O] Complexes of Cobalt(II)

The synthesis and molecular structure of trans‐{bis[(acetato‐κO)‐(2‐(1‐aziridinyl)ethanol‐κ²N,O)]}cobalt(II) ( 4 ) and cis‐{bis[chlorido‐(2‐(1‐aziridinyl)ethanol‐κ²N,O)]}cobalt(II) ( 5 ) is reported. Both neutral chelate complexes are prepared from the corresponding Co^II salt [CoX₂; X = OAc ( 1 ), Cl ( 2 )] and 2‐(1‐aziridinyl)ethanol (azolH, 3 ) in dry dichloromethane. A third, ionic complex, cis‐{bis[aqua‐(2‐(1‐aziridinyl)ethanol‐κ²N,O)]}cobalt(II) diacetate ( 6 ) is formed from 4 in the presence of water and could be crystallized from aqueous dichloromethane. In all cases, 2‐(1‐aziridinyl)ethanol is coordinating as bidentate chelate ligand by the nitrogen and oxygen atom of the aziridinyl and hydroxy moiety. After purification, the compounds have been fully characterized using IR spectroscopy and FAB⁺‐MS. The single‐crystal X‐ray structure analysis revealed a distorted octahedral geometry for all complexes with either trans ( 4 ) or cis ( 5 , 6 ) configuration.     

Effect of lipophilicity of wingtip groups on the anticancer potential of mono N‐heterocyclic carbene silver(I) complexes: Synthesis,crystal structures and in vitro anticancer study

A series of symmetrically n ‐alkyl‐substituted mono benzimidazolium salts with steady increase in n ‐alkyl chain length have been prepared by stepwise N ‐alkylation resulting in salts ( 1 – 8 ). The mono N‐heterocyclic carbene (NHC)–Ag(I) complexes ( 9 – 16 ) derived from the respective salts were readily accessible by in situ deprotonation using Ag₂O. All the salts and the complexes were characterized using Fourier transform infrared, ¹H NMR, ¹³C NMR and elemental analyses. Furthermore, the structures of salts 3 and 7 and complex 16 were elucidated using X‐ray crystallography, which established that this mono NHC–Ag(I) complex has a linear bis‐carbene arrangement (C₂–Ag). The proligands and the respective Ag(I) complexes were studied for their in vitro anticancer potential against human colon cancer cell line (HCT‐116) using 5‐fluorouracil as a standard. From the IC₅₀ values of all the tested compounds, it can be postulated that there is an influential relationship between the increase in chain length of the wingtip n ‐alkyl groups and the anticancer potential. The proligands 4 – 8 and their respective complexes 12 – 16 with long n ‐alkyl chain lengths (n  = 6–10) showed better IC₅₀ values (0.3–3.9 μM) than the standard drug with the complexes displaying markedly better antiproliferation activity against HCT‐116 cell line than the respective proligands and the standard drug (IC₅₀ = 10.2 μM).     

Tricarbonylrhenium(I) complexes with the N,6-dimethylpyridine-2-carbothioamide ligand: combined experimental and calculation studies

Abstract

A new series of tricarbonyl complexes of rhenium(I) in the “2 + 1” system with the bidentate ligand N,6-dimethylpyridine-2-carbothioamide ((CH₃)NC₅H₄-CS-NH-CH₃, MeLH(Me)_NS) and a monodentate ligand (halides Cl, Br, or I, and the pseudohalide NCS anion) was synthesized. The use of mixed ligands led to the formation of neutral tricarbonylrhenium(I) complexes [Re(CO)₃(MeLH(Me)_NS)X] (X = Cl, Br, I, NCS) (1–4). Single-crystal X-ray diffraction was used to determine the crystal structures of all four compounds and those results were compared with molecular structures obtained from DFT calculations using the PBE0/def2-TZVPD approach. The complexes were also characterized by spectroscopic (FT-IR, NMR, and UV–vis) and analytical (HPLC, TGA, EA, ESI-MS) techniques. IR and UV–vis spectra were also calculated by DFT and TD-DFT methods. The cytotoxicity of these complexes was estimated using human ovarian cancer cell lines (A2780 and A2780cis), cervical cancer cells (HeLa), and non-cancerous human embryonic kidney cells (Hek-293). The toxicity of most complexes was moderate or low toward cancer cell lines (IC₅₀ = 46–231 μM) and similar against non-cancerous cells (IC₅₀ = 41-121 μM). Only the complex with chlorido ligand remarkably inhibited growth of ovarian cancer cells (IC₅₀ = 3 and 12 μM for A2780 and A2780cis, respectively). The cytotoxicity of 1 was higher than that of cisplatin.     

Isolable Anionic,Neutral and Cationic Radicals from Reactions of N,N′-Dimesityldiamidocarbene and Lewis Acids

B(C₆F₅)₃ undergoes nucleophilic attack by N,N′-dimesityldiamidocarbene (DAC) with fluoride transfer to the boron center, resulting in a new zwitterion ( 1 ). This B−F fluoride can be replaced or abstracted to give the corresponding hydride ( 2 ) or triflate ( 3 ) derivatives or the corresponding cation ( 4 ). These species are reduced with KC₈ or Cp₂Co to give isolable anionic and neutral radicals ( 5 – 8 ). Similarly, the [Ph₃C] cation undergoes nucleophilic attack by DAC resulting in the spontaneous formation of the radical cation ( 9 ).     

Multistep oligometal complexation of the macrocyclic tris(N2O2) hexaoxime ligand

A macrocyclic oxime ligand H₆L, which has an O₆ cavity surrounded by three N₂O₂ chelate sites, was synthesized and the multistep oligometal complexation behavior was investigated. Upon complexation with zinc(II), the H₆L ligand afforded two kinds of hexanuclear complexes, L₂Zn₆ then LZn₆. Each of the complexation steps proceeded highly efficiently. In the latter complex, a Zn₃(μ₃‐OH) unit was incorporated into the trimetalated ligand, LZn₃. The integrated N₂O₂ chelate coordination sites provide a unique environment for a homometallic complex. The different nature of the peripheral N₂O₂ sites and the central O₆ site is particularly suitable for the selective formation of heterometallic complexes. Complexation with the zinc(II) ion in the presence of alkaline earth (Ca and Ba) or rare earth (La, Eu, Lu) metal ions afforded the heterotetranuclear complexes LZn₃M (M=Ca, Ba, La, Eu, Lu), in which zinc(II) and ion M occupied the N₂O₂ and O₆ sites, respectively. Titration experiments showed that the heterometallic complexes LZn₃Ca and LZn₃Ba were converted into the homometallic complex LZn₆ whereas LZn₃La was not. As a result, the binding affinity in the central O₆ site of the LZn₃ unit is apparently in the order of Ca²⁺, Ba²⁺3(μ₃‐OH)3+. This difference in the affinities of metal ions as well as the ionic sizes makes the novel conversion efficient, particularly in the case of the three‐step conversion from H₆L to H₂LZn₂Ba, LZn₃Ba, then LZn₆.     

Binuclear Ru(III) Schiff base complexes: synthesis,spectral characterization,oxidation, C?C coupling reactions and antibacterial activities

New hexa‐coordinated binuclear Ru(III) Schiff base complexes of the type {[(B)₂X₂Ru]₂L} (where B = PPh₃ or AsPh₃; X = Cl or Br; L = binucleating N₂O₂ Schiff bases) were synthesized and characterized by elemental analysis, magnetic susceptibility measurement, FT‐IR, UV–vis, ¹³C{¹H}‐NMR, ESR at 300 and 77 K, cyclic voltammetric technique, powder X‐ray diffraction pattern and SEM. The new complexes were used as catalysts in phenyl–phenyl coupling reaction and the oxidation of alcohols to their corresponding carbonyl compounds using molecular oxygen atmosphere at room temperature. Further, the new Schiff base ligands and their Ru(III) complexes were also screened for their antibacterial activity against K. pneumoniae, Shigella sp., M. luteus, E. coli and S. typhi. From this study, it was found that the activity of the ruthenium(III) Schiff base complexes almost reaches the effectiveness of the conventional bacteriocide standards. Copyright © 2009 John Wiley & Sons, Ltd.     

A half‐sandwich TaV dichlorido complex containing an O,N,O′‐tridentate Schiff base ligand: synthesis,crystal structure and in vitro cytotoxicity

A new electroneutral half‐sandwich tantalum(V) dichlorido complex containing pentamethylcyclopentadienyl (Cp*) and the double‐deprotonated version of the Schiff base 2‐ethoxy‐6‐{(E)‐[(2‐hydroxyphenyl)imino]methyl}phenol (H₂L) as ligands, namely cis‐dichlorido(2‐ethoxy‐6‐{(E)‐[(2‐oxidophenyl)imino]methyl}phenolato‐κ³O,N,O′)(η⁵‐pentamethylcyclopentadienyl)tantalum(V), [Ta(C₁₀H₁₅)(C₁₅H₁₃NO₃)Cl₂] or [Ta(η⁵‐Cp*)(L)Cl₂], has been prepared and thoroughly characterized by elemental analysis, IR and NMR spectroscopy, mass spectrometry, density functional theory (DFT) calculations and single‐crystal X‐ray diffraction. The molecular structure revealed that the Ta^V centre is coordinated by a η⁵‐Cp* ligand, two monodentate chlorido ligands and one O,N,O′‐tridentate L^2? ligand. The crystal structure is stabilized by C—H…C, C—H…Cl and C…C intermolecular interactions. Moreover, the complex shows notable in vitro cytotoxicity against the A2780 human ovarian carcinoma cell line, with IC₅₀ = 14.4 µM, which is higher than that of the conventional platinum‐based anticancer drug cisplatin (IC₅₀ = 20.1 µM).     

Metal complexes of 2-acetylpyridine N(4)-dihexyl- and N(4)-dicyclohexylthiosemicarbazones

Summary 2-Acetylpyridine N(4)-dihexyl- and N(4)-dicyclohexylthiosemicarbazone, HAc4DHex and HAc4DCHex, respectively, and Fe^III, Co^II, Co^III, Ni^II, Cu^II and Zn^II complexes have been prepared and characterized by molar conductivities, magnetic susceptibilities and spectroscopic techniques. For many of the complexes, loss of the N(2)H hydrogen occurs, and the ligands coordinate to the metal centres as NNS monoanionic, tridentate ligands, e.g., [M(NNS)X] (M = Co^II, Ni^II, Cu^II, NNS = Ac4DHex or Ac4DCHex and X = Cl or Br), [Fe(NNS)₂]ClO₄, [Co(NNS)₂]BF₄, [Cu(NNS)NO₃] and [Zn(NNS)OAc]. Zn^II ion is also chelated by neutral ligands in [Zn(HNNS)X₂] (X = Cl, Br). In addition, [Ni(Ac4DHex)-(HAc4DHex)]X (X = BF₄, ClO₄) and [Ni(HAc4DCHex)₂]-(BF₄)₂ are reported where the neutral thiosemicarbazone is coordinated via the pyridyl nitrogen, azomethine nitrogen and thione sulfur. Crystal structure determinations of HAc4DCHex and [Cu(Ac4DHex)Br] show the former to contain the bifurcated hydrogen bonded form and the latter to be planar with no significant interaction between neighbouring centres.     

Synthesis, structures and electrochemical properties of ruthenium (II) complexes bearing bidentate 1,8-naphthyridine and terpyridine analogous (N,N,C)-tridentate ligands

1,8-Naphthyridine (napy) and terpyridine-analogous (N,N,C) tridentate ligands coordinated ruthenium (II) complexes, [RuL(napy-κ²N,N′) (dmso)](PF₆)₂ (1: L=L¹=N″-methyl-4′-methylthio-2,2′:6′,4″-terpyridinium, 2: L = L² = N″-methyl-4′-methylthio-2,2′:6′,3″-terpyridinium) were prepared and their chemical and electrochemical properties were characterized. The structure of complex 1 was determined by X-ray crystallographic study, showing that it has a distorted octahedral coordination style. The cyclic voltammogram of 1 in DMF exhibited two reversible ligand-localized redox couples. On the other hand, the CV of 2 shows two irreversible cathodic peaks, due to the Ru-C bond of 2 containing the carbenic character. The IR spectra of 1 in CO₂-saturated CH₃CN showed the formation of Ru-(η¹-CO₂) and Ru-CO complexes under the controlled potential electrolysis of the solution at −1.44 V (vs. Fc/Fc⁺). The electrochemical reduction of CO₂ catalyzed by 1 at −1.54 V (vs. Fc/Fc⁺) in DMF-0.1 M Me₄NBF₄ produced CO with a small amount of HCO₂H.     

Synthesis and Structural Characterization of Metal Complexes of 2‐Formylpyrrole‐4N‐ethylthiosemicarbazone (4 EL1) and 2‐Acetylpyrrole‐4N‐ethylthiosemicarbazone (4 EL2)

The reactions of ⁴N‐ethyl‐2‐[1‐(pyrrol‐2‐yl)methylidene(hydrazine carbothioamide ( 4 EL₁ ) and ⁴N‐ethyl‐2[1‐(pyrrol‐2‐yl)ethylidene(hydrazine carbothioamide ( 4 EL₂ ) with Group 12 metal halides afforded complexes of types [M(L)₂X₂] (M = Zn, Cd; L = 4 EL₁, 4 EL₂; X = Cl, Br, I; 1 – 6 , 14 – 19 ) and [M(L)X₂] (M = Hg; L = 4 EL₁, 4 EL₂; X = Cl, Br, I; 7 – 9 , 20 – 22 ). In addition, reaction of 4 EL₁ with salts of Cu^II, Ni^II, Pd^II and Pt^II afforded compounds of type [M(4 EL₁–H)₂] ( 10 – 13 ). The new compounds were characterized by elemental analysis, FAB mass spectrometry, IR and electronic spectroscopy and, for sufficiently soluble compounds, ¹H, ¹³C and, when appropriate, ¹¹³Cd or ¹⁹⁹Hg NMR spectrometry. The spectral data suggest that in their complexes with Group 12 metal cations, both thiosemicarbazones are neutral and S‐monodentate; and for [Zn(4 EL₁)₂I₂] ( 3 ), [Cd(4 EL₁)₂Br₂] ( 5 ) and [Hg(4 EL₁)Cl₂]₂ ( 7 ) this was confirmed by X‐ray diffractometry. By contrast, in its complexes with Cu^II and Group 10 metal cations, 4 EL₁ is monodeprotonated and S,N‐bidentate, as was confirmed by X‐ray diffractometry for [Ni(4 EL₁–H)₂] ( 11 ) and [Pd(4 EL₁–H)₂] ( 12 ).     

Photochemical reactions of metal carbonyls [M(CO)6 (M=Cr,Mo, W)] with N,N′ -bis(salicylidene)-1,2-bis- ( o -aminophenoxy)ethane

The complexes [M(CO)₄(η²-H₂L)] [M?=?Cr; 1, Mo; 2, W; 3] have been synthesized by photochemical reactions of VIB metal carbonyls [M(CO)₆] [M?=?Cr,?Mo,?W] with N,N′-bis(salicylidene)-1,2-bis-(o-aminophenoxy)ethane (H₂L) in THF and characterized by elemental analyses, FTIR, ¹H?NMR and mass spectra. The H₂L ligand is coordinated to the central metal as a bidentate ligand via the central azomethine nitrogen atoms in 1–3.