N2S2 Ligands Research Articles

X-ray crystal structural and spectral studies of copper(II) and nickel(II) complexes of functionalized bis(thiosemicarbazone) ligands and investigation of their electrochemical behavior

Neutral bivalent copper and nickel bis(thiosemicarbazone) complexes bearing the methoxy and bromine substituents on the dialdehyde-backbone of the ligand have been synthesized. All of them have been characterized by spectroscopic methods and in two cases by X-ray crystallography. Upon formation of these complexes, the each two bis(thiosemicarbazone) arms is deprotonated, acting as dianionic, tetradentate N2S2 ligands. The geometrical distortion from square planar in the copper complex is very greater than the nickel complex. Cyclic voltammetry studies of Cu(II) and Ni(II) complexes in DMF show that all complexes are able to stabilize low oxidation states of Cu(I) and Ni(I). The introduction of different substitutions on the aromatic ring attached to the imine carbon led to two consequences. First, The E1/2 values for the CuI/CuII and NiI/NiII redox couples were cathodically shifted in comparison with the unsubstituted analog. Second, the copper complexes underwent a quasi-reversible one-electron oxidation (CuII/CuIII).

Palladium complexes bearing pyridylthioether ligands. Synthesis and application as efficient phosphine-free catalysts in Suzuki-Miyaura couplings

Abstract Pyridylthiother-ligated Pd(II) complexes have been synthesized and efficiently applied in Suzuki-Miyaura couplings using microwave irradiation in DMF and water. The pyridylthioether NS (NS1 and NS2) and pyridyldithiother (SNS) ligands and their corresponding palladium complexes Pd-NS1, Pd-NS2, Pd-SNS were easily synthesized and fully characterized by various analytical techniques. The molecular structures of the ligand SNS and the Pd(II) complexes Pd-NS2, Pd-SNS were unequivocally determined by single crystal X-ray diffraction analysis. From these compounds, complex Pd-SNS exhibits the ligand SNS coordinated in a N,N-bidentated rather than the typical SNS-pincer manner in the solid state, giving place to a seven membered palladacycle whereas in solution it behaves as a typical SNS-pincer complex. This compound was also found to be the most efficient catalyst of the series of complexes in Suzuki-Miyaura couplings with different p-substituted aryl bromides.

Electrochemical Behavior of Ni(II) Complexes with N2S2 and N6 Ligands as Potential Catalysts in Hydrogen Evolution Reaction

In this work, two Ni(II) complexes with the tetradentate ligand N2S2 (pdto=1,8-bis(2-pyridyl)-3,6-dithioctane,) and the hexa-dentate ligand N6 (bdahp= 2,9-bis-(2’,5’-diazahexanyl)-1,10-phenan-throline) were prepared in order to explore its electrochemical behavior, that indicate their potential use as molecular catalysts for the hydrogen evolution reaction. The Ni(II)-pdto complex presented two consecutive one electron transfer [Ni(ΙΙ)-(pdto)] + 1e- [Ni(Ι)-(pd-to)] and [Ni(Ι)-(pdto)] + 1 e- → Ni(0) + pdto. On the other hand the Ni(II)-bdahp complex presented the electrochemical reduction Ni(ΙΙ)-(bdahp) + 1e- Ni(Ι)-(bdahp) followed by a coupled chemical reaction in an ECi mechanism, where a de-coordination of the diimin-ic moiety of the bdahp ligand was proposed. It was demonstrated that the pdto ligand promotes reduction over Ni(II) at less negative reduc-tion potential in comparison when the ligand bdahp is presented.

Steric Enforcement about One Thiolate Donor Leads to New Oxidation Chemistry in a NiSOD Model Complex

Ni-containing superoxide dismutase (NiSOD) represents an unusual member of the SOD family due to the presence of oxygen-sensitive Ni-SCys bonds at its active site. Reported in this account is the synthesis and properties of the NiII complex of the N3S2 ligand [N3S2Me2]3- ([N3S2Me2]3- = deprotonated form of 2-((2-mercapto-2-methylpropyl)(pyridin-2-ylmethyl)amino)-N-(2-mercaptoethyl)acetamide), namely Na[Ni(N3S2Me2)] (2), as a NiSOD model that features sterically robust gem-(CH3)2 groups on the thiolate α-C positioned trans to the carboxamide. The crystal structure of 2, coupled with spectroscopic measurements from 1H NMR, X-ray absorption, IR, UV-vis, and mass spectrometry (MS), reveal a planar NiII (S = 0) ion coordinated by only the N2S2 basal donors of the N3S2 ligand. While the structure and spectroscopic properties of 2 resemble those of NiSODred and other models, the asymmetric S ligands open up new reaction paths upon chemical oxidation. One unusual oxidation product is the planar NiII-N3S complex [Ni(Lox)] (5; Lox = 2-(5,5-dimethyl-2-(pyridin-2-yl)thiazolidin-3-yl)-N-(2-mercaptoethyl)acetamide), where two-electron oxidation takes place at the substituted thiolate and py-CH2 carbon to generate a thiazolidine heterocycle. Electrochemical measurements of 2 reveal irreversible events wholly consistent with thiolate redox, which were identified by comparison to the ZnII complex Na[Zn(N3S2Me2)] (3). Although no reaction is observed between 2 and azide, reaction of 2 with superoxide produces multiple products on the basis of UV-vis and MS data, one of which is 5. Density functional theory (DFT) computations suggest that the HOMO in 2 is π* with primary contributions from Ni-dπ/S-pπ orbitals. These contributions can be modulated and biased toward Ni when electron-withdrawing groups are placed on the thiolate α-C. Analysis of the oxidized five-coordinate species 2ox* by DFT reveal a singly occupied spin-up (α) MO that is largely thiolate based, which supports the proposed NiIII-thiolate/NiII-thiyl radical intermediates that ultimately yield 5 and other products.

Crystal structure, Hirshfeld surface, physicochemical, thermal and DFT studies of (N1E, N2E)-N1,N2-bis((5-bromothiophen-2-yl)methylene)ethane-1,2-diamine N2S2 ligand and its [CuBr(N2S2)]Br complex

A new tetradentate N2S2 Schiff base ligand derived from 5-bromothiophene-2-carbaldehyde and its [CuBr(N2S2)]Br complex were synthesized in good yield. FT-IR was investigated to monitor the condensation reaction during the ligand synthesis process. The ligand, N2S2, and its complex, [CuBr(N2S2)]Br, complex have been characterized with the aid of several spectroscopic techniques such as UV–vis., MS, FT-IR, EA, EDS, NMR (for N2S2), as well as by thermal (TG/DTG) analysis. In addition, cyclic voltammetry has been employed to examine the redox behavior of [CuBr(N2S2)]Br complex in N,N’-dimethylformamide (DMF) containing 0.10 M tetra-n-butylammonium perchlorate (TBAP). The anti-conformation EE isomer of the ligand (N2S2) was confirmed by means of X-ray crystallography; ligand crystallizes in to the monoclinic P21/c space group. N2S2 ligand was subjected to DFT-theoretical calculations and results are consistent with the experimental chemical analysis.

Silver(I) thiosemicarbazone complex [Ag(catsc)(PPh3)2]NO3: Synthesis, characterization, crystal structure, and antibacterial study

We report the synthesis, characterization and crystal structure of a new mononuclear silver(I) complex, [Ag(catsc)(PPh 3 ) 2 ]NO 3 (catsc = 3-phenylpropenalthiosemicarbazone). The complex was prepared by the reaction of catsc and AgNO 3 in the presence of PPh 3 and characterized by elemental analysis (CHN), FTIR, 1 H, 13 C and 31 P NMR spectroscopy, and single-crystal X-ray diffraction. In the complex, catsc acts as a bidentate NS ligand while the nitrate is a counter ion. The silver ion is coordinated by a bidentate ligand and two PPh 3 in the form of a distorted tetrahedron. In addition, the antibacterial effect of the complex was studied against the standard strains of two gram-positive ( Staphylococcus aureus and Enterococcus faecalis ) and two gram-negative ( Escherichia coli and Pseudomonas aeruginosa ) bacteria.

Mononuclear, Dinuclear, and Trinuclear Iron Complexes Featuring a New Monoanionic SNS Thiolate Ligand

The new tridentate ligand, S(Me)N(H)S = 2-(2-methylthiophenyl)benzothiazolidine, prepared in a single step from commercial precursors in excellent yield, undergoes ring-opening on treatment with Fe(OTf)2 in the presence of base affording a trinuclear iron complex, [Fe3(μ2-S(Me)NS(-))4](OTf)2 (1) which is fully characterized by structural and spectroscopic methods. X-ray structural data reveal that 1 contains four S(Me)NS(-) ligands meridionally bound to two pseudooctahedral iron centers each bridged by two thiolates to a distorted tetrahedral central iron. The combined spectroscopic (UV-vis, Mössbauer, NMR), magnetic (solution and solid state), and computational (DFT) studies indicate that 1 includes a central, high-spin Fe(II) (S = 2) with two low-spin (S = 0) peripheral Fe(II) centers. Complex 1 reacts with excess PMePh2, CNxylyl (2,6-dimethylphenyl isocyanide), and P(OMe)3 in CH3CN to form diamagnetic, thiolate-bridged, dinuclear Fe(II) complexes {[Fe(μ-S(Me)NS(-))L2]2}(OTf)2 (2-4). These complexes are characterized by elemental analysis; (1)H NMR, IR, UV-vis, and Mössbauer spectroscopy; and single crystal X-ray diffraction. Interestingly, addition of excess P(OMe)3 to complex 1 in CH2Cl2 produces primarily the diamagnetic, mononuclear Fe(II) complex, {Fe(S(Me)NS(-))[P(OMe)3]3}(OTf) (5).

Synthesis and X-ray crystallographic characterization of [In(tsalen)(OAc)] (tsalen = N,N′-ethylenebis(thiosalicylideneimine))

The first synthesis and crystallographic characterization of a main-group metal complex of the N2S2 ligand N,N′-ethylenebis(thiosalicylideneimine) (tsalen) is reported, with the isolation and characterization of the indium(III) compound [In(tsalen)(OAc)]. This compound has been crystallographically characterized and is shown to have a distorted trigonal bipyramidal geometry with a ligand that is unusually distorted from planarity. A byproduct of the synthesis, [In(en)2(OAc)2](OAc), has also been isolated and characterized.

Nickel(II) complexes of N2S2 donor set ligand and halide/pseudohalides: Synthesis, crystal structure, DNA and bovine/human serum albumin interaction

A series of neutral hexacoordinated nickel(II) complexes of formula [Ni II(L)X2] (where L =3,4-bis(2-pyridylmethylthio)toluene with tetradentate N2S2 donor set and X = chloride (1), azide (2), cyanate (3) and isothiocyanate anion (4)) have been synthesized and isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods along with detailed structural characterization of 1,2 and 3 by single crystal X-ray diffraction analyses. The structural study showed that the nickel(II) ion has a distorted octahedral geometry being chelated by the tetradentate N2S2 ligand and bound to cis- located choride or pseudohalide anions. In dimethylformamide solution the complexes showed quasi-reversible Ni II/NiIII redox couples in cyclic voltammograms with E1/2 values of + 0.723, + 0.749, + 0.768 and + 0.868 V for 1, 2, 3 and 4, respectively. The study of interaction of the complexes with calf thymus DNA, bovine serum albumin (BSA) and human serum albumin (HSA) using spectroscopic and physicochemical tools clearly indicates that the complexes interact with DNA via groove binding mode. Four new neutral distorted octahedral nickel(II) complexes of general formula, [NiII(L)X2] have been synthesized and structurally characterized. The spectroscopic and physicochemical studies of interaction of the complexes with calf thymus DNA, BSA and HSA have also been included.

The potential of SOCTA as a chelator for radiolabeling of trastuzumab with 99mTc

Radioimmunoscintigraphy is the administration of radio-labeled monoclonal antibodies (MAbs) and imaging with an external gamma camera. In this study, the ability of a new bifunctional N2S2 ligand, (succinimidyl 3,6-diaza-5-oxo-3-[2-((triphenylmethyl)thio)ethyl]-8-[(triphenylmethyl)thio]octanoate) (SOCTA), was evaluated for labeling of trastuzumab (a humanized anti-HER2/neu MAb) with 99mTc. Trastuzumab was labeled with 99mTc using SOCTA. The radiochemical purity, stability, immunoreactivity, biodistribution and imaging study was performed in the mice bearing breast tumor. The good results showed that SOCTA has the good potentials as a chelator for radiolabeling of antibody with 99mTc that needs more investigation in the future.

Synthesis, characterization and biological evaluation of transition metal complexes derived from N, S bidentate ligands.

Two bidentate NS ligands were synthesized by the condensation reaction of S-2-methylbenzyldithiocarbazate (S2MBDTC) with 2-methoxybenzaldehyde (2MB) and 3-methoxybenzaldehyde (3MB). The ligands were reacted separately with acetates of Cu(II), Ni(II) and Zn(II) yielding 1:2 (metal:ligand) complexes. The metal complexes formed were expected to have a general formula of [M(NS)2] where M = Cu2+, Ni2+, and Zn2+. These compounds were characterized by elemental analysis, molar conductivity, magnetic susceptibility and various spectroscopic techniques. The magnetic susceptibility measurements and spectral results supported the predicted coordination geometry in which the Schiff bases behaved as bidentate NS donor ligands coordinating via the azomethine nitrogen and thiolate sulfur. The molecular structures of the isomeric S2M2MBH (1) and S2M3MBH (2) were established by X-ray crystallography to have very similar l-shaped structures. The Schiff bases and their metal complexes were evaluated for their biological activities against estrogen receptor-positive (MCF-7) and estrogen receptor-negative (MDA-MB-231) breast cancer cell lines. Only the Cu(II) complexes showed marked cytotoxicity against the cancer cell lines. Both Schiff bases and other metal complexes were found to be inactive. In concordance with the cytotoxicity studies, the DNA binding studies indicated that Cu(II) complexes have a strong DNA binding affinity.

Assembly of photoluminescent [CunIn] (n = 4, 6 and 8) clusters by clickable hybrid [N,S] ligands

The controlled growth of luminescent copper(i)-iodide clusters has been achieved by tuning the structure of hybrid NS ligands using click chemistry.

First example of bridge mono-coordination mode for the ligand 1,8-bis-(2-pyridyl)-3,6-dithiaoctane (pdto) in a Co(II) tetrahedral complex

The reaction between CoCl2·6H2O and the ligand 1,8-bis(2-pyridyl)-3,6-dithiaoctane (pdto) in acetonitrile leads to the formation of the tetrahedral Co(II) complex, [Co(κ-1N-pdto)Cl2]. This compound presents an unusual bridge mono-coordination mode of the tetradentate N2S2 ligand, pdto, not observed with other transition metals before. It was found that the complex presents a similar coordination environment around the Co(II) ion, either in solid sate or in solution, with an important role of chloride ions. Single crystal X-ray diffraction analysis of the compound shows a polymeric structure, where pdto acts as a bimetallic bridge with supramolecular array via intermolecular contacts C–H⋯X, with X=Cl, N and S.

Electrochemical Behavior of Metal Complexes with a N2S2 Ligand

In this work we present a solid state characterization and the electrochemical behavior of metal complexes with Cu(II) and Co(II) and the ligand 1,8-bis(2-pyridyl)-3,6-dithiaoctane pdto;[Cu(pdto)H2O](NO3)2, [Cu(pdto)H2O](PF6)2, and [Co(pdto)Cl2] in non-aqueous solvents, in order to understand how the flexibility and the electronic properties of pdto affect the electrochemical response of each coordination compound.

Preparation and Spectroscopic Study of New NS Ligand and its Cd(II) and Zn(II) Metal Complexes

A new nitrogen sulphur Schiff base has been prepared from the condensation 1-(pyridin-4-yl) ethanone with 3-methylbenzyl hydrazinecarbodithioate leading the formation of new ligand 3-methylbenzyl (2Z)-2-[1-(pyridin-4-yl)ethylidene]hydrazine carbodithioate (PE3MBC). The ligand was reacted with Cd(II) and Zn(II) metal salts to form new coordinated complexes. The new ligand and its metal complexes were characterized via various physico-chemical and spectroscopic techniques and conductivity, magnetic susceptibility of metal complexes based on the data analysis the metal complexes are expected to be tetrahedral in geometry.

Five-electron donor bridging thionitrosyl groups in unsaturated binuclear manganese carbonyl derivatives

Metal carbonyl thionitrosyls are potentially accessible by reactions of metal carbonyl anions and related nucleophiles with N3S3Cl3 as illustrated by the reported synthesis of (η5-C5H5)Cr(NS)(CO)2 from N3S3Cl3 and NaCr(CO)3(η5-C5H5). Related manganese carbonyl thionitrosyls provide the opportunity to examine the behavior of the NS ligand in both mononuclear and binuclear systems that have a reasonable chance of experimental realization by related synthetic methods. In this connection the two low energy structures for Mn2(NS)2(CO)7 are a doubly NS-bridged structure and an unbridged (OC)5Mn–Mn(NS)2(CO)2 structure. A triply bridged Mn2(NS)2(CO)7 structure analogous to the experimental triply bridged Fe2(CO)9 structure is not found at competitive energies. The lowest energy structures for the unsaturated Mn2(NS)2(CO)n (n=6, 5) all have a five-electron donor bridging η2-NS group, showing the propensity of a bridging NS group to bond to metals through both the nitrogen and sulfur atoms. The lowest energy Mn2(NS)2(CO)6 structure of this type is a particularly attractive synthetic objective since it lies at least 15kcal/mol below any other Mn2(NS)2(CO)6 structures.

Oxidative Reactivity of (N2S2)PdRX Complexes (R = Me, Cl; X = Me, Cl, Br): Involvement of Palladium(III) and Palladium(IV) Intermediates

A series of (N2S2)PdRX complexes (N2S2 = 2,11-dithia[3.3](2,6)pyridinophane; R = X = Me, 1; R = Me, X = Cl, 2; R = Me, X = Br, 3; R = X = Cl, 4) were synthesized, and their structural and electronic properties were investigated. X-ray crystal structures show that for the corresponding Pd(II) complexes the N2S2 ligand adopts a κ2 conformation, with the pyridine N donors binding in the equatorial plane. Cyclic voltammetry (CV) studies suggest that the Pd(III) oxidation state is accessible at moderate redox potentials. In situ EPR, ESI-MS, UV–vis, and low-temperature electrochemical studies were employed to detect the formation of Pd(III) species during the oxidation of Pd(II) precursors. In addition, the [(N2S2)PdIVMe2](PF6)2 ([12+](PF6)2) complex was isolated by oxidation of 1 with 2 equiv of FcPF6, and its structural characterization reveals an octahedral Pd(IV) center. The reversible PdIV/III redox couple for the Pd(IV) species supports the observed formation of the Pd(III)–dimethyl species upon chemical...

The Trivalent Copper Complex of a Conjugated Bis-dithiocarbazate Schiff Base: Stabilization of Cu in Three Different Oxidation States

The new tribasic N(2)S(2) ligand H(3)ttfasbz has been synthesized by condensation of 4-thenoyl 2,2,2-trifluoroacetone and S-benzyl dithiocarbazate. On complexation with copper(II) acetate, spontaneous oxidation to the Cu(III) oxidation state is observed, and the complex [Cu(ttfasbz)] has been isolated and characterized structurally. Reduction to the EPR active Cu(II) analogue has been achieved chemically and also electrochemically, and in both cases, the process is totally reversible. The Cu(III/II) redox potential of the complex is remarkably low and similar to that of the ferrocenium/ferrocene couple. Further reduction to the formally monovalent (d(10)) dianion [Cu(I)(ttfasbz)](2-) may be achieved electrochemically. Computational chemistry demonstrates that the three redox states [Cu(ttfasbz)], [Cu(ttfasbz)](-), and [Cu(ttfasbz)](2-) are truly Cu(III), Cu(II), and Cu(I) complexes, respectively, and the potentially noninnocent ligand does not undergo any redox reactions.

ChemInform Abstract: Crystal Structures, Dynamic Behavior and Electrochemical Properties of the Copper(I) and -(II) Complexes of a New N2S2 Ligand.

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Helical metallomacrocyclic nickel(II) complexes of a tetradentate N2S2 ligand derived from N-methyldithiocarbazic acid

The structure of the tetradentate sulphur-nitrogen chelating agent, 1,2-phenylenebis(methylene) bis(1-methylhydrazinecarbodithioate) (NSSN) has been determined by X-ray diffraction. In the solid state, the two arms of the ligand remain in E configurations about the hydrazinic C-N bonds. The ligand reacts with hydrated nickel(II) salts in a 3:2 ligand-to-metal ratio yielding dimeric triple helical complexes of general formula, [Ni2(NSSN) 3]X4•nH2O (X = Cl, Br, I, NCS; n = 5, 6, 9) which contain two nickel(II) ions in distorted octahedral environments. An X-ray crystallographic structure determination of the [Ni2(NSSN) 3]Cl4•9H2O complex shows that it is a metallomacrocycle in which each ligand acts as a bis-bidentate chelating agent providing NS donors of one arm to one nickel(II) ion and NS donors of the second arm to a second nickel(II) ion. Each nickel(II) ion adopts a distorted octahedral geometry with a NiN3S3 coordination core as shown by their common electronic spectra.