Novel hydridotris(pyrazolyl)borate ruthenium(II) complexes containing the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane: Synthesis and evaluation of DNA binding properties

A series of half-sandwich ruthenium(II) complexes containing κ³(N,N,N)-hydridotris(pyrazolyl)borate (κ³(N,N,N)-Tp) and the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane (PTA) [RuX{κ³(N,N,N)-Tp}(PPh₃)_2−n(PTA)_n] (n = 2, X = Cl (1), n = 1, X = Cl (2), I (3), NCS (4), H (5)) and [Ru{κ³(N,N,N)-Tp}(PPh₃)(PTA)L][PF₆] (L = NCMe (6), PTA (7)) have been synthesized. Complexes containing 1-methyl-3,5-diaza-1-azonia-7-phosphaadamantane(m-PTA) triflate [RuCl{κ³(N,N,N)-Tp}(m-PTA)₂][CF₃SO₃]₂ (8) and [RuX{κ³(N,N,N)-Tp}(PPh₃)(m-PTA)][CF₃SO₃] (X = Cl (9), H (10)) have been obtained by treatment, respectively, of complexes 1, 2 and 5 with methyl triflate. Single crystal X-ray diffraction analysis for complexes 1, 2 and 4 have been carried out. DNA binding properties by using a mobility shift assay and antimicrobial activity of selected complexes have been evaluated.     

Tricyclic ligands on cyclam core and X-ray crystallographic structure of hexachloro-(1,11:4,8-bis(pyridine-2,6-diyl-bis(2-(N-(2-formidoylethylene)carbamoyl)ethylene))-1,8-diazonia-4,11-diazacyclotetradecane) - dimanganese(II) dimethanol dihydrate solvate

The synthesis of tricyclic compounds on functionalized cyclam core is described. The addition of four methyl acrylate molecules and consecutive condensation of this derivative with ethylenediamine resulted in formation of 1,4,8,11-tetrakis(2-(N-(2-aminoethyl)carbamoyl)ethyl)-1,4,8,11-tetraazacyclotetradecane (3). Compound 3 was the substrate for further condensation with dialdehydes: iso-phthaldialdehyde and 2,6-pyridinedicarbaldehyde, resulting in spontaneous macrocycle ring closure to give tricyclic derivatives: 1,11:4,8-bis(benzene-1,3-diyl-bis(2-(N-(2-formidoylethylene)carbamoyl)ethylene))-1,4,8,11-tetraazacyclotetradecane (4) in the reaction of 3 with iso-phthaldialdehyde and three isomers: 1,4:8,11-bis(pyridine-2,6-diyl-bis(2-(N-(2-formidoylethylene)carbamoyl)ethylene))-1,4,8,11-tetraazacyclotetradecane (5A), 1,11:4,8-bis(pyridine-2,6-diyl-bis(2-(N-(2-formidoylethylene)carbamoyl)ethylene))-1,4,8,11-tetraazacyclotetradecane (5B), and 1,8:4,11-bis(pyridine-2,6-diyl-bis(2-(N-(2-formidoylethylene)carbamoyl)ethylene))-1,4,8,11-tetraazacyclotetradecane (5C) when 2,6-pyridinedicarbaldehyde was used. The compounds 4, 5B, and 5C were identified crystallographically. The isolated 5A converted in solution into the mixture of 5B and 5C as monitored by the ¹H NMR spectroscopy. The tricycle 5 is able to accept two manganese(II) metal ions by reacting with manganese(II) dichloride with simultaneous diprotonation of 5. Structure of the resulting Mn₂(5BH₂)Cl₆·(CH₃OH)₂(H₂O)₂ was determined crystallographically.     

Five-membered ring chelate complexes of Ni(II), Pd(II) and Pt(II) derived of di-(2-pyridyl)-N-ethylimine

Cis-diaquobis{di-(2-pyridyl)-N-ethylimine}nickel(II) chloride (2) was obtained from the reaction of di-(2-pyridyl)-N-ethylimine (1) and [NiCl₂dppe] [dppe = cis-1,2-bis(diphenylphosphino)ethylene] in a 2:1 ratio in hot acetonitrile. Cis-dichloro{di-(2-pyridyl)-N-ethylimine}palladium(II) (3) and cis-dichloro{di-(2-pyridyl)-N-ethylimine}platinum(II) (4) complexes were obtained from the reaction of MCl₂ (M = Pd, Pt) and (1) in equimolar ratio in hot acetonitrile. Compounds 1–4 were characterized by IR spectroscopy, elemental analysis, and mass spectrometry; the complexes 3 and 4 were characterized in solution by NMR. In addition, solid state structures of compounds 1–4 were determined using single crystal X-ray diffraction analyses. X-ray diffraction data of the complexes 3 and 4 showed a distorted square planar local geometry at palladium and platinum atoms with the chlorine atoms in a cis-coordination; in 2 a local octahedral geometry at nickel atom was observed. Complexes 3 and 4 are arranged as dimers with a M?M distance of 3.4567(4) Å (M = Pd) and 3.4221(4) Å (M = Pt), respectively; 2 consists of units linked by intermolecular hydrogen bonding.     

Synthesis,characterization and antimicrobial activity of Ni(II) and Zn(II) complexes with N′,N′-bis[(1E)-1-(2-pyridyl)ethylidene]propanedihydrazide. Crystal structures of two highly solvated bimetallic complexes of Ni(II)

The bimetallic [Ni₂(H₂L2)₂](ClO₄)₄ (1), [Ni₂(HL2)(H₂L2)](ClO₄)₃ (2) and [Zn₂(H₂L2)₂](BF₄)₄ (3) complexes (H₂L2 = N′,N′²-bis[(1E)-1-(2-pyridyl)ethylidene]propanedihydrazide) were synthesized and characterized. The structure of complexes (1) and (2) was established by X-ray analysis. NMR spectroscopy was used for the characterization of complex (3). The complexes (1) and (2) were obtained from the same synthetic reaction and two crystal types of these complexes have been isolated during the fractional crystallization process.     

Synthesis and characterization of N-(2-pyridyl)benzamide-based nickel complexes and their activity for ethylene oligomerization

A series of N-(2-pyridyl)benzamides (1)-(11) and their nickel complexes, [N-(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide (12)-(16) and (aryl)[N-(2-pyridyl)benzamido](triphenylphosphine)nickel(II) (17)-(24), were synthesized and characterized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17, 19 and 23 is each has a six-membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12-16/MAO systems is up to 3.3 × 10⁴ g mol⁻¹ h⁻¹ whereas for 17-24/MAO systems it is up to 4.94 × 10⁵ g mol⁻¹ atm⁻¹ h⁻¹. The influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh₃/Ni molar ratio on catalytic activity was investigated.     

Anion directed templated synthesis of mono- and di-Schiff base complexes of Ni(II)

Two sets of Schiff base ligands, set-1 and set-2 have been prepared by mixing the respective diamine (1,2-propanediamine or 1,3-propanediamine) and carbonyl compounds (2-acetylpyridine or pyridine-2-carboxaldehyde) in 1:1 and 1:2 ratios, respectively and employed for the synthesis of complexes with Ni(II) perchlorate and Ni(II) thiocyanate. Ni(II) perchlorate yields the complexes having general formula [NiL₂](ClO₄)₂ (L = L¹ [N¹-(1-pyridin-2-yl-ethylidine)-propane-1,3-diamine] for complex 1, L² [N¹-pyridine-2-ylmethylene-propane-1,3-diamine] for complex 2 or L³ [N¹-(1-pyridine-2-yl-ethylidine)-propane-1,2-diamine] for complex 3) in which the Schiff bases are mono-condensed terdentate whereas Ni(II) thiocyanate results in the formation of tetradentate Schiff base complexes, [NiL](SCN)₂ (L = L⁴ [N,N′-bis-(1-pyridine-2-yl-ethylidine)-propane-1,3-diamine] for complex 4, L⁵ [N,N′-bis(pyridine-2-ylmethyline)-propane-1,3-diamine] for complex 5 or L⁶ [N,N′-bis-(1-pyridine-2-yl-ethylidine)-propane-1,2-diamine] for complex 6) irrespective of the sets of ligands used. Formation of the complexes has been explained by anion modulation of cation templating effect. All the complexes have been characterized by elemental analyses, spectral and electrochemical results. Single crystal X-ray diffraction studies confirm the structures of four representative members, 1, 3, 4 and 5; all of them have distorted octahedral geometry around Ni(II). The bis-complexes of terdentate ligands, 1 and 3 are the mer isomers and the complexes of tetradentate ligands, 4 and 5 possess trans geometry.     

2-(Benzimidazol-2-yl)-1,10-phenanthrolyl metal (Fe and Co) complexes and their catalytic behaviors toward ethylene oligomerization

The N^∧N^∧N-tridentate metal complexes, LMCl₂ (M = Fe or Co; L represents a ligand of 2-(benzimidazol-2-yl)-1,10-phenanthrolines), were synthesized and fully characterized with spectroscopic and elemental analysis. The single-crystal X-ray crystallographic analyses revealed complex 1a with a distorted octahedron geometry due to incorporating one methanol molecule, and complexes 5a and 9b with a distorted trigonal-bipyramidal geometry. Upon activation with modified methylaluminoxane (MMAO), these complexes showed good to high catalytic activities toward ethylene oligomerization. The detailed investigations were carried out to disclose the influences of various reaction conditions and nature of ligands on their performing activities of metal complexes.     

1-Methyl-4-ferrocenylmethyl-3,5-diphenylpyrazole: A versatile ligand for palladium(II) and platinum(II)

The syntheses and characterization of two novel ferrocene derivatives containing 3,5-diphenylpyrazole units of general formula [1-R-3,5-Ph₂-(C₃N₂)-CH₂-Fc] {Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄) and R = H (2) or Me (3)} together with a study of their reactivity with palladium(II) and platinum(II) salts or complexes under different experimental conditions is described. These studies have allowed us to isolate and characterize trans-[Pd{1-Me-3,5-Ph₂-(C₃N₂)-CH₂-Fc]}₂Cl₂] (4a) and three different types of heterodimetallic complexes: cis-[M{1-Me-3,5-Ph₂-(C₃N₂)-CH₂-Fc]}Cl₂(dmso)] {M = Pd (5a) or Pt (5b)}, the cyclometallated products [M{κ²-C,N-[3-(C₆H₄)-1-Me-5-Ph-(C₃N₂)]-CH₂-Fc}Cl(L)] with L = PPh₃ and M = Pd (6a) or Pt (6b) or L = dmso and M = Pt (8b) and the trans-isomer of [Pt{1-Me-3,5-Ph₂-(C₃N₂)-CH₂-Fc]}Cl₂(dmso)] (7b). In compounds 4a, 5a, 5b and 7b, the ligand behaves as a neutral N-donor group; while in 6a, 6b and 8b it acts as a bidentate [C(sp²,phenyl),N(pyrazole)]⁻ group. A comparative study of the spectroscopic properties of the compounds, based on NMR, IR and UV-Visible experiments, is also reported.     

Structural and spectral studies of nickel(II) complexes with N(4),N(4)-(butane-1,4-diyl) thiosemicarbazones

Nickel(II) complexes of quinoline-2-carbaldehyde N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone (HL¹) and 2-benzoylpyridine N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone (HL²) have been synthesized and physico-chemically characterized by means of partial elemental analyses, molar conductance measurements, magnetic measurements, electronic and infrared spectral studies. Three complexes were given the formulae [Ni(HL¹)₂]Cl₂ (1), [Ni(HL²)L²]ClO₄ · 7H₂O (2) and [NiL²Cl] · 0.5H₂O (3). The structure of compound 1 has been solved by single crystal X-ray crystallography and is found to be distorted octahedral. Compound 2, when crystallized in DMSO solution, got deprotonated to form a new compound [Ni(L²)₂] (2a), with a distorted octahedral Ni(II) center. In compound 1, HL¹ coordinates to the metal in the thione form, while in compounds 2a and 3, HL² coordinates in its deprotonated thiolate form.     

Copper(II) complexes of tridentate selenobisphenolate ligand in mixed ligand environments: Synthesis, crystal structure, EPR and electrochemical studies

A series of square-pyramidal copper(II) complexes, [Cu(L^Se)(N^∧N)] (H₂L^Se = seleno-bisphenolate; N^∧N = bipyridyl, phenanthroline or N,N-dimethylethylenediamine) have been synthesized and characterized by elemental analyses, magnetic measurements, IR, EPR, and electronic spectral studies. Single crystal X-ray structures of [Cu(L^Se)(bpy)]·H₂O (2), [Cu(L^Se)(phen)]·CH₂Cl₂ (3) and [Cu(L^Se)(N,N-Me₂en)] (4) showed that all the complexes have approximately square-pyramidal geometry. In complexes 2 and 3, the square plane is occupied by O(1), O(2), N(1) and N(2) and the apical position by Se atom of L^{Se 2−} ligand. The asymmetric unit of complex 4 contains two crystallographically independent discrete molecules A and B with CuN₂OSe chromophore comprising the square plane and the axial position being occupied by another phenolate oxygen atom. Complexes 2, 3 and 4 are found to be paramagnetic and EPR parameters extracted are: g_∥ = 2.232, g_⊥ = 2.069; 〈g_eff〉 = 1.95; and g_∥ = 2.232, g_⊥ = 2.083 for complexes 2, 3 and 4, respectively. Both the complexes 2 and 4 show three reduction processes: (a) a quasi-reversible reduction of Cu^II to Cu^I, (b) an irreversible reduction of Cu^I to Cu⁰ with the release of free ligand, and (c) a reduction process occurs at this coordinated ligand. They also show a well-defined quasi-reversible oxidation of Cu^II to Cu^III and an irreversible oxidation peak at ∼1.30 and 1.40 V vs. Ag/AgCl for 4 and 2, respectively, with no cathodic counterpart, and were attributed to the oxidation of the metal coordinated ligand.     

The (phosphino)tetraphenylborate ligand in ruthenium-arene chemistry

The synthesis of a series of anionic half-sandwich ruthenium-arene complexes [E][RuCl₂(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (E = Bu₄N⁺: R = Ph, 1a, ⁱPr, 1b or Cy, 1c; E = bis(triphenylphosphine)iminium or PNP⁺: R = Ph, 1a′, ⁱPr, 1b′ or Cy, 1c′) are reported. X-ray crystallographic studies of 1a′ and 1b′ confirmed the three-legged piano-stool coordination geometry. In solution, complexes 1a-c and 1a′-c′ are proposed to form monomer-dimer equilibria as a result of chloride ligand dissociation. Complexes 1a-c and 1a′-c′ also form the formally neutral zwitterionic complexes [RuCl(L)(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (L = pyridine: R = Ph, 2a, ⁱPr, 2b or Cy, 2c; L = MeCN: R = Ph, 3a, ⁱPr, 3b or Cy, 3c) via chloride ligand abstraction using AgNO₃ or MeOTf.     

cis-Palladium(II) complexes of derivatives of di-(2-pyridyl)methane: Study of the influence of the bridge group in the coordination mode

Palladium(II) complexes containing di-(2-pyridyl)-N-methylimine (1), di-(2-pyridyl)methanol (2) and di-(2-pyridyl)methyl-N,N-diethyldithiocarbamate (4) ligands were synthesized and characterized by ¹H and ¹³C NMR in solution, IR and X-ray single crystal diffraction. Crystal structures of cis-dichloro[di-(2-pyridyl)-N-methylimine]palladium(II) (5), cis-dichloro[di-(2-pyridyl)methanol]palladium(II) (6) and cis-dichloro[di-(2-pyridyl)methyl-N,N-diethyldithiocarbamate]palladium(II) (7) showed a bidentate coordination mode of the di-(2-pyridyl)methane derivatives 1, 2 and 4. In these complexes is observed the formation of a five-membered chelate ring with the iminic ligand 1 and six-membered chelate rings with the pyridinic ligands 2 and 4. In all complexes the palladium atom displays a distorted square planar geometry.     

Some new DTPA-N,N″-bis(amides) functionalized by alkyl carboxylates: Synthesis,complexation and stability properties

A new series of DTPA-N,N″-bis(amide) ligands functionalized by alkyl carboxylates on the amide side-arms (1a–1l) and their Gd(III) complexes of the type [Gd(1)(H₂O)] · xH₂O (2a–2l) were synthesized and characterized by analytical and spectroscopic techniques. Potentiality of 2a–2l as contrast agent for magnetic resonance imaging (MRI CA) was investigated by measuring some relevant physicochemical properties such as (i) the protonation constants of 1a–1l, (ii) thermodynamic and conditional stability constants of 2a–2l, (iii) the selectivity (pGd) of 1a–1l for the Gd(III) ion over the endogenous metal ions such as Zn(II), Ca(II), and Cu(II), and (iv) the relaxivities (R₁ and R₂) of 2a–2l in aqueous and aqueous HP-β-CD solutions. Comparative studies reveal that most of new Gd(III) complexes show enhanced thermodynamic stability and selectivity as compared with those of [Gd(DTPA-BMA)(H₂O)] (DTPA-BMA = N,N″-di(methylcarbamoylmethyl)diethylenetriamine-N,N′,N″-triacetate). Also enhanced with 1a–1l (except 1f and 1h) is affinity for Gd(III) as compared with [DTPA-BMA]³⁻ under physiological conditions. The relaxivities (R₁ and R₂) of aqueous solutions of 2a–2l, on the other hand, drop significantly as compared with [Gd(DTPA-BMA)(H₂O)] although they increase dramatically (6–10 fold) in aqueous hydroxypropyl-β-cyclodextrin (HP-β-CD) solutions.     

Alkyne activation by half-sandwich ruthenium(II) complexes bearing the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane (PTA)

Complex [RuCl{κ³(N,N,N)-Tp}(PPh₃)(PTA)] (κ³(N,N,N)-Tp = hydridotris(pyrazolyl)borate) containing the water-soluble phosphane 1,3,5-triaza-7-phosphatricyclo[3.3.1.1^3,7]decane (PTA) reacts with terminal alkynes producing to the corresponding neutral alkynyl complexes [Ru(CCR){κ³(N,N,N)-Tp}(PPh₃)(PTA)] (R = Ph (1a), ⁿBu (1b), 1-cyclopentenyl (1c), p-methoxyphenyl (1d), 6-methoxynaft-2-yl (1e)). When halide is extracted from complex [RuCl{κ³(N,N,N)-Tp}(PPh₃)(PTA)] followed by treatment with propargyl alcohols, the corresponding allenylidene complexes [Ru{κ³(N,N,N)-Tp}(PPh₃)(PTA)(CCCPh₂)][X] (X = PF₆ (2a), CF₃SO₃ (2b)) and [Ru{κ³(N,N,N)-Tp}(PPh₃)(PTA)(CCCC₁₂H₈)][PF₆] (3) result. Electrophilic attack on the complexes thus obtained leads chemoselectively to the alkynyl complexes [Ru(CCR){κ³(N,N,N)-Tp}(PPh₃)(1-CH₃-PTA)][CF₃SO₃] (R = Ph (4a), ⁿBu (4b), and 1-cyclopentenyl (4c)) and to the dicationic allenylidene complexes [Ru{κ³(N,N,N)-Tp}(PPh₃)(1-H-PTA)(CCCC₁₂H₈)][PF₆]₂ (5) and [Ru{κ³(N,N,N)-Tp}(PPh₃)(1-CH₃-PTA)(CCCPh₂)][CF₃SO₃]₂ (6).     

Structural diversity in Cu(II), Cd(II) and Hg(II) coordination complexes with the rigid N,N′-bis(2/3-aryl)-1,4-benzenedicarboxamide ligand

The syntheses and structures of a series of metal complexes, namely Cu₂Cl₄(L¹)(DMSO)₂·2DMSO (L¹ = N,N′-bis(2-pyridinyl)-1,4-benzenedicarboxamide), 1; {[Cu(L²)_1.5(DMF)₂][ClO₄]₂·3DMF}_∞ (L² = N,N′-bis(3-pyridinyl)-1,4-benzenedicarboxamide), 2; {[Cd(NO₃)₂(L³)]·2DMF}_∞ (L³ = N,N′-bis-(2-pyrimidinyl)-1,4-benzenedicarboxamide), 3; {[HgBr₂(L³)]·H₂O}_∞, 4, and {[Na(L³)₂][Hg₂X₅]·2DMF}_∞ (X = Br, 5; I, 6) are reported. All the complexes have been characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. Complex 1 is dinuclear and the molecules are interlinked through S?S interactions. In 2, the Cu(II) ions are linked through the L² ligands to form 1-D ladder-like chains with 60-membered metallocycles, whereas complexes 3 and 4 form 1-D zigzag chains. In complexes 5 and 6, the Na(I) ions are linked by the L³ ligands to form 2-D layer structures in which the [Hg₂X₅]⁻ anions are in the cavities. The L² ligand acts only as a bridging ligand, while L¹ and L³ show both chelating and bridging bonding modes. The L¹ ligand in 1 adopts a trans-anti conformation and the L² ligand in 2 adopts both the cis-syn and trans-anti conformations, whereas the L³ ligands in 3–6 adopt the trans conformation.     

Synthesis and characterisation of new pyrazole-phosphinite ligands and their ruthenium(II) arene complexes

The new potentially bidentate pyrazole-phosphinite ligands [(3,5-dimethyl-1H-pyrazol-1-yl)methyl diphenylphosphinite] (L¹) and [2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl diphenylphosphinite] (L²) were synthesised and characterised. The reaction of L¹ and L² with the dimeric complexes [Ru(η⁶-arene)Cl₂]₂ (arene = p-cymene, benzene) led to the formation of neutral complexes [Ru(η⁶-arene)Cl₂(L)] (L = L¹, L²) where the pyrazole-phosphinite ligand is κ¹-P coordinated to the metal. The subsequent reaction of these complexes with NaBPh₄ or NaBF₄ produced the [Ru(η⁶-p-cymene)Cl(L²)][BPh₄] and [Ru(η⁶-benzene)Cl(L²)][BF₄] compounds which contain the pyrazole-phosphinite ligand κ²-P,N bonded to ruthenium. All the complexes were fully characterised by analytical and spectroscopic methods. The structure of the complex [Ru(η⁶-p-cymene)Cl(L²)][BPh₄] was also determined by a X-ray single crystal diffraction study.     

Syntheses and structures of iron carbonyl complexes derived from N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine and N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine

The reaction of N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine (1) with Fe₂(CO)₉ in refluxing acetonitrile yielded di-(μ₃-thia)nonacarbonyltriiron (2), μ-[N-(5-methyl-2-thienylmethyl)-η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido]hexacarbonyldiiron (3), and N-(5-methyl-2-thienylmethylidene)amine (4). If the reaction was carried out at 45 °C, di-μ-[N-(5-methyl-2-thienylmethylidene)-η¹(N);η¹(S)-2-thiolethylamino]-μ-carbonyl-tetracarbonyldiiron (5) and trace amount of 4 were obtained. Stirring 5 in refluxing acetonitrile led to the thermal decomposition of 5, and ligand 1 was recovered quantitatively. However, in the presence of excess amount of Fe₂(CO)₉ in refluxing acetonitrile, complex 5 was converted into 2-4. On the other hand, the reaction of N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine (6) with Fe₂(CO)₉ in refluxing acetonitrile produced 2, μ-[N-(6-methyl-2-pyridylmethyl)-η¹ (N_py);η¹:η¹(N); η¹:η¹(S)-2-thiolatoethylamido]pentacarbonyldiiron (7), and μ-[N-(6-methyl-2-pyridylmethylidene)-η²(C,N);η¹:η¹(S)-2- thiolethylamino]hexacarbonyldiiron (8). Reactions of both complex 7 and 8 with NOBF₄ gave μ-[(6-methyl-2-pyridylmethyl)-η¹(N_py);η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido](acetonitrile)tricarbonylnitrosyldiiron (9). These reaction products were well characterized spectrally. The molecular structures of complexes 3, 7-9 have been determined by means of X-ray diffraction. Intramolecular 1,5-hydrogen shift from the thiol to the methine carbon was observed in complexes 3, 7, and 9.     

Synthesis and structure of highly substituted pyrazole ligands and their complexes with platinum(II) and palladium(II) metal ions

Reaction of 3-methoxycarbonyl-2-methyl- or 3-dimethoxyphosphoryl-2-methyl-substituted 4-oxo-4H-chromones 1 with N-methylhydrazine resulted in the formation of isomeric, highly substituted pyrazoles 4 (major products) and 5 (minor products). Intramolecular transesterification of 4 and 5 under basic conditions led, respectively, to tricyclic derivatives 7 and 8. The structures of pyrazoles 4a (dimethyl 2-methyl-4-oxo-4H-chromen-3-yl-phosphonate) and 4b (methyl 4-oxo-2-methyl-4H-chromene-3-carboxylate) were confirmed by X-ray crystallography. Pyrazoles 4a and 4b were used as ligands (L) in the formation of ML₂Cl₂ complexes with platinum(II) or palladium(II) metal ions (M). Potassium tetrachloroplatinate(II), used as the metal ion reagent, gave both trans-[Pt(4a)₂Cl₂] and cis-[Pt(4a)₂Cl₂], complexes with ligand 4a, and only cis-[Pt(4b)₂Cl₂] isomer with ligand 4b. Palladium complexes were obtained by the reaction of bis(benzonitrile)dichloropalladium(II) with the test ligands. trans-[Pd(4a)₂Cl₂] and trans-[Pd(4b)₂Cl₂] were the exclusive products of these reactions. The structures of all the complexes were confirmed by IR, ¹H NMR and FAB MS spectral analysis, elemental analysis and Kurnakov tests.     

Copper(II) complexes of N4 tetradentate ligands with flexible alkyl spacers: Crystal structure,DNA binding and cleavage studies

Mononuclear copper(II) complexes, [Cu L1] (ClO₄)₂ (1), [Cu L2] (ClO₄)₂ (2) and [Cu L3] (ClO₄)₂ (3) with quadridentate Schiff base ligands L1 (N,N′-bis-pyridin-2-ylmethyl-butane-1,4-diimine), L2 (N,N′-bis-pyridin-2-ylmethyl-pentane-1,5-diimine) and L3 (N,N′-bis-pyridin-2-ylmethyl-hexane-1,6-diimine) have been synthesized and characterized. The crystal structure data of 1 reveals the existence of the complex in two different geometries, namely a square pyramid and a distorted octahedron, which eventually leads to the packing of the molecule into helical and anti-parallel structures respectively. Absorption titration studies with calf thymus DNA for all three complexes are suggestive of groove binding with binding constant values for 1, 2 and 3 being 2.6 ± 0.2 × 10⁴ M⁻¹, 11.5 ± 0.2 × 10⁴ M⁻¹ and 1.83 ± 0.2 × 10⁴ M⁻¹ respectively. Control cleavage experiments using pBR 322 plasmid DNA and distamycin suggest minor groove binding for these complexes. In the presence of ascorbic acid, the complexes show efficient DNA cleavage, the order of efficiency being 1 > 2 ≅ 3.