Synthesis and bioelectrochemical behavior of aromatic amines

Four aromatic amines 1-amino-4-phenoxybenzene (A₁), 4-(4-aminophenyloxy) biphenyl (A₂), 1-(4-aminophenoxy) naphthalene (A₃) and 2-(4-aminophenoxy) naphthalene (A₄) were synthesized and characterized by elemental, spectroscopic (FTIR, NMR), mass spectrometric and single crystal X-ray diffraction methods. The compounds crystallized in monoclinic crystal system with space group P2₁. Intermolecular hydrogen bonds were observed between the amine group and amine/ether acceptors of neighboring molecules. Electrochemical investigations were done using cyclic voltammetry (CV), square wave voltammetry (SWV) and differential pulse voltammetry (DPV). CV studies showed that oxidation of aromatic amines takes place at about 0.9 V (vs. Ag/AgCl) and the electron transfer (ET) process has irreversible nature. After first scan reactive intermediate were generated electrochemically and some other cathodic and anodic peaks also appeared in the succeeding scans. DPV study revealed that ET process is accompanied by one electron. DNA binding study of aromatic amines was performed by CV and UV–visible spectroscopy. These investigations revealed groove binding mode of interaction of aromatic amines with DNA.     

Synthesis of [SnPh2(SR)2] SR = SC6F4-4-H, SC6F5: Reactivity towards group 10 transition metal complexes

The organometallic tin(IV) complexes [SnPh₂(SR^F)₂] SR^F = ⁻SC₆F₄-4-H (1), ⁻SC₆F₅ (2), were synthesized and their reactivity with [MCl₂(PPh₃)₂] M = Ni, Pd and Pt explored. Thus, transmetallation products were obtained affording polymeric [Ni(SR^F)(μ-SR^F)]_n, monomeric cis-[Pt(PPh₃)₂(SC₆F₄-4-H)₂] (3) and cis-[Pt(PPh₃)₂(SC₆F₅)₂] (4) and dimeric species [Pd(PPh₃)(SC₆F₄-4-H)(μ-SC₆F₄-4-H)]₂ (5) and [Pd(PPh₃)(SC₆F₅)(μ-SC₆F₅)]₂ (6) for Ni, Pt and Pd, respectively. The crystal structures of complexes 1, 2, 3, 4 and 6 were determined.     

Main group derivatives of a cyclometallated iron carbonyl anion. Crystal structures of Fe(CO)2{P(OPh)3}{(PhO)2POC6H4}(SnPh3) and two isomers of Fe(CO)2{P(OPh)3}{(PhO)2POC6H4}(I)

The iron hydrido complex HFe(CO)₂{P(OPh)₃}{(PhO)₂POC₆H₄} (1), was rapidly deprotonated by DBU or [BzMe₃N][OH] in THF to afford the new carbonyl iron anion [Fe(CO)₂{P(OPh)₃}{(PhO)₂POC₆H₄}]⁻ ([2]⁻), containing an ortho-metallated triphenyl phosphite ligand. Complex [2]⁻ reacted with triorganostannyl and plumbyl salts and with halogens to give the octahedral Fe^II compounds Fe(CO)₂{P(OPh)₃}{(PhO)₂POC₆H₄}(X) (X=SnPh₃, 3; SnMe₃, 4; PbPh₃, 5; PbMe₃, 6; Cl, 7; Br, 8; I, 9). The Group 14 complexes 3-6 were obtained in one isomeric form in which the P^III-donor atoms are mutually cis, the carbonyl ligands are cis and the P(OPh)₃ and MR₃ (M=Sn, Pb; R=Ph, Me) groups are trans as determined by solution-state IR, ³¹P and ¹³C NMR spectroscopic data. This geometry was confirmed for 3 by a single crystal X-ray diffraction study. The halide complexes, however, were obtained as a mixture of isomers. The major isomer (7, X=Cl; 8a, X=Br; 9a, X=I) has cis P atoms, trans CO groups and the halide located trans to the phosphorus atom of the ortho-metallated phosphite ligand. The structure of 9a was confirmed by an X-ray diffraction study. Two other isomers, designated 8b (X=Br) and 9b (X=I), with cis P atoms and cis CO groups were isolated from the reactions of [2]⁻ with Br₂ and I₂, respectively. The structure of the latter was established by X-ray crystallography and is related to 9a by exchange of the P(OPh)₃ ligand and a carbonyl group such that the metal-bound C atom of the five-membered metallacycle is trans to CO. The stereo-geometry of 8b could not be unambiguously assigned from the spectroscopic data; however, two of the seven possible geometric isomers were suggested as plausible structures.     

Synthesis of rhodium porphyrin aryls via intermolecular arene carbon-hydrogen bond activation

(meta-Cyanophenyl) rhodium porphyrins have been synthesized from the selective activation of a meta carbon-hydrogen bond of PhCN via the reaction of RhCl₃ with porphyrins in refluxing PhCN.     

Synthesis, characterization, and reactivity of organometallic Zr(IV) carboxylate complexes

A series of zirconium(IV) complexes, [ZrX₂(XDK)], where XDK is the constrained carboxylate ligand m-xylylenediamine bis(Kemp's triacid imide), were prepared and structurally characterized. The solid state structure of the mononuclear carboxylate alkyl complex [Zr(CH₂Ph)₂(XDK)] reveals that one benzyl group is bonded in an η²-fashion to the metal center. The reactivity of [Zr(CH₂Ph)₂(XDK)] displays its electrophilic character toward nucleophiles strong enough to displace the η²-benzyl group. Thus, weak sigma donor ligands such as CO, alkynes and anilines do not react, whereas strong sigma donors, such as pyridines and isocyanides, rapidly form the monoadduct [Zr(CH₂Ph)₂(4-tert-butylpyridine)(XDK)] and [Zr{η²-2,6-Me₂PhNCCH₂Ph}₂(XDK)], an η²-iminoacyl derivative, respectively. Attempts to prepare zirconium amido complexes with H₂XDK generally afforded the eight-coordinate [Zr(XDK)₂] complex but use of the small amido ligand precursorZr(NMe₂)₄ allowed [Zr(NMe₂)₂(4-tert-butylpyridine)(XDK)] to be isolated in good yield.     

Synthesis and crystal structures of water-soluble rhodium(III) complexes with 1,4,7-triazacyclononane and 2,2-bipyridine supporting ligands

New water-soluble rhodium(III) complexes with a tacn (1,4,7-triazacyclononane) and a bpy (2,2^′-bipyridine) supporting ligands were synthesized. The reaction of [Rh^III(tacn)Cl₃] (1) with equimolar amount of bpy and two equivalents of AgNO₃ in H₂O at reflux for 10 h gave a water-soluble chloro complex [Rh^III(tacn)(bpy)Cl](NO₃)₂ {2(NO₃)₂}. Complex 2(NO₃)₂ was treated with equimolar amount of AgNO₃ in H₂O at reflux for 10 h to give a water-soluble nitrato complex [Rh^III(tacn)(bpy)(NO₃)](NO₃)₂ {3(NO₃)₂}. Water-solubility of 3 with NO₃ ⁻ ligand (46.5 mg/mL) is high compared with that of 2 with Cl⁻ ligand (14.5 mg/mL) under the same conditions (at pH 7.0 at 25 °C). The structures of 2 and 3 were unequivocally determined by X-ray analysis. Their structures in H₂O were also examined by ¹H NMR, IR, and electrospray ionization mass spectrometry (ESI-MS).     

Syntheses, structures, and properties of novel one dimensional copper cyanide coordination polymers

Three new one-dimensional copper coordination polymers have been prepared and fully characterized by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and magnetic susceptibility measurements. The structure of [Cu(CN)₂(bpy)] (1) (bpy = 2,2-bipyridyl) (monoclinic P2₁/c, a = 8.9761(7) Å, b = 16.731(1) Å, c = 8.0224(6) Å, β = 114.437(1)°) consists of Cu(II) metal centers coordinated by three cyanide ligands and chelated by one bpy to form the monomers Cu(CN)₃(bpy) with distorted square pyramidal geometry. Each monomer shares two cyanide ligands with two adjacent monomers to form infinite -Cu(II)-CN-Cu(II)-CN-Cu zigzag chains along the c-axis. The one-dimensional structure of [Cu(CN)(bpy)] (2) (hexagonal P3₂, a = 14.4883(6) Å, b = 12.921(1) Å) is built of tetrahedral Cu(CN)₂bpy metal complexes in which Cu(I) metal centers are coordinated by one nitrogen and one carbon from two different CN ligands, and two nitrogens from one bpy. The two CN ligands act as bridging ligands between adjacent monomers to form helical chains along the 3₂ screw axis. The crystal structure of [Cu₂Cl(CN)(bpy)] (3) (orthorhombic Pbca, a = 17.853(2) Å, b = 6.9724 (9) Å, c = 18.7357 (9) Å) consists of two monomers, CuCl₂(CN) and Cu(bpy)(CN) that share a cyanide ligand to form Cu₂Cl₂(CN)(bpy) dimers. The dimers link to each other by sharing Cl ligands leading to the formation of infinite Cu-Cl-Cu chain decorated by the complex Cu(CN)(bpy). Variable-temperature magnetic measurement shows an overall ferromagnetic behavior for compound 1. The magnetic pathway of compound 1 is through the cyanide bridge connecting apical and equatorial positions of adjacent copper (II) ions.     

Synthesis and structural characterization of two cis-dioxorhenium(V) ReO2[SN][P] mixed-ligand complexes

Two novel five-coordinate cis-dioxorhenium(V) complexes of the general formula ReO₂[R₂NCH₂CH₂S][PPh₃] (R₂N=Et₂N, complex 1 and R₂N=(o-CH₃O---C₆H₄N(CH₂CH₂)₂N, complex 2) have been synthesized by reacting ReOCl₃(PPh₃)₂ with the respective bidentate ligands R₂NCH₂CH₂SH. The complexes have been characterized by elemental analysis, IR, NMR spectroscopies and X-ray crystallography. X-ray crystallographic studies showed that the coordination geometry around rhenium is distorted trigonal bipyramidal. The basal plane is defined by the two doubly bonded oxygen atoms and the sulfur of the bidentate ligand, while the nitrogen of the ligand and the phosphorus occupy the apical positions.     

Synthesis and characterisation of Pd(II) allyl complexes derived from the diterpene carvone

A series of cationic allyl complexes of Pd(II) derived from the diterpene carvone have been synthesised and characterised using the chelating ligands, bipyridine, 1,8-phenanthroline, neocuproin, S,S (-)-Chiraphos and R (+)-Binap as co-ligands. These complexes can be readily converted to new organic products in which one C---H bond of the allyl methyl has been substituted. The structure of a bipyridyl complex as its tetraphenyl borate salt has been determined via X-ray diffraction. 2-D NOESY studies on the Chiraphos and Binap complexes are reported. The Binap, but not the Chiraphos, complex reveals η³-η³η³ isomerisation at ambient temperature.     

The use of the borocaptate anion as a ligand. Synthesis and X-ray crystal structure of pentaammine (1-thiolato-closo-undecahydrododecaborane)ruthenium(III) dihydrate

The complex [Ru(SB₁₂H₁₁)(NH₃)₅]·2H₂O has been prepared by the reaction of Cs₂B₁₂H₁₁SH with [RuCl(NH₃)₅]Cl₂ in aqueous solution. The complex represents the first reported example of the borocaptate anion acting as a ligand. The structure of the complex has been determined by single crystal X-ray diffraction analysis. The crystal parameters are monoclinic, space group P2₁/c, A = 8.056(1), B = 14.240(2), C = 15.172(2) Å, β=98.48° and Z = 4. The ruthenium atom has a distorted octahedral coordination. The distortion is probably due to the high (3⁻) charge and the large bulk of the borocaptate ligand. These features can also be observed in the spectroscopic properties of the complex.     

Synthesis of ruthenium(II) monosubstituted squarates: 1. Procedural considerations

Attempted syntheses of ruthenium(II) monosubstituted squarate complexes in acetonitrile using cis-[RuCl₂(dmso)₄] and anisole-, methoxy-, methyl- and diphenylamino-squarate ligands, respectively, resulted in the formation in each case of the monomer cis, fac-Ru(CH₃CN)Cl₂(dmso)₃ (1) with the ruthenium atom in a distorted octahedral environment. A second crop of crystals harvested from the reaction with the methoxysquarate ligand was identified as the oxalato-bridged dimer [{cis-(CH₃CN)(Cl)(dmso)₂Ru}₂(μ-C₂O₄)] (2). When cis-[RuCl₂(dmso)₄] and methylsquarate were reacted in aqueous solution instead of acetonitrile, the dimer [{fac-(Cl)(dmso)₃Ru}₂(μ-C₂O₄)] (3) was produced. The dimers 2 and 3 are formed from oxidation/ring opening of the methoxy- and methyl-squarate ligands, respectively. Use of the salts of these ligands instead of their non-ionised forms under different reaction conditions, afforded [Na] fac-[RuCl₃(dmso)₃] (4) and [(C₄H₉)₄N]₂[(C₄O₄)(C₄H₂O₄)₂] (7), respectively, which were shown to be products of competing reactions. The information acquired from these failed attempts has provided the basis for the development of a strategy to overcome these problems and lead to a successful synthetic route to ruthenium(II) monosubstituted squarates.     

Synthesis and characterization of polypyridineruthenium(II) complexes containing a linear ambidentate ligand, NCO or NCS, and reaction of isocyanato complexes under acidic conditions

Isocyanato and isothiocyanatopolypyridineruthenium complexes, [Ru(NCX)Y(bpy)(py)₂]ⁿ⁺ (bpy=2,2′-bipyridine, PY=pyridine; X=O, Y=NO₂ for n=0, and Y=py for n=1; X=S, Y=NO₂ for n=0, Y=NO for n=2, and Y=py for n=1), were synthesized by the reaction of polypyridineruthenium complexes with potassium cyanate or sodium thiocyanate salt. Isocyanatoruthenium(II) complexes, [Ru(NCO)(NO₂)(bpy)(py)₂] and [Ru(NCO)(bpy)(py)₃]⁺, react under acidic conditions to form the corresponding ammineruthenium complexes, [Ru(NO)(NH₃)(bpy)(py)₂]³⁺. The molecular structures of [Ru(NCO)(bpy)(py)₃]ClO₄, [Ru(NCS)(NO)(bpy)(py)₂](PF₆)₂ and [Ru(NO)(NH₃)(bpy)(py)₂](PF₆)₃ were determined by X-ray crystallography.     

Synthesis and X-ray characterization of nickel(II) arsenatotungstate complexes: isolation of an intermediate leading to the formation of a sandwich-type polyoxometalate

The nickel arsenatotungstate K₁₀[As₂W₁₉(H₂O){Ni(H₂O)}₂O₆₇]·18H₂O (1) has been synthesized. Due to its instability in water, attempts to obtain crystals of 1 suitable for X-ray diffraction have failed. The stabilization of the [As₂W₁₉(H₂O){Ni(H₂O)}₂O₆₇]¹⁰⁻ core has been reached by synthesizing the analogue mixed {CsK} salt. The crystal structure of Cs₆K₂[Ni(H₂O)₆][As₂W₁₉(H₂O){Ni(H₂O)}₂O₆₇]·17H₂O (2) has been resolved. It consists of two [α-AsW₉O₃₃]⁹⁻ sub-units linked via a belt containing a tungsten and two nickel cations. Comparison of infrared and electronic absorption spectroscopic data for 1 and 2 has confirmed the structure proposed for 1. The instability of 1 led us to investigate the behavior of 1 in water. UV-Vis spectroscopy revealed that the formation of this complex is a multi-step reaction. An intermediate, the complex K₈[Ni(H₂O)₆]_1.5[As₂W₁₉(H₂O){K(H₂O)}{Ni(H₂O)₄}O₆₇]·21H₂O (3), has been isolated and characterized by elemental analysis, UV-Vis and infrared spectroscopies, and X-ray diffraction. In 3, the two vacant sites of the [As₂W₁₉O₆₇]¹⁴⁻ anion are occupied by a nickel and a potassium, forming a {WNiK} belt. It follows that the stability of 2 in water is due to the large ionic radius of Cs⁺, which prevents the inclusion of the alkaline cation into the cavity of the [As₂W₁₉O₆₇]¹⁴⁻ anion. The complex 3 represents a unique example of a fully characterized intermediate leading to the formation of a sandwich-type polyoxometalate.     

Synthesis and characterization of mono- and dinuclear nickel complexes with dichalcogenolate o-carboranyl ligands

Three mono- and dinuclear nickel complexes with dichalcogenolate o-carboranyl ligands were synthesized and characterized by X-ray crystallography. The reactions of Ni(COD)₂(COD=1,5-octadiene) with [(THF)₃LiE₂C₂B₁₀H₁₀Li(THF)]₂ (E=S, Se) in THF in the presence of air in different ratios afforded the mono- and dinuclear nickel complexes of formulae Li(THF)₄]₂[Ni(E₂C₂B₁₀H₁₀)₂] (E=S, 1a; E=Se, 1b) and [Li(THF)₄]₂[Ni₂(E₂C₂B₁₀H₁₀)₃] (E=S, 2a; E=Se, 2b). In 2a, two nickel atoms are connected by one chalcogen (η¹,η²-S₂C₂B₁₀H₁₀) bridging ligand with strong metal-metal interaction. Complex of formula (PPh₃)₂Ni(S₂C₂B₁₀H₁₀) · 0.5THF (3a) was also obtained from the reaction of (PPh₃)₂NiCl₂ and [(THF)₃LiS₂C₂B₁₀H₁₀Li(THF)]₂.     

Synthesis and structural analysis of calix[4]arene-supported iron(III) complexes

The paper describes the reactivity of calix[4]arene dialkyl- or -silylethers H₂R₂calix, R=Me (1), Bz (2), or SiMe₃ (3) (p-tert.butyl-calix[4]arene=H₄calix), towards the iron(III) complex [FeCl(NSiMe₃)₂(thf)] 4. Bis(silylation) of H₄calix was achieved using a mixture of NEt₃ and Me₃SiCl as silylating agent, which is probably the most convenient and cheapest way for the preparation of H₂(Me₃Si)₂calix 3. [FeCl(N{SiMe₃}₂)₂(thf)] 4 has been obtained from the reaction of [FeCl₃] and commercially available K[N(SiMe₃)₂] in THF. The reactions of 4 with H₂Me₂calix and H₂Bz₂calix afford mononuclear iron(III) chloro compounds [FeCl(R₂calix)] 5 (R=Me) and 6 (R=Bz). The usage of calix[4]arene silyl ether 3 leads to a dinuclear complex [Fe₂({Me₃Si}calix)₂] 7, presumably under Me₃SiCl cleavage of a mononuclear calixarene iron(III) chloro complex. The calix[4]arene ether stabilized iron(III) chloro complexes are susceptible to nucleophilic substitution reactions, as exemplified by the reaction of 5 with sodium azide yielding an azido complex [Fe(N₃)(Me₂calix)] 8. The molecular structures of 4, 5, 6, 7, and 8 in the solid state have been determined by X-ray diffraction.     

Synthesis and structural studies of gallium(III) and indium(III) complexes of 2-acetylpyridine thiosemicarbazones

Four 2-acetylpyridine ⁴N-alkyl thiosemicarbazones, and their Ga(III) and In(III) complexes have been prepared and characterised by fluorescence, UV-Vis, IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry and X-ray crystallographic analysis. Comparison of the crystal structures gave an insight into the nature of the complexes formed, demonstrating a preference for [ML₂]⁺ type complexes with gallium and [MLX₃] species with indium. Stability studies on two candidates indicated that complex [InL³Cl₂MeOH] was stable to chemical degradation for prolonged periods in human serum, giving this complex potential for further biological evaluation.     

Synthesis and characterisation of palladium(II) and platinum(II) compounds containing pyrazole-derived ligands: crystal structure of [PdCl2(HL)] (HL = 3-phenyl-5-(2-pyridyl)pyrazole)

Reaction of the ligands 3-phenyl-5-(2-pyridyl)pyrazole (HL¹), 3,5-bis(2-pyridyl)pyrazole (HL²), 3-methyl-5-(2-pyridyl)pyrazole (HL³) and 3-methyl-5-phenylpyrazole (HL⁴) with [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) or [PdCl₂(cod)] gives complexes with stoichiometry [PdCl₂(HL)₂] (HL = HL¹, HL², HL³), [Pt(L)₂] (L = L¹, L², L³) and [MCl₂(HL⁴)₂] (M = Pd(II), Pt(II)). The new complexes were characterised by elemental analyses, conductivity measurements, infrared and ¹H NMR spectroscopies. The crystal and molecular structure of [PdCl₂(HL¹)] was resolved by X-ray diffraction, and consists of monomeric cis-[PdCl₂(HL¹)] molecules. The palladium centre has a typical square planar geometry, with a slight tetrahedral distortion. The tetra-coordinated metal atom is bonded to one pyridine nitrogen, one pyrazolic nitrogen and two chloro ligands in a cis disposition. The ligand HL¹ is not completely planar.     

Equilibrium and structure of thallium(III)–ethylenediamine complexes in pyridine solution and in solid

The formation of three [Tl(en)_n]³⁺ complexes (n=1–3) in a pyridine solvent has been established by means of ²⁰⁵Tl and ¹H NMR. Their stepwise stability constants based on concentrations, K_n=[Tl(en)_n ³⁺]/{[Tl(en)_n−1 ³⁺]·[en]}, at 298 K in 0.5 M NaClO₄ ionic medium in pyridine, were calculated from ²⁰⁵Tl NMR integrals: log K₁=7.6±0.7; log K₂=5.2±0.5 and log K₃=2.64±0.05. Linear correlation between both the ²⁰⁵Tl NMR shifts and spin–spin coupling ²⁰⁵Tl–¹H versus the stability constants has been found and discussed. A single crystal with the composition [Tl(en)₃](ClO₄)₃ was synthesized and its structure determined by X-ray diffraction. The Tl³⁺ ion is coordinated by three ethylenediamine ligands via six N-donor atoms in a distorted octahedral fashion.     

The propensity of alkoxide and aryloxide derivatives of tungsten carbonyls to aggregate in solution. Synthesis and X-ray structures of dinuclear, trinuclear and tetranuclear complexes derived from the MeOW(CO)5 anion

The complex [Et₄N][W(CO)₅OMe] (1) has been prepared from the reaction of the photochemically generated W(CO)₅THF adduct and [Et₄N][OH] in methanol. Complex 1 was shown to undergo rapid CO dissociation in THF to quantitatively provide the dimeric dianion, [W(CO)₄OMe]₂²⁻. The resulting THF insoluble salt [Et₄N]₂[W(CO)₄OMe]₂ (2) has been structurally characterized by X-ray crystallography, with the doubly bridging methoxide ligands being in an anti configuration. Complex 2 was found to subsequently react with excess methoxide ligand in a THF slurry to afford the face-sharing octahedron complex [Et₄N]₃[W₂(CO)₆(OMe)₃] (3) which contains three doubly bridging methoxide groups. In the absence of excess methoxide ligand complex 2 cleanly yields the tetrameric complex [Et₄N]₄[W(CO)₃OMe]₄ (4) which has been structurally characterized as a cubane-like arrangement with triply bridging μ³-methoxide groups and W(CO)₃ units. Although complex 3 was not characterized in the solid state, the closely related glycolate derivative [Et₄N]₃[W₂(CO)₆(OCH₂CH₂OH)₃] (5) was synthesized and its structure determined by X-ray crystallography. The trianions of complex 5 are linked in the crystal lattice by strong intermolecular hydrogen bonds. Crystal data for 2: space group P2₁/n, a = 7.696(2), b = 22.019(4), c = 9.714(2) Å, β = 92.22(3)°, Z = 4, R = 6.43%. Crystal data for 4: space group Fddd, a = 12.433(9), b = 24.01(2), c = 39.29(3) Å, Z = 8, R = 8.13%. Crystal data for 5: space group P2₁2₁2₁, a = 11.43(2), b = 12.91(1), c = 29.85(6) Å, Z = 8, R = 8.29%. Finally, the rate of CO ligand dissociation in the closely related aryloxide derivatives [Et₄N][W(CO)₅OR] (R = C₆H₅ and 3,5-F₂C₆H₃) were measured to be 2.15 × 10⁻² and 1.31 × 10⁻³ s⁻¹, respectively, in THF solution at 5°C. Hence, the value of the rate constant of 2.15 × 10⁻² s⁻¹ establishes a lower limit for the first-order rate constant for CO loss in the W(CO)₅OMe⁻ anion, since the methoxide ligand is a better π-donating group than phenoxide.