Oxime Ligands Research Articles

Study of complex formation with 2-hydroxyiminocarboxylates: specific metal binding ability of 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid

Complex formation properties of a novel water soluble thiazolyloxime 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid (H 3L 1) with Cu 2+ and Ni 2+ were investigated in solution by potentiometrical and spectral (UV–Vis, EPR, NMR) methods. All Cu 2+ and most of Ni 2+ complex species detected in solution were found to have square-planar MN 4 core with oxime and heterocyclic nitrogen atoms which was rationalized in terms of destabilizing effect of repulsive interaction between oxygen atom of carboxylic group and nitrogen atom of thiazole ring in N, O-coordinated ligand conformation. It has been found that stability of metal complexes in a series of oxime ligands is dependent upon basicity of nitrogen atom of oxime group. The thiazolyloxime forms less stable complexes with Cu 2+ but stronger ones with Ni 2+ ions when compared to parent 2-(hydroxyimino)propanoic acid. The lower stability obtained for Cu 2+ complexes was elucidated in terms of negative inductive effect of the thiazole and nitrile substituents as well as an effect of intramolecular attractive interaction between thiazolyl sulfur and oxime oxygen atoms in thiazolyloxime. In the case of Ni 2+ the complexes formed are square-planar and it is why thiazolyl ligand is more effective in metal ion binding than simple 2-(hydroxyimino)propanoic acid forming only octahedral species. The solid state structure of the Co 3+ complex K 3[Co(HL 1) 3]·5.5H 2O ( 1) was studied by X-ray analysis. The thiazolyloxime ligand is coordinated to Co 3+ via oxime nitrogen and carboxylate oxygen atoms forming five-membered chelate rings.

Stabilization of the trivalent oxidation state of copper by tetradentate imine–oxime ligands

Copper(III) complexes stabilized by tetradentate imine-oxime ligands were characterized by elemental analysis, cyclic voltammetry, u.v.-visible, and e.s.r. spectra. Electrode potentials of copper(III/II) couples having five-, six-, five-membered chelate rings are pH-dependent. Copper(III/II) couples with five-, five-, five-membered chelate rings were independent of pH. The magnitude of E 0 1 / 2 is affected by both the size and electron-donor ability of substituent groups.

A linear cyclic oximate-bridged tetracopper(II) complex.

The crystal structure of the title complex, tetrakis[mu-6-amino-3-methyl-4-azahex-3-en-2-one oximato(1-)-kappa4N,N',N":O]tetracopper(II) tetraperchlorate 0.6-hydrate, [Cu4(C6H12N3O)4](ClO4)4*0.6H2O, shows the cation to be an oximate-bridged tetramer composed of four 6-amino-3-methyl-4-azahex-3-en-2-one oxime ligands and four copper(II) ions and to have crystallographically imposed 4 symmetry. Each Cu(II) atom is four-coordinated by the three N atoms of one oxime ligand and by the O atom of another oxime ligand in a distorted square-planar geometry.

New Alkyl−Cobalt(III) Complexes with Tridentate Amino−Oxime Ligands: Synthesis, Structure, and Reactivity

In Figure 1 on page 269 a wrong ORTEP diagram of 2a is shown; the correct ORTEP representation for 2a is given below.

New Alkyl−Cobalt(III) Complexes with Tridentate Amino−Oxime Ligands: Synthesis, Structure, and Reactivity

In Figure 1 on page 269 a wrong ORTEP diagram of 2a is shown; the correct ORTEP representation for 2a is given below.

SPECTRAL STUDIES OF VANADYL(V) AND URANYL(VI) COMPLEXES WITH o-HYDROXYOXIMES

Oxime ligands were synthesized using 2-hydroxy-1-napthaldehyde and 2′,4′-dihydroxy-acetophenone. Vanadyl and uranyl complexes of these oximes were synthesized having the metal:ligand stoichiometry 1:2. The ligands and their metal complexes were characterised for various analytical parameters and spectral features. The structures of these complexes were proposed on the basis of UV-Vis, IR and ESR spectral data.

Formation of folded complexes retaining intramolecular H-bonding in the extraction of nickel(ii) by phenolic oxime and aliphatic diamine ligands

Solvent extraction of NiII by phenolic oximes is enhanced significantly by addition of aliphatic diamines; octahedral [Ni(II)(phenolate-oxime)2(diamine)] complexes have been characterised that contain a novel folded conformation, retaining intramolecular hydrogen bonding between the two oxime ligands.

Synthesis and Study of New Clathrochelates with 1-Phenyl-2-(1′-Piperidinyl) Ethanone Oxime Ligand

The synthesis and characterization of new complex compounds of [M(L-H)X2], [ML(L-H)]X and [M(L-H)2] types (M= Co, Ni, Cu, X = Cl, CH3COO) and L=1-phenyl-2-(1'-piperidinyl) ethanone oxime is presented. In reactions of [ML(L-H)]X (M = Ni, Cu) with Lewis acids like TiCl4 and SnCl4 semiclathrochelates of [M(L-H)2MCl2] type (M′ = Ti, Sn) were obtained and characterized (electronic, FT-IR, RPE, NMR spectra, conductivity measurements, as well as TD-analysis). Such complexes should be potential oxygen molecular carriers.

New Alkyl−Cobalt(III) Complexes with Tridentate Amino−Oxime Ligands: Synthesis, Structure, and Reactivity

The oxidative addition of alkyl halides to the CoI species generated by the reduction of [CoIII(LNHpy)(HLNHpy)](ClO4)2 (1), where HLNHpy is the tridentate 2-(2-pyridylethyl)amino-3-butanone oxime ligand and LNHpy is its conjugate base, led to the formation of a new class of organocobalt complexes of general formula [RCoIII(LNHpy)(HLNHpy)](ClO4) [R = Me (2a), Et (2b), CH2CF3 (2c), nBu (2d), and CH2Cl (2e)]. All the complexes were characterised by 1H and 13C NMR spectroscopy. The X-ray structures of 2a, 2b and 2c provide evidence for a pseudo-octahedral configuration, where HLNHpy and LNHpy act as bi- and tridentate ligands, respectively. The axial geometry in 2a is closer to that found in methylcobalamin than that reported for other models, suggesting steric and electronic cis influences of the equatorial ligands close to those of the corrin nucleus. The solution properties and the reactivity show strong analogies with those of the previously known Vitamin B12 models.

Cis-Bis(bipyridine)(dimethylglyoxime)ruthenium(II): an electrochemical and spectroscopic investigation of proton-coupled electron transfer

Reaction of cis-[Ru(bpy) 2(Cl) 2] (bpy=2,2′-bipyridine) with AgSO 3CF 3 then dimethylglyoxime (dmgH 2) results in the formation of cis-[Ru(bpy) 2(dmgH 2)] 2+. The cis geometry of the complex is confirmed by the asymmetry of the 1H and 13C NMR spectra. The oxime ligand of the isolated complex is doubly protonated, enabling the complex to undergo two acid dissociations with p K a 1 4.60 and p K a 2 7.33. The potential versus pH diagram (Pourbaix diagram) shows that the complex is capable of up to two proton and two electron transfers.

Synthesis and characterization of monomeric and dimeric manganese(II) and zinc(II) complexes of pyridine-2-carbaldoxime

The syntheses and characterization of two complexes of manganese(II) and one complex of zinc(II) with the ligand pyridine-2-carbaldoxime, C6H6N2O, are described. The monomeric manganese(II) complex cis-[Mn(C6H6N2O)2Cl2] (1) crystallizes in the orthorhombic space group Pbcn with 4 formula units in a cell of dimensions a = 12.479(3) Å, b = 10.348(2) Å, and c = 11. 974(2) Å. The structure has been refined to a final value of the conventional R-factor of 0.0330 based on 1513 observed independent reflections. The analogous zinc(II) complex, cis-[Zn(C6H6N2O)2Cl2] (2) also crystallizes in the orthorhombic space group Pbcn with 4 formula units in a cell of dimensions a = 12.215(2) Å, b = 10.383(2) Å, and c = 12. 016(2) Å. The structure has been refined to a final value of the conventional R-factor of 0.0377 based on 1117 observed independent reflections. The two complexes are isostructural, with the central metal atom lying on a crystallographic 2-fold axis. Both complexes are approximately octahedral, the coordination being provided by two trans pyridine nitrogen atoms and two cis amine nitrogen atoms from the oxime ligands, and by two cis chlorides. The dimeric manganese(II) complex [(C6H6N2O)(CH3OH)ClMnCl2MnCl(CH3OH)(C6H6N2O)] (3) crystallizes in the monoclinic space group P21/n with 2 formula units in a cell of dimensions a = 7.895(2) Å, b = 11.196(3) Å, and c = 12. 544(2) Å, and b = 98.39(2)o. The structure has been refined to a final value of the conventional R-factor of 0.0312 based on 1568 observed independent reflections. There is a crystallographic inversion center in the middle of the dimer relating one manganese center to the other. The geometry at each manganese(II) center is again roughly octahedral, coordination being provided by two nitrogen atoms from the oxime ligand, a terminal chloride ion trans to the amine nitrogen, the oxygen atom of the coordinated methanol molecule, and two bridging chlorides that link the two halves of the dimer. The Mn$$$Mn separation is 3.647(1) Å and the bridging Mn-Cl-Mn angle is 91.8(1)o. The temperature dependence of the magnetic susceptibility of 3 exhibits a maximum at approximately 8 K, indicative of a weak antiferromagnetic interaction between the two metal centers with J = 1.94(1) cm-1. The EPR spectrum of 1 diluted into the corresponding Zn(II) host has been fitted to the parameters g = 2.00, A = 0.0084 cm-1, D = 0.157 cm-1, and E = 0.0005 cm-1. The small value of E/D is consistent with the observed symmetry of the complex. (Received January 19, 2000; revised July 6, 2000)Bull. Chem. Soc. Ethiop. 2000, 14(2), 128-142Bulletin of the Chemical Society of Ethiopia. ISSN: 1011-3924

New Coordination Modes of an Oxime Ligand in a Triosmium Cluster. Stabilization by Intra- and Intermolecular C−H···O Hydrogen Bonds

Reaction of the hydroxyamine 7-chloro-4-(hydroxyamino)quinoline with the triosmium cluster Os3(CO)10(NCMe)2 gave the complex (μ-H)Os3(CO)10(μ2-η1-O-C9H6N2Cl) (3), in which a new mode of μ2-η1-O-oximato ligand bridged two osmium centers by an oxygen atom. This complex was slowly converted to (μ-H)Os3(CO)10(μ2-η2-ON-C9H6NCl) (4), where an aromatic C−H moiety in the μ2-η2-ON-oximatoquinoline group formed an unusual short intramolecular C−H···O−N hydrogen bond and an intermolecular C−H···OC hydrogen bond simultaneously. The formation of the intramolecular hydrogen bond may provide a stabilization effect for the generation of the η2-ON complex 4 and a driving force for the transformation of 3 to 4.

Microelectrochemical measurements at expanding droplets (MEMED): investigation of cupric ion stripping kinetics in a two-phase oil/water system

Microelectrochemical measurements at expanding droplets (MEMED) are used as a new approach for investigating the stripping kinetics of metals ions between an organic phase containing an extractant ligand, which complexes the metal ion of interest, and an aqueous acid solution. The approach is illustrated with measurements of the stripping of cupric ion from 1,2-dichloroethane (DCE) droplets containing CuL2 (where L is the oxime ligand, Acorga P50) that are formed periodically through a capillary tip submerged in an aqueous receptor phase containing HCl. First-order dependences of the stripping rate constants on the bulk concentration of CuL2 in the DCE phase (5–20 mmol dm−3) and HCl in the aqueous phase (0.25–2.0 mol dm−3) were found, with an effective bimolecular rate constant of (6.2±1.0)×10−5 cm s−1 M−1. The results obtained demonstrate that the cupric ion stripping process is likely to be heterogeneous, occurring at the immiscible liquid/liquid interface, with the first attack of protons on CuL2 as the rate-limiting step. The prospects for using MEMED more generally to investigate metal extraction/stripping kinetics are discussed.

Ruthenium-mediated reduction of oximes to imines. Synthesis, characterization and redox properties of imine complexes of ruthenium

Reaction of three oxime ligands (oximes of salicylaldehyde (HL1–O), 2-hydroxyacetophenone (HL2–O) and 2-hydroxynaphthylaldehyde (HL3–O); where H stands for the phenolic proton and O for the oxime oxygen) with [Ru(PPh3)3Cl2] in a 1∶1 molar ratio brings about reduction of the oximes to imines and affords complexes of the form [Ru(PPh3)2(L)Cl2], where L stands for the deprotonated imine ligand which is coordinated as a N,O-donor forming a six-membered chelate ring. The structure of the [Ru(PPh3)2(L2)Cl2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is composed of NOP2Cl2 with the two PPh3 ligands in mutually trans and the two chlorides in mutually cis positions. The [Ru(PPh3)2(L)Cl2] complexes are one-electron paramagnetic (low-spin d5, S = 1/2) and show rhombic EPR spectra in 1∶1 dichloromethane–toluene solution at 77 K. In dichloromethane solution the [Ru(PPh3)2(L)Cl2] complexes show several intense LMCT transitions in the visible region, together with a weak ligand field transition near 1700 nm. Cyclic voltammetry on the [Ru(PPh3)2(L)Cl2] complexes shows a ruthenium(III)–ruthenium(II) reduction near −0.4 V vs. SCE and a ruthenium(III)–ruthenium(IV) oxidation in the range 0.88–1.15 V vs. SCE.

On the rational synthesis and properties of exchange-coupled heterotrinuclear systems containing [MAMBMB] and [MAMBMC] cores †

Six new modular linear heterotrinuclear complexes of the types [MAMBMB] and [MAMBMC] with FeIIICuIINiII1, FeIIINiIINiII2, CoIIICuIINiII3, FeIIICuIICuII4, FeIIINiIICuII5 and FeIIIMnIICuII6 cores were synthesized using selective template reactions involving the ligands 1,4,7-trimethyl-1,4,7-triazacyclononane, tmtacn, and N,N′-bis(2-hydroxy-3-hydroxyiminomethyl-5-methylphenylmethylene)-1,3-propanediamine, H4Lox. The complexes were characterised by elemental analysis (C, H, N, and the metals), IR, UV-vis, Mössbauer and EPR spectroscopies and variable temperature and variable field magnetic susceptibility measurements. The crystal structure of 2 was determined by X-ray diffraction. It is comparable to those of the previously published compounds 1 and 3 and consists of high-spin FeIII and six-co-ordinated NiII embedded in the imine–oxime ligand, with an intramolecular Fe⋯Ni distance of 3.79 Å and Ni⋯Ni distance of 3.14 Å. The magnetic behaviour of the compounds is complex and exhibits a predominant antiferromagnetic exchange coupling acting along the pathway dx2 − y2∥sp2∥dx2 − y2∥sp2∥dx2 − y2. The coupling constant JMA-MB ranges from −5 to −20 cm−1, while JMB-MC ranges from −66 to −395 cm−1 (except for JNi-Ni = −21 cm−1). The coupling constant JMA-MC was kept fixed to zero during the fitting procedure. Compounds 1 and 5 with isoelectronic structures exhibit ground and first excited states inverted to one another due to their spin topology.

Diaqua{hydrogen bis[1-(2-pyridyl)ethanone oximato-N,N']}nickel(II) perchlorate hydrate

In the title compound, [Ni(C 7 H 8 N 2 O)(C 7 H 9 N 2 O)(H 2 O) 2 ]ClO 4 .H 2 O, the Ni atom lies on a twofold axis and is in a distorted octahedral environment. The coordination consists of two planar bidentate oxime ligands with cis oxime groups and two trans water molecules above and below this plane. The two oxime molecules have lost one proton to give a very short symmetrical hydrogen bond between the oxime O atoms. The O...O separation is 2.432 (3) A.

Regiospecific Oximato Coordination at the Oxygen Site: Ligand Design and Low-Spin Mn(II) and Fe(II/III) Species.

The (pyridylazo)oxime ligand (C(5)H(4)N)N=NC(=NOH)C(6)H(4)R(p), HRL (R = H, Me), has been synthesized with the objective of promoting the very rare mononuclear oximato-O coordination. The synthesis involves hydrazone nitrosation. HRL reacts with M(ClO(4))(2).6H(2)O, affording [M(RL)(2)] (M = Mn, Fe), and X-ray structure determinations have indeed revealed the presence of the desired oximato-O coordination mode in the distorted octahedral MN(4)O(2) sphere characterized by a 2-fold axis of symmetry relating the two tridentate ligands, all chelate rings being five-membered. The M-N and M-O distances are relatively short (1.84-1.99 Å), consistent with spin-pairing (M = Mn, S = (1)/(2); M = Fe, S = 0). The M-N bond length trend, Mn(II) > Fe(II), is in accord with the larger radius of the low-spin Mn(II) atom. The M-O length order is, however, Mn(II) < Fe(II). This reversal occurs because of the rigidity of the ligand skeleton. Significant M-azo back-bonding is present (N=N length approximately 1.30 Å). [Mn(RL)(2)] displays hyperfine-split axial EPR spectra (g( parallel) approximately 1.98, g( perpendicular) approximately 2.06, A( parallel) approximately 170 G, A( perpendicular) approximately 65 G) in frozen solution as well as in polycrystalline [Fe(RL)(2)] lattices. The quasireversible Fe(III)/Fe(II) couple of [Fe(RL)(2)] has E(1/2) approximately 0.7 V. The oxidized complex [Fe(RL)(2)]PF(6) has been electrosynthesized. It is low-spin (S = (1)/(2)) and displays axial EPR spectra (g( parallel) approximately 1.98, g( perpendicular) approximately 2.14) in frozen solution. The Mn(II) --> Mn(III) oxidation ( approximately 1.0 V) in [Mn(RL)(2)] is irreversible. Crystal data for [Mn(HL)(2)].CH(2)Cl(2): crystal system monoclinic, space group I2/a, a = 14.142(7) Å, b = 10.721(7) Å, c = 16.933(10) Å, beta = 93.01(4) degrees, Z = 4. Crystal data for [Fe(HL)(2)].CH(2)Cl(2): crystal system monoclinic, space group I2/a, a = 14.254(6) Å, b = 10.742(6) Å, c = 16.719(8) Å, beta = 92.35(4) degrees, Z = 4.

Mono- and Trinuclear Nickel(II) Complexes with Sulfur-Containing Oxime Ligands: Uncommon Templated Coupling of Oxime with Nitrile.

4,7-Dithiadecane-2,9-dione dioxime forms both violet and purple-black nickel(II) complexes with unexpected structural properties, quite unlike the square-planar chelates formed by its dithiaundecane homologue. Their perchlorate salts were isolated and examined crystallographically. The lilac product [Ni{(Dtox)(CH(3)CNH)(2)}](ClO(4))(2) entails a bis(iminoether) ligand formed by coupling of the dioxime with two moles of acetonitrile. The purple-black complex results from further ligand deprotonation, to yield trinuclear, antiferromagnetic [Ni(3)(Dtox)(DtoxH)(2)](ClO(4))(2).CH(3)CN, which maintains its structure in solution. The first one-electron electrochemical oxidation step is relatively facile for the trimer, yielding a Ni(2)(II)Ni(III) complex, whereas for [Ni{(Dtox)(CH(3)CNH)(2)}](ClO(4))(2) a transient Ni(I) species is accessible. Comment is made on those properties (coordination number, donor type, core charge) of nickel(II) coordination spheres that affect the accessibility of the corresponding nickel(I) and nickel(III) forms. [Ni(3)(Dtox)(DtoxH)(2)](ClO(4))(2).CH(3)CN crystallizes in the monoclinic space group P2(1)/n, with cell parameters a = 12.295(2) Å, b = 17.360(2) Å, c = 20.764(2) Å, alpha = 90 degrees, beta = 94.080(10) degrees, gamma = 90 degrees, V = 4420.7(6) Å(3), Z = 4. [Ni{(Dtox)(CH(3)CNH)(2)}](ClO(4))(2) crystallizes in the rhombohedral space group R&thremacr;, with cell parameters a = 32.954(2) Å, b = 32.954(2) Å, c = 13.477(2) Å, alpha = 90 degrees, beta = 90 degrees, gamma = 120 degrees, Z = 18.

Synthesis of retinoid X receptor-specific ligands that are potent inducers of adipogenesis in 3T3-L1 cells.

A novel series of oxime ligands has been synthesized that displays potent, specific activation of the retinoid X receptors (RXRs). The oximes of 3-substituted (tetramethyltetrahydronaphthyl)carbonylbenzoic acids are readily available by condensation with hydroxyl- or methoxylamine; alkylation of the hydroxyl oxime provides a variety of analogues. Oximes and variously substituted oxime derivatives demonstrate high binding affinity for the RXRs and specific RXR activation and, hence, are called rexinoids. These oxime rexinoids are activators of the RXR:PPARgamma heterodimer and are potent inducers of differentiation of 3T3-L1 preadipocytes to adipocytes. We have recently reported that ligands which activate the RXR:PPARgamma heterodimer in this manner are effective in the treatment of type II diabetes (non-insulin-dependent diabetes mellitus, NIDDM). Thus, these new oxime rexinoids are potential therapeutic agents for the treatment of metabolic disorders, such as obesity and diabetes.

Unusual coordination mode of a 2-pyridyl ketone oxime ligand in bis(4-butylphenyl 2-pyridyl ketone oximate)palladium(II)

In the complex PdL 2 (HL = 4-butylphenyl 2-pyridyl ketone oxime), characterised by spectroscopic techniques and X-ray diffraction analysis, the deprotonated ligand displays a N,O coordination, with the pyridyl nitrogen and the oxime oxygen, which is without precedence in this class of compounds; 1 H NMR spectra, together with structural data on PdL 2, make it possible to distinguish between the N,O and N,N coordination mode in analogous compounds.