Open-chain Complexes Research Articles

Piperazine-Based N4-Type 16-Membered Macroheterocycles and Their Nickel(II) Complexes

Square-planar diamagnetic nickel(II) complexes 5a and 5b containing 16-membered diamino-diimino ligands were prepared from the corresponding open-chain complexes 2a and 2b via condensation with o-phthalic dialdehyde in methanol. The solid-state structure of the starting complex 2b revealed the cisoid conformation of aryl groups compared to the transoid one found in the case of 2a. At the same time, the cisoid conformation is not retained in acetone solution: rather, the tert-Bu-substituted complex 2b was fully transformed into the trans form whereas its analogue 2aexhibits both cis and transforms in acetone solution. The cisoid conformation was also observed for the cyclic structures 5a and 5b by X-ray analysis and VT NMR experiments. The borohydride reduction of 5a with subsequent cyanide-assisted removal of nickel led to a new 16-membered tetraazamacrocycle 6. Its X-ray structure showed a cisoid conformation supported by two intramolecular hydrogen bonds that was also sustained in solution. VT NMR experiments revealed the degenerative interconvertion of a macrocycle with activation energy ca. 41.9±0.8 kJ/mol.

Open-chain and crown ether-substituted bimetallic ruthenium vinyl complexes: synthesis, characterization, and electrochemical studies

Two open-chain and closed-crown ether-substituted binuclear ruthenium vinyl complexes (E,E)-[{(PMe3)3-(CO)ClRu}2(μ-HC=CH–Ar–CH = CH)], in which the 1,4-diethenylphenylene bridge bears two different crown groups at the 2,3-positions, have been prepared and characterized by spectroscopic methods and by cyclic voltammetry. In addition, the X-ray crystal structure of complex 7a was determined. The electrochemical studies showed that both complexes undergo two successive one-electron oxidation processes, and the closed-crown complex better stabilized the mixed valence bimetallic ruthenium complex.

Cyclopentadienyl Ruthenium(II) Complexes with Bridging Alkynylphosphine Ligands: Synthesis and Electrochemical Studies

The reaction of [CpRuCl(PPh(3))(2)] (Cp = cyclopentadienyl) and [CpRuCl(dppe)] (dppe = Ph(2)PCH(2)CH(2)PPh(2)) with bis- and tris-phosphine ligands 1,4-(Ph(2)PC[triple bond]C)(2)C(6)H(4) (1) and 1,3,5-(Ph(2)PC[triple bond]C)(3)C(6)H(3) (2), prepared by Ni-catalysed cross-coupling reactions between terminal alkynes and diphenylchlorophosphine, has been investigated. Using metal-directed self-assembly methodologies, two linear bimetallic complexes, [{CpRuCl(PPh(3))}(2)(mu-dppab)] (3) and [{CpRu(dppe)}(2)(mu-dppab)](PF(6))(2) (4), and the mononuclear complex [CpRuCl(PPh(3))(eta(1)-dppab)] (6), which contains a "dangling arm" ligand, were prepared (dppab =1,4-bis[(diphenylphosphino)ethynyl]benzene). Moreover, by using the triphosphine 1,3,5-tris[(diphenylphosphino)ethynyl]benzene (tppab), the trimetallic [{CpRuCl(PPh(3))}(3)(mu(3)-tppab)] (5) species was synthesised, which is the first example of a chiral-at-ruthenium complex containing three different stereogenic centres. Besides these open-chain complexes, the neutral cyclic species [{CpRuCl(mu-dppab)}(2)] (7) was also obtained under different experimental conditions. The coordination chemistry of such systems towards supramolecular assemblies was tested by reaction of the bimetallic precursor 3 with additional equivalents of ligand 2. Two rigid macrocycles based on cis coordination of dppab to [CpRu(PPh(3))] were obtained, that is, the dinuclear complex [{CpRu(PPh(3))(mu-dppab)}(2)](PF(6))(2) (8) and the tetranuclear square [{CpRu(PPh(3))(mu-dppab)}(4)](PF(6))(4) (9). The solid-state structures of 7 and 8 have been determined by X-ray diffraction analysis and show a different arrangement of the two parallel dppab ligands. All compounds were characterised by various methods including ESIMS, electrochemistry and by X-band ESR spectroscopy in the case of the electrogenerated paramagnetic species.

Comparative study of the physicochemical properties of six clinical low molecular weight gadolinium contrast agents

This paper compares the physicochemical properties of six low molecular weight clinical complexes of gadolinium studied under identical experimental conditions. Magnevist, Dotarem, Omniscan, ProHance, MultiHance and Gadovist were investigated by oxygen-17 relaxometry at different temperatures and by proton relaxometry at various magnetic fields, temperatures and media [pure water, zinc(II)-containing aqueous solutions and HSA-containing solutions]. Osmolality, viscosity and stability versus transmetallation by zinc(II) ions were added for a more comprehensive description. The relaxivities of the clinical formulations as measured in water are similar in the imaging magnetic field region, with a slightly better performance for MultiHance. This can be explained by a shorter distance between the hydrogen nuclei of the water molecule bound to the Gd(3+) ion and this paramagnetic centre. In contrast to the open-chain complexes, all macrocyclic systems (Dotarem, ProHance and Gadovist) are insensitive to transmetallation by zinc ions. The stability of the open-chain complexes with respect to transmetallation depends on the chemical structure of the ligand, with a better stability for MultiHance. The presence of human serum albumin has no significant effect on the proton relaxivity of Magnevist, Dotarem, Omniscan, ProHance and Gadovist but markedly increases the relaxivity of MultiHance because of a non-covalent interaction with the protein. As a result, the relaxivity of MultiHance in HSA-containing media of fixed concentration decreases with increasing concentration of the contrast agent.

Diversity in the structural chemistry of (phosphine)gold(I) 1,3,4-thiadiazole-2,5-dithiolates (bismuthiolates I).

A series of dinuclear (phosphine)gold(I) complexes of the ambidentate 1,3,4-thiadiazoledithiolate ligand (SSS) were prepared in high yield from the corresponding (phosphine)gold(I) chlorides and K(2)(SSS) in methanol. While mononuclear components (R(3)P)AuCl with R(3) = Ph(3), Ph(2)Py, or Me(3) (1-3) gave open-chain complexes, the dinuclear components ClAu(Ph(2)P-E-PPh(2))AuCl with E = (CH(2))(6), (C(5)H(4))Fe(C(5)H(4)), or 1,4-CH(2)C(6)H(4)CH(2) afforded cyclic complexes (4-6). The products have been characterized by analytical and spectroscopic methods, and the crystal structures of 1-4 have been determined by single-crystal X-ray techniques. Crystals of 1 [(CH(2)Cl(2))(2)] and 2 (CH(2)Cl(2)) contain the molecules aggregated in strings with long and probably very weak intermolecular Au.S contacts. The P-Au-S groups are aligned parallel head-to-tail and shifted in opposite directions to reduce steric conflicts, thus ruling out aurophilic Au...Au bonding. By contrast, in crystals of 3 (CH(2)Cl(2)) with smaller tertiary phosphine ligands, the molecules are aggregated via short [3.0089(3) and 3.1048(5) A] and probably strong aurophilic bonding to give a two-dimensional network with tetranuclear units formed from four (Me(3)P)AuS moieties of four different molecules as the connecting elements. In these tetranuclear units [(Me(3)P)AuS-](4), the P-Au-S axes are rotated against each other ("crossed swords") by 108.5 degrees (P2-Au2...Au2'-P2') or 116.9 degrees (P2-Au2...Au1'-P1'), respectively, to minimize steric conflicts. There is also significant bending of the P-Au-S axes to bring the metal atoms closer together: P1-Au1-S1 = 171.88(8) degrees and P2-Au2-S2 = 165.52(8) degrees. In the crystals of the cyclic complex 4 which contain no solvent molecules, the molecular units are aggregated in strings with short closed-shell interactions between the gold atoms of neighboring molecules [3.1898(3) A]. Because of the metallocyclic structure, the shielding of the gold atoms is reduced to allow aurophilic bonding as the P-Au-S groups are rotated against each other (crossed) by a dihedral angle P-Au...Au-P of 74.6 degrees.

Synthesis, structure and spectroscopic properties of nickel(II) macrocyclic and open-chain complexes resulted from 1-phenyl-butane-1,3-dione mono- S-methylisothiosemicarbazone template self-condensation

Self-condensation of 1-phenyl-butane-1,3-dione mono- S-methylisothiosemicarbazone ( 6) in the presence of nickel(II) acetate in methanol gives rise to a mixture of two complexes: [2,9-bis(methylthio)-5,13-dimethyl-7,14-diphenyl-1,3,4,8,10,11-hexaazacyclotetradeca-2,4,6,9,11,13-hexaenato(2-) N 1, N 4, N 8, N 11]nickel(II) ( 7) and [1-amino-1,6-bis(methylthio)-4,9-dimethyl-11-phenyl-2,3,4,7,8-pentaazaundeca-1,3,6,8,10-pentaenato(-)-11-olato(-) N 2, N 4, N 8, O]nickel(II) ( 8). Both the macrocyclic complex 7 and the open-chain chelate 8 are characterised by X-ray diffraction methods, which reveal their square-planar structure. Electronic, IR, NMR, electron impact mass spectra and cyclic voltammograms of new compounds are also reported.

Structural changes of hydrogen bonded hexagonal trimers upon ionization

Hexagonal trimers, (QH) 3, formed from the monomers QH=(NH 3, H 2O, and HF) are investigated by ab initio quantum chemical geometry optimizations. All trimers have three hydrogen bonds, which decrease in length as the electronegativity of Q increases. The structures of the cations, ( QH) 3 +, are also determined. The hexagonal structure of the trimers is absent in the cations, which have two hydrogen bonds of shorter length than found in the trimer. The length of the hydrogen bonds in the cations decrease with increasing electronegativity of Q. The structures of the cations may be described as open chain complexes of the form Q–[HQH] +–QH.

1H T1 and T2 measurements of the MR imaging contrast agents Gd-DTPA and Gd-DTPA BMA at 1.5T.

We report in vitro T1 and T2 relaxation studies for the open-chain complexes Gd-DTPA and Gd-DTPA BMA. Measurements were performed on phantoms containing aqueous and plasma solutions of different concentrations by MR imaging in a 1.5T superconducting whole-body scanner. Longitudinal relaxation times T1 were evaluated from serial turbo-FLASH experiments for concentrations less than 1 mM, whereas for larger concentrations the values were obtained from a standard inversion recovery (IR) sequence. Transverse relaxation times T2 were determined using multi-echo spin-echo MRI protocols. The T1 and T2 relaxivities of the nonionic Gd-DTPA BMA are similar to those of the Gd-DTPA. The temperature dependencies of the relaxivities were determined over a temperature interval ranging from 21 to 50 degrees C and were found to be slightly different for the two contrast agents. In the case of Gd-DTPA BMA a larger deviation of the expected temperature behavior of the relaxivities was observed as compared with Gd-DTPA. Deviations from a strictly linear dependence of relaxation times on temperature were found at lower concentrations in aqueous solutions. In plasma solutions a high T1/T2 ratio was observed for low concentrations, which decreased monotonically with increasing concentrations.

Soluble and supported carbonylation catalysts derived from rhodium-phosphonate-phosphane complexes

Phosphonate-phosphanes form both chelate and open-chain complexes with rhodium, which can easily be converted into each other. This property has been used in the development of new and efficient carbonylation catalysts. During the catalytic cycle, the phosphane group is assumed to be coordinated to the transition metal, while the phosphoryl-oxygen of the phosphonate group is supposed to change between a free and a coordinated state, thus vacating or occupying a coordination site. IR studies support the hemilabile behaviour of surface Rh-complexes under the reaction conditions. Activation enthalpies, obtained for hemilabile rhodium catalysts in homogeneous methanol carbonylation, increased significantly with growing distance between phosphonate and phosphane group. Attempts of preparing stable rhodium complex catalysts adsorbed on silica or alumina for slurry-phase or vapour-phase carbonylations failed. Activated carbon has been shown to be a suitable support for hemilabile rhodium complexes, but normal diffusion of reactants begins to limit the carbonylation rate over the supported catalysts.

Hemilabile Phosphonate-Phoshane Complexes of Rhodium and Iridium -Synthesis and Catalytical Properties

Abstract New phosphonate-phosphane ligands la-d1 were converted into the Rh and Ir complexes 2a-d and 3a-c. The open-chain Rh complexes 2a-d are more effective catalysts for liquid-phase MeOH-carbonylation with respect to known bisphosphane and phosphane-monoxide phosphane complexes [Rh(CO)L1]n, [Rh(cod)L2] (L1: Ph2P(CH2)2PPh2, Ph2P(CH2)3PPh2; L2: Ph2P(CH2)2PPh2).

Gold(I)-Purine Interactions: Synthesis and Characterization of Cyclic and Open Chain Polynuclear Gold(I) Complexes Containing Xanthine Derivatives and Bis(phosphine) as Bridging Ligands. Crystal Structures of [Au(2)(&mgr;-HX)(&mgr;-dmpe)].3H(2)O and [Au(2)(&mgr;-TT)(&mgr;-dmpe)].H(2)O (H(3)X = Xanthine; H(2)TT = 8-Mercaptotheophylline).

The reaction of [(AuBr)(2)(&mgr;-PR(2)P(CH(2))(n)()PR(2))] (where R = CH(3) for n = 1; R = Ph for n = 1, 3, 4) with N-alkylxanthine and thioxanthine derivatives, containing two ionizable protons in close positions, yields, under basic conditions, neutral heterobridged dinuclear gold(I) ring complexes [Au(&mgr;-L)(2)(&mgr;-PR(2)P(CH(2))(n)()PR(2))], which have been investigated by means of (1)H- and (31)P-NMR and FAB spectroscopies. Crystal structures of two of these complexes are reported. [Au(2)(&mgr;-HX)(&mgr;-dmpe)].3H(2)O (1) (H(3)X = xanthine; dmpe = 1,2-bis(dimethylphosphine)ethane) crystallizes in the monoclinic space group P2(1)/n with a = 9.348(2) Å, b = 8.656(2) Å, c = 24.585(5) Å, beta = 98.24(2) degrees, Z = 4, and R = 0.040. [Au(2)(&mgr;-TT)(&mgr;-dmpe)].H(2)O (2) crystallizes in the monoclinic space group P2(1)/n with a = 10.853(4) Å, b = 14.031(6) Å, c = 13.574(5) Å, beta = 100.80(4) degrees, Z = 4, and R = 0.063. The structures of 1 and 2 are similar and consist of dinuclear nine-membered ring molecules, in which the two linear two-coordinate gold atoms are bridged on one side by a dmpe ligand and on the other side by a bidentate xanthinato dianion, with intramolecular Au.Au distances of 3.053(1) and 2.952 (2) Å, respectively. In the former, the coordination of the xanthinato ligand to the gold atoms takes place through the N3 and N9 nitrogen atoms whereas, in the latter, N7,S8-chelate coordination of the 8-thiotheophyllinato dianion occurs. The magnitude of the Au.Au separation is analyzed in terms of the twisting of the xanthine derivative ligand from the plane containing the gold(I) and phosphorus atoms. For n = 6 the steric requirements of the Au(&mgr;-dpph)Au group prevents the formation of dinuclear ring complexes and open chain complexes are obtained. Finally, when the xanthine derivatives do not contain two close active coordination sites dinuclear open chain complexes are formed.

The template synthesis and characterization of alkaline earth metal ion nitrate macroacyclic Schiff base complexes

The template reaction of 2,6-diacetylpyridine with 1,8-diaminonaphthalene in the presence of calcium(II), strontium(II) and barium(II) nitrates produced the new hexadentate N 4O 2 open-chain complexes as a result of [2 + 1] Schiff base condensation, irrespective of the molar ratio of starting materials used in the synthesis. They were characterized by IR, UV-vis, 1H NMR and analytical data. No [2 + 2] macrocyclic complexes were isolated, either in the template synthesis, nor on the treatment of the [2 + 1] acyclic complexes with diamine.

Stability assessment of gadolinium complexes by P‐31 and H‐1 relaxometry

Longitudinal P-31 relaxation rate enhancements of phosphate groups have been measured at pH 7-7.2 and 310 degrees K on aqueous solutions containing adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pi) and some lanthanide complexes (Gd-DOTA, Gd-HPDO3A, Gd-DO3A, Gd-DTPA, Gd-DTPA-BMA). The macrocyclic complexes induce linear enhancements of the relaxation rates of all phosphorus nuclei. For Gd-DOTA and Gd-HPDO3A, the mechanism of the interaction with the P-31 nuclei seems to be of the outer sphere type and a better efficiency is noted for the "neutral" Gd-HPDO3A. A short-lived ternary complex between Gd-DO3A and the phosphorylated metabolites appears to be formed enabling an inner sphere interaction. In solutions containing the open chain complexes, Gd-DTPA and Gd-DTPA-BMA, P-31 relaxation rates of ATP exhibit significant and nonlinear enhancements that are much larger than those observed for PCr and Pi. A ternary complex involving the lanthanide ion, its original chelator, and the ATP molecule is precluded by various experiments which confirm that the lanthanide ion shifts from the original complexes to the ATP phosphate groups.

Kinetics of the acid dissociation of cyclic and open-chain tetramine complexes of cobalt(II): general acid catalysis with co-ordinating phosphate—citric acid buffers

The kinetics of dissociation of the cobalt(II) complexes of the quadridentate ligands 1.4.8.11-tetraazacyclotetradecane (cyclam), triethylenetetramine (trien) and 2,2′,2″-triaminotriethylamine (tren) was followed spectrophotometrically in the ranges 10 < T < 50 °C and 0.8 < pH < 4.0 in perchloric acid and Mcllvaine phosphate–citrate buffer system, an an ionic strength I= 1.0 mol dm–3, NaClO4. The complexes were prepared in situ in preaerated solutions under a nitrogen atmosphere, by the addition of a 10% excess of the ligand in the form of the free base to a solution of CoCl2·6H2O. The ligand dissociation reaction was then initiated by the addition of perchloric acid or Mcllvaine phosphate-citrate buffer. No dissociation was observed for the cyclam complex in perchloric acid media. It was, however, observed in the buffer and obeyed biphasic kinetics comprising two consecutive first-order steps. The action of the phosphate and/or citrate is attributed to their complexing ability and to their association through hydrogen bonding to the axial aqua ligand, thus bringin the proton closer to the dissociating nitrogen and hence catalysing the dissociation. The dissociation kinetics of the open-chain unbranched trien and the tripod tren was observed in perchloric acid as well as the Mcllvaine buffer system. Except when too fast to follow by conventional spectrophotometry, the reaction obeyed biphasic kinetics comprising two consecutive first-order steps. The tren complex dissociates at a rate 5–10 times faster than that of trien, the first step being too fast to follow except at 10 °C in the buffer system. The observed rate dependence is explained on the basis of mechanisms involving solvation, specific acid catalysis and general acid catalysis. The cyclam complex dissociates at a rate 5–30 times slower than those of the two open-chain complexes. This is attributed to the stabilization due to the hindered rotation of the dissociating nitrogen (entropic effect) and to the higher ligand-field stabilization of the macrocycle (enthalpic effect). Mechanisms covering the entire range of pH studied and conforming to the observed rate laws are given.

X-ray structural and nuclear magnetic resonance study of open chain and macrocyclic thioether complexes

Preparations of the thiophenophane and open chain thioether complexes MX2•BBTE(M = Pd; X = Cl, I)(M = Pt; X = Cl) (BBTE = 1,2-bis(benzylthio)ethane) and MX2•L (M = Pd; X = Cl, Br, I, SCN) (M = Pt; X = Cl) (L = 2,5,8-trithia[9](2,5)thiophenophane) are described. The molecular structure of PdBr2•L which contains a weak thiophene-sulfur-to-palladium interaction has been determined: space group P21/n, a = 8.3569(3), b = 16.3254(15), c = 11.1462(3) Å, β = 92.833(4)°, Z = 4, Rf = 0.060, Rw = 0.058. The electronic, low frequency ir, and 13C nmr spectra are described. Variable temperature 1H nmr spectra are discussed and it is concluded that the open chain complexes undergo rapid conformational exchange at room temperature but are configurationally rigid unless the temperature is increased. In contrast, the macrocyclic complexes undergo very limited conformational and no configurational exchange up to their decomposition temperatures. They are also nonfluxional in the same temperature range. Chemical exchange of acidic ligand hydrogens and a metal–ligand dissociative equilibrium were also detected when X = SCN. Keywords: thiophene, thioether, macrocyclic metal complexes.

ChemInform Abstract: Reactions of Tris[(2S)‐2‐(aminomethyl)pyrrolidine]nickel(II) Ion with Alk‐3‐en‐ 2‐ones or 4‐Hydroxyalkan‐2‐ones: Formation of an Optically Active Tetra‐aza Macrocycle.

AbstractDer aus dem Liganden und Ni‐perchlorat in EtOH dargestellte Titelkomplex (I) reagiert mit dem Butenon (II) bzw. dem Hydroxybutanon (III) über definierte Zwischenprodukte selektiv an der sek. Aminogruppe des Aminomethylpyrrolidins zu zwei offenkettigen Verbindungen (IV) und (V) (zwei Stereoisomere möglich), von denen (IV) mit einem weiteren Butenon den makrocyclischen Komplex (VI) bildet.

Reactions of tris[(2S)-2-(aminomethyl)pyrrolidine]nickel(II) ion with alk-3-en-2-ones or 4-hydroxyalkan-2-ones: formation of an optically active tetra-aza macrocycle

Reactions of [Ni(ampr)3]2+[ampr =(2S)-2-(aminomethyl)pyrrolidine] and several alk-3-en-2-ones or 4-hydroxyalkan-2-ones were carried out, and the resulting nickel(II) complexes separated chromatographically. Structures of the complexes are proposed based on i.r., c.d., proton n.m.r., and elemental analytical data. The products with but-3-en-2-one were a tetra-aza macrocyclic complex and an open-chain complex, where reaction at the secondary amino-group of ampr is selective. The products with 4-hydroxybutan-2-one were the same open-chain complex as above and another open-chain complex. The reactions with 4-methylpent-3-en-2-one and pent-3-en-2-one occurred specifically at the primary amino-group, due to steric repulsions involving the methyl group(s) on the β-carbon, and resulted in open-chain complexes.

Application of the Edwards equation to formation of adducts of Cu(II) open-chain tetraamine complexes with anions

Application of the Edwards equation to formation of adducts of Cu(II) open-chain tetraamine complexes with anions

Chemistry of Dienyl Anions. II. Crystalline Bis(dienyl)magnesium. Selective Dienylation and Structure in Solution and in the Solid State

Abstract Seven different crystalline bis(dienyl)magnesium·TMEDA complexes of open chain or cyclic structure were prepared by metal exchange reaction of corresponding potassium dienides. They are fluxional in solution due to the rapid 1,3-rearrangement. Terminally σ-bonded trans or (E) structure exists primarily in the open chain complexes while centrally σ-bonded cis structure in cyclic dienylmagnesium·TMEDA complexes. The former gave 1,3-dienes exclusively but the latter gave 1,4-dienes upon hydrolysis. Molecular structure of bis(2,4-dimethyl-2,4-pentadienyl)magnesium determined by X-ray crystallography showed that it has terminally σ-bonded structure. Addition of dienylmagnesium compounds to acetone followed by hydrolysis gave 1,4-diene derivatives regioselectively but that to diisopropyl ketone gave 1,3-diene derivatives selectively. Unsaturated alcohols with an elongated carbon chain were synthesized by thermal cracking of cyclic ether complexes. 1,3,7-Trienes can be obtained selectively by reaction of appropriate allyl halides in the presence of CuCl catalyst and regioselective dienylation occurred by using TiCl2(η5-C5H5)2 as catalyst.

ChemInform Abstract: HYDROGEN‐1 AND CARBON‐13 NUCLEAR MAGNETIC RESONANCE STUDIES OF NICKEL(II) COMPLEXES OF UNINEGATIVE QUADRIDENTATE LIGANDS DERIVED FROM DIAMINES AND β‐DIKETONES

AbstractDie Komplexe (I) wurden durch Kondensation von Äthylen‐ oder Propylendiamin mit einem β‐Diketon im Molverhältnis 2: l dargestellt.