NMR Spectra (nmr + spectrum)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of NMR Spectra

  • high-resolution nmr spectrum
  • proton nmr spectrum
  • solid-state nmr spectrum
  • two-dimensional nmr spectrum

  • Selected Abstracts

    Identification of Chiral cis- and trans- 2-Stannyloxazolidines by Their NMR Spectra and Solid-State Structures

    Jean-Christophe Cintrat
    Abstract The assignment of cis and trans configurations in N -protected 4-substituted 2-tributylstannyl-1,3-oxazolidines by NMR has been achieved through the use of extrapolations of Karplus,Kitching-type relationships for 3J(119Sn,C,Z,13C) to establish the shape of the oxazolidine ring. Examination of 3J(H,H) allowed the determination of torsion angles for the substituents on C4 and C5, discrimination being completed by comparison of the H2 chemical shifts, together with the 2J(Sn,C,H2) values. The validity of the method was subsequently corroborated by comparison of the results obtained for the liquid phase with those obtained from radiocrystallographic structures of triphenylstannyl analogues or DFT calculations on trimethylstannyl analogues. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    NMR Spectra of Terminal Oxo Gold and Platinum Complexes: Relativistic DFT Predictions,

    ANGEWANDTE CHEMIE, Issue 6 2010
    Alessandro Bagno Prof.
    NMR-Orakel: Relativistische Dichtefunktionalverfahren bilden eine zuverlässige Grundlage für Vorhersagen über die 195Pt-, 183W- und 17O-NMR-Spektren von Pt- und Au-Komplexen mit terminalen Oxoliganden (siehe Bild: [P2W20O70Au(O)(OH2)3]9,: Au,gelb, W,blau, P,orange, O,rot, N,blau, H,weiß). Die Komplexe verfügen über sehr kleine HOMO-LUMO-Abstände, und beide Orbitale sind je an einem MO-Fragment lokalisiert. [source]

    Syntheses, Crystal Structures, UV-Vis Spectra and First NMR Spectra of New Potassium Salts of Chalcogenogermanates.

    CHEMINFORM, Issue 52 2007
    Maike Melullis
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    A Computational and Experimental Study of the Structure and Raman and 77Se NMR Spectra of SeX3+ and SeX2 (X: Cl, Br, I): FT-Raman Spectrum of (SeI3)[AsF6].

    CHEMINFORM, Issue 23 2005
    J. Mikko Rautiainen
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    ChemInform Abstract: Synthesis, Crystal Structures, and Vibrational Spectra of [Pt(N3)6]2- and [Pt(N3)Cl5]2- , 195Pt and 15N NMR Spectra of [Pt(N3)nCl6-n]2- and [Pt(15NN2)n (N215N)6-n]2- , n = 0,6.

    CHEMINFORM, Issue 25 2001
    S. Schroeder
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Toward the Complete Prediction of the 1H and 13C NMR Spectra of Complex Organic Molecules by DFT Methods: Application to Natural Substances

    Alessandro Bagno Prof.
    Abstract The NMR parameters (1H and 13C chemical shifts and coupling constants) for a series of naturally occurring molecules have been calculated mostly with DFT methods, and their spectra compared with available experimental ones. The comparison includes strychnine as a test case, as well as some examples of recently isolated natural products (corianlactone, daphnipaxinin, boletunone B) featuring unusual and/or crowded structures and, in the case of boletunone B, being the subject of a recent revision. Whenever experimental spectra were obtained in polar solvents, the calculation of NMR parameters was also carried out with the Integral Equation-Formalism Polarizable Continuum Model (IEF-PCM) continuum method. The computed results generally show a good agreement with experiment, as judged not only by statistical parameters but also by visual comparison of line spectra. The origin of the remaining discrepancies is attributed to the incomplete modeling of conformational and specific solvent effects. [source]

    Computational Study of 19F NMR Spectra of Double Four Ring-Containing Si/Ge-Zeolites

    CHEMPHYSCHEM, Issue 5 2006
    Angeles Pulido
    Abstract 19F NMR chemical shifts are calculated in order to study the F, environment in double four ring (D4R) containing Si/Ge-zeolites. The calculations with the DFT/CSGT/B3PW91 methodology yielded an agreement within 2 ppm with respect to the experimental peaks corresponding to the D4R units containing 8Si0Ge, 7Si1Ge and 0Si8Ge of the octadecasil zeolite. The optimisation of the 7Si1Ge-, 6Si2Ge-, 5Si3Ge- and 4Si4Ge-D4R units with DFT/B3LYP methodology shows that a covalent GeF bond is formed and therefore a Ge atom in the D4R is pentacoordinated. The displacement of the fluoride ion towards a Ge atom in the Ge-containing D4R units locates four Si/Ge atoms in the close vicinity of the F, and this makes possible a rationalization of the 19F NMR signals in groups according to the number of Si (n) and Ge (m) atoms in the nearest F, environment, F,SinGem (where n+m=4). Thus, the calculated chemical shifts show that higher values are observed when the number of Ge atoms in the nearest F, environment increases. [source]

    Fingerprints of Damped Quantum Rotation Observed in Solid-State Proton NMR Spectra

    CHEMPHYSCHEM, Issue 4 2006
    Peter Gutsche Dr.
    Abstract 1H NMR spectra of the methyl group in an oriented crystal sample of methylmalonic acid with all three non-methyl protons replaced by deuterons are interpreted in terms of the damped quantum rotation (DQR) theory of NMR line shapes. The DQR approach offers a perfect theoretical reproduction of the observed spectra while the conventional Alexander-Binsch line-shape model shows evident defects in the present case. The temperature trends of the quantities characterizing the coherent and incoherent dynamics of the methyl group in the DQR approach (the effective tunnelling frequency and two coherence-damping rates) derived from the spectra are fairly reproduced using a model reported previously. The present findings provide further evidence of limitations to the validity of the common belief that molecular rate processes in condensed phases are necessarily classical. [source]

    The Anomalous Deuterium Isotope Effect in the NMR Spectrum of Methane: An Analysis in Localized Molecular Orbitals

    CHEMPHYSCHEM, Issue 9 2008
    Stephan P. A. Sauer Prof. Dr.
    Anomaly explained: The secondary isotope effect on the carbon,hydrogen indirect nuclear spin,spin coupling constant in methane, which is larger than the primary isotope effect, is explained in terms of contributions to the coupling constant from localized molecular orbitals. [source]

    Nuclear magnetic moments from NMR spectra,Experimental gas phase studies and nuclear shielding calculations

    Karol Jackowski
    Abstract NMR spectra of gaseous compounds and quantum chemical calculations are combined to determine new accurate values of magnetic dipole moments for a series of nuclei. We have analyzed shielding constants, resonance frequencies, and nuclear magnetic moments for a group of simple molecules. The chemical shifts and resonance frequencies are measured at 300 K and extrapolated to the zero-density limit in order to remove all the intermolecular effects from the experimental parameters. The absolute shielding constants in the studied molecules are obtained from ab initio calculations. Assuming the proton magnetic moment as the reference, we determine the nuclear magnetic moments of 13C, 14N, 15N, 17O, 19F, 29Si, 31P, 33S, and 73Ge. The new nuclear magnetic moments are consistent with the experimental NMR parameters, and using these new values one can for the first time predict successfully the shielding constant of a nucleus in a molecule when the corresponding resonance frequency is known. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 246,260, 2007. [source]

    Generalized treatment of NMR spectra for rapid chemical reactions

    Matthew D. Christianson
    Abstract Application of NMR spectroscopy to fast irreversible reactions (t1/2 < 0.7 s) has been hampered by limitations in instrumentation and general methods for modeling the complicated spectra that result. Analytical descriptions of nuclear spin dynamics during fast reactions, first solved by Ernst and coworkers, are limited to first-order reaction kinetics. We demonstrate that numeric methods enable simulation of NMR spectra for fast reactions having any form of rate law. Simulated stopped-flow NMR spectra are presented for a variety of common kinetic scenarios including reversible and irreversible reactions of first and second-order, multistep reactions, and catalytic transformations. The simulations demonstrate that a wealth of mechanistic information, including reaction rates, rate laws, and the existence of intermediates, is imbedded in a single NMR spectrum. The sensitivity of modern NMR instrumentation along with robust methods for simulating and fitting kinetic parameters of fast reactions make stopped-flow NMR an attractive method for kinetic studies of fast chemical reactions. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 165,183, 2007. [source]

    HR-MAS NMR spectroscopy in the characterization of human tissues: Application to healthy gastric mucosa

    Luisa Schenetti
    Abstract The HR-MAS is an ideal technique for the investigation of intact tissue specimens (10,50 mg) and permits the obtainment of spectra with a resolution comparable to that observed in solution in a time that does not exceed a half of an hour for a routine analysis. The potentialities of HR-MAS NMR spectroscopy in the identification of the metabolites characterizing the healthy gastric mucosa are here presented. The direct inspection of the 1D 1H NMR spectra enables only few metabolites to be confidently assigned, and the use of selected 2D experiments strongly amplify the analytical effectiveness of the technique. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 430,443, 2006 [source]

    Alignment and structural analysis of membrane polypeptides by 15N and 31P solid-state NMR spectroscopy

    Burkhard Bechinger
    Abstract In contrast to solution NMR spectroscopy, where complete or almost complete averaging leads to isotropic values, the anisotropic character of nuclear interactions is apparent in solid-state NMR spectra. The orientation dependence of chemical shift and dipolar or quadrupolar interactions has been used to obtain dynamic as well as angular information from polypeptides that strongly interact with phospholipid bilayers. This article illustrates the advantageous characteristics of the anisotropic 15N or 31P chemical shift interactions that in a direct manner allow one to obtain information on the alignment of helical polypeptides or of phospholipid head groups with respect to the membrane normal. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 18A: 130,145, 2003 [source]

    Maximum likelihood constrained deconvolution.

    I: Algorithm, qualitative, quantitative enhancement in synthetic two-dimensional NMR spectra
    Abstract The maximum likelihood method is a constrained iterative spectral deconvolution technique in which a spectral fitting model is determined by minimizing the variance of fit in the time domain in a nonlinear iterative manner. Application of this method to synthetic 2-dimensional (2-D) NMR spectra, which have heavily overlapped multiplets associated with low signal to noise ratios, yields contrast-enhanced spectra with simultaneous noise suppression and resolution improvement. This protocol greatly facilitates peak recognition and often partitions overlapping multiplets into individual components, leading to a more accurate interpretation of resonance frequencies, coupling constants, and multiplets than does the conventional apodization or Fourier transform method. These advantages are useful for constructing reliable 3-D molecular structures for complex molecular systems. © 2002 Wiley Periodicals, Inc. Concepts Magn Reson 14: 402,415, 2002 [source]

    Crystal structures and spectroscopic characterization of chiral and racemic 4-phenyl-1,3-oxazolidin-2-one

    S. Kitoh
    Abstract Crystal structures of (R)- and (rac)-4-phenyl-1,3-oxazolidin-2-one (4-POO) have been determined by X-ray diffraction and characterized by the solid state 13C NMR and IR spectra. Molecular geometries and intermolecular interactions in (R)- and (rac)-4-POO crystals are very similar to each other; 4-POO molecules are linked via the N-H,O intermolecular hydrogen bonds to form the chained structure. Chemical shifts of the solid state 13C NMR spectra are very similar to each other, whereas the 1H spin-lattice relaxation times (T1H) value for (R)-4-POO is five times as large as that for (rac)-4-POO, reflecting the more restricted mobility of the (R)-4-POO chain. Although both crystals contain an unique molecule in the asymmetric unit, a doublet feature is observed for the C=O stretching mode in the IR spectra of (R)- and (rac)-4-POO crystals. The frequency gap of the C=O bands are correlated with the strength of the dipole-dipole interactions between the neighboring C=O groups. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [source]

    Macrocyclic Receptor Showing Improved PbII/ZnII and PbII/CaII Selectivities

    Raquel Ferreirós-Martínez
    Abstract Herein we report on the macrocyclic receptor N,N,-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-15-crown-5 (H2bp15c5) and its coordination properties towards ZnII, CdII, PbII, and CaII. The stability constants of these complexes determined by pH-potentiometric titration at 25 °C in 0.1 M KNO3 vary in the following order: PbII > CdII >> ZnII > CaII. As a result, bp15c5 presents very important PbII/ZnII and PbII/CaII selectivities. These results are in contrast to those reported for the related receptor derived from 1,7-diaza-12-crown-4, which provides very similar complex stabilities for ZnII and PbII. The X-ray crystal structure of [Cd(Hbp15c5)]+ shows heptadentate binding of the ligand to the metal ion, with two oxygen atoms of the macrocyclic unit remaining uncoordinated. The 1H NMR spectra of the complexes formed with PbII, ZnII, and CaII (D2O) show very broad peaks in the region 2,5 ppm, indicating an important degree of flexibility of the crownmoiety in these complexes. On the contrary, the 1H and 13C NMR spectra recorded for the CdII complex are well resolved and could be fully assigned. A detailed conformational investigation using theoretical calculations performed at the DFT (B3LYP) level predict a minimum energy conformation for [Cd(bp15c5)] that is very similar to that observed in the solid state. Analogous calculations performed on the [M(bp15c5)] (M = Zn or Pb) systems predict hexadentate binding of the ligand to these metal ions. In the case of the PbII complex our calculations indicate that the 6s lone pair is stereochemically active, which results in a hemidirected coordination geometry around the metal ion. The minimum energy conformations calculated for the ZnII, CdII, and PbII complexes are compatible with the experimental NMR spectra obtained in D2O solution. [source]

    Solid-State and Solution Structure of Lanthanide(III) Complexes with a Flexible Py-N6 Macrocyclic Ligand

    Cristina Núñez
    Abstract Lanthanide complexes of a hexaaza macrocyclic ligand containing a pyridine head unit (L) were synthesized (Ln = La,Lu, except Pm). The solid-state structures of the corresponding La, Ce, Pr, Nd, and Lu complexes were determined by single-crystal X-ray crystallography, and they reveal the presence of three different mononuclear complexes with three different conformations of the macrocycle and coordination environments around the metal ions. In all complexes the lanthanide ion is coordinated in an endomacrocyclic manner to the six nitrogen donor atoms of the ligand. In the La, Ce, and Pr complexes the metal ions show a 12-coordinate mononuclear environment in which 3 nitrate anions coordinate in a bidentate fashion. However, in the Nd analogue the metal ion displays a 10-coordinated environment with the coordination of 2 bidentate nitrate groups, whereas Lu shows a 9-coordinate environment interacting with 2 nitrate ligands, one of them acting as bidentate and the second one coordinating in a monodentate fashion. The 1H and 13C NMR spectra of the complexes recorded in CD3CN suggest that the complexes adopt in solution a similar structure to that observed for the Nd complex in the solid state. The [Ln(L)(NO3)3] and [Ln(L)(NO3)2]+ complexes were characterized by density functional theory (DFT) calculations (B3LYP model). The structures obtained from these calculations for La, Ce, Pr, and Nd are in good agreement with the experimental solid-state structures. The relative stabilities of the [Ln(L)(NO3)2]+ complexes with respect to the [Ln(L)(NO3)3] ones (Ln = La, Nd, Gd, Ho, or Lu) were studied both in vacuo and in acetonitrile solution (PCM model) at the same computational level. Our calculations indicate that in solution the [Ln(L)(NO3)2]+ species is the most stable one along the whole lanthanide series, in agreement with the NMR spectroscopic data.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Synthesis and Structure Determination of Selenium(IV) Cyanides

    Stefanie Fritz
    Abstract The reaction of SeF4 with Me3SiCN did not result in thepreparation of the designated Se(CN)4 but Se(CN)F3 and Se(CN)2F2 were obtained as first known selenium(IV)cyanide compounds and characterized by their NMR spectra. Se(CN)2F2 was crystallized as 1,2-dimethoxyethane solvate as well as the corresponding tellurium compound Te(CN)2F2 with very similar structures. NMR spectroscopic data of some more miscellaneous tellurium cyanides and the crystal structures of solvates of Se(CN)2 and oxygen-bridged TeO(CN)2 are presented. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Dynamic Stereochemical Behaviour of Congested Ruthenium(II) Complexes Containing Asymmetric Thioether Ligands Based on Pyridine and Pyrimidine

    Giuseppe Tresoldi
    Abstract The asymmetric thioethers L [L = 2-pyridylmethyl 2,-pyrimidyl sulfide (pps) and 2-(4-methylpyrimidyl) 2,-pyridylmethyl sulfide (mps)] reacted with cis -[RuCl2(N,N -L,)2] [L, = di-2-pyridyl sulfide (dps); 2,2,-bis(4-methylpyridyl) sulfide (4mdps); 2,2,-bis(5-methylpyridyl) sulfide (5mdps)] to give the five-membered-ring chelate complexes [Ru(N,N -L,)2(Npyridine,S -L)]++ as the major products (92,95,%). Because the sulfur and ruthenium atoms are stereogenic centres, with (R) and (S) and , and , configurations, respectively, four isomers, including the enantiomers were obtained. At low temperature and in the methylene region of the 1H NMR spectra, two AB systems due to the enantiomer couples ,S ,R (a) and ,R ,S (b) were observed with abundances of 77,89 and 6,18,%, respectively. Furthermore, NMR spectroscopic investigations showed that the hybrid polydentate ligands L change their coordination mode. Thus, although a and b largely predominate, a mixture of species containing L and the Ru(N,N -L,)2 unit in the ratio 1:1 are present. The four-membered-ring chelate complexes [Ru(N,N -L,)2(Npyrimidine,S -L)]++ (c), as minor species (abundance 1,8,%), are always observed, whereas the dinuclear species [{Ru(N,N -L,)2}2(,-L)2]+4 (d, e) are observed when L, = dps or 5mdps. In these cases, four AB systems are assigned to dinuclear species d and e containing two bridging L that act as Npyridine,S- or Npyridine,Npyrimidine -donor ligands. The 1H NMR spectra are temperature dependent in that at low temperature the complexes undergo inversion of the chiral centre of the coordinated sulfur atom (a [rlhar2] b) and the dimer (d, e) and monomer (c) are in equilibrium; at higher temperatures the complexes undergo a structural dynamic rearrangement, which involves exchange between the coordinated and uncoordinated N atoms (b [rlhar2] c). One-dimensional band-shape analysis of the exchanging methylene and methyl proton signals showed that the energy barriers for inversion of the sulfur centre are in the 50,53 kJ,mol,1 range, whereas those for the higher-temperatures process are in the 62,68 kJ,mol,1 range. The possible mechanisms of the processes are discussed. NMR spectroscopic findings suggest that inversion at the sulfur centre occurs without any bond rupture, whereas the exchange, at higher temperatures (b [rlhar2] c), is a dissociative process involving the breaking of a Ru,Npyridine bond.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Variable Coordination Modes of Benzaldehyde Thiosemicarbazones , Synthesis, Structure, and Electrochemical Properties of Some Ruthenium Complexes

    Swati Dutta
    Abstract Reaction of benzaldehyde thiosemicarbazones [H2LR, where H2 stands for the two protons, the hydrazinic proton, and the phenyl proton at the ortho position, with respect to the imine function and R (R = OCH3, CH3, H, Cl, and NO2) for the para substituent] with [Ru(PPh3)2(CO)2Cl2], carried out in refluxing ethanol, afforded monomeric complexes of type [Ru(PPh3)2(CO)(HLR)(H)]. The crystal structure of the [Ru(PPh3)2(CO)(HLNO2)(H)] complex was determined. The thiosemicarbazone ligand is coordinated to the ruthenium center as a bidentate N,S-donor ligand forming a four-membered chelate ring. When the reaction of the thiosemicarbazones with [Ru(PPh3)2(CO)2Cl2] was carried out in refluxing toluene, a family of dimeric complexes of type [Ru2(PPh3)2(CO)2(LR)2] were obtained. The crystal structure of [Ru2(PPh3)2(CO)2(LCl)2] was determined. Each thiosemicarbazone ligand is coordinated to one ruthenium atom, by dissociation of the two protons, as a dianionic tridentate C,N,S-donor ligand, and at the same time the sulfur atom is also bonded to the second ruthenium center. 1H NMR spectra of the complexes of both types are in excellent agreement with their compositions. All the dimeric and monomeric complexes are diamagnetic (low-spin d6, S = 0) and show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry of the [Ru(PPh3)2(CO)(HLR)(H)] and [Ru2(PPh3)2(CO)2(LR)2] complexes show the ruthenium(II),ruthenium(III) oxidation within 0.48,0.73 V vs. SCE followed by a ruthenium(III),ruthenium(IV) oxidation within 1.09,1.47 V vs. SCE. Potentials of both the oxidations are found to correlate linearly with the electron-withdrawing character of the substituent R. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    The Detection of PHIP Effects Allows New Insights into the Mechanism of Olefin Isomerisation during Catalytic Hydrogenation

    Alessandra Viale
    Abstract PHIP (parahydrogen-induced polarisation) effects in the 1H NMR spectra of the products of Rh-complex-catalysed alkyne hydrogenation brings to light the fact that the cis,trans isomerisation of the formed olefin occurs through the formation of a ,-bonded intermediate stabilised by the reversible addition of a hydrogen molecule at the metal centre. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Nitroamino Triazoles: Nitrogen-Rich Precursors of Stable Energetic Salts

    Yangen Huang
    Abstract 1-Nitroamino-1,2,3-triazole (5) was synthesized and its zwitterionic structure was established using single-crystal X-ray diffraction. The calculated detonation properties for 4-nitroamino-1,2,4-triazole (2) (P = 33.4 GPa, vD = 8793 m/s) and 1-nitroamino-1,2,3-triazole (5) (P = 33.0 GPa, vD = 8743 m/s) are comparable with RDX. A new family of energetic salts 7,21 based on either the 1-nitroamino-1,2,3-triazolate or the 4-nitroamino-1,2,4-triazolate anion were prepared and characterized by vibrational spectroscopy (IR), multinuclear NMR spectra, elemental analyses, density, TGA and DSC. The heats of formation (,fH°298) and detonation properties for these stable salts were calculated using Gaussian 03 and Cheetah 4.0, respectively. Comparison of the properties of the 1,2,3- and 1,2,4-triazolate salts indicates that while the 1,2,4-derivatives are more stable thermally, the 1,2,3-analogs invariably have higher heats of formation. In contrast to its salts, 1-nitroamino-1,2,3-triazole (5) is extremely shock-sensitive with an impact sensitivty of <1 J. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Syntheses and Fluxional Processes of Diphenyl(2-thienyl)phosphane Derivatives of Triosmium Clusters

    Nitsa K. Kiriakidou Kazemifar
    Abstract Thermal treatment of [Os3(CO)12] with diphenyl(2-thienyl)phosphane, Ph2P(C4H3S), results in the formation of [Os3(CO)12,x{Ph2P(C4H3S)}x] (x = 1,3, 1,3), but no C,H bond activation was observed. Reaction of [H2Os3(CO)10] with diphenyl(2-thienyl)phosphane at ambient temperature affords [HOs3(,-H)(CO)10{Ph2P(C4H3S)}] (4), but when the samereaction is repeated at elevated temperatures, the cyclometallated species [(,-H)Os3(CO)9{,3 -Ph2P(C4H2S)}] (5) and[(,-H)Os3(CO)8{,3 -Ph2P(C4H2S)}{Ph2P(C4H3S)}] (6) are formed. In addition, two more products, tentatively assigned as [(,-H)Os3(CO)6{,3 -Ph2P(C4H2S)}{,-Ph2P(C4H3S)}{Ph2P(C4H3S)}] (7) and [(,-H)Os3(CO)7{,-Ph2P(C4H2S)}{,-Ph2P(C4H3S)}{Ph2P(C4H3S)}] (8) are obtained. The dynamic behaviours of 2, 5 and 6 have been studied by variable-temperature (VT) 1H and 31P{1H} NMR spectroscopy. The VT 31P{1H} NMR spectra of [Os3(CO)10{Ph2P(C4H3S)}2] (2) demonstrate that a mixture of two isomers, which are in rapid exchange at room temperature, is present and that the less common cis - trans isomer, whose structure has been determined by X-ray crystallography, is favoured for this cluster. The VT 1H NMR spectra of 5 indicate the presence of two isomers which are proposed to arise from an oscillation of the ,,,2 -vinyl group of the thienyl moiety between two metal atoms. A similar fluxional process is proposed to occur in 6 and the assignment of the room-temperature structure(s) of this cluster was confirmed by 1H- 187Os 2D HMQC spectroscopy. In addition to 2, the solid-state structures of 3, 5 and 6 have been determined by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Synthesis and Structural Characterisation of Palladium and Group-12 Metal Complexes with a Hybrid Phosphanylphosphonate Ferrocene Ligand


    Abstract Diethyl [1,-(diphenylphosphanyl)ferrocenyl]phosphonate (1) was synthesised by stepwise metallation/functionalisation of 1,1,-dibromoferrocene and studied as a ligand for palladium(II) and group-12 metals. Treatment of [PdCl2(cod)] (cod = ,2:,2 -cycloocta-1,5-diene) with 1 in 1:1 or 1:2 molar ratios gave, respectively, the dinuclear, chloride-bridged complex [{Pd(,-Cl)Cl(1 -,P2)}2] (2) and the mononuclear complex trans -[PdCl2(1 -,P2)2] (3), where 1 coordinates exclusively through the phosphane function. The reactions between 1 and group-12 metal bromides MBr2 in a 1:1 molar ratio gave the adducts [MBr2(1)] [M = Zn (4), Cd (5), and Hg (6)], whose crystal structures change considerably with the metal ion. Thus, whereas 4 is a molecular complex with 1 coordinating as an O1,P2 -chelate, its cadmium(II) analogue is a polymer built up from symmetric {CdBr(,-Br)}2 units interconnected by pairs of O1,P2 -bridging phosphanylphosphonate ligands. Finally, the mercury(II) complex 6 is a halide-bridged dimer, [{Hg(,-Br)Br(1 -,P2)}2]. However, this compound is structurally fluxional in solution (NMR spectra) and, in the crystal, it attains a structure similar to 5 owing to weak interactions between mercury and phosphonate-O1 atoms from adjacent molecules. An isomer to 6, [{HgBr2(1 -,2O1,P2)}2] (7), was isolated from attempted alkylation of 6 and structurally characterised as a dimer, where ligands 1 bridge two {HgBr2} units. All compounds were studied by spectroscopic methods (IR, NMR, mass) and the solid-state structures of 1, 2·,H2O, 3·4,CHCl3, 4, 5, 6·5,C6H6, and 7 have been determined by single-crystal X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Monophosphanylcalix[6]arene Ligands: Synthesis Characterization, Complexation, and Their Use in Catalysis

    Yasushi Obora
    Abstract Novel phosphanylcalix[6]arenes having mono- O -diphenylphosphanylmethyl (3) and mono- O -(4-diphenylphosphanylphenyl)methyl substituents (5) have been synthesized. The structures of these monophosphanylcalix[6]arenes were determined by NMR spectroscopy, mass spectrometry, and X-ray crystal structure analysis. The X-ray structure reveals that 3 adopts a flattened 1,2,3-alternate conformation in the crystalline state, while the NMR spectra show that 3 and 5 have a cone conformation in solution. Structure optimization and energy calculations for 3 and 5 at the B3LYP/LANL2DZ-CONFLEX5/MMFF94s level of theory show that the cone conformation is slightly more stable than the 1,2,3-alternate conformation by 0.36 kcal,mol,1 for 3 and 0.96 kcal,mol,1 for 5. Complexation of 3 with [PtCl2(COD)] and [Rh(COD)2]BF4 gives cis -coordinated [PtCl2(3)2] and [Rh(COD)(3)2]BF4, respectively. The X-ray analysis of [PtCl2(3)2] shows that 3 adopts a cone conformation upon complexation. Combination of 3 and 5 with [Rh(COD)2]BF4 provides an active catalyst for the hydroformylation of a variety of terminal alkenes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Synthesis, Characterization, and Electrochemical Properties of Dinuclear Complexes Assembled from Asymmetric CoIII Bis(dioximates) and Boronic Acids

    Renata Dreos
    Abstract Bis(methylphenylglyoximate)cobalt(III) complexes exist both as cis and trans isomers due to the asymmetry of the equatorial ligand, and, when the axial ligands are different, the trans isomer is chiral. The reaction of racemic trans -[CH3Co(mpgH)2py] (1) with either 3- or 4-pyridylboronic acid affords dimeric units arranged on a crystallographic symmetry center such that the pyridyl nitrogen of one moiety coordinates to the Co atom of the symmetry-related unit. In principle, three structurally different dimeric species (two homodimers and one heterodimer) can be obtained. Time-resolved 1H NMR spectra of a 1:1 mixture of racemic 1 and either 3- or 4-pyridylboronic acid in CDCl3/CD3OD show that the reaction does not converge toward a unique species in solution. Nevertheless, X-ray structures show that the heterochiral dimers are the only products that crystallize from the reaction mixture. The nature of the dioximate side groups does not affect the geometry of the dimeric arrangements assembled by 4-pyridylboronic acid ("molecular box"). On the contrary, the geometry of the species assembled by 3-pyridylboronic acid varies from the "molecular parallelogram" obtained from the bis(dimethylglyoximates) to the highly squeezed "molecular box" obtained from bis(methylphenylglyoximates). Cyclic voltammetry studies show that the metal centers in the dimeric species do not interact with each other and undergo a simultaneous redox process. However, depending on the geometry of the systems, the redox process involves a single four-electron reduction for 3 and 5 or two consecutive two-electron reduction steps for 4 and 6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Characterization by NMR Spectroscopy, X-ray Analysis and Cytotoxic Activity of the Ruthenium(II) Compounds [RuL3](PF6)2(L = 2-Phenylazopyridine or o -Tolylazopyridine) and [RuL'2L"](PF6)2(L', L" = 2-Phenylazopyridine, 2,2'-Bipyridine)

    Anna C. G. Hotze
    Abstract Tris(ligand) complexes [RuL3](PF6)2 (L = 2-phenylazopyridine or o -tolylazopyridine) and mixed ligand [RuL'2L"](PF6)2 (L' and L" are 2-phenylazopyridine or 2,2'-bipyridine) have been synthesized, structurally characterized and investigated for cytotoxic activity. These complexes are important to study the hypothesis that the compound ,-[Ru(azpy)2Cl2] (azpy = 2-phenylazopyridine) exhibits a high cytotoxicity due to its two cis chloride ligands, which might be exchanged for biological targets as DNA. Molecular structures of mer -[Ru(azpy)3](PF6)2 (1) and mer -[Ru(tazpy)3](PF6)2 (5) (tazpy = o -tolylazopyridine) have been determined by X-ray diffraction. Series of complexes [RuL3](PF6)2 and [RuL'2L"](PF6)2 show interesting NMR spectroscopic data; e.g. the spectrum of mer -[Ru(azpy)3](PF6)2 (1) shows extremely broadened resonances at room temp. but sharpened resonances at low temperature. In the 1H NMR spectra of compounds [Ru(azpy)2(bpy)]2+ and [Ru(bpy)2(azpy)]2+ (bpy = 2,2-bipyridine), respectively, less broadened (room temp.) or completely sharp resonances (room temp.) occur in comparison to 1 (under same conditions). By selecting the right temperature and/or concentration, NMR spectra of these series of compounds have been resolved using 2D COSY and NOESY NMR spectroscopy. Remarkably, the cytotoxicity data against a series of human tumor cell lines (A498, EVSA-T, H226, IGROV, M19, MCF-7 and WIDR) show a moderate cytotoxicity for these series of tris(ligand) complexes. So, even though no chloride ligands are present in these tris(ligand) complexes, a considerable cytotoxic activity is observed. This would imply that the 2-phenylazopyridine ruthenium(II) complexes act by a completely different mechanism than the well-known cisplatin. This finding is important, because an anticancer compound acting via a different mechanism is a prerequisite in designing new anticancer drugs. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Bis(fluoromesityl) Palladium Complexes, Archetypes of Steric Crowding and Axial Protection by ortho Effect , Evidence for Dissociative Substitution Processes , Observation of 19F,19F Through-Space Couplings

    Camino Bartolomé
    Abstract Bisarylated complexes trans -[Pd(Fmes)2(SR2)2] [Fmes = 2,4,6-tris(trifluoromethyl)phenyl (fluoromesityl); SR2 = SMe2, tht; tht = tetrahydrothiophene] are precursors for various bisarylated fluoromesityl palladium(II) complexes by ligand-substitution reactions. Boiling under reflux in acetonitrile gives the mixed complexes trans -[Pd(Fmes)2(NCMe)(SR2)], whereas boiling under reflux in toluene leads to trans -[PdCl2L2] (L = PMe3, tBuNC, pTol-NC, 4-MePy), in the presence of neutral monodentate ligands, or to (NnBu4)[trans -Pd(Fmes)2I(SR2)] when treated with (NnBu4)I. trans -[Pd(Fmes)2(SMe2)2] reacts with bidentate ligands, also boiling under reflux in toluene, to give [Pd(Fmes)2(L,L)] [L,L = Me2bipy, 2,2, - biquinolyl, ,2N,N, -OCPy2, dppm (Ph2PCH2PPh2), dppe (Ph2PCH2CH2PPh2), pte (PhSCH2CH2SPh), ,2S,N -SPPh2Py, ,2O,N -OPPhPy2], or the bimetallic complex [Pd(Fmes)2(,-1,N:1,2,O:2,N -Py2MeCO)Pd(Fmes)(SMe2)] (characterized by X-ray diffractometry) when treated with (OH)(CH3)CPy2. The crowding associated with two Fmes groups produces several interesting features: (1) trans complexes are preferred over cis complexes, against the expected electronic preferences; (2) the low-temperature NMR spectra of several complexes, or the X-ray diffraction structure of [Pd(Fmes)2(2,2, - biquinolyl)], reveal significant structural distortions associated with steric crowding; (3) the need for boiling under reflux in the synthesis suggests a dissociative substitution mechanism, which is unknown so far for Pd; (4) some of the complexes show 19F,19F through-space couplings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Tellurated Schiff Bases Formed from {2-[(4-Methoxyphenyl)telluro]ethyl}amine and Bis(2-aminoethyl) Telluride with o -Hydroxyacetophenone: Synthesis and Complexation Reactions with HgII, PdII and RuII , Crystal Structures of the Ligands, [Ru(p -cymene)Cl{H2NCH2CH2TeC6H4 -4-OCH3}]Cl·H2O and [RuCl{4-MeOC6H4TeCH2CH2NHCH(CH3)C6H4 -2-O,}]

    Raghavendra Kumar P.
    Abstract {2-[(4-Methoxyphenyl)telluro]ethyl}amine and bis(2-aminoethyl) telluride on treatment with o -hydroxyacetophenone gave the Schiff bases 4-MeOC6H4TeCH2CH2N=C(CH3)C6H4 -2-OH (L1) and 2-HOC6H4(CH3)C=NCH2CH2TeCH2CH2N=C(CH3)C6H4 -2-OH (L3), respectively. The reduction of L1 and L3 with NaBH4 resulted in 4-MeOC6H4TeCH2CH2NHCH(CH3)C6H4 -2-OH (L2) and 2-HOC6H4(CH3)CHNHCH2CH2TeCH2CH2NHCH(CH3)C6H4 -2-OH (L4), respectively, which have 1 or 2 chiral centers. The 1H and 13C NMR spectra of L1 to L4 were found to be characteristic. Treatment of L1 with [Ru(p -cymene)Cl2]2 resulted in [Ru(p -cymene)(4-MeOC6H4TeCH2CH2NH2)Cl]Cl·H2O (1) whereas in the reaction of L2 with [Ru(p -cymene)Cl2]2, the p -cymene ligand is lost resulting in [RuCl(L2 -H)] (4). The reactions of L1, L3 and L4 with HgBr2 resulted in complexes of the type [HgBr2·(L)2] while Na2PdCl4 reacted with L1 to give [PdCl(L1 -H)]. The solid-state structures of L1, L3, 1 and 4 were determined by single-crystal X-ray diffraction studies. The very swift formation of the tellurated amine from a tellurated Schiff base (L1) by hydrolysis has been observed for the first time and has resulted in 1. The Ru,N and Ru,Te bond lengths in 1 are 2.142(3) and 2.6371 (4) Å, respectively. The replacement of the p -cymene ligand with a hybrid organotellurium ligand (L2 -H), resulting in 4, is also a first example of its kind. The Ru center in 4 has a square-planar geometry, with the Ru,N, Ru,Te, Ru,O and Ru,Cl bond lengths being 2.041(6), 2.4983(8), 2.058(5) and 2.308(2) Å, respectively. In the crystals of 4 there are secondary intermolecular Te···Cl interactions and intermolecular N,H···O hydrogen bonds. This is the first example in which coordinated Te in a complex is engaged in two intermolecular secondary interactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Application of Gel-Phase 195Pt NMR Spectroscopy in a Novel Solid-Phase Synthesis of a Primary Amine Dichloroplatinum(II) Complex

    Marc S. Robillard
    Abstract Gel-phase 195Pt NMR spectroscopy of dichloroplatinum peptide complexes attached to a solid support is described. The observed 195Pt chemical shifts of the support-bound platinum complexes are in good agreement with the solution-state 195Pt NMR spectra of the soluble and deprotected analogs. This non-destructive analytical method for on-resin-compound analysis was applied in the optimization of the solid-phase synthesis of the primary amine dichloroplatinum complex 6, which represents a new class of platinum complexes now available via solid-phase synthetic chemistry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]