NMR kinetic study of ligand exchange on a (µ-oxo)bis(µ-acetato)diruthenium(III) complex. A special kinetic case of introduction of a more labile ligand

1997 ◽  
Vol 75 (6) ◽  
pp. 890-898 ◽  
Author(s):  
Joana Mara Santos ◽  
Cecília Cipriano ◽  
Roberto B. Faria ◽  
J. Daniel Figueroa-Villar
Keyword(s):  
Ligand Exchange ◽  
Chemical Shifts ◽  
Variable Temperature ◽  
Forward Direction ◽  
Reverse Direction ◽  
H Nmr ◽  
Diruthenium Complex ◽  
Solvent Substitution ◽  
Kinetics Of ◽  
Oxo Bridge

We have prepared the new [Ru2(μ-O)(μ-O2CCH3)2(4-pic)6](PF6)2 complex and followed the kinetics of exchange of the 4-picoline ligands, trans to the oxo bridge, with dimethyl sulfoxide (DMSO-d6) by 1H NMR at 30, 40, 50, and 60 °C. The 1H NMR spectra of this complex in DMSO gradually change in the acetyl methyl region as solvent substitution of the 4-picoline trans to the oxo bridge takes place. This substitution is in accordance with the lability of the ligands trans to the RuIII-O-RuIII bridge in this kind of complex. The kinetic data fit in a series of double reversible reactions, pseudo first order in the forward direction and second order in the reverse direction, with ΔH≠ = 115, 105, 116, and 106 kJ mol−1 and ΔS≠ = 35.7, 17.2, 38.8, and 16.9 JK−1 mol−1 associated with k1, k−1, k2, and k−2 rate constants, respectively.[Formula: see text]A, B and C stand for the nonexchanged, monoexchanged, and diexchanged complexes, respectively. The large ΔH≠ and positive ΔS≠ values agree with the dissociative nature of the mechanism in both forward and reverse reactions. The differences in 1H and I3C NMR chemical shifts of the three complexes are explained in terms of the effect of the ligand exchange on the N—Ru bond lengths and the geometry of the dimetal core. It is evident from our data that the exchange on one metallic site modifies the reactivity at the other site in this kind of dinuclear complex. Keywords: diruthenium complex, variable temperature NMR, ligand exchange kinetics.

A NMR Study of the Exchange Kinetics of the Nonamethylimidodiphosphoramide with its Complexes of Diamagnetic Cations

1978 ◽  
Vol 33 (6) ◽  
pp. 684-685 ◽  
Author(s):  
P. R. Rubini ◽  
L. Rodehüser ◽  
J.-J. Delpuech
Keyword(s):  
Nmr Spectroscopy ◽  
Ligand Exchange ◽  
H Nmr ◽  
Nmr Study ◽  
Exchange Kinetics ◽  
Monodentate Ligands ◽  
Kinetics Of

Abstract The ligand exchange on nonamethylimidodiphosphoramide (NIPA) complexes is found to be very slow comparatively to analogous monodentate ligands; the rates determined by 1H or 31P NMR spectroscopy are: k(25°C)=4.3 × 10-2 s-1; 31.6 s-1 • M-1; 3.7 × 104 S-1 • M-1 and 1.35 × 104 s-1 · M-1 for Mg2+, Ca2+, Sr2+ and Li+ cations respectively. For the Al3+, Ga3+, In3+ and Be2+ ions no exchange could be detected by 1H NMR spectroscopy up to 120 °C, indicating rates lower than about 10-3 s-1

Four- and five-step kinetic models of lactate dehydrogenase

1976 ◽  
Vol 54 (10) ◽  
pp. 915-918 ◽  
Author(s):  
Uwe Borgmann ◽  
Keith J. Laidler ◽  
Thomas W. Moon
Keyword(s):  
Lactate Dehydrogenase ◽  
Forward Direction ◽  
Reverse Direction ◽  
Similar Data ◽  
State Data ◽  
Incomplete Model ◽  
Step Model ◽  
The Relationship ◽  
Kinetics Of ◽  
Different Sources

A five-step model for the reaction catalyzed by beef heart lactate dehydrogenase (EC 1.1.1.27) reconciles differences observed in the four-step model if pre-steady-state data in the forward direction are compared with similar data in the reverse direction. The relationship between the four- and five-step models indicates what problems can develop when an incomplete model is proposed. Nevertheless, there are advantages to using the less complicated four-step model when comparing the molecular kinetics of enzymes catalyzing the same reaction but obtained from different sources.

scholarly journals Kinetics of ligand exchange between a uranium(IV) β-diketonate and free β-diketone

1977 ◽  
Vol 55 (20) ◽  
pp. 3559-3561 ◽  
Author(s):  
G. Folcher ◽  
N. Keller ◽  
C. Kiener ◽  
J. Paris
Keyword(s):  
Ligand Exchange ◽  
Free Ligand ◽  
Exchange Mechanism ◽  
First Order ◽  
H Nmr ◽  
Coordination Site ◽  
Exchange Kinetics ◽  
Kinetics Of

The intermolecular ligand exchange kinetics between a uranium(IV) β-diketonate and free β-diketone were studied by 1H nmr as a function of temperature and concentration. The reaction was found to be of first order in both chelate and free ligand. The results suggest that the exchange mechanism involves a ninth coordination site in the uranium(IV) chelate.

Mechanistische Untersuchungen zum reversiblen Gleichgewicht von metallorganischen Tripeldecker- und Sandwichkomplexen des Typs [Bis{(η5-CpR)Co}-μ-{η4:η4-aren}] und [(η5-CpR)Co(η6-aren)] / Mechanistic Studies towards the Reversible Equilibrium between Metal Organic Triple Decker and Sandwich Complexes [Bis{(η5 -CpR)Co}-μ-{η4 :η4-arene}] and [{(η5-CpR)Co(η6-arene)]

1998 ◽  
Vol 53 (11) ◽  
pp. 1267-1272 ◽  
Author(s):  
Jörg J. Schneider ◽  
Dirk Wolf
Keyword(s):  
Ligand Exchange ◽  
Sandwich Complexes ◽  
Valuable Metal ◽  
H Nmr ◽  
Synthetic Utility ◽  
Metal Organic ◽  
Arene Ligand ◽  
Benzene Toluene

The arene ligand exchange mechanism of slipped arene triple deckers [Bis{(η5-CpR)Co}-μ-{η4:η4-arene}] (R = Me5, 1,2,4 tri-tert butyl, arene = benzene, toluene) 1 was studied by 1H-NMR spectroscopy for different concentrations and solvents. It has been found that triple deckers of type 1 decompose slowly in solution. A unique equilibrium, between these triple deckers and the mixed sandwich complexes [(η6-arene)Co(η5-CpR)] and 14 e [(η5-Cp)Co]solv fragments generated in situ by decomposition o f 1 exists. In addition to this equilibrium arene lability of the thus formed mixed sandwich complex type has been detected by NMR making slipped triple deckers 1 ideal single source compounds for the generation of two [(η5-Cp)Co] fragments in one reaction step. Such fragments are valuable metal ligand components with high synthetic utility in organometallic chemistry.

scholarly journals 13C and 1H NMR Spectra of Synthetic (25R)-5α-Spirostanes

1999 ◽  
Vol 23 (1) ◽  
pp. 48-49
Author(s):  
Martín A. Iglesias Arteaga ◽  
Carlos S. Pérez Martinez ◽  
Roxana Pérez Gil ◽  
Francisco Coll Manchado
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
1H Nmr Spectra ◽  
H Nmr ◽  
C 23 ◽  
Main Effects ◽  
Nmr Signals

The assignment of 13C and 1H NMR signals of synthetic (25 R)-5α-spirostanes is presented; the main effects on chemical shifts due to substitution at C-23 are briefly discussed.

High field 1H NMR Studies of Sol-Gel Kinetics

1986 ◽  
Vol 73 ◽  
Author(s):  
Bruce D. Kay ◽  
Roger A. Assink
Keyword(s):  
Equilibrium Distribution ◽  
Sol Gel ◽  
Nmr Studies ◽  
H Nmr ◽  
Rate Limiting Step ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Product Species ◽  
Rate Limiting ◽  
Kinetics Of

ABSTRACTHigh resolution 1H NMR spectroscopy at high magnetic fields is employed to study the reaction kinetics of the Si(OCH3)4:CH3OH:H2O sol-gel system. Both the overall extent of reaction as a function of time and the equilibrium distribution of species are measured. In acid catalyzed solution, condensation is the rate limiting step while in base catalyzed solution, hydrolysis becomes rate limiting. A kinetic model in which the rate of hydrolysis is assumed to be independent of the adjacent functional groups is presented. This model correctly predicts the distribution of product species during the initial stages of the sol-gel reaction.

scholarly journals A bipyridine-ligated zinc(II) complex with bridging flavonolate ligation: synthesis, characterization, and visible-light-induced CO release reactivity

2017 ◽  
Vol 73 (9) ◽  
pp. 703-709 ◽  
Author(s):  
Shayne Sorenson ◽  
Marina Popova ◽  
Atta M. Arif ◽  
Lisa M. Berreau
Keyword(s):  
Visible Light ◽  
Ligand Exchange ◽  
Distorted Octahedral Geometry ◽  
Conductivity Measurements ◽  
Bidentate Coordination ◽  
H Nmr ◽  
Distorted Octahedral ◽  
Spectroscopic Identification ◽  
Synthetic Models ◽  
Weak Coordination

Metal–flavonolate compounds are of significant current interest as synthetic models for quercetinase enzymes and as bioactive compounds of importance to human health. Zinc–3-hydroxyflavonolate compounds, including those of quercetin, kampferol, and morin, generally exhibit bidentate coordination to a single ZnII center. The bipyridine-ligated zinc–flavonolate compound reported herein, namely bis(μ-4-oxo-2-phenyl-4H-chromen-3-olato)-κ3 O 3:O 3,O 4;κ3 O 3,O 4:O 3-bis[(2,2′-bipyridine-κ2 N,N′)zinc(II)] bis(perchlorate), {[Zn2(C15H9O3)2(C10H8N2)2](ClO4)2} n , (1), provides an unusual example of bridging 3-hydroxyflavonolate ligation in a dinuclear metal complex. The symmetry-related ZnII centers of (1) exhibit a distorted octahedral geometry, with weak coordination of a perchlorate anion trans to the bridging deprotonated O atom of the flavonolate ligand. Variable-concentration conductivity measurements provide evidence that, when (1) is dissolved in CH3CN, the complex dissociates into monomers. 1H NMR resonances for (1) dissolved in d 6-DMSO were assigned via HMQC to the H atoms of the flavonolate and bipyridine ligands. In CH3CN, (1) undergoes quantitative visible-light-induced CO release with a quantum yield [0.004 (1)] similar to that exhibited by other mononuclear zinc–3-hydroxyflavonolate complexes. Mass spectroscopic identification of the [(bpy)2Zn(O-benzoylsalicylate)]+ ion provides evidence of CO release from the flavonol and of ligand exchange at the ZnII center.

scholarly journals Protected Gold Nanoparticles with Thioethers and Amines As Surrogate Ligands

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
M. Rafiq H. Siddiqui
Keyword(s):  
Gold Nanoparticles ◽  
Variable Temperature ◽  
Size Control ◽  
Analytical Techniques ◽  
High Resolution Electron Microscopy ◽  
Phase Method ◽  
Two Phase ◽  
H Nmr ◽  
Resolution Electron ◽  
Vis Spectroscopy

Dodecyl sulfide, dodecyl amine, and hexylamine were shown to act as surrogate ligands (L) via metastable gold nanoparticles. By collating analytical and spectroscopic data obtained simultaneously, empirical formula Au24L was assigned. These impurity-free nanoparticles obtained in near quantitative yields showing exceptional gold assays (up to 98%Au) were prepared by a modification of the two-phase method. Replacement reactions on the Au24L showed that Au:L ratios may be increased (up to Au55:L (L= (H25C12)2S)) or decreased (Au12:L (L= H2NC12H25and H2NC6H13)) as desired. This work encompassing the role of analytical techniques used, that is, elemental analysis, variable temperature1H NMR, FAB mass spectrometry, UV-Vis spectroscopy, thin film X-ray diffraction, and high-resolution electron microscopy (HREM) has implications in the study of size control, purity, stability, and metal assays of gold nanoparticles.

scholarly journals N.M.R. studies of ligand exchange on acetylacetonatotrimethylplatinum(IV)

1975 ◽  
Vol 28 (4) ◽  
pp. 759 ◽  
Author(s):  
NS Ham ◽  
JR Hall ◽  
GA Swile
Keyword(s):  
Activation Energy ◽  
Quantitative Analysis ◽  
Ligand Exchange ◽  
Variable Temperature ◽  
Order Reaction ◽  
First Order Reaction ◽  
First Order ◽  
Cdcl3 Solution ◽  
Made In

A quantitative analysis of the variable-temperature 1H N.M.R. spectra of acetylacetonatotrimethyl-platinum(IV) has been made. In CDCl3 solution the exchange of acetylacetonate ligands is a first-order reaction and proceeds predominantly by dissociation of the dimer into two separated five-coordinate activated complexes. The activation energy is 61.5 � 0.8 kJ mol-1.

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