Ligand Substitution Processes Research Articles

Coordination chemistry of semiconductor photoelectrodes: reactions of etched n-gallium arsenide with cobalt(III) complexes

The authors report studies of the reactivity of n-GaAs surfaces with transition-metal complexes. Generally, adsorption of metal ions at semiconductor junctions has been observed to increase carrier trapping rates. A notable exception is the improved performance of n-GaAs interfaces after exposure to acidic aqueous solutions of Ru(III) ions and other metal cations, but little information is available regarding the chemistry of these surface treatments. Except for systems in which metal ions act as precursors for the deposition of metals or metal alloys, no information is available regarding the oxidation state or chemical environment of chemisorbed transition-metal complexes on semiconductor electrodes. Possible but undocumented mechanisms of metal ion attachment to the semiconductor surface include electrostatic binding, ligand substitution processes, and redox reactions. To explore the various possible modes of reaction, they have investigated the chemistry of n-GaAs surfaces in contact with aqueous solutions of Co(III) complexes.

ChemInform Abstract: Ligand Substitution Processes in Tetranuclear Carbonyl Clusters. Part 10. X‐Ray Structural Characterization of Products (I) Resulting from Reactions of Co4(CO)9(tripod), tripod = HC(PPh2)3, with Phosphine Ligands.

Abstract(Ia) crystallizes in the space group Pbca with Z = 8, (Ib) in P21/c, Z=4 and (Ic) in Pca21, Z=4.

Ligand substitution processes in tetranuclear carbonyl clusters. 10. X-ray structural characterization of products resulting from reactions of nonacarbonyl[tris(diphenylphosphino)methane]tetracobalt with phosphine ligands

Co 4 (CO) 8 (PMe 3 )(tripod) cristallise dans le systeme orthorhomtique, groupe Pbca et sa structure est affinee jusqu'a R=0,0626. Co 4 (CO) 7 (dppm)(tripod) cristallise dans le systeme monoclinique, groupe P2 1/c avec R=0,09. Co 4 (CO) 7 (PMe 3 ) 2 (tripod) cristallise dans Pca2 1 avec R=0,0706

Solid-phase ligand substitution processes by outer-sphere anions in isomeric mixed-ligand hexamine chromium(III) complexes

The mixed-ligand complex compoundscis- andtrans-[Cr(en)2(NH2CH3)2]Br(B10H10) were synthetized. It was demonstrated by IR spectroscopy that the hydrogen atoms of the anions B10H 10 2− carrying the negative charge interact with the proton of the amino group in the coordinated amine, forming the bond system N-H-H-B. The complex salts obtained have high densities (d 20=1.55 g/cm3 and 1.47 g/cm3 for thecis andtrans isomer, respectively) and high thermal stability 230–250 °C. At 250–270 °C both thecis and thetrans compound dissociate, with simultaneous substitution of two methylamine molecules in the coordination sphere of the chromium(III) ion by the anions Br− and B10H 10 2− . The process is described by the topochemical equationf(α)=(1−α)2/3 (reaction on the interface of the phases), and is characterized by high values of the kinetic parameters: Ea=510–524 kJ/mol, logA=49.9–50.2. We found that the value ofE a for the amine substitution process in thecis compound, determined by evolved gas analysis under non-isothermal conditions, decreases by 220 kJ/mol when the heating rate is increased from 5.0 to 7.5 deg/min. This finding can be explained in that when the heating rate is increased, the intervals in which thecis- trans isomerization and ligand substitution reactions proceed come closer to one another, and finally overlap; the activation energy of the isomerization process then compensates part of the energy required for activation of the ligand substitution process.

Ligand substitution processes in tetranuclear carbonyl clusters. 9. Reactions of Co4(CO)9(tripod), tripod = HC(PPh2)3, and its derivatives

Preparation facile de Co 4 (CO) 8 (L)(tripod) L=P(OMe) 3 , PMe 3 et P(n-Bu) 3 par reaction de CO 4 (CO) (tripod) avec les coordinats donneurs de P. Mesure de la vitesse de perte de CO dans Co 4 (CO) 7 (dppm)(tripod). Spectres RMN

Ligand substitution processes in tetranuclear carbonyl clusters. 8. Reactions of dodecacarbonyltetracobalt (Co4(12CO)12/Co4(13CO)12) with phosphorus donor ligands. Further evidence for cluster integrity during ligand substitution processes

Etude par spectrometrie IR de la reaction de Co 4 ( 12 CO) 12 /Co 4 ( 13 CO) 12 avec un coordinat donneur de P, conduisant a 12 Co 4 (CO) 11 L

Ligand substitution processes in tetranuclear carbonyl clusters. 7. Molecular structure and carbon monoxide exchange processes of Co4(CO)9(tripod), tripod = 1,1,1-tris(diphenylphosphino)methane or HC(PPh2)3

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLigand substitution processes in tetranuclear carbonyl clusters. 7. Molecular structure and carbon monoxide exchange processes of Co4(CO)9(tripod), tripod = 1,1,1-tris(diphenylphosphino)methane or HC(PPh2)3Donald J. Darensbourg, David J. Zalewski, and Terry DelordCite this: Organometallics 1984, 3, 8, 1210–1217Publication Date (Print):August 1, 1984Publication History Published online1 May 2002Published inissue 1 August 1984https://doi.org/10.1021/om00086a012RIGHTS & PERMISSIONSArticle Views62Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (955 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

HIGH PRESSURE NMR STUDY ON THE KINETICS OF LIGAND EXCHANGE REACTION IN PENTAKIS(DIMETHYL SULFOXIDE)OXOVANADIUM(IV)

Abstract The kinetics of ligand exchange in [VO(dmso)5]2+ (dmso = dimethyl sulfoxide) has been studied by the high pressure NMR method. The volume of activation ΔV≠ for the dmso exchange at the basal positions of [VO(dmso)5]2+ was determined to be (−5.3±0.4) cm3/mol. This negative value of ΔV≠ is consistent with associative behavior in the ligand substitution processes of oxovanadium(IV) complexes.

Ligand substitution processes in tetranuclear carbonyl clusters. 6. Steric contribution to ligand dissociation in multisubstituted tetrairidium dodecacarbonyl derivatives

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLigand substitution processes in tetranuclear carbonyl clusters. 6. Steric contribution to ligand dissociation in multisubstituted tetrairidium dodecacarbonyl derivativesDonald J. Darensbourg and Brenda J. Baldwin-ZuschkeCite this: J. Am. Chem. Soc. 1982, 104, 14, 3906–3910Publication Date (Print):July 1, 1982Publication History Published online1 May 2002Published inissue 1 July 1982https://doi.org/10.1021/ja00378a020RIGHTS & PERMISSIONSArticle Views113Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (668 KB) Get e-Alerts Get e-Alerts

Ligand-substitution processes in tetranuclear carbonyl clusters. 5. A kinetic and infrared investigation of carbon-13 monoxide incorporation into tri-.mu.-carbonyl-nonacarbonyltetracobalt and its monosubstituted derivatives

Ligand-substitution processes in tetranuclear carbonyl clusters. 5. A kinetic and infrared investigation of carbon-13 monoxide incorporation into tri-.mu.-carbonyl-nonacarbonyltetracobalt and its monosubstituted derivatives

Studies on the chemical reactivity of copper bleomycin

The copper(II) complex of the clinically used antitumor agent bleomycin (Blm) has cytotoxic as well as antitumor properties. To understand the relationship of the bleomycin ligand, copper bleomycin, and other possible metal complexes of this agent, kinetic studies of the formation of Cu(II)Blm, ligand substitution reactions of CuBlm with ethylenediaminetetraaletic acid, and the redox reaction of CuBlm with thiols have been completed and interpreted along with previous studies of the thermodynamic stability of Cu 2+ with bleomycin. Cu(II)Bm is found to be kinetically and thermodynamically stable in ligand substitution processes and is only slowly reduced and dissociated by sulfhydryl reagents. The rate constant of reduction of the complex by 2-mercaptoethanol (2-ME) at pH 7.4 and 25°C is 9.5 × 10 −3 M −1 sec −1, explaining the inhibition of Fe 2+-dependent strand scission of DNA by Cu 2+ in the presence of 2-ME. CuBlm forms in preference to Fe(II) Blm and cannot be reduced and dissociated rapidly enough by thiols to liberate Blm and form the reactive iron complex. In agreement with the observed chemical stability of CuBlm, it is also shown that the complex is stable in human plasma and in the presence of Ehrlich cells suspended in ascites fluid. Interestingly, little CuBlm enters these cells to carry out cytotoxic reactions. Finally, it is shown that both Cu 2+ and Zn 2+, at equivalent concentrations to Fe 2+, effectively inhibit the strand scission of DNA by Fe(II)Blm plus oxygen. However, at substoichiometric amounts of Cu 2+, the ferroxidase activity of Blm enables the drug to remain effective in the strand-scission reaction, despite the lowered Cu-free Blm/Fe 2+ ratio. These results are discussed in light of the proposed mechanism of action of bleomycin.

ChemInform Abstract: LIGAND SUBSTITUTION PROCESSES IN TETRANUCLEAR CARBONYL CLUSTERS. 3. MOLECULAR R STRUCTURES OF CO4(CO)8(μ‐CO)3(P(C6H5)3) AND CO4(CO)7(μ‐CO)3(P(OCH3)3)2

Chemischer InformationsdienstVolume 12, Issue 36 Physical Organic Chemistry ChemInform Abstract: LIGAND SUBSTITUTION PROCESSES IN TETRANUCLEAR CARBONYL CLUSTERS. 3. MOLECULAR R STRUCTURES OF CO4(CO)8(μ-CO)3(P(C6H5)3) AND CO4(CO)7(μ-CO)3(P(OCH3)3)2 D. J. DARENSBOURG, D. J. DARENSBOURGSearch for more papers by this authorM. J. INCORVIA, M. J. INCORVIASearch for more papers by this author D. J. DARENSBOURG, D. J. DARENSBOURGSearch for more papers by this authorM. J. INCORVIA, M. J. INCORVIASearch for more papers by this author First published: September 8, 1981 https://doi.org/10.1002/chin.198136072AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue36September 8, 1981 RelatedInformation

Hydrogen migration mechanism for ligand substitution reactions in metal carbonyl hydrides

It has been known for some time that certain transition metal carbonyl hydrides are unusually labile in ligand substitution processes. A mechanism explaining this unusual lability was offered involving a ligand migration of hydrogen to a carbonyl group, attack at the vacated coordination site y the entering ligand, loss of a CO ligand, and back-migration of H to the metal. The following recent experiments offer strong support for this hydride migration. (A) In acetone at -70/sup 0/C H/sub 2/Fe(CO)/sub 4/ reacts within 3 min with PPh/sub 3/ to give H/sub 2/Fe(CO)PPh/sub 3/ and with P(OMe)/sub 3/ to give H/sub 2/Fe(CO)/sub 3/P(OMe)/sub 3/ and H/sub 2/Fe(CO)/sub 2/(P(OMe)/sub 3/)/sub 2/. The phosphine and phosphites are cis to both hydrogens, and the hydrogens are probably cis to each other. The same results are found in methanol at room temperature. These substitutions are at least 30 times as fast as the thermal decomposition of H/sub 2/Fe(CO)/sub 4/ in methanol. H/sub 2/Fe(CO)/sub 3/PPh/sub 3/ decomposes at a rate similar to that of H/sub 2/Fe(CO)/sub 4/ and yields trans-Fe(CO)/sub 3/(PPh/sub 3/)/sub 2/ in the presence of triphenylphosphine. (B) H/sub 2/Ru(CO)/sub 4/ in acetone at -70/sup 0/C also gives H/sub 2/Ru(CO)/sub 3/P(OMe)/sub 3/ in a few minutesmore » with the phosphite cis to hydrogen. Upon warming H/sub 2/Ru(CO)/sub 2/(P(OMe)/sub 3/)/sub 2/ is formed. (C) In methanol at 25/sup 0/C the ion HRu(CO)/sub 4//sup -/, as the PPN/sup +/ salt, is converted immediately into HRu/sub 3/(CO)/sub 11//sup -/. Adding excess sodium methoxide (about 0.4 M) slows the reaction time down to about 15 min, but the same product is formed.« less

Photochemical reactions of surfactant molecules in condensed monolayer assemblies--environmental control and modification of reactivity.

AbstractAn investigation of the effects of a controlled microenvironment on reactivity has been carried out by the synthesis and study in organized monolayers of surfactant molecules containing photochemically reactive chromophores. Reactions where substantial environmental effects have been observed include the cis‐trans isomerization of olefins, ketone photoeliminations, ligand substitution processes, excimer and photodimer formation, and photoredox reactions. Both reactions occurring within the organized assemblies as well as interfacial phenomena have been investigated. Results obtained in these studies suggest possible extensions and applications for the development of new catalyst systems, biological models and controlled syntheses.

Ligand substitution processes at five coordinate copper(II) centres in hydrophilic and hydrophobic environments

In [Cu(Me6tren)H2O]2+[where Me6tren is 2,2′,2″-(N,N-dimethylamine]triethylamine] the aqualigand occupies a hydrophobic environment resembling the sites of aqua ligands in some metalloenzymes, whereas in [Cu(tren)H2O]2+(where tren is 2,2′,2″-triaminotriethylamine) the aqua ligand occupies a hydrophilic site. The lability of the aqua ligand in [Cu(Me6tren)H2O]2+ towards ligand substitution (e.g. for substitution by azide through an Id mechanism: k23(298 K)= 34.6 ± 1.3 s–1; ΔH#= 54.8 ± 1.0 kJ mol–1; ΔS#=–31.7 ± 3.5 J K–1 mol–1) is several orders of magnitude less than that for the aqua ligand in [Cu(tren)H2O]2+. These differences in lability are discussed in relation to the possible influences of the local environment at the site of substitution.

Ion reactivity in reversed-micellar systems. Kinetics of reaction between micelles containing hydrated nickel(II) and murexide-containing micelles in the system aerosol–OT + water + heptane

A stopped-flow kinetic study has been made of a metal–ligand substitution process taking place in Aerosol–OT stabilised water pools in n-heptane. In a typical stopped-flow experiment, reversed micelles containing solubilised metal ion are mixed with micelles containing ligand such that the total concentration of micelles is unchanged on mixing. Micelle sizes are dependent on the water: surfactant mole ratio “R”(where R=[H2O]/AOT]) and the system has been characterised by ultracentrifugation methods over the range R= 0.26–16.9. The kinetic results for complexation in the reversed micellar system support a mechanism involving rapid exchange of reactants between aqueous pools followed by rate-limiting loss of a solvated water molecule from the metal-ion in a water pool. Rate constants for ligand release and water-exchange in the water pools are close to the bulk water values and are not very dependent on pool size.

Kinetics and mechanism of fast metal–ligand substitution processes in aqueous and micellar solutions studied by means of a dye laser photochemical relaxation technique

Rapid metal–ligand substitution reactions have been studied in aqueous and sodium lauryl sulphate (SLS) micellar solutions by means of a dye-laser induced photochemical relaxation method. Perturbation of the system involving Ni2+(aq) and the bidentate nitrogen ligand PADA produces two relaxation effects in both aqueous and micellar solutions. The faster relaxation process is concentration independent and is identified with a ring-closure reaction to reform the initial Ni(PADA)2+ complex. Rate constants and activation energies for this process are found to be similar in both media. The slower relaxation time is associated with the recombination reaction between Ni2+(aq) and PADA, for which k298.2f in water is found to be 1.4 × 103 dm3 mol–1 s–1, which is in good agreement with previous measurements. In the surfactant solutions, the rate of complexation is greatly enhanced close to the c.m.c. followed by a decrease as the concentration of SLS is further increased. This is due to the increased local concentration of Ni2+ at the micelle surface as the c.m.c. is approached. It is shown that it may not be valid to make the assumption kRCk–2 in the kinetic scheme of the reaction. However, the effect on kf is small, such that kf is still dominated by the rate of loss of water from the metal ion.The faster reaction between Zn2+(aq) and PADA was also studied, but only one concentration dependent relaxation time was observed. This was consistent with the complex re-formation reaction and k298.2 was found to be 6.4 × 106 dm3 mol–1 s–1.

Problemes de stereochimie dynamique en serie du titanocene : I. Synthese de diastereoisomeres chloroaryloxy et diaryloxy derives de complexes presentant une chiralite planaire sur Lún des ligands cyclopentadienyle

From the two dichlorides η 5-Cp-η 5-Cp′TiCl 2 (Cp = C 5H 5; Cp′ = C 5H 3MeCHMe 2-1,2 or -1,3), couples of diastereoisomeric chloroaryloxy [η 5-Cp-η 5-Cp′Ti(Cl)OPh] or of diastereoisomeric diaryloxy [η 5-Cp-η 5-Cp′Ti(OPh′)OPh], titanocene derivatives, are prepared in several ways. In each case, the diastereoisomeric complexes are separated and identified. These complexes are starting substrates which can be used for dynamic stereochemistry of the ligand substitution process which will be discussed in a following paper.

STERIC EFFECTS IN REACTIONS OF METAL COMPLEXES. THE LIGAND SUBSTITUTION PROCESSES

Abstract A model for the calculation of the activation energy for the ligand substitution processes in the metal complexes, occuring in the polar solvents, is suggested. The model takes into account sharp repulsion between the ligands at small distances. The structure of the transition state is analysed depending on the sharp repulsion distance between the ligands, symmetry factor α, and position of the incoming group with respect to the outgoing group (cis or trans). It is shown that for certain values of the parameters cis-substitution may be preferable than trans-substitution.

Drug-Biomolecule Interactions: Mechanism of Ligand Interactions with Carbonic Anhydrase Studied by Magnetic Resonance Relaxation and Rapid Reaction Methods

Kinetics of interaction between the metalloenzyme carbonic anhydrase and either monovalent anions or aromatic sulfonamides were examined by three distinct fast reaction techniques: stopped flow, equilibrium perturbation, and magnetic resonance relaxation. By correlating spectroscopic data on conformational and ionization equilibria of the complex and free species with the reaction kinetics, a relatively complete description of the mechanism can be presented. A proton‐dependent equilibrium between two coordination forms of the free enzyme can be demonstrated spectroscopically. Anions selectively combine with the form predominating at low pH. For a series of carboxylate ligands, formate and substituted acetates, anion association is found to be three orders of magnitude greater than similar ligand substitution processes known in inorganic chemistry. For sulfonamide association, the attacking species are the form of carbonic anhydrase predominating at high pH and the neutral sulfonamide. Combination involving the neutral species is followed by loss of a proton to form the sulfonamido anion in the stabilized complex. This obligate proton transfer offers a probable explanation for the unique specificity of sulfonamides in inhibiting this enzyme. The anionic sulfonamido moiety can be shown to resemble closely a transition intermediate in the catalytic step of substrate hydration.