26194-23-0Relevant academic research and scientific papers
Kinetics of Ligand Substitution in Bis(N-t-butylsalicylideneiminato)-copper(II): Aprotic Organic Solvents as Media
Elias, Horst,Froehn, Uwe,Giegerich, Gabriele,Stenger, Monika,Wannowius, Klaus J.
, p. 577 - 582 (1982)
Stopped-flow spectrophotometry has been used to study the kinetics of ligand substitution in the title complex tsaln)2> with N-ethylsalicylideneimine in a variety of aprotic organic solvents.The rate of substitution follows a two-term rate law, rate = (k0 + Kligand)complex>, with the substitution of the first ligand being rate controlling.It is shown that the ligand-independent rate term k0 represents the sum of the genuine solvent contribution kS' of a water contribution (kH2OI + kH2OII2), and of contributions caused protic admixtures such as methanol, e.g.kMeOH.The investigation of the dependence K0 = f() reveals that for toluene and carbon tetrachloride KS = 0.The kS values obtained for the aprotic solvents dimethylformamide, dimethylacetamide, tetramethylurea, dimethyl sulphoxide, acetonitrile, nitromethane, and pyridine lie in the range E-4-E-2S-1.Their correlation with solvent parameters such as dielectric constant, donor or acceptor number, fluidity, or Reichardt's ET(30) value is unsatisfactory, whereas the activation energy for the K0 path correlates reasonably well with the heat of vaporization of the solvents.The size of kligand,kMeOH, and especially KH2OI varies with the type of aprotic solvent, the reactivity of water, kH2OI being 2000-fold greater in toluene than in dimethylformamide.Admixtures of 2,4-dimethylpentan-3-ol and 3-ethylpentan-3-ol to carbon tetrachloride act as water scavengers and suppress the water contribution to k0.The mechanism of the various substitution patways induced by the solvent, by water, and by the incoming ligand is discussed.
Preparation of nanostructured materials through thermolysis of metal chelate complexes
Pomogailo,Burlov,Golubeva,Petrova,Mashchenko,Pomogailo,Dzhardimalieva,Garnovskii
, p. 876 - 883 (2011/10/13)
We demonstrate that nanocomposites (metals and metal carbides and sulfides) can be produced by thermolysis (370 and 600°C) in a self-generated atmosphere using Cu(II), Co(II), and Ni(II) 2-hydroxy- and 2-N- tosylaminobenzaldehyde azomethine bis-chelates a
Tribochemically active chelate complexes of salicylideneimines
Garnovskii,Burlov,Lysenko,Garnovskii,Borodkina,Ponomarenko,Chigarenko,Nikolaevskii,Minkin
, p. 120 - 127 (2009/07/10)
N-Alkylsalicylideneimines and their complexes with 3d metals were obtained by chemical (from metal salts) and electrochemical methods (from metals in the zero oxidation state). The compounds obtained were characterized by IR and 1H NMR spectros
Effect of the coordination geometry and of substituent shielding on the kinetics of ligand substitution in copper(II) chelates
Elias, Horst,Hasserodt-Taliaferro, Christina,Hellriegel, Ludwig,Sch?nherr, Walter,Wannowius, Klaus J.
, p. 3192 - 3198 (2008/10/08)
Stopped-flow spectrophotometry has been used to study the kinetics of ligand substitution in bis(N-R-salicylaldiminato)copper(II) complexes CuA2 (R = H, OH, Me, Et, i-Pr, t-Bu, neo-Pe, phenyl) by bidentate ligands HB (N-ethylsalicylaldimine, acetylacetone) in methanol and ethylene glycol monomethyl ether at 298 K. A two-term rate law, rate = (kS + kHB[HB])[complex], has been found. The substitution of the first ligand in CuA2 is rate determining. The relative contributions of the terms kS and kHB[HB] to the overall rate are controlled by the N-alkyl group R in the following sense: (i) small groups R (such as R = Me) favor a planar trans- N2O2 coordination geometry of the complex, whereas bulky groups (such as R = t-Bu) force the complex to become strongly tetrahedrally distorted, and (ii) with increasing extent of tetrahedral distortion (due to the effect of R) the size of kS increases, whereby the contribution of the term kHB[HB] can become negligibly small. A systematic study of the kinetic effect of substituents X3 and X5 (introduced in the 3- and 5-positions of the salicylaldehyde ring) and substituents Y2, Y4, and Y6 (introduced in the 2-, 4-, and 6-positions of the N-phenyl ring) reveals that substituents X3 = CH3, Cl, Br, I, NO2, which are neighboring to the oxygen donor atom, reduce the size of kS according to their steric substituent constant Es. Substituents Y2 = CH3, F, Cl, Br, I and Y2 = Y6 = CH3, Cl (neighboring the nitrogen donor atom in the N-phenyl complexes) reduce both kS and kHB, which can be correlated with the electronic and steric properties of these substituents. The sum of the experimental results supports consistently the following mechanistic interpretation of the observed rate law, namely: (i) the second-order rate constant kHB describes the nucleophilic attack of the entering ligand HB at the copper; (ii) the first-order rate constant kS describes the attack of a protic solvent molecule, surprisingly not at the copper but at the oxygen donor atom instead.
Ligand Substitution in Bis(N-alkylsalicylideneiminato)copper(II) Complexes: Comparison of Activation and Transfer Data obtained from Solvent Mixtures
Elias, Horst,Muth, Horst,Niederhoefer, Beate,Wannowius, Klaus J.
, p. 1825 - 1830 (2007/10/02)
Stopped-flow spectrophotometry has been used to study the kinetics of ligand substitution in three bis(N-alkylsalicylideneiminato)copper(II) complexes (R=Et, Pri, or But) with N-ethylsalicylideneimine (H-Etsaln) or N-phenylsalicylideneimine (H-Phsaln) in solvent mixtures of methanol-butan-2-ol and methanol-2-methylbutan-2-ol.The rate of substitution follows a two-term rate law, rate=(kS+kligand), although for most systems studied the second-order contribution kligand is negligibly small, so that rate=ka.The determination of ka, the so-called solvent path, in alcohol mixtures of different composition has led to δΔG++.From the temperature dependence of ka, the activation parameters ΔH++ and ΔS++ have been obtained.On the basis of solubilities determined spectrophotometrically, the Gibbs free energy of transfer, δGtr, has been obtained for the various mixtures.An attempt is made to correlate the activation data δΔG++ for the solvent path with the transfer data δΔGtr and this is discussed in terms of ground- and transition-state solvation.The significance of the different co-ordination geometry of the three complexes studied for the kinetics and for solvation is examined.It is shown that there is a correlation between lnka and Reichardt's solvent polarity parameter ET(30) which is of mechanistic importance.
Kinetics of ligand substitution in bis(N-tert-butylsalicylaldiminato)copper(II) in various alcoholic media: Mechanism of the solvent path
Elias, Horst,Fr?hn, Uwe,Von Irmer, Arved,Wannowius, Klaus J.
, p. 869 - 876 (2008/10/08)
Stopped-flow spectrophotometry has been used to investigate the kinetics of ligand substitution in bis(N-tert-butylsalicylaldiminato)copper(II) (Cu(SA=N-t-Bu)2) with N-ethylsalicylaldimine (HSA=N-Et) in various alcohols (ROH) according to Cu(SA=N-t-Bu)2 + 2HSA=N-Et ? Cu(SA=N-Et)2 + 2HSA=N-t-Bu (K298 = 1.7 × 105 in MeOH). The rate of ligand substitution follows a two-term rate law, namely, rate = (kROH[ROH] + kHSA=N-Et[HSA=N-Et])[Cu(SA=N-t-Bu)2], although for most alcohols the ligand path kHSA=N-Et[HSA=N-Et] cannot compete with the solvent path kROH[ROH]. In the presence of water an additional linear term contributes, namely, kH2O[H2O][Cu(SA=N-t-Bu)2]. It is concluded from spectrophotometric equilibrium studies that the mechanism of the solvent path is made up of the following steps: (i) fast equilibrium Cu(SA=N-t-Bu)2 + ROH ? Cu(SA=N-t-Bu)2·ROH; (ii) fast proton transfer from bound ROH to the phenolic oxygen of the coordinated tert-butyl ligand; (iii) rearrangement in the coordination sphere with breaking of the Cu-OH(ligand) bond; and (iv) stepwise but fast substitution of the two-tert-butyl ligands by the ethyl ligands. Rearrangement step (iii) is presumably rate determining. It follows from the kinetic data that the intermediate Cu(SA=N-t-Bu, SA=N-Et) reacts faster than Cu(SA=N-t-Bu)2. The observed order in kROH is MeOH > EtOH > 1-PrOH ≈ 1-BuOH > 2-Me-1-PrOH > 2-PrOH > 2-BuOH > 2-Me-2-PrOH > 2-Me-2-BuOH for the nonsubstituted alcohols ROH, whereas for substituted alcohols the differences in kROH are small. Attempts to correlate kROH with solvent parameters like fluidity, heat of vaporization, dielectric constant, PKaROH, and σR*(Taft) are described. For Me2SO/ROH mixtures the correlation of kMe2SOROH ～ KMe2SOROH is very satisfying (KMe2SOROH = acid dissociation constant of ROH in Me2SO). It follows, therefore, that the acidity of the coordinated ROH molecules is kinetically significant. The ligand path kHSA=N-Et[HSA=N-Et] can be described as a bimolecular reaction between Cu(SA=N-t-Bu)2 and HSA=N-Et. Activation parameters as determined with a commercial stopped flow apparatus are critically analyzed and compared to those obtained with a properly thermostated device.
