Thermodynamics of complex formation reactions in non-aqueous solvents

Ahlers, C.H.; Vuuren, C.P.J. Van

doi:10.1016/0040-6031(89)85152-4

Cited by 2 publications

(2 citation statements)

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“…The number of kinetic studies on neutral bis chelate oxovanadium(IV) complexes, VO(A ∩ B) 2 , in organic media is rather limited. In agreement with the present findings, it was shown that the addition of bases such as pyridine to the complex VO(pd) 2 (Hpd = pentane-2,4-dione) in benzene is a very fast process with rate constants of the order of 10 9 s -1 . , For the kinetics of ligand exchange in the system VO(pd) 2 /Hpd, as studied with isotopically labeled pentane-2,4-dione in dichloroethane at −33 °C, a second-order rate constant k = 0.071 m -1 s -1 was reported . Ligand substitution in VO(pd) 2 by salicylaldoxime (=H 2 sao), as investigated in toluene, was found to proceed in two second-order steps, and the mixed-ligand complex, VO(pd)(Hsao), was postulated to be the intermediate of the consecutive reaction sequence …”

Section: Resultssupporting

confidence: 90%

Kinetics and Mechanism of Ligand Substitution in Bis(N-alkylsalicylaldiminato)oxovanadium(IV) Complexes

2003

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Conventional and stopped-flow spectrophotometry was used to to study the kinetics of ligand substitution in a number of bis(N-alkylsalicylaldiminato)oxovanadium(IV) complexes (=VO(R-X-sal)(2)) by 1,1,1- trifluoropentane-2,4-dione (=Htfpd) in acetone, according to the following reaction: VO(R-X-sal)(2) + 2Htfpd --> VO(tfpd)(2) + 2R-X-salH. The acronym R-X-salH refers to N-alkylsalicylaldimines with substituents X = H, Cl, Br, CH(3), and NO(2) in the 5-position of the salicylaldehyde ring and N-alkyl groups R = n-propyl, isopropyl, phenyl, and neopentyl. Under excess conditions ([Htfpd](0) >> [VO(R-X-sal)(2)](0)), substitution by Htfpd occurs in two observable steps, as characterized by pseudo-first-order rate constants k(obsd(1)) and k(obsd(2)). Both rate constants increase linearly with [Htfpd](0) according to k(obsd(1)) = k(s(1)) + k(1)[Htfpd](0) and k(obsd(2)) = k(s(2)) + k(2)[Htfpd](0), with k(s(1)) and k(s(2)) describing small contributions of solvent-initiated pathways. Depending on the nature of R and X, second-order rate constants k(1) and k(2) lie in the range 0.098-0.87 M(-1) s(-1) (k(1)) and 0.022-0.41 M(-1) s(-1) (k(2)) at 298 K. For ligand substitution in the system VO(n-propyl-sal)(2)/Htfpd, the activation parameters DeltaH++ = 35.8 +/- 2.8 kJ mol(-1) and DeltaS++ = -146 +/- 23 J K(-1) mol(-1) (k(1)) and DeltaH++ = 40.2 +/- 1.3 kJ mol(-1) and DeltaS++ = -142 +/- 11 J K(-1) mol(-1) (k(2)) were obtained. The Lewis acidity of the complexes VO(n-propyl-X-sal)(2) with X = H, Cl, Br, CH(3), and NO(2) was quantified spectrophotometrically by determination of equilibrium constant K(py), describing the formation of the adduct VO(n-propyl-X-sal)(2).pyridine. The adduct VO(tfpd)(2).n-propyl-salH, formed as product in the system VO(n-propyl-sal)(2)/Htfpd, was characterized by its dissociation constant, K(D) = (3.30 +/- 0.10) x 10(-3) M. The mechanism suggested for the two-step substitution process is based on initial formation of the adducts VO(R-X-sal)(2).Htfpd (step 1) and VO(R-X-sal)(tfpd).Htfpd (step 2).

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Section: Resultssupporting

confidence: 90%

Kinetics and Mechanism of Ligand Substitution in Bis(N-alkylsalicylaldiminato)oxovanadium(IV) Complexes

2003

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“…A transition metal complex that has been applied as a catalyst in many organic reactions is VO(acac) 2 . Its properties have been studied by several researchers, [11][12][13][14][15][16][17] and the crystal structure was published in 1962. 18 In the solid state VO(acac) 2 is fivecoordinated; however, upon dissolution in organic solvents, the vanadium may coordinate to a donor molecule in the vacant position, generating [VO(acac) 2 S] (where S = solvent donor molecule).…”

Section: Introductionmentioning

confidence: 99%

Structural characterization and DFT study of VIVO(acac)2 in imidazolium ionic liquids

Mota¹,

Hallett

Kuznetsov³

et al. 2011

Phys. Chem. Chem. Phys.

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We report the structural characterization of vanadyl acetylacetonate in imidazolium room temperature ionic liquids--bbimNTf(2), bmimNTf(2), C(3)OmimNTf(2), bm(2)imNTf(2), bmimPF(6), bmimOTf, bmimBF(4), bmimMeCO(2), bmimMeSO(4), bmimMe(2)PO(4) and bmimN(CN)(2)--and organic solvents. The complex was characterized by visible electronic (Vis) and EPR spectroscopies. VO(acac)(2) shows solvatochromism in the selected ionic liquids and behaves as in organic solvents, evidencing coordination of the ionic liquid anion in the solvents with higher coordinating ability. The Lewis basicity order obtained for the IL anions was: PF(6)(-) < NTf(2)(-) < OTf(-)≈ MeCO(2)(-) < MeSO(4)(-) < BF(4)(-)≈ N(CN)(2)(-) < Me(2)PO(4)(-). The solvent effect on the spectroscopic data was tentatively examined using linear solvation energy relationships based on the Kamlet-Taft solvent scale (α, β and π*), however no suitable correlation was found with all data. The EPR characterization showed the presence of two isomers in bmimOTf, bmimMeCO(2) and bmimMe(2)PO(4), suggesting coordination of the ionic liquid anions in both equatorial and axial positions. The full geometry optimization of cis-/trans-VO(acac)(2)(OTf)(-) and cis-/trans-VO(acac)(2)(OTf)(mmim) structures was done at the B3P86/6-31G* level of theory. The calculations confirm that the anion OTf(-) is able to coordinate to VO(acac)(2) with the trans isomer being more stable than the cis by 4.8 kcal mol(-1).

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Thermodynamics of complex formation reactions in non-aqueous solvents

Cited by 2 publications

References 4 publications

Kinetics and Mechanism of Ligand Substitution in Bis(N-alkylsalicylaldiminato)oxovanadium(IV) Complexes

Kinetics and Mechanism of Ligand Substitution in Bis(N-alkylsalicylaldiminato)oxovanadium(IV) Complexes

Structural characterization and DFT study of VIVO(acac)2 in imidazolium ionic liquids

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