A kinetic study of the ligand exchange between bis(acetylacetonato)oxovanadium(IV) and acetylacetone[14C] in organic solvents.
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概要
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Square pyramidal [VO(acac)<SUB>2</SUB>] (acac, acetylacetonate) undergoes ligand exchange with Hacac[<SUP>14</SUP><I>C</I>] in 1,2-dichloroethane (DCE) without side reactions. The rate is expressed by <I>R</I>=<I>k</I><SUB>2</SUB>[complex] [Hacac], where [Hacac] stands for the concentration of free acetylacetone in enol form. The second order rate constant and activation parameters are 0.071 M<SUP>−1</SUP> s<SUP>−1</SUP> (M=mol dm<SUP>−3</SUP>) at −33 °C, <I>ΔH</I><SUP>\neweq</SUP>=(46.7±1.7) kJ mol<SUP>−1</SUP> and <I>ΔS</I><SUP>\neweq</SUP>=(−61.9±8.4) J· mol<SUP>−1</SUP> K<SUP>−1</SUP>. The deuterium isotope effect is <I>k</I><SUB>H</SUB>⁄<I>k</I><SUB>D</SUB>=1.3±0.2. It appears as if the free Hacac first interacts with the complex as unidentate and the chelation of the unidentate accompanied by proton transfer to the leaving acac<SUP>−</SUP> is the rate determining step. On addition of a donor solvent the exchange rate decreases, and the extent is correlated with Gutmann's donor number. The <I>k</I><SUB>2</SUB>, <I>ΔH</I><SUP>\neweq</SUP> and <I>ΔS</I><SUP>\neweq</SUP> in 0.06 M dimethyl sulfoxide (DMSO) in DCE are 0.0038 M<SUP>−1</SUP> s<SUP>−1</SUP> at −33 °C, (71.9±10.0) kJ mol<SUP>−1</SUP>, and (−4±40) J mol<SUP>−1</SUP> K<SUP>−1</SUP>, respectively. The DMSO molecule seems to interact with the intermediate species with a unidentate Hacac and inhibits the associative rate determining step.
- 公益社団法人 日本化学会の論文
著者
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Nishizawa Masato
Chemistry Department, Faculty of Science, Tohoku University
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Saito Kazuo
Chemistry Department, Faculty of Science, Tohoku University
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