Kinetics of ligand exchange between tris(acetylacetonato[2-14C])cobalt(III) and acetylacetone in acetonitrile. Evidence for SN1 mechanism.
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概要
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Tris(acetylacetonato[2-<SUP>14</SUP><I>C</I>]) cobalt (III) undergoes ligand isotopic exchange with acetylacetone (Hacac) in acetonitrile at 85–100 °C without decomposition and solvolysis. The exchange rate is proportional to the complex concentration (0.002–0.007 M, 1 M=1 mol dm<SUP>−3</SUP>), the first-order rate constant k<I><SUB>o</SUB></I> being independent of [Hacac] (0.001–0.97 M). <I>k<SUB>o</SUB></I>=1.6×10<SUP>−5</SUP> s<SUP>−1</SUP> at 93.2 °C. The activation enthalpy and entropy are 38±4 kcal mol<SUP>−1</SUP> (1 cal= 4.18J) and 23±8 cal K<SUP>−1</SUP> mol<SUP>−1</SUP>, respectively. Trichloroacetic acid (<0.02 M) gives acid catalysis. The ratedetermining step should be the <I>S</I><SUB>N</SUB>1 Co–O cleavage in a chelate ring to give a five coordinate intermediate.
- 公益社団法人 日本化学会の論文
著者
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Saito Kazuo
Chemistry Department, Faculty of Science, Tohoku University
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Kido Hiroaki
Chemistry Department, Faculty of Science, Tohoku University
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