Kinetics and mechanisms of ligand exchange reactions of tris(acetylacetonato)-chromium(III), -cobalt(III), -ruthenium(III), and -rhodium(III) in acetylacetone.

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概要

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• Tris(acetylacetonato[2-<SUP>14</SUP><I>C</I>])-cobalt(III), -chromium(III), -ruthenium(III), and -rhodium(III) undergo ligand exchange in acetylacetone (Hacac) at 85–190 °C without decomposition of the complexes. The exchange rate is proportional to the complex concentration, and the first-order rate constant <I>k</I><SUB>0</SUB> decreases in the sequence Co(III)>Cr(III)>Ru(III)>Rh(III), <I>k</I><SUB>0</SUB>⁄10<SUP>−5</SUP> s<SUP>−1</SUP> being 2.4 (93 °C), 5.6 (117 °C), 9.5 (158 °C), and 2.4 (185 °C), respectively. The activation enthalpies and entropies and deuterium isotope effect on <I>k</I><SUB>0</SUB> are significantly different between the Co(III) and the Cr(III), Ru(III) and Rh(III) complexes. An intermediate involving an one-ended acetylacetonate and a solvent molecule(Hacac) is concluded to be formed in the rate-determining step. The <I>S</I><SUB>N</SUB>1 and the <I>S</I><SUB>N</SUB>2 mechanism are assigned to the exchange reactions of the Co(III) complex and the others, respectively, for the rate-determining steps.

• 公益社団法人 日本化学会の論文

著者

• Kido Hiroaki

  Chemistry Department, Faculty of Science, Tohoku University

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