Kinetics and mechanism of aquation and formation reactions of carbonato complexes. 12. Deuterium solvent isotope effect on the rate of acid-catalyzed decarboxylation of the carbonatobis(ethylenediamine)cobalt(III) complex ion. A mechanistic reappraisal
| Autor: | K. E. Hyde, G. M. Harris |
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| Rok vydání: | 1978 |
| Předmět: | |
| Zdroj: | Inorganic Chemistry. 17:1892-1896 |
| ISSN: | 1520-510X 0020-1669 |
| DOI: | 10.1021/ic50185a039 |
| Popis: | A recent study of the acid-catalyzed decarboxylation of the carbonatotetrakis(pyridine)cobalt(III) complex ion showed there to be rate acceleration in D/sub 2/O solvent, consistent with a proton-preequilibration mechanism. This observation directly contradicts the results of a similar study made some years ago of the analogous ion, carbonatobis(ethylenediamine)cobalt(III), for which there appeared to be deceleration in D/sub 2/O solvent. A reinvestigation of the latter reaction over a much wider acidity range has now shown the earlier work to be in error. The previously proposed generalized mechanism for aquation of chelated carbonato complex ions of the form CoN/sub 4/CO/sub 3//sup +/ (N/sub 4/ identical with various tetramine ligand groupings of uni-, bi-, or quadridentate type) has thus been revised to include a proton equilibration step. An unexpected complication arises in the interpretation of the data for the bis(ethylenediamine) complex ion in the acidity range 0.1 < (H/sup +/) < 1.0. Within these limits, the pseudo-first-order rate constant for carbonato chelate ring opening, which includes a (H/sup +/) term, overtakes and exceeds the true first-order rate constant for CO/sub 2/ release. The interesting implications of this unusual first-order successive reaction system are fully explored in the context of the present study. |
| Databáze: | OpenAIRE |
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