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Kinetics and mechanism of the acid dissociation of the Cobalt(II) complex of novel C‐functionalized 13‐membered macrocyclic dioxotetraamines
Author(s) -
Zhang Y. S.,
Wang Z. M.,
Lin H. K.,
Zhu S. R.,
Chen Y. T.
Publication year - 1999
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1999)31:11<804::aid-jck7>3.0.co;2-o
Subject(s) - chemistry , tautomer , dissociation (chemistry) , protonation , kinetics , intramolecular force , cobalt , reaction rate constant , imine , rate determining step , computational chemistry , photochemistry , medicinal chemistry , stereochemistry , inorganic chemistry , organic chemistry , catalysis , ion , physics , quantum mechanics
The kinetics of acid dissociation of cobalt(II) complexes of novel C‐functionalized 13‐membered macrocyclic dioxotetraamines was studied using stopped‐flow spectrophotometry at different temperatures. The results indicated the dissociation rate follows the law v d = C com kK 1 K 2 [H] 2 /(1 + K 1 [H] + K 1 K 2 [H] 2 ). On the basis of the experiment facts obtained, the dissociation kinetics is interpreted by a mechanism involving the negatively charged carbonyl oxygen of the complex being rapidly protonated in a pre‐rate‐determining step, the rate‐determining step being intramolecular hydrogen (enolic tautomer) migration (to imine nitrogen). The dissociation rate reached a plateau in strongly acidic solution. K 1 and K 2 of the pre‐rate‐determining steps and k of the rate‐determining step were obtained by means of non‐linear least‐squares fitting method, and corresponding activation parameters were also obtained by means of temperature coefficient method. The influence of the substituents to the acid dissociation rates has been discussed. The Brönsted type linear‐free energy relationship does exist in these C‐functionalized dioxotetraamine cobalt(II) complexes. It is first found that the linear relationship between the Δ H ≠ and Δ S ≠ of the rate‐determining step does exist in this and another analogous system. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 804–809, 1999