Kinetics of Formation of Mixed-Ligand Complexes. II. 2, 2′-Bipyridylcopper(II) Reactions with Ethylenediamine, a-Alanine, and /3-Alanine
The temperature-jump technique has been used to determine the rate constants (μ = 0.1, 25°) for the formation and dissociation of the mixed complexes Cu(bipyridyl)(ethylenediamine)2+, Cu(bipyridyl)(α-alaninate)+, and Cu(bipyridyl)(0-alaninate)+. The values found for the forward rate constants for the reaction Cu(bipy) + L Cu(bipy)L are as follows: for ethylenediamine, (2.0 ± 0.4) X 109 M~l sec-1; for the protonated form of ethylenediamine, (2.2 ± 0.6) X 101 M~l sec-1; for α-alaninate, (1.0 ± 0.2) X 10® M~l sec-1; and for β-alaninate, (3.4 ± 0.7) X 108 JW-1 sec-1. The rate constants for attack by the zwitterion form of these amino acids are zero within experimental error. The reverse rate constants are as follows: for ethylenediamine, 1.4 ± 0.3 sec-1; for the protonated form of ethylenediamine, (1.2 ± 0.4) X IO6 ili-1 sec-1; for α-alaninate, 10 ± 2 sec-1; for β-alaninate, 110 ± 20 sec-1. These values are compared with the rate constants for the formation of the respective binary complexes Cu + L <=∗ CuL and CuL + L <=∗ CuLî. Mechanistic arguments are developed which lead to the conclusion that complexation reactions of copper(II) are likely Sn2 and that sterically controlled substitution can occur for ternary systems as well as binary ones. © 1972, American Chemical Society. All rights reserved.
Pasternack, Robert F.; Pasternack, Robert F.; Huber, Peter R.; Huber, Peter R.; Huber, U. M.; Huber, U. M.; Sigel, Helmut; and Sigel, Helmut, "Kinetics of Formation of Mixed-Ligand Complexes. II. 2, 2′-Bipyridylcopper(II) Reactions with Ethylenediamine, a-Alanine, and /3-Alanine" (1972). Faculty Articles Indexed in Scopus. 2766.