Abstract
The temperature-jump method has been used to study the complex formation of copper(II) with ethylenediamine (en) at 25° and ionic strength 0·1M. Both the neutral form of the ligand and the protonated H en+ species react according to the overall processes (i) and (ii) where n= 1 or 2. The values of k1=(3·8 ± 1·6)× 109 and k2=(Cu enn–1)2++ en [graphic omitted] Cu enn(i), (Cu enn–1)2++(H en)+ [graphic omitted] Cu enn+ H (ii)(1·9 ± 0·3)× 109 l. mole–1 sec.–1 are relatively large for reaction with a neutral ligand and seem to indicate either the presence of an internal conjugate base mechanism, or a classical associative SN2 mechanism. The substantially lower values of k′1=(1·4 ± 0·3)× 105 and k′2=(3·1 ± 2·1)× 104 l. mole–1 sec.–1 reflect the fact that deprotonation of the intermediate must occur before chelation. Results of temperature-jump and stopped-flow experiments at pH ⩽ 4·3 indicate the presence of a dissociative path involving direct attack of a proton on [Cu en]2+.