Kinetics and mechanism of the base hydrolysis of cis-eq-[Cr(NCS)(S-pdtra)]-, trans-eq-[Cr(NCS)(edtrp)]- and trans-eq-[Cr(NCS)(R-pdtrp)]- complexes. Strong rate enhancement for NCS- ligand release with an increase of [OH-] only for the trans-equatorial isomers

The [Cr(NCS)(edtrp)]^sup -^, [Cr(NCS)(R-pdtrp)]^sup -^ and [Cr(NCS)(S-pdtra)]^sup -^ complexes, that are derivatives of the trans-equatorial isomers of [Cr(edtrp)(H^sub 2^O)]° and [Cr(R-pdtrp)(H^sub 2^O)]° and the cis-equatorial isomer of [Cr(S-pdtra)-(H^sub 2^O)]° (edtrp = ethylenediamine-N,N,N...

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Published in:Transition metal chemistry (Weinheim) 2000-01, Vol.25 (4), p.363
Main Authors: Kaizaki, Sumio, Kita, Przemysaw, Winiewska, Joanna, Sakagami, Narumi
Format: Article
Language:English
Online Access:Get full text
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Summary:The [Cr(NCS)(edtrp)]^sup -^, [Cr(NCS)(R-pdtrp)]^sup -^ and [Cr(NCS)(S-pdtra)]^sup -^ complexes, that are derivatives of the trans-equatorial isomers of [Cr(edtrp)(H^sub 2^O)]° and [Cr(R-pdtrp)(H^sub 2^O)]° and the cis-equatorial isomer of [Cr(S-pdtra)-(H^sub 2^O)]° (edtrp = ethylenediamine-N,N,N'-tripropionate, R-pdtrp = R-propane-1,2-diamine-N,N,N'-tripropionate, S-pdtra = S-propane-1,2-diamine-N,N,N'-triacetate) undergo aquation in alkaline media with a strong dependence of the rate on [OH^sup -^] for the trans-equatorial isomers and a very weak dependence for the cis-equatorial isomer. The thiocyanate ligand release follows a stereoretentive course for all reactants. Based on kinetic data the reaction mechanism has been discussed. Rate differences between the isomers are interpreted in terms of an interchange via a conjugate base (I c.b.) mechanism, assuming an equilibrium between the cis-equatorial-Cr^sup III^-S-pdtra complexes with penta- and tetradentate coordination of the edta-like ligand.[PUBLICATION ABSTRACT]
ISSN:0340-4285
1572-901X
DOI:10.1023/A:1007043210504