Kinetics and Mechanism of the Demetallation of Macrocyclic Nickel(II) Complexes by Cyanide

✍ Scribed by Liselotte Siegfried; Thomas A. Kaden

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: German
• Weight: 114 KB
• Volume: 88
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200590024

✦ Synopsis

Abstract

The kinetics and the mechanism of the cyanide‐induced demetallation of a series of Ni^2+^ complexes with macrocyclic ligands of different ring size (12‐ to 14‐membered; see 1–4) and steric constraints was studied. Although the rates differ by almost five orders of magnitude when compared to each other under fixed experimental conditions (pH 10.5, [CN^−^]=10^−2^ M), all reactions proceed through the relatively rapid formation of cyano adducts [Ni(CN)~n~L] (n=1, 2), which then react with additional CN^−^ or HCN to give the final products. Of paramount importance for the reaction rate is the geometry and configuration of the cyano adducts [Ni(CN)~n~L] (n=1,2). cis‐Dicyano derivatives with a folded macrocycle react faster than trans‐compounds. In the case of (1,4,8,11‐tetraazacyclotetradecane)nickel(2+) ([Ni (4)]^2+^), which gives a trans‐ dicyano adduct, the base‐catalyzed N‐inversion necessary to obtain the __cis‐__dicyano derivative becomes rate determining at high CN^−^ concentrations.