Kinetics And Mechanism Of Ligand Substitution In Some Chromium(Iii) Tetraaza Macrocyclic Complexes In Acidic Media: Differences In Reactivity Between Cis And Trans Isomers

Thiocyanate anation of the macrocyclic complexes cis[Cr(cycb)(OH2)(2)](3+) and trans-[Cr(cyca)(OH2)(2)](3+) (cycb and cyca are rac- and meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, respectively), and mercury(Il)-induced aquation of the product thiocyanato-N complexes, has been studied in acidic solution. The rate retardation with an increase of the acid concentration for both types of reactions follows the rate expression k(obs)=(k(1)+k(2)K(a)/[H-(aq)(+)])/(1+K-a/ [H-(aq)(+)]), corresponding to parallel reaction paths through aqua and hydroxo complexes. Some general trends in the differences in reactivity between the two geometrical isomers have been observed and are discussed. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)