AXIAL LABILIZATION BY MACROCYCLIC LIGANDS. 5. AXIAL SUBSTITUTION IN Co(III) COMPLEXES OF A SERIES OF 14-MEMBERED TETRAAZA MACROCYCLIC LIGANDS
- 1 April 1986
- journal article
- research article
- Published by Taylor & Francis in Journal of Coordination Chemistry
- Vol. 14 (4) , 293-307
- https://doi.org/10.1080/00958978608075847
Abstract
The results of studies of the kinetics of(1) in acetonitrile solvent are presented Here L[dbnd] any of three tetraaza-tetraimine macrocyclic ligands, X− [dbnd] Br − or Cl−; and An [dbnd] acetonitrile. Our results indicate that (1) occurs by a modified interchange mechanism involving formation of and interchange within both 1:1 and 2:1 ion pairs. The first-order rate constant for interchange within the 2:1 ion pairs. ki2-, increases from 0.873 for the least to 48.5 s−1 for the most electron-withdrawing macrocycle, L, at 30°. The activation parameters governing the temperature dependence of ki2 are ΔH∗ = 45 kJ/mole, ΔS∗ = -98 J/mol[sbnd]K for L[dbnd]L1 (methyl substituents); ΔH∗ = 33.6 kJ/mole, ΔS∗ = -111 J/mole-K for L[dbnd]L2 (methyl and phenyl substituents); and ΔH∗ = 46 kJ/mole, ΔS∗ = -64 J/mole-K for L[dbnd]L5 (phenyl substituents) (vide infra). The data suggest that (1) occurs via associative interchange (Ia) rather than by the usual dissociative interchange (Id) route.Keywords
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