
Journal of the Chemical Society, Dalton Transactions p. 3271 - 3276 (1990)
Update date:2022-08-03
Topics:
Canovese, Luciano
Cattalini, Lucio
Uguagliati, Paolo
Tobe, Martin L.
The kinetics of displacement of R-py from the [Pd(dien)(R-py)]2+ cation in acid and basic solution in the absence and presence of chloride ions are reported. In acid solution the rate of displacement of 4-chloropyridine is independent of [H+] but that for 4-aminopyridine is acid catalysed, the pyridylammonium ligand being a much better leaving group. In basic solution, the rate of displacement of 4-chloropyridine obeys the rate equation l03kobs. = 8.7 + 11.5[OH-] + 122[OH-]2 s-1, while that for the 4-aminopyridine complex is independent of [OH-]. The reaction between [Pd(dien)(4Cl-py)]2+ and Cl- leads to the rapid formation of a stable intermediate species which is in equilibrium with [Pd(dien)Cl]+ and 4Cl-py. No such intermediate is observed in the reaction of the 4-aminopyridine complex which loses the ligand by the normal path for substitution in square-planar complexes. In the presence of acid the entry of Cl- is irreversible and both substrates revert to the classical mechanism for ligand substitution.
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