Abstract
The kinetics of the replacement of dmso in FePc(dmso)2 by piperidine and 11 substituted pyridines, to form FePc(base)2 species, have been studied by stopped-flow techniques. For the first step a linear free energy relationship (LFER) exists between the rate constant for fission of base from FePc(base)(dmso) and the gas phase proton affinity of the base, from bases with low proton affinity (CO) to high proton affinity (CN−). The rate constant for dmso fission from FePc(dmso)2 was estimated to be ca. 420,000 s−1, and this fission process largely governs the rate of the first step for neutral bases. The slow first step for the reaction with cyanide ion as base can be explained when the energy needed to de-pair cyanide and potassium ions is taken into account.
In the second step the formation rate constants of FePc(base)2 species cover one order of magnitude for neutral bases, and the base dissociation rate constants cover two orders of magnitude, with a good LFER between these constants and the pKBH of the leaving group. There is also a good LFER between the equilibrium constant for bis-base complex formation and these same dissociation rate constants.
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Farrington, D.J., Jones, J.G., Robinson, N.D. et al. Replacement reactions at a ferrous phthalocyanine centre. Piperidine and substituted pyridines as entering ligands. Transition Metal Chemistry 24, 697–702 (1999). https://doi.org/10.1023/A:1006943102638
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DOI: https://doi.org/10.1023/A:1006943102638