Replacement reactions at a ferrous phthalocyanine centre. Piperidine and substituted pyridines as entering ligands

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 relatio nship (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 neu tral bases. The slow first step for the reaction with cyanide ion as base c an be explained when the energy needed to de-pair cyanide and potassium ion s is taken into account. In the second step the formation rate constants of FePc(base)(2) species co ver one order of magnitude for neutral bases, and the base dissociation rat e constants cover two orders of magnitude, with a good LFER between these c onstants and the pK(BH+) of the leaving group. There is also a good LFER be tween the equilibrium constant for bis-base complex formation and these sam e dissociation rate constants.