REACTIVITY OF CHLORO(PHTHALOCYANINATO)IRON(III) IN PYRIDINE WATER

The reaction of [Fe(pc)Cl] (pc = phthalocyaninate) in water-containing pyridine (py) has been followed by spectrophotometric and conductometric techniques. It is a two-step process: the first step is first-order on [H2O] and is accompanied by an increase in conductance, the second is kinetically independent of water and does not involve ionic species. The complex [Fe(pc) (py)2] is formed during both steps and about 70-80% of the initial iron(III) is finally recovered in this form. The infinite-time conductance is quantitatively explained in terms of 100% formation of py.HCl. Addition of PPh3 has a remarkable effect: when added to py before [Fe(pc)Cl] the second step tends to vanish as the concentration of PPh3 increases and, for [PPh3] greater-than-or-equal-to 4 x 10(-3) mol dm-3 the overall reaction appears as a one-step process; if the phosphine is added after the first step and before the second, two consecutive reactions take place, the first kinetically phosphine-dependent, the second independent of PPh3. Virtually quantitative oxidation to OPPh3 occurs when the complex is allowed to react with a slight excess of PPh3. The observations are explained in terms of a rapid Cl- release from [Fe(pc)Cl(py)] to give [Fe(pc)(py)2]+, Cl- which, in turn, undergoes substitution of an axial py by water. A hydroxo species forms which readily dimerises and the dimer disproportionates to give [Fe(pc)(py)2] and the iron(IV) species [Fe(pc)O(py)]. Considerations based on the instability of analogous oxoporphyrinatoiron(IV) species and on the nearly 75% overall yield of [Fe(pc)(py)2] lead to the suggestion that the iron(IV) compound is in the form of a mu-peroxo or di-mu-oxo dimer.