Details

Autor(en) / Beteiligte

• Monacelli, Fabrizio
• Viola, Elisa

Titel

The reaction of [bispyridinotetrakis(t-butyl)phthalocyaninato]iron(II) with dioxygen to give μ-oxo-bis[tetrakis(t-butyl)phthalocyaninato]iron(III)

Ist Teil von

• Journal of porphyrins and phthalocyanines, 2006-01, Vol.10 (1), p.13-21

Ort / Verlag

World Scientific Publishing Company

Erscheinungsjahr

2006

Link zum Volltext

Beschreibungen/Notizen

• The reaction of [bispyridinotetrakis(t-butyl)phthalocyaninato]iron(II), (py)2FePct, with dioxygen in CH2Cl2, gives almost quantitatively the oxo-bridged μ-oxo-bis[tetrakis(t-butyl)phthalocyaninato]iron(III) as the final, stable product. The reaction order with respect to the starting complex changes within a run. For t = 0, the rate is proportional to the ratio $a_{1}\sqrt{y_{0}}/(a_{2} + \sqrt{y_{0}})$ (Equation 1) where y0 is the initial absorbance of the solution and a1 and a2 are linear functions of [O2]. For t > 0, the instantaneous rate is instead described by the equation Rate = b [O2][A]/([A]0 - [A]) (Equation 2), where A is (py)2FePct and the coefficient b is again proportional to [O2]. A mechanism is proposed implying the presence of trace amounts of (py)(S)FePct (S = axially boundCH2Cl2) in equilibrium with (py)2FePct. Both species are able to generate the transient pentacoordinate (py)FePct that may react with py and S, giving back the hexacoordinate precursors, or with dioxygen, giving ultimately the μ-oxo complex. At t = 0, the species (py)(S)FePct, expected to be much more labile than (py)2FePct, is at its maximum concentration and is assumed to give the prevaling contribution to the instantaneous rate. As the reaction proceeds, and free pyridine accumulates in the solution, the concentration of (py)(S)FePct decreases rapidly and the transient (py) FePct is produced essentially by the bispyridino complex. This fact and the still growing concentration of free pyridine account for the Equation 2. Finally, when the py concentration is buffered by addition of small amounts of base, the reaction attains a simple first order law. Present data further support the iron(III) formulation of the final μ-oxo product and are inconsistent with the iron(II) hypothesis put forward by some authors. The reaction of the title complex, (py)2FePct, and O2, carried out in CH2Cl2, yields almost quantitatively the oxo-bridged (FePct)2O, via the attack of an O2 molecule on the pentacoordinate intermediate pyFePct. The asymptotic, square root, dependence of the initial rates on the zero-time substrate concentration can be related to the presence of trace amounts of the very labile (py)FePct(S) (S = CH2Cl2).