High-valent diiron species generated from N-bridged diiron phthalocyanine and H2O2

N-bridged diiron tetra-tert-butylphthalocyanine activates H2O2 to form anionic hydroperoxo complex [(Pc)Fe-IV=N-Fe-III(Pc)-OOH](-) prone to heterolytic cleavage of O-O bond with the release of OH-and formation of neutral diiron oxo phthalocyanine cation radical complex, PcFeIV=N-Fe-IV(Pc+center dot)=O. ESI-MS data showed stability of the Fe-N-Fe binuclear structure upon formation of this species, capable of oxidizing methane and benzene via O-atom transfer. The slow formation kinetics and the high reactivity preclude direct detection of this oxo complex by low temperature UV-vis spectroscopy. However, strong oxidizing properties and the results of EPR study support the formation of PcFeIV=N-Fe-IV(Pc+center dot)=O. Addition of H2O2 at -80 degrees C led to the disappearance of iron EPR signal and to the appearance of the narrow signal at g = 2.001 consistent with the transient formation of PcFeIV=N-Fe-IV(Pc+center dot)=O. In the course of this study, another high valent diiron species was prepared in the solid state with 70% yield. The Mossbauer spectrum shows two quadrupole doublets with delta 1 = -0.14 mm s(-1), Delta E-Q1 = 1.57 mm s(-1) and delta(2) = -0.10 mm s(-1), Delta E-Q2 = 2.03 mm s(-1), respectively. The negative delta values are consistent with formation of Fe(IV) states. Fe K-edge EXAFS spectroscopy reveals conservation of the diiron Fe-N-Fe core. In XANES, an intense 1s -> 3d pre-edge feature at 7114.4 eV suggests formation of Fe(IV) species and attaching of one oxygen atom per two Fe atoms at the 1.90 angstrom distance. On the basis of Mossbauer, EPR, EXAFS and XANES data this species was tentatively assigned as (Pc)Fe-IV=N-Fe-IV(Pc)-OH which could be formed from PcFeIV=N-Fe-IV(Pc+center dot)=O by hydrogen atom abstraction from a solvent molecule. Thus, despite unfavourable kinetics, we succeeded in the preparation of the first dirion(IV) phthalocyanine complex with oxygen ligand, generated in the (Pc)Fe-IV=N-Fe-III(Pc) - H2O2 system capable of oxidizing methane.