First synthesis of a binuclear [Mn-II(bipy)-Fe-III(porphyrin)] complex: Spectroscopic characterization and first evidence of reversible formation of manganese(III) as manganese peroxidase

A [(P)Fe-III-Mn-II] bimetallic complex, mimicking the active site of manganese peroxidase, has been synthesized. A modified highly fluorinated porphyrin, 5,10,15-tris(pentafluorophenyl)-20-(o-aminophenyl)porphyrin has been used to introduce, through a short spacer linked to the amino function, a manganese auxiliary ligand, 6-aminomethyl-2,2'-bipyridine. Two successive metalations by FeCl2 and MnCl2 afforded the [(P)Fe-III-Mn-II] bimetallic complex that has been characterized by elemental analysis and FAB(+) mass spectrometry. X-band EPR spectroscopy and magnetic susceptibility measurements were in agreement with two high spin Fe(III) and Mn(II) centers without magnetic exchange interaction. Moreover, there is no higher intermolecular association through mu-chloro bridging as observed by EPR with a simpler chloromanganese complex, Mn(bipy)(2)Cl-2, at high concentration. Addition of pentafluoroiodosobenzene in methanol at 0 degrees C led to the progressive and complete disappearance of the EPR Mn(II) signals, that were recovered after addition of a phenol. This result is consistent with Mn(III) formation. This production of Mn(III) requires the presence of the iron porphyrin and is proposed to occur through the intermediate formation of a Fe(IV) dimethoxide species which can be related to the oxidation of Mn(II) catalyzed by manganese peroxidase compound II.