Search

For the catalytic cycle of soluble methane monooxygenase (sMMO), it has been proposed that cleavage of the O-O bond in the ([mu]-peroxo)diiron(III) intermediate P gives rise to the diiron(IV) intermediate Q with an [Fe.sub.2][([mu]-O).sub.2] diamond core, which oxidizes methane to methanol. As a model for this conversion, ([mu]-oxo)-diiron(III) complex 1 ([[[Fe.sup.III.sub.2]([mu]-O)([mu]-[[O.sub.2][H.sub.3])[(L).sub.2]].sup.3+], L = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) has been treated consecutively with one eq of [H.sub.2][O.sub.2] and one eq of HCl[O.sub.4] to form 3 ([[[Fe.sup.IV.sub.2][([mu]-O).sub.2][(L).sub.2]].sup.4+]). In the course of this reaction a new species, 2, can be observed before the protonation step; 2 gives rise to a cationic peak cluster by ESI-MS at m/z 1,399, corresponding to the [{[[Fe.sub.2][O.sub.3][L.sub.2]H][(OTf).sub.2]}.sup.+] ion in which 1 oxygen atom derives from 1 and the other two originate from [H.sub.2][O.sub.2]. Mossbauer studies of 2 reveal the presence of two distinct, exchange coupled iron(IV) centers, and EXAFS fits indicate a short Fe-O bond at 1.66 [Angstrom] and an Fe-Fe distance of 3.32 [Angstrom]. Taken together, the spectroscopic data point to an HO-[Fe.sup.IV]-O-[Fe.sup.IV] = O core for 2. Protonation of 2 results in the loss of [H.sub.2]O and the formation of 3. Isotope labeling experiments show that the [[Fe.sup.IV.sub.2]([mu]-O)2] core of 3 can incorporate both oxygen atoms from [H.sub.2][O.sub.2]. The reactions described here serve as the only biomimetic precedent for the conversion of intermediates P to Q in the sMMO reaction cycle and shed light on how a peroxodiiron(III) unit can transform into an [[Fe.sup.IV.sub.2][([mu]-O).sub.2]] core. diiron(IV) | iron-oxo | Mossbauer spectroscopy | nonheme | oxygen activation