Diiron diamond core

Kim, C., Dong, Y. H., and Que, L., Jr., 1997, Modeling nonheme diiron enzymesoHydrocar-bon hydroxylation and desaturation by a high-valent Fe202 diamond core, J. Am. Chem. Soc. 119 3635n3636. 

In MMO, compound Q has been identified as a coupled diiron(IV,IV) species, on the basis of its Mossbauer spectrum. While different structures for compound Q are possible, there is now some spectroscopic evidence (X-ray absorption fine structure and Mossbauer spectroscopy) that the diiron center in compound Q is a high-valent Fe2(/A-0)2 diamond core (Scheme 2). In the proposed mechanism, reaction... 

When the precursor to the Fe(III,IV) compound is [Fe 2(/r-0)2(6-Me3-TPA)2] +, one-electron oxidation affords a Fe k 0-Fe =0 core structure derived from the isomerization of the Fe2(/r-0)2 diamond core, demonstrating the accessibility of a terminal Fe =0 unit in a nonheme environment. A different approach to achieve the Fe(III,IV) unit has also been carried out by Lippard etal. In this method, a tetracarboxylate-bridged diiron(II,II) complex (4-t-BuPy)2Fe2(/r-RC02)4 where RC02 is the bulky carboxylate Ar C02 (Schemed) is exposed to dioxygen at -79°C. Among the products identified by Mossbauer and EPR spectroscopy is an Fe(III,IV) species. 

Mononuclear iron(II) complexes supported by aminopyridine ligands (TPA and its derivatives) self-assemble into bis-hydroxo-bridged diamond core-like structures under basic conditions. The donor atom sets in these diiron complexes are similar to the coordination environment created by dinucleating ligands such as HPTB. The differences in observed oxygenation rates, detailed below, can be attributed to significant steric hindrance about coordinatively saturated iron centers.73... 

Similar reactions of dinuclear complexes sometimes give rise to mixed-valent intermediates, for example, diamond core Fera( a,-0)2FeIV species obtained from diiron(III) TPA complexes and H202.85... 

Dioxygen diiron complexes have been synthesized by mimicking the probable intermediate structures in methane monooxygenase oxygenations. Examples are summarized in the recent review. One is the Fc2(i7-0)2 diamond core type and the other is the Fe2(tJ-02) peroxo type. Recently, an unusual Fe"-X-Fe (tl -02) species has been suggested in the reaction of O2 with carboxylate-bridged diiron(II,II) paddlewheel complexes, but its role in the oxygenation has not been clarified. ... 

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