Oxene chemistry

The pL-independent IEs have therefore been interpreted580 as indicating that DOD shifts the acid-base equilibrium from (Fem—OO-) to the protonated intermediate (Fenl—OOH) and increases in that way the rate of synthesis of products formed via oxene chemistry (inverse SDIE) and decreases the rate of products formed through the peroxide chemistry... 

Before leaving the area of oxene chemistry, there is one further system worthy of mention the manganese Schiff-base complexes. The Schiff-base complexes were prepared in response to the Katsuki-Sharpless system for stereospecific epoxidation (Figure 2.19).57 The Katsuki-Sharpless system consists of titanium(IV) isopropoxide and ( + )- or (—)-diethyl tartrate with... 

A family of oxidation systems whose activity is probably due partly to oxene chemistry is the Gif/Goagg group, generally involving use of iron (sometimes copper or cobalt) in acetic acid with pyridine or similar ligands present [41]. The systems can be driven by H2O2 or air. Up to now, it does not appear that they lend themselves to cleanly-designed industrial processes. 

Metal(V) species derived from the complexes in Table I are rare. In fact, only one such species, L1Cr(V) (presumably a dioxo or hydro-oxo species), has been observed and characterized by ESR and UV-visible spectroscopies (45,69), Figs. 5 and 6. This Cr(V) species, which has a lifetime of several seconds at room temperature, was generated from a hydroperoxo precursor by an intramolecular transformation that closely resembles the proposed, but so far unobserved step in the chemistry of cytochrome P450, whereby the hydroperoxoiron(III) is transformed to the FeIV(P + ) form also known as oxene (P += porphyrin radical cation). All the steps in Scheme 1 for the L1Cr(H20)2+/02 reaction have been observed directly (45,69). 

Because the sideon configuration (1, Scheme 4-2) of the Fe(n)(ROOH)2+ adduct appears to be the reactive form, the lower yields for the ni-ClPhC(O)OOH oxidant indicate that the oxene configuration (2, Scheme 4-2) is dominant for the peracid. The chemistry for the reaction of Eq. (4-22) is equivalent to that of glutathione peroxidase (an enzyme that contains selenocysteine in its active site), and the Feh(ROOH)2+ complex may represent a reaction mimic for the enzyme. 

A recent summary25 of the activation of O2 by cytochrome P-450 (an iron(III)-heme protein with a axial cysteine thiolate ligand) concludes that the reactive form of this mono-oxygenase also contains an oxene-ferryl group (RS)(por)FeV=O. The mono-oxygenase chemistry of cytochrome P-450 has been modeled via the use of (TPP)Fei lCl(TPP=tetraphenylporphyrin) and (OEP)Fe JCl (OEP=octaethylporphyrin) with peracids,26,27 iodosobenzene,26,27... 

Swinney, D.C. and A.Y. Mak (1994). Androgen formation by cytochrome P450 CYP17. Solvent isotope effect and pL studies suggest a role for protons in the regulation of oxene versus peroxide chemistry. Biochemistry 33, 2185-2190. 

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