Alkylperoxo iron

X-ray absorption spectroscopic studies of high-spin nonheme (alkylperoxo)iron(III) intermediates... 

A mononuclear diastereopure high-spin Fe alkylperoxo complex with a pen-tadentate N,N,N,0,0-ligand 33 (Scheme 17) was reported by Klein Gebbink and coworkers [109, 110]. The complex is characterized by unusual seven-coordinate geometry. However, in the oxidation of ethylbenzene the iron complex with 33 and TBHP yielded with large excess of substrate only low TON s (4) and low ee (6.5%) of 1-phenylethanol. 

The 0-0 stretch for the hydroperoxo complexes (60,86,88,90,94,95,99- ) falls in the range 780 900 cm-1. In the case of a nonheme iron complex it was found that the low-spin hydroperoxo form absorbs at a lower frequency than the high-spin peroxo complex (89,102). This trend also holds for some iron alkylperoxo complexes, and DFT calculations have shown the high-spin alkylperoxide form to have a larger activation energy for the 0-0 bond cleavage than the corresponding low-spin alkylperoxo form (104). 

Arasingham RD, Cornman CR, Balch AL. Detection of alkylperoxo and ferryl, (FeIV = 0)2 +, intermediates during the reaction of tert-butyl hydroperoxide with iron porphyrins in toluene solution. J Am Chem Soc 1989 111 7800-7805. 

E.I. Solomon (2001). Electronic structure of high-spin iron(III)-alkylperoxo complexes and its relation to low-spin analogues Reaction coordinate of 0-0 bond homolysis. J. Am. Chem. Soc. 123, 12802-12816. 

The first step of this process is apparently the photoexcitation of the iron chloride species to stimulate homolysis of the Fe-Cl bond [60h]. The chlorine radical (free or in the solvent cage without entering to the solvent) attacks the alkane. The iron(II) derivative that is formed can be oxidized either by molecular oxygen or the alkylperoxo radical (Scheme IX.8). 

Another interesting feature of these enzymes is the formation of an intense purple intermediate upon the addition of excess hydroperoxy product. It has been noted that this chromophore resembles the iron-alkylperoxo complexes previously characterized by Que and co-workers. While no spectroscopic evidence has been obtained for the LO systems, such a complex would not be rationalized by the mechanism put forth in Figure 25 as the peroxy-substrate species would need to be positioned in a trans position to the iron. 

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