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Heterolytic Cleavage of Peroxide by a Diferrous Compound Generates Metal‐Based Intermediates Identical to Those Observed with Reactions Utilizing Oxygen‐Atom‐Donor Molecules
Author(s) -
Rowe Gerard T.,
RybakAkimova Elena V.,
Caradonna John P.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800283
Subject(s) - heterolysis , peroxide , chemistry , photochemistry , bond cleavage , deprotonation , molecule , hydrogen peroxide , catalysis , oxygen , metal , medicinal chemistry , stereochemistry , organic chemistry , ion
Under cryogenic stopped‐flow conditions, addition of 2‐methyl‐1‐phenylprop‐2‐yl hydroperoxide (MPPH) to the diiron(II) compound, [Fe 2 (H 2 Hbamb) 2 (NMeIm) 2 ] ( 1 ; NMeIm= N ‐methylimidazole; H 4 HBamb: 2,3‐bis(2‐hydroxybenzamido)dimethylbutane) results in heterolytic peroxide OO bond cleavage, forming a high‐valent species, 2 . The UV/Vis spectrum of 2 and its kinetic behavior suggest parallel reactivity to that seen in the reaction of 1 with oxygen‐atom‐donor (OAD) molecules, which has been reported previously. Like the interaction with OAD molecules, the reaction of 1 with MPPH proceeds through a three step process, assigned to oxygen‐atom transfer to the iron center to form a high‐valent intermediate ( 2 ), ligand rearrangement of the metal complex, and, finally, decay to a diferric μ‐oxo compound. Careful examination of the order of the reaction with MPPH reveals saturation behavior. This, coupled with the anomalous non‐Arrhenius behavior of the first step of the reaction, indicates that there is a preequilibrium peroxide binding step prior to OO bond cleavage. At higher temperatures, the addition of the base, proton sponge, results in a marked decrease in the rate of OO bond cleavage to form 2 ; this is assigned as a peroxide deprotonation effect, indicating that the presence of protons is an important factor in the heterolytic cleavage of peroxide. This phenomenon has been observed in other iron‐containing enzymes, the catalytic cycles of which include peroxide OO bond cleavage.