Low‐Spin and High‐Spin Perferryl Intermediates in Non‐Heme Iron Catalyzed Oxidations of Aliphatic C−H Groups

The selectivity patterns of iron catalysts of the Fe(PDP) family in aliphatic C−H oxidation with H2O2 have been studied (PDP=N,N′‐bis(pyridine‐2‐ylmethyl)‐2,2′‐bipyrrolidine). Cyclohexane, adamantane, 1‐bromo‐3,7‐dimethyloctane, 3,7‐dimethyloctyl acetate, (−)‐acetoxy‐p‐menthane, and cis‐1,2‐dimethyl...

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Published in:Chemistry : a European journal Vol. 27; no. 28; pp. 7781 - 7788
Main Authors: Zima, Alexandra M., Lyakin, Oleg Y., Bryliakov, Konstantin P., Talsi, Evgenii P.
Format: Journal Article
Language:English
Published: Germany Wiley Subscription Services, Inc 17.05.2021
Subjects:
Acetic acid
Aliphatic compounds
biomimetic chemistry
Catalysts
Chemistry
Congeners
Cyclohexane
Decay rate
Enantiomers
Epoxidation
Heme
Hydrogen peroxide
Intermediates
Iron
mechanism
Oxidation
Pyridines
Rate constants
Regioselectivity
Selectivity
Substrates
selectivity
oxidation
iron
biomimetic chemistry
intermediates
mechanism
ISSN:0947-6539, 1521-3765, 1521-3765
Online Access:Get full text
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Summary:The selectivity patterns of iron catalysts of the Fe(PDP) family in aliphatic C−H oxidation with H2O2 have been studied (PDP=N,N′‐bis(pyridine‐2‐ylmethyl)‐2,2′‐bipyrrolidine). Cyclohexane, adamantane, 1‐bromo‐3,7‐dimethyloctane, 3,7‐dimethyloctyl acetate, (−)‐acetoxy‐p‐menthane, and cis‐1,2‐dimethylcyclohexane were used as substrates. The studied catalyst systems generate low‐spin (S=1/2) oxoiron(V) intermediates or high‐spin (S=3/2) oxoiron(V) intermediates, depending on the electron‐donating ability of remote substituents at the pyridine rings. The low‐spin perferryl intermediates demonstrate lower stability and higher reactivity toward aliphatic C−H groups of cyclohexane than their high‐spin congeners, according to the measured self‐decay and second‐order rate constants k1 and k2. Unexpectedly, there appears to be no uniform correlation between the spin state of the oxoiron(V) intermediates, and the chemo‐ and regioselectivity of the corresponding catalyst systems in the oxidation of the considered substrates. This contrasts with the asymmetric epoxidations by the same catalyst systems, in which case the epoxidation enantioselectivity increases when passing from the systems featuring the more reactive low‐spin perferryl intermediates to those with their less reactive high‐spin congeners. Direct C−H activation: Investigation of the oxidation of aliphatic C−H groups in the presence of nonheme iron catalysts of the Fe(PDP) family exhibits no uniform correlation between the spin state and reactivity of the oxoiron(V) intermediates and the chemo‐ and regioselectivity of the corresponding catalyst systems, thus witnessing apparent violation of the common “reactivity‐selectivity” principle for this reaction.
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ISSN:0947-6539
1521-3765
1521-3765
DOI:10.1002/chem.202004395