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A Density Functional Study on a Biomimetic Non‐Heme Iron Catalyst: Insights into Alkane Hydroxylation by a Formally HOFe V O Oxidant
Author(s) -
Bassan Arianna,
Blomberg Margareta R. A.,
Siegbahn Per E. M.,
Que Lawrence
Publication year - 2005
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.200400383
Subject(s) - hydroxylation , chemistry , alkane , hydrogen atom abstraction , heterolysis , catalysis , methane monooxygenase , photochemistry , solvent , medicinal chemistry , stereochemistry , organic chemistry , hydrogen , enzyme
The reactivity of [HO(tpa)Fe V O] (TPA=tris(2‐pyridylmethyl)amine), derived from OO bond heterolysis of its [H 2 O(tpa)Fe III OOH] precursor, was explored by means of hybrid density functional theory. The mechanism for alkane hydroxylation by the high‐valent iron–oxo species invoked as an intermediate in Fe(tpa)/H 2 O 2 catalysis was investigated. Hydroxylation of methane and propane by HOFe V O was studied by following the rebound mechanism associated with the heme center of cytochrome P450, and it is demonstrated that this species is capable of stereospecific alkane hydroxylation. The mechanism proposed for alkane hydroxylation by HOFe V O accounts for the experimentally observed incorporation of solvent water into the products. An investigation of the possible hydroxylation of acetonitrile (i.e., the solvent used in the experiments) shows that the activation energy for hydrogen‐atom abstraction by HOFe V O is rather high and, in fact, rather similar to that of methane, despite the similarity of the HCH 2 CN bond strength to that of the secondary CH bond in propane. This result indicates that the kinetics of hydrogen‐atom abstraction are strongly affected by the cyano group and rationalizes the lack of experimental evidence for solvent hydroxylation in competition with that of substrates such as cyclohexane.