Iron-catalyzed halogenation of alkanes: modeling of nonheme halogenases by experiment and DFT calculations.
When the dichloroiron(II) complex of the tetradentate bispidine ligand L=3,7-dimethyl-9-oxo-2,4-bis(2-pyridyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate methyl ester is oxidized with H(2)O(2), tBuOOH, or iodosylbenzene, the high-valent Fe=O complex efficiently oxidizes and halogenates cyclohexane. Kinetic D isotope effects and the preference for the abstraction of tertiary over secondary carbon-bound hydrogen atoms (quantified in the halogenation of adamantane) indicate that C-H activation is the rate-determining step. The efficiencies (yields in stoichiometric and turnover numbers in catalytic reactions), product ratios (alcohol vs. bromo- vs. chloroalkane), and kinetic isotope effects depend on the oxidant. These results suggest different pathways with different oxidants, and these may include iron(IV)- and iron(V)-oxo complexes as well as oxygen-based radicals.
Comba
Peter
P
Universität Heidelberg, Anorganisch-Chemisches Institut, INF 270, 69120 Heidelberg, Germany. peter.comba@aci.uni-heidelberg.de
Wunderlich
Steffen
S
D000473:Alkanes / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D054879:Halogenation; D058085:Iron Compounds / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D016877:Oxidants / Q000737:chemistry*; D013329:Structure-Activity Relationship
D000473:Alkanes; D058085:Iron Compounds; D008024:Ligands; D016877:Oxidants