Oxidation of cyclohexane by high-valent iron bispidine complexes: tetradentate versus pentadentate ligands.
The iron-bispidine-catalyzed oxidation of cyclohexane with H(2)O(2), where either a tetradentate or a pentadentate bispidine ligand is coordinated to the iron center, yields up to 35% cyclohexanol and cyclohexanone (alcohol/ketone ratio of up to 4). Product distribution (including (18)O labeling studies), kinetic isotope effects, and the ratio of tertiary/secondary alcohols with adamantane as a substrate (tertiary/secondary) suggest that (i) H abstraction by a ferryl complex is the rate-determining step and that the emerging cyclohexyl radical is short-lived, (ii) there is a parallel reaction involving oxidation by OH radicals, and (iii) there are considerable differences in the reaction pathways between the tetradentate and pentadentate ligand catalyst. These interpretations are fully supported by a DFT-based computational analysis.
Comba
Peter
P
Universität Heidelberg, Anorganisch-Chemisches Institut, INF 270, D-69120 Heidelberg, Germany. peter.comba@aci.uni-heidelberg.de
Maurer
Martin
M
Vadivelu
Prabha
P
D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry*; D002384:Catalysis; D003198:Computer Simulation; D003510:Cyclohexanes / Q000737:chemistry*; D006588:Hexanones / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011789:Quantum Theory
D019086:Bridged Bicyclo Compounds, Heterocyclic; D003510:Cyclohexanes; D006588:Hexanones; D008024:Ligands; C495809:bispidine; C506365:Cyclohexane; D007501:Iron