title: Theoretical study of cyclohexane hydroxylation by three possible isomers of [FeIV(O)(R-TPEN)] 2+: does the pentadentate ligand wrapping around the metal center differently lead to the different stability and reactivity?
abstract: Density functional theory calculations have been carried out to elucidate the mechanism of cyclohexane hydroxylation by three possible isomers of [Fe(IV)(O)(N-R-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine)](2+) (R is methyl or benzyl) (Klinker et al. in Angew Chem Int Ed 44:3690-3694, 2005). The calculations offer a mechanistic view and reveal the following features: (a) all the three isomers possess triplet ground states and low-lying quintet excited states, (b) the relative stability follows the order isomer A > isomer B > isomer C, in agreement with the conclusions of Klinker et al., (c) the theoretical investigations provide a rationale to explain the interconversion of the three isomers, (d) the reaction pathways of the C-H hydroxylation are initiated by a hydrogen-abstraction step, and (e) the three isomers react with cyclohexane via two-state-reactivity patterns on competing triplet and quintet spin-state surfaces. As such, in the gas phase, the relative reactivity exhibits the trend isomer B > isomer A, while at the highest level, B2//B1 with zero point energy and solvation corrections, the relative reactivity follows the order isomer B > isomer A > isomer C. Thus, the calculated reaction pathway shows that pyridine rings perpendicular to the Fe-O axis result in more reactive species, and a pyridine ring coordinated trans to the oxygen atom leads to the least reactive isomer.
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, People's Republic of China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.forename: Keli
authors.initials: K
authors.lastname: Han
mesh_terms: D002614:Chelating Agents / Q000737:chemistry; D003510:Cyclohexanes / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D006900:Hydroxylation; D007501:Iron / Q000737:chemistry*; D007536:Isomerism; D008024:Ligands; D008956:Models, Chemical; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry
chemical_list: D002614:Chelating Agents; D003510:Cyclohexanes; D005029:Ethylenediamines; D008024:Ligands; C506365:Cyclohexane; D006859:Hydrogen; D007501:Iron; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine; D010100:Oxygen