Theoretical investigation on the oxidative chlorination performed by a biomimetic non-heme iron catalyst.

The present study is a part of an effort to understand the mechanism of the oxidative chlorination, as performed by a biomimetic non-heme iron complex. This catalytically active complex is generated from a peroxide and [(TPA)Fe(III)Cl(2)]+ [TPA is tris(2-pyridylmethyl)amine]. The reaction catalyzed by [(TPA)FeCl(2)]+/ROOH involves either [(TPA)ClFe(V)=O](2+) or [(TPA)ClFe(IV)=O]+ as an intermediate. On the basis of density functional theory the reaction of these two possible catalysts with cyclohexane is investigated. A question addressed is how the competing hydroxylation of the substrate is avoided. It is demonstrated that the high-valent iron complex [(TPA)Cl-Fe(V)=O](2+) is capable of stereospecific alkane chlorination, based on an ionic rather than on a radical pathway. In contrast, the results found for [(TPA)ClFe(IV)=O]+ cannot explain the experimental findings. In this case the transition states for chlorination and hydroxylation are energetically too close. The exclusive chlorination of the substrate by Cl-Fe(IV)=O may be explained by an indirect or a direct effect, altering the position of the competing rebound barriers.