Group transfer to an aliphatic bond: A biomimetic study inspired by nonheme iron halogenases.

In this work, we predict a group-transfer reaction to an aliphatic substrate on a biomimetic nonheme iron center based on the structural and functional properties of nonheme iron halogenases. Transferring groups other than halogens to C–H bonds on the same catalytic center would improve the versatility and applicability of nonheme iron halogenases and enhance their use in biotechnology; however, few studies have been reported on this matter. Furthermore, very few biomimetic models are known that are able to transfer halogens or other groups to aliphatic C–H bonds. To gain insight into group transfer to an aliphatic C–H bond, we performed a detailed computational study on a biomimetic nonheme iron complex and studied the reactivity patterns with a model substrate (ethylbenzene). In particular, we investigated the reaction mechanisms of [Fe^IV(O)(TPA)X]⁺, TPA = tris(2-pyridylmethy1)amine, and X = Cl, NO₂, N₃ with ethylbenzene leading to 1-phenylethanol and 1-phenyl-1-X-ethane products. Interestingly, we find that the product distributions vary with the nature of the equatorial X-substituent on the metal center. Thus, [Fe^IV(O)(TPA)NO₂]⁺ reacts with ethylbenzene by dominant hydroxylation of the substrate, whereas with halide/azide in the cis-position a group transfer is more likely. As such, we predict a catalytic mechanism of azidation of aliphatic groups using a biomimetic nonheme iron oxidant. The results have been analyzed with thermochemical cycles, valence bond schemes and electronic assignments of reactants and products, which put our results in a broad perspective and predict the effect of other substituents. Finally, predictions are given on how these systems could be utilized in vivo.