Does the TauD Enzyme Always Hydroxylate Alkanes, While an Analogous Synthetic Non-Heme Reagent Always Desaturates Them?

This theoretical work addresses the mechanistic switch between hydroxylase (alcohol formation) and desaturase (olefin formation) activities during alkane oxidation by two non-heme high-valent oxoiron reagents, the enzyme taurine:alpha-ketoglutarase dioxygenase (TauD) and the synthetic shape-selective catalyst (TpOBzFe), toward cyclohexadiene, cyclohexane, cyclopentane, and ethane. As we show, the desaturase/hydroxylase steps obey unique orbital selection rules, and the mechanistic switch is determined by intrinsic reactivity factors that depend on the ligand-sphere flexibility of the oxoiron species, the substrate, and the spin states of the reaction pathways. Testable predictions are outlined.