High‐Spin and Low‐Spin State Perferryl Intermediates: Reactivity‐Selectivity Correlation in Fe(PDP) Catalyzed Oxidation of (+)‐Sclareolide

Five iron complexes of the Fe(PDP) family, giving rise to the low‐spin (S=1/2) and high‐spin (S=3/2) perferryl oxygen‐transferring intermediates, have been screened in the C−H oxidation of the bulky steroidal substrate (3aR)‐(+)‐sclareolide with H2O2. The regioselectivity of oxidation (preferentially at the C2 methylenic site) increases when passing from the catalyst systems exhibiting more reactive, low‐spin perferryl oxygen‐transferring species to those featuring their less reactive, high‐spin counterparts. Furthermore, the C2 hydroxylation chemoselectivity increases in the same order, being the highest for the least reactive intermediate in the series; this observation is explained in terms of the more product‐like transition state. Spin state vs. selectivity: This work provides a so far lacking example of a uniform relationship between the spin state and C−H activation reactivity of the active perferryl intermediates formed in bioinspired catalyst systems based on Fe complexes of the PDP family, on the one hand, and their chemo‐ and regioselectivity in C−H oxidation of a complex substrate of natural origin on the other hand.