The common chemical logic of 'bridged' peroxo species in mononuclear non-heme iron systems.

Abstract

Mononuclear non-heme iron enzymes catalyze a wide array of important oxidative transformations. They are correspondingly diverse in both structure and mechanism. Despite significant evolutionary distance, it is becoming increasingly apparent that these enzymes nonetheless illustrate a compelling case of mechanistic convergence via the formation of peroxo species bridging metal and substrate. Aromatic amino acid hydroxylases and 2-oxoglutarate (2OG)-dependent enzymes, for example, form bridged acyl- or alkylperoxo intermediates en route to highly oxidizing ferryl species, while catechol dioxygenases utilize such 'bridged' peroxos directly. Analogous acylperoxoiron intermediates have also been demonstrated to precede a perferryl oxidant in biomimetic systems. Herein, we synthesize the results of structural, spectroscopic and computational studies on these systems to gain insight into the shared chemical logic that drives iron-peracid formation and reactivity. In all cases, reactions are tuned via the electron-donating properties of coordinating ligands. Second-sphere residues have also been demonstrated to modulate the orientation of the bridge, thereby influencing reaction outcomes. The effect of carboxylic acid addition to relevant biomimetic catalyst reactions further underscores these fundamental chemical principles. Altogether, we provide a comprehensive analysis of the cross-cutting mechanisms that guide peroxo formation and subsequent oxidative chemistry performed by non-heme mononuclear iron catalysts.