Nucleophilic Reactivity of a Metal-Bound Superoxide Ligand

Abstract

Metal-superoxide species have frequently been implicated as transient intermediates in dioxygen activating metalloenzymes. The metal-bound superoxide moiety has been proposed to react both as an electrophile and a nucleophile. In general, model complexes that mimic metalloenzyme function have been shown to react as electrophiles, and none have displayed nucleophilic reactivity. Herein, we highlight a recent contribution from our group in which we demonstrated the first well-defined example of a metal-superoxide acting as a nucleophile. We have shown the propensity for a copper-superoxide species to perform nucleophilic deformylation of various aldehydes. In doing so, we have provided experimental support for the postulated role of an iron(III)-superoxide reacting as a nucleophile in the α-ketoglutaratedependent dioxygenases amongst others.

Electronic Structure and Reactivity of Mononuclear Nonheme Iron–Peroxo Complexes as a Biomimetic Model of Rieske Oxygenases: Ring Size Effects of Macrocyclic Ligands

“…As alluded above, the ring size of the macrocyclic n -TMC ligands, as well as the nature of the metal ions, plays a vital role in determining the geometric and electronic structures of metal–O 2 intermediates as well as their reactivities in oxidation reactions. For example, it has been shown that side-on metal-peroxo species are nucleophiles in aldehyde deformylation reactions, whereas end-on metal-superoxo species are electrophiles in the oxidation of organic substrates . It has also been shown that iron­(III)-peroxo n -TMC complexes exhibit diverse reactions depending on the ring size of the TMC ligands, such as nucleophilic versus electrophilic reactivity and olefin epoxidation versus cis -dihydroxylation. , Thus, the structurally and spectroscopically well characterized synthetic [Fe III (O 2 )­( n -TMC)] + complexes provide us with a unique opportunity to systematically investigate the ring size effect of the macrocyclic TMC ligands on the physicochemical properties of iron-peroxo complexes.…”