Structural and Spectroscopic Evidence for a Side-on Fe(III)–Superoxo Complex Featuring Discrete O–O Bond Distances

Abstract

The O–O bond length is often used as a structural indicator to determine the valence states of bound O 2 ligands in biological metal–dioxygen intermediates and related biomimetic complexes. Here, we report very distinct O–O bond lengths found for three crystallographic forms (1.229(4), 1.330(4), 1.387(2) Å at 100 K) of a side-on iron–dioxygen species. Despite their different O–O bond distances, all forms possess the same electronic structure of Fe(III)–O 2 •– , as evidenced by their indistinguishable spectroscopic features. Density functional theory and ab initio calculations, which successfully reproduce spectroscopic parameters, predict a flat potential energy surface of an η 2 -O 2 motif binding to the iron center regarding the O–O distance. Therefore, the discrete O–O bond lengths observed likely arise from differential intermolecular interactions in the second coordination sphere. The work suggests that the O–O distance is not a reliable benchmark to unequivocally identify the valence state of O 2 ligands for metal–dioxygen species in O 2 -utilizing metalloproteins and synthetic complexes.

Incorporation of Cu into Goethite Stimulates Oxygen Activation by Surface-Bound Fe(II) for Enhanced As(III) Oxidative Transformation

“…As a result, this induces a notable stretching of the O−O bond from 1.21 Å for O 2 molecule 55 to 1.46−1.48 Å (Figures 5b and S18b), suggesting a probability of forming ROS (i.e., 1.33 Å for • O 2 H and 1.49 Å for • O 2 ). 55,56 Key ROS Identification and Underlying Mechanisms for Enhanced As(III) Oxidation. It is documented that the surface-bound Fe(II) can directly activate O 2 through a singleelectron transferring process.…”

DFT Mechanistic Insights into Aldehyde Deformylations with Biomimetic Metal–Dioxygen Complexes: Distinct Mechanisms and Reaction Rules

“…Aldehyde deformylations are chemical reactions taking place in organisms during metabolism and biosynthesis. , These biochemical reactions are catalyzed by metalloenzymes such as cytochrome P450 and aldehyde decarbonylase (ADO). − By binding to molecular oxygen, the metal cofactors of the metalloenzymes form metal–dioxygen active cores that perform these reactions. − Inspired by these biological processes, much effort has been devoted to the study of small-molecule transition-metal–dioxygen complexes (denoted TM–O 2 complexes hereafter). − On the one hand, TM–O 2 complexes serve as biomimetic models to deeply understand the relevant biological processes like deformylations; on the other hand, studying the chemistry of TM–O 2 complexes could lead to the discovery of aerobic catalytic transformations. − The use of abundant molecular O 2 as an oxidant offers a green and sustainable approach to produce valuable chemical products.…”

Isolating Fe-O2 Intermediates in Dioxygen Activation by Iron Porphyrin Complexes

“…However, the complexity of the surrounding protein superstructure restricts access to the metalloporphyrin active sites, resulting in the big challenge in studying the intermediates in O 2 activation by metalloenzymes. To deal with this big challenge, the last several decades have seen numerous researchers turn towards the development of molecular model complexes with heme and nonheme ligands that mimic the local coordination environment of the active site in enzymes [ 31 , 32 , 33 , 34 , 35 , 36 , 37 ]. Due to the simplicity of molecular model complexes, the metal–dioxygen intermediates can be stabilized and directly characterized using current techniques.…”