Extensive Redox Non-Innocence in Iron Bipyridine-Diimine Complexes: a Combined Spectroscopic and Computational Study.

Ranjeesh Thenarukandiyil,Renana Gershoni-Poranne,Eno Paenurk,Gabriel Ménard,Graham De Ruiter,Amir Karton,Raanan Carmieli,Natalia Fridman,Anthony Wong

doi:10.1021/acs.inorgchem.1c02925

Abstract

Metal–ligand cooperation is an important aspect in earth-abundant metal catalysis. Utilizing ligands as electron reservoirs to supplement the redox chemistry of the metal has resulted in many new exciting discoveries. Here, we demonstrate that iron bipyridine-diimine (BDI) complexes exhibit an extensive electron-transfer series that spans a total of five oxidation states, ranging from the trication [Fe(BDI)]3+ to the monoanion [Fe(BDI]−1. Structural characterization by X-ray crystallography revealed the multifaceted redox noninnocence of the BDI ligand, while spectroscopic (e.g., 57Fe Mössbauer and EPR spectroscopy) and computational studies were employed to elucidate the electronic structure of the isolated complexes, which are further discussed in this report.

Highlights

Over the past decade, metal−ligand cooperativity has established itself as a valuable asset in catalysis.[1]
We have demonstrated that monometallic complexes of the type [Fe(BDI)(OTf)2] (2) can exist in five stable oxidation states
Crystallographic, spectroscopic, and computational studies have shown that the multiple redox events are characterized by extensive ligand-based reductions (BDI ⇄ BDI3−), where the metal is only involved in redox processes MII ⇄ MIII

Summary

■ INTRODUCTION

Metal−ligand cooperativity has established itself as a valuable asset in catalysis.[1]. The realization that ligands can participate in redox processes was recognized in the early 1960s by Gray and coworkers.[8] Since many redox-active ligands have been developed that typically feature electron-donating or πaccepting systems capable of stabilizing radical cations and/ or anions.6a−d Typical examples include (i) 1,2-substituted semibenzoquinone based architectures8a,9 or (ii) those that contain α-imino substituents.[10] In particular, redox noninnocent pyridinediimine based ligands (Figure 1) have gained significant interest as their iron,[11] cobalt,[12] nickel,[13] and manganese[14] complexes have proven to be active catalysts in a variety of transformations.[15]. Crystallographic, spectroscopic, and computational studies provided insight into the electronic structure of these complexes and how the consecutive one-electron reductions lead to the formation of a ligand-based trianion, which is further discussed in this study

■ RESULTS AND DISCUSSION

■ SUMMARY AND CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES

Solid and Solution State Flexibility of Sterically Congested