Synthesis and electronic structure of a series of first-row transition-metal pyrazine(diimine) complexes in two oxidation states

Abstract

The synthesis, molecular and electronic structures, and redox properties of pyrazine(diimine) (P^zDI) metal dihalide complexes (^DiPPP^ZDI)MX₂ (DiPP = 2,6-diisopropylphenyl; M = Mn, Fe, Co, Ni; X = Cl, Br) are presented and compared. The dihalide complexes are reduced to (^DiPPP^ZDI)MX monohalide complexes, and the role of ligand redox non-innocence in the electronic structure of the reduced compounds is examined and compared to related pyridine(diimine) (PDI) compounds. The compounds were characterized by NMR spectroscopy, UV-VIS spectroscopy, cyclic voltammetry, X-ray crystallography, and Evans method magnetometry. Similar to previously reported PDI compounds, the reduced monohalide complexes are best described as divalent metal centers coupled to a reduced radical anion ligand. Structural and computational analyses show that the ligand in (^DiPPP^ZDI)MX is reduced by one electron and bears significant spin density. Comparison across the series of first-row transition metals shows increasing metal-ligand covalency for the later metals. These results may be useful in the design of modified heteroarene(diimine) ligands for first-row transition-metal catalysis in the future.

Graphical Abstract

Keywords:

• Redox non-innocence
• pincer ligands
• first-row transition metal complexes
• pyrazine diimine ligands
• electronic structure

Acknowledgement

The Mississippi Center for Supercomputing Research is thanked for providing computational resources.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors gratefully acknowledge Mississippi State University for startup funding. NMR analysis was supported by the Omics and Bioinformatics Core of the Center for Biomedical Research Excellence in Pathogen Host Interactions (grant #P20GM103646) funded by the National Institute for General Medical Sciences.