Stabilizing an exotic dianionic tetrazine bridge in a Ln₂ metallocene

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Redox Chemistry

Background:

• The 1,2,4,5-tetrazine (tz) ring exhibits unique electronic properties, leading to significant scientific interest.
• Tetrazines are known for their coordination chemistry with metal ions and rich redox behavior, existing in dihydro, neutral, and radical anion forms.
• Previous studies suggested the possibility of a tetrazine dianion, but its high reactivity prevented isolation and characterization.

Purpose of the Study:

• To stabilize and characterize the elusive dianionic tetrazine species.
• To explore the coordination chemistry of tetrazines with lanthanide ions.
• To investigate the structural and electronic properties of the dianionic tetrazine ligand within lanthanocene complexes.

Main Methods:

• Synthesis of dinuclear lanthanocene complexes under strictly anhydrous and inert conditions.
• Utilized strong reducing agents and non-acidic solvents.
• Employed lanthanide ions to coordinate with tetrazine nitrogen atoms, sterically protecting the dianion.

Main Results:

• Successfully isolated and characterized three dinuclear metallocene complexes: [(Cp*₂Ln)₂(tz˙^-)(THF)₂](BPh₄) and [(Cp*₂Ln)₂(tz^2-)(THF)₂]·2THF.
• Demonstrated the stabilization of the tetrazine radical anion (tz˙^-) in one complex and the dianionic tetrazine (tz^2-) in others.
• The dianionic tetrazine (tz^2-) was confirmed as a closed-shell planar species with distinct structural features compared to other tetrazine forms.

Conclusions:

• This work reports the first structurally and physically characterized complexes containing the dianionic tetrazine radical.
• The coordination to lanthanide ions effectively stabilized the highly reactive tz^2- ligand.
• The findings offer new insights into the redox chemistry of tetrazines and their potential applications in molecular systems and extended networks.