Synthesis and Characterization of a Stable Nickelocenium Dication Salt

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Materials Science

Background:

• Metallocenes, such as nickelocene (NiCp2), are organometallic compounds with significant electronic and catalytic properties.
• The study of highly charged metallocene species is crucial for understanding bonding and electronic structure.

Purpose of the Study:

• To synthesize and characterize novel nickelocenium cations, specifically [NiCp2]+ and [NiCp2]2+.
• To isolate and study the first unsubstituted parent metallocene dication, [NiCp2]2+.
• To investigate the structural and electronic differences between mono- and di-cationic nickelocene species.

Main Methods:

• Synthesis of nickelocenium salts using [NO]+[F-{Al(ORF)3}2]- as an oxidant.
• Characterization via single-crystal and powder X-ray diffraction (XRD).
• Electrochemical analysis using cyclic voltammetry (CV) in 1,2,3,4-tetrafluorobenzene (4FB).
• Nuclear Magnetic Resonance (NMR) spectroscopy (1H NMR).

Main Results:

• Successful synthesis and isolation of [NiCp2]+ and [NiCp2]2+ as [F-{Al(ORF)3}2]- salts.
• Diamagnetic [NiCp2]2+ is the first isolated unsubstituted parent metallocene dication.
• XRD revealed shorter Ni-Cp bond lengths in the dicationic salt compared to the monocationic salt.
• CV showed quasi-reversible redox waves at -0.44 V (0→1) and +1.17 V (1→2) vs Fc/Fc+.
• 1H NMR spectra showed distinct signals for the dication (singlet at 8.6 ppm) and the paramagentic monocation (upfield shift to -103.1 ppm).

Conclusions:

• The successful isolation of the unsubstituted nickelocenium dication ([NiCp2]2+) provides a new platform for studying metallocene electronic structures.
• Structural and electrochemical data highlight the impact of charge on metal-ligand bonding and redox potentials in nickelocene systems.
• The characterized salts offer insights into the stability and properties of highly charged metallocene species.