Synthesis and Characterization of a Stable Nickelocenium Dication Salt.

We report the synthesis and characterization of the nickelocenium cations [NiCp2]⋅+ and [NiCp2]2+ as their [F‐{Al(ORF)3}2]− (Cp = C5H5; RF=C(CF3)3) salts. Diamagnetic [NiCp2]2+ represents the first example for the isolation of an unsubstituted parent metallocene dication. Both salts were generated by reacting neutral NiCp2 with [NO]+[F‐{Al(ORF)3}2]− in 1,2,3,4‐tetrafluorobenzene (4FB). The salts were characterized by single crystal X‐ray diffraction (XRD), indicating shorter metal‐ligand bond lengths for the higher charged salt. Powder XRD shows the salts to be phase pure, cyclic voltammetry in 4FB gave quasi reversible redox waves at −0.44 (0→1) and +1.17 V (1→2) vs Fc/Fc+. The 1H NMR of [NiCp2]2+ is a singlet at 8.6 ppm, whereas paramagnetic [NiCp2]⋅+ is significantly shifted upfield to −103.1 ppm. [ABSTRACT FROM AUTHOR]