Nickel can be used in low-cost, sustainable catalytic systems. Usually, nickel in oxidation states between 0 and +III is involved in these processes. Ni(IV) complexes are much rarer overall, and thus, seldom proposed as intermediates in catalysis. Ni(IV)–CF₃ complexes are one example of this type of compound. They are comparatively stable and simple to synthesize.

Melanie S. Sanford, University of Michigan, Ann Arbor, USA, and colleagues have developed a Ni(IV)-catalyzed C–H trifluoromethylation reaction of arenes. The team used TpNi^IV(CF₃)₃ (Tp = tris(pyrazolyl)borate) as a catalyst, electron-rich arenes and heteroarenes as substrates, 2,8-difluoro-5-(trifluoromethyl)-5H-dibenzo[b,d]thiophen-5-ium trifluoromethanesulfonate as a CF₃⁺ source, and dimethyl sulfoxide (DMSO) as the solvent. The reaction was performed at 25 °C.

The desired trifluoromethylated arenes were obtained in moderate to excellent yields. Based on density functional theory (DFT) calculations and experimental studies using ¹⁹F NMR spectroscopy, the team proposes a radical chain mechanism with Ni(IV), Ni(III), and Ni(II) intermediates. According to the researchers, this is the first example of Ni(IV) intermediates implicated in catalysis based on spectroscopic measurements.

• Nickel(IV)-Catalyzed C–H Trifluoromethylation of (Hetero)arenes,
  Elizabeth A. Meucci, Shay N. Nguyen, Nicole M. Camasso, Eugene Chong, Alireza Ariafard, Allan J. Canty, Melanie S. Sanford,
  J. Am. Chem. Soc. 2019.
  https://doi.org/10.1021/jacs.9b06383