Chasing the Mond Cation: Synthesis and Characterization of the Homoleptic Nickel Tetracarbonyl Cation and its Tricarbonyl-Nitrosyl Analogue.

130 years after Mond discovered the first homoleptic carbonyl complex Ni(CO)4, we report on a [Ni(CO)4]∙+ salt as the first synthesis of any homoleptic nickel carbonyl cation in the condensed phase. It was prepared by oxidation of nickel metal with the synergistic oxidant Ag[F{Al(ORF)3}2] / 0.5 I2 (RF = C(CF3)3) in CO atmosphere. This D2d-symmetric metalloradical represents the last missing entry among the structurally characterized homoleptic carbonyl cations of group 6 to 11. Additionally, the nickel tricarbonyl-nitrosyl cation [Ni(CO)3(NO)]+ was obtained by usage of NO[F{Al(ORF)3}2] and all pro-ducts were fully characterized by means of IR, Raman, NMR/EPR, single crystal and powder XRD.