[Ni(CO)₄ ]⁺ as Ni^I Synthon: Synthesis and Characterization of Ni^I Half-Sandwich and Sandwich Cations

The stable, easily accessible salt [Ni(CO)₄ ]⁺ [F{Al(OR^F )₃ }₂ ]^- (R^F =C(CF₃ )₃ ) was used as a Ni^I synthon to generate the novel half-sandwich complexes [Ni(arene)(CO)₂ ]⁺ (arene=C₆ H₆ , o-dfb=1,2-F₂ C₆ H₄ ). By irreversible removal of CO from the equilibrium, even the rather endergonic reaction to a [Ni(o-dfb)₂ ]⁺ salt was successful (Δ_r G°_(solv) =+78 kJ mol^-1 ). The latter displays an unprecedented slipped η³ ,η³ -sandwich structure and is the ultimate synthon to Ni^I -chemistry.