[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(ORF)(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=C6H6, o-dfb=1,2-F2C6H4). By irreversible removal of CO from the equilibrium, even the rather endergonic reaction to a [Ni(o-dfb)(2)](+) salt was successful (Delta(r)G degrees((solv))=+78 kJ mol(-1)). The latter displays an unprecedented slipped eta(3),eta(3)-sandwich structure and is the ultimate synthon to Ni-I-chemistry.