From the Iron Pentacarbonyl Cation to Heteroleptic η6-arene Carbonyls and bis-η6-arene Cations

Partial ligand substitution at the iron pentacarbonyl radical cation generates novel half-sandwich complexes of the type [Fe(eta(6)-arene)(CO)(2)]& sdot;(+) (arene=1,3,5-tri-tert-butylbenzene, 1,3,5-trimethylbenzene, benzene and fluorobenzene). Of those, the bulkier 1,3,5-tri-tert-butylbenzene (mes*) derivative [Fe(mes*)(CO)(2)]& sdot;(+) was fully characterized by XRD analysis, IR, NMR, cw-EPR, M & ouml;ssbauer spectroscopy and cyclic voltammetry as the [Al(ORF)(4)](-) (R-F=C(CF3)(3)) salt. Chemical electronation, i. e., the single electron reduction, with decamethylferrocene generates neutral [Fe(mes*)(CO)(2)], whereas further deelectronation under CO-pressure leads to a dicationic three-legged [Fe(mes*)(CO)(3)](2+) salt with [Al(ORF)(4)](-) counterion. The full substitution of the carbonyl ligands in [Fe(CO)(5)]& sdot;(+)[Al(ORF)(4)](-) mainly resulted in disproportionation reactions, giving solid Fe(0) and the dicationic bis-arene salts [Fe(eta(6)-arene)(2)](2+)([Al(ORF)(4)](-))(2) (arene=1,3,5-trimethylbenzene, benzene and fluorobenzene). Only by employing the very large fluoride bridged anion [F-{Al(ORF)(3)}(2)](-), it was possible to isolate an open shell bis-arene cation salt [Fe(C6H6)(2)]& sdot;(+)[F-{Al(ORF)(3)}(2)](-). The highly reactive cation was characterized by XRD analysis, cw-EPR, M & ouml;ssbauer spectroscopy and cyclic voltammetry. The disproportionation of [Fe(C6H6)(2)]& sdot;(+) salts to give solid Fe(0) and [Fe(C6H6)(2)](2+) salts was analyzed by a suitable cycle, revealing that the thermodynamic driving force for the disproportionation is a function of the size of the anion used and the polarity of the solvent.