From the Iron Pentacarbonyl Cation to Heteroleptic η 6 -arene Carbonyls and bis-η 6 -arene Cations.

Partial ligand substitution at the iron pentacarbonyl radical cation generates novel half-sandwich complexes of the type [Fe(η 6 -arene)(CO) 2 ]⋅ + (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 ]⋅ + was fully characterized by XRD analysis, IR, NMR, cw-EPR, Mössbauer spectroscopy and cyclic voltammetry as the [Al(OR F ) 4 ] - (R F =C(CF 3 ) 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(OR F ) 4 ] - counterion. The full substitution of the carbonyl ligands in [Fe(CO) 5 ]⋅ + [Al(OR F ) 4 ] - mainly resulted in disproportionation reactions, giving solid Fe(0) and the dicationic bis-arene salts [Fe(η 6 -arene) 2 ] 2+ ([Al(OR F ) 4 ] - ) 2 (arene=1,3,5-trimethylbenzene, benzene and fluorobenzene). Only by employing the very large fluoride bridged anion [F-{Al(OR F ) 3 } 2 ] - , it was possible to isolate an open shell bis-arene cation salt [Fe(C 6 H 6 ) 2 ]⋅ + [F-{Al(OR F ) 3 } 2 ] - . The highly reactive cation was characterized by XRD analysis, cw-EPR, Mössbauer spectroscopy and cyclic voltammetry. The disproportionation of [Fe(C 6 H 6 ) 2 ]⋅ + salts to give solid Fe(0) and [Fe(C 6 H 6 ) 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.