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Partial ligand substitution at the iron pentacarbonyl radical cation generates novel half‐sandwich complexes of the type [Fe(η6‐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(ORF)4]− (RF=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]⋅+[Al(ORF)4]− mainly resulted in disproportionation reactions, giving solid Fe(0) and the dicationic bis‐arene salts [Fe(η6‐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]⋅+[F‐{Al(ORF)3}2]−. The highly reactive cation was characterized by XRD analysis, cw‐EPR, Mössbauer spectroscopy and cyclic voltammetry. The disproportionation of [Fe(C6H6)2]⋅+ 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. [ABSTRACT FROM AUTHOR]

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., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

We report the synthesis and characterization of the nickelocenium cations [NiCp 2 ]⋅ + and [NiCp 2 ] 2+ as their [F-{Al(OR F ) 3 } 2 ] - (Cp = C 5 H 5 ; R F =C(CF 3 ) 3 ) salts. Diamagnetic [NiCp 2 ] 2+ represents the first example for the isolation of an unsubstituted parent metallocene dication. Both salts were generated by reacting neutral NiCp 2 with [NO] + [F-{Al(OR F ) 3 } 2 ] - in 1,2,3,4-tetrafluorobenzene (4FB). The salts were characterized by single crystal X-ray diffraction (XRD), indicating shorter metal-ligand bond lengths for the higher charged salt. Powder XRD shows the salts to be phase pure, cyclic voltammetry in 4FB gave quasi reversible redox waves at -0.44 (0→1) and +1.17 V (1→2) vs Fc/Fc + . The 1 H NMR of [NiCp 2 ] 2+ is a singlet at 8.6 ppm, whereas paramagnetic [NiCp 2 ]⋅ + is significantly shifted upfield to -103.1 ppm., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The open-shell iron pentacarbonyl cation [Fe(CO) 5 ] .+ was isolated by deelectronation, i.e., the single-electron oxidation of the parent neutral Fe(CO) 5 using [phenazine F ] .+ as the [Al(OR F ) 4 ] - and [F-{Al(OR F ) 3 } 2 ] - salt (R F =C(CF 3 ) 3 ; phenazine F =perfluoro-5,10-bis(perfluorophenyl)-5,10-dihydrophenazine). [Fe(CO) 5 ] .+ [Al(OR F ) 4 ] - was fully characterized (scXRD analysis, IR, NMR, EPR, 57 Fe spectroscopy, CV and SQUID magnetization study) and, apart from being a compound of fundamental interest, may serve as a precursor for low-valent iron coordination chemistry., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)