Cationic Niobium‐Sandwich and Piano‐Stool Complexes

The syntheses of the homoleptic bis(arene) niobium cations [Nb(arene)(2)](+) (arene = C(6)H(3)Me(3), C(6)H(5)Me) with 16 valence electrons and heteroleptic arene‐carbonyl cations [(CO)Nb(arene)(2)](+) (arene = C(6)H(3)Me(3), C(6)H(5)Me) and [(arene)M(CO)(4)](+) (arene = C(6)H(3)Me(3), C(6)H(6)) obeying 18 valence electrons are described. Stabilization of these complexes was achieved by using the weakly coordinating anions [Al(OR(F))(4)](−) or [F{Al(OR(F))(3)}(2)](−) (R(F) = C(CF(3))(3)). The limits of two synthesis routes starting from neutral Nb(arene)(2) (arene = C(6)H(3)Me(3), C(6)H(5)Me) or [NEt(4)][M(CO)(6)] (M = Nb, Ta) were investigated. All compounds were analyzed by single crystal X‐ray determination, vibrational and NMR spectroscopy. DFT calculations were executed to support the experimental data.