Cationic Niobium-Sandwich And Piano-Stool Complexes

The syntheses of the homoleptic bis(arene) niobium cations [Nb(arene)(2)](+) (arene = C6H3Me3, C6H5Me) with 16 valence electrons and heteroleptic arene-carbonyl cations [(CO)Nb(arene)(2)](+) (arene = C6H3Me3, C6H5Me) and [(arene)M(CO)(4)](+) (arene = C6H3Me3, C6H6) obeying 18 valence electrons are described. Stabilization of these complexes was achieved by using the weakly coordinating anions [Al(ORF)(4)](-) or [F{Al(ORF)(3)}(2)](-) (R-F = C(CF3)(3)). The limits of two synthesis routes starting from neutral Nb(arene)(2) (arene = C6H3Me3, C6H5Me) or [NEt4][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.