Cationic Niobium-Sandwich and Piano-Stool Complexes.

The syntheses of the homoleptic bis(arene) niobium cations [Nb(arene) ] (arene = C H Me , C H Me) with 16 valence electrons and heteroleptic arene-carbonyl cations [(CO)Nb(arene) ] (arene = C H Me , C H Me) and [(arene)M(CO) ] (arene = C H Me , C H ) obeying 18 valence electrons are described. Stabilization of these complexes was achieved by using the weakly coordinating anions [Al(OR ) ] or [F{Al(OR ) } ] (R = C(CF ) ). The limits of two synthesis routes starting from neutral Nb(arene) (arene = C H Me , C H Me) or [NEt ][M(CO) ] (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.