Hydrocarbon-soluble, hexaanionic fulleride complexes of magnesium

The reaction of the magnesium(I) complexes [{(Arnacnac)Mg}2], (Arnacnac = HC(MeCNAr)2, Ar = Dip (2,6-iPr2C6H3), Dep (2,6-Et2C6H3), Mes (2,4,6-Me3C6H2), Xyl (2,6-Me2C6H3)) with fullerene C60 afforded a series of hydrocarbon-soluble fulleride complexes [{(Arnacnac)Mg}nC60], predominantly with n = 6, 4 and 2. 13C{1H} NMR spectroscopic studies show both similarities (n = 6) and differences (n = 4, 2) to previously characterised examples of fulleride complexes and materials with electropositive metal ions. The molecular structures of [{(Arnacnac)Mg}nC60] with n = 6, 4 and 2 can be described as inverse coordination complexes of n [(Arnacnac)Mg]+ ions with C60n- anions showing predominantly ionic metal-ligand interactions, and include the first well-defined and soluble complexes of the C606- ion. Experimental studies show the flexible ionic nature of the {(Arnacnac)Mg}+∙∙∙∙C606- coordination bonds. DFT calculations on the model complex [{(Menacnac)Mg}6C60] (Menacnac = HC(MeCNMe)2) support the formulation as an ionic complex with a central C606- anion and comparable frontier orbitals to C606- with a small HOMO-LUMO gap. The reduction of C60 to its hexaanion gives an indication about the reducing strength of dimagnesium(I) complexes.