Hydrocarbon-soluble, hexaanionic fulleride complexes of magnesium

Abstract

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.