Reduced Arene Complexes of Scandium

Abstract

Alkali metal naphthalenide or anthracenide reacted with scandium(III) anilides [Sc(X){N(tBu)Xy}₂ (thf)] (X=N(tBu)Xy (1); X=Cl (2); Xy=C₆ H₃ -3,5-Me₂ ) to give scandium complexes [M(thf)_n ][Sc{N(tBu)Xy}₂ (RA)] (M=Li-K; n=1-6; RA=C₁₀ H₈ ^2- (3-Naph-K) and C₁₄ H₁₀ ^2- (3-Anth-M)) containing a reduced arene ligand. Single-crystal X-ray diffraction revealed the scandium(III) center bonded to the naphthalene dianion in a σ² :π-coordination mode, whereas the anthracene dianion is symmetrically attached to the scandium(III) center in a σ² -fashion. All compounds have been characterized by multinuclear, including ⁴⁵ Sc NMR spectroscopy. Quantum chemical calculations of these intensely colored arene complexes confirm scandium to be in the oxidation state +3. The intense absorptions observed in the UV/Vis spectra are due to ligand-to-metal charge transfers. Whereas nitriles underwent C-C coupling reaction with the reduced arene ligand, the reaction with one equivalent of [NEt₃ H][BPh₄ ] led to the mono-protonation of the reduced arene ligand.

Keywords: NMR spectroscopy; UV/Vis spectroscopy; alkali metals; arenes; charge transfer; scandium.