Synthesis and characterization of scandium complexes with reduced ligands: Crystal structures of Cp∗ScI2, [Cp∗ScI(bpy)]2, and [Cp∗ScCl(bpy)]2

The synthesis and characterization of complexes containing a Cp∗Sc(R2bpy) (Cp∗ = pentamethylcyclopentadienyl, bpy = 4,4′-R,R-2,2′-bipyridine, R = H, Me) motif are described. Cp∗ScI2 (1) was prepared from Cp∗Sc(acac)2 (acac = acetylacetonate) and AlI3 (2 equiv) in pentane. Compound 1 reacted with bipyridine and 4,4′-dimethyl-2,2′-bipyridine (dmb) in benzene to yield Cp∗ScI2(bpy) (3) and Cp∗ScI2(dmb) (4), respectively. Compound 3 was reduced by alkali metal reductants such as Na/Hg, NaK2, and K in aromatic solvents to yield [Cp∗ScI(bpy)]2 (5). The chloride analog of 5, [Cp∗ScCl(bpy)]2 (7), was prepared from Cp∗ScCl2 by salt metathesis with Li2(dme)2bpy (6) (dme = dimethoxyethane) in toluene. Compounds 1, 5, and 7 have been structurally characterized. Analysis of the bond distances of the bipyridine ligands in 5 and 7, together with infrared and UV/vis spectroscopic data, suggest that the bipyridine ligands in these molecules exist as radical anions. The bipyridine ligands in 5 and 7 are arranged co-facially and are in close proximity (⩽3.30 Å), suggesting the presence of a π–π interaction.