Synthesis of Cationic N-Heterocyclic Carbene Lanthanide Bromide and the Influence of N-Heterocyclic Carbene and Lanthanide Metals

The lithium salt of the novel amido-phenoxo-functionalized NHC L (L = [3,5-Bu-t(2)-2-(O)C6H2CH-(Bu-n)NH(CH2)(2)(C{N(CH)(2)(NPr)-Pr-i})]), (LiL)(2) (1), was synthesized by the direct reaction of the salicylaldimino-functionalized imidazolium salt H2L'Br (L' = [3,5-Bu-t(2)-2-(O)C6H2CH=N(CH2)(2)(C{N(CH)(2)(NPr)-Pr-i})]) with 2 equiv of (LiBu)-Bu-n and structurally characterized, Treatment of LnCl(3) with in situ formed 1 in a molar ratio of 1:1 at room temperature yielded the first cationic complexes [LnL(2)](+)[Br](-) (Ln = Y (2), Lu (3), Er (4)) in good yields. Treatment of Li(THF)Ln((NPr2)-Pr-i)(4) with 2 equiv of H2L'Br at -78 degrees C afforded the cationic complexes [L'(2)Ln(THF)(+)[Br](-) (Ln = Y (5) and Yb (6)) in desired yields. Each central metal in cations [LnL(2)](+) for 2-4 is coordinated by two L ligands, while the central metal in [L'(2)Ln(THF)](+) for 5 and 6 is ligated by two ligands and one THF molecule. The structures of NHC lanthanide bromides have been found to depend on both the size of the metal and the ligand.