Reactivity of functionalized indoles with rare-earth metal amides. Synthesis, characterization and catalytic activity of rare-earth metal complexes incorporating indolyl ligands

Abstract

The reactivity of several functionalized indoles 2-(RNHCH₂)C₈H₅NH (R = C₆H₅ (1), ^tBu (2), 2,6-ⁱPr₂C₆H₃ (3)) with rare-earth metal amides is described. Reactions of 1 or 2 with [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ (RE = Eu, Yb) respectively produced the europium complexes [2-(C₆H₅NCH)C₈H₅N]₂Eu[N(SiMe₃)₂] (4) and [2-(^tBuNCH)C₈H₅N]Eu[N(SiMe₃)₂]₂ (5), and the ytterbium complex [2-(^tBuNCH)C₈H₅N]₂Yb[N(SiMe₃)₂] (6), containing bidentate anionic indolyl ligands via dehydrogenation of the amine to the imine. In contrast, reactions of the more sterically bulky indole 3 with [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ afforded complexes [2-(2,6-ⁱPr₂C₆H₃NCH₂)C₈H₅N]RE[N(SiMe₃)₂](THF)₂ (RE = Yb (7), Y (8), Er (9), Dy (10)) with the deprotonated indolyl ligand. While reactions of 3 with yttrium and ytterbium amides in refluxing toluene respectively gave the complexes [2-(2,6-ⁱPr₂C₆H₃NCH)C₈H₅N]₃Y (11) and [2-(2,6-ⁱPr₂C₆H₃NCH)C₈H₅N]₂Yb^II(THF)₂ (12), along with transformation of the amino group to the imino group, and also with a reduction of Yb³⁺ to Yb²⁺ in the formation of 12. Reactions of 3 with samarium and neodymium amides provided novel dinuclear complexes {[μ–η⁵:η¹:η¹-2-(2,6-ⁱPr₂C₆H₃NCH₂)C₈H₅N]RE[N(SiMe₃)₂]}₂ (RE = Sm (13), Nd (14)) having indolyl ligands in μ–η⁵:η¹:η¹ hapticities. The pathway for the transformation of the amino group to the imino group is proposed on the basis of the experimental results. The new complexes displayed excellent activity in the intramolecular hydroamination of aminoalkenes.