Synthesis and characterization of rare-earth metallate amido complexes bearing the 2-amidate-functionalized indolyl ligand and their application in the hydroboration of esters with pinacolborane

Abstract

The reactions of 2-amidate-functionalized indolyl proligand 2-(2,6-ⁱPr₂C₆H₃NHCO)C₈H₅NH (H₂L) with [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ were studied leading to the synthesis and characterization of a series of novel discrete trinuclear rare-earth metallate amido complexes containing the anion [{η¹:(μ₂-η¹:η¹):η¹-LREN(SiMe₃)₂}₃(μ₃-Cl)]⁻ and cation Li⁺(THF)₄ (RE = Y(1a), Nd (1b), Sm (1c), Gd (1d), Dy (1e), Er (1f), and Yb (1g)) in good yields by silylamine elimination. All of the complexes were characterized by spectroscopic methods, elemental analyses and single-crystal X-ray diffraction, and complexes 1a and 1c were additionally characterized by NMR spectroscopy. As proof of principle of their activity, these complexes were used as precatalysts for the hydroboration of esters using HBpin as the hydride source displaying high activity under neat and room temperature conditions. As a result, the ligand, ionic and multinuclear cooperative effects on catalytic activity were observed.