Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth Metal Complexes Containing Trost Ligands

Four
chiral dinuclear rare-earth metal complexes [REL1]2 (RE = Y­(1), Eu­(2), Nd­(3), La (4)) stabilized by Trost proligand H3L1 (H3L1 = (S,S)-2,6-bis­[2-(hydroxydiphenylmethyl)­pyrrolidin-1-ylmethyl]-4-methylphenol)
were first prepared, and all were characterized by X-ray diffraction.
Complex 4 was employed as the catalyst for enantioselective
hydroboration reaction of substituted ketones, and the corresponding
secondary alcohols with excellent yields and high ee values were obtained
using reductant HBpin. The same result was also achieved using the
combination of lanthanium amides La­[N­(SiMe3)2]3 with Trost proligand H3L1 in
a 1:1 molar ratio. The experimental findings and DFT calculation revealed
the possible mechanism of the enantioselective hydroboration reaction
and defined the origin of the enantioselectivity in the current system.