Synthesis and characterization of amidate rare-earth metal amides and their catalytic activities toward hydrophosphonylation of aldehydes and unactivated ketones

Abstract

Two novel amidate rare-earth metal amides Ln[N(SiMe3)2](κ2-L1)2(THF) (L1=C6H5C(O)NC6H3(iPr)2) (Ln=Yb (1), Y (2)) were prepared through simple silylamine elimination reactions of the benzamide proligand HL1 with Ln[N(SiMe3)2]3 in tetrahydrofuran at 60°C. These complexes were well characterized by elemental and single-crystal X-ray diffraction analyses, and the yttrium complex 2 was also characterized by NMR spectroscopic analyses. Investigation on the catalytic behaviors of amidate rare-earth metal amides, including two new complexes 1, 2 and three known amidate divalent rare-earth metal amides {Ln[N(SiMe3)2](μ-O:κ2-L1)(THF)}2 (Ln=Yb (3), Eu (4)), and Eu2[N(SiMe3)2]2(μ-O:κ2-L2)2(THF)3 (L2=C6H5C(O)NC6H3(Me)2) (5), revealed that all complexes exhibited high catalytic activities toward the hydrophosphonylation of aldehydes and some of them showed moderate to good activities toward unactivated ketones. Complex 1 showed the highest activity, which afforded a series of α-hydroxy phosphonates in good to excellent yields at room temperature after short time with low catalyst loadings.