Lanthanide Amido Complexes Incorporating Amino-Coordinate-Lithium Bridged Bis(indolyl) Ligands: Synthesis, Characterization, and Catalysis for Hydrophosphonylation of Aldehydes and Aldimines

Two series of new lanthanide amido complexes supported by bis(indolyl) ligands with amino-coordinate-lithium as a bridge were synthesized and characterized. The interactions of [(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3 with 2 equiv of 3-(CyNHCH2)C8H5NH in toluene produced the amino-coordinate-lithium bridged bis(indolyl) lanthanide amides [μ-{[η1:η1:η1:η1-3-(CyNHCH2)Ind]2Li}Ln[N(SiMe3)2]2] (Cy = cyclohexyl, Ind = Indolyl, Ln = Sm (1), Eu (2), Dy (3), Yb (4)) in good yields. Treatment of [μ-{[η1:η1:η1:η1-3-(CyNHCH2)Ind]2Li}Ln[N(SiMe3)2]2] with THF gave new lanthanide amido complexes [μ-{[η1:η1-3-(CyNHCH2)Ind]2Li(THF)}Ln[N(SiMe3)2]2] (Ln = Eu (5), Dy (6), Yb (7)), which can be transferred to amido complexes 2, 3, and 4 by reflux the corresponding complexes in toluene. Thus, two series of rare-earth-metal amides could be reciprocally transformed easily by merely changing the solvent in the reactions. All new complexes 1–7 are fully characterized including X-ray structural determination. The catalytic activities of these new lanthanide amido complexes for hydrophosphonylation of both aromatic and aliphatic aldehydes and various substituted aldimines were explored. The results indicated that these complexes displayed a high catalytic activity for the C–P bond formation with employment of low catalyst loadings (0.1 mol % for aldehydes and 1 mol % for aldimines) under mild conditions. Thus, it provides a convenient way to prepare both α-hydroxy and α-amino phosphonates.