Lanthanide anilido complexes: synthesis, characterization, and use as highly efficient catalysts for hydrophosphonylation of aldehydes and unactivated ketones

Lanthanide anilido complexes stabilized by the 2,6-diisopropylanilido ligand have been synthesized and characterized, and their catalytic activity for hydrophosphonylation reaction was explored. A reaction of anhydrous LnCl(3) with 5 equivalents of LiNHPh-Pr-i(2)-2,6 in THF generated the heterobimetallic lanthanide-lithium anilido complexes (2,6-(Pr2PhNH)-Pr-i)(5)LnLi(2)(THF)(2) [Ln = Sm(1), Nd(2), Y(3)] in good isolated yields. These complexes are well characterized by elemental analysis, IR, NMR (for complex 3) and single-crystal structure determination. Complexes 1-3 are isostructural. In these complexes, the lanthanide metal ion is five-coordinated by five nitrogen atoms from five 2,6-diisopropylanilido ligands to form a distorted trigonal bipyramidal geometry. The lithium ion is coordinated by two nitrogen atoms from two 2,6-diisopropylanilido ligands, and one oxygen atom from a THF molecule. It was found that these simple lanthanide anilido complexes are highly efficient for catalyzing hydrophosphonylation reactions of various aldehydes and unactivated ketones to generate alpha-hydroxyphosphonates in good to excellent yields (up to 99%) within a short time (5 min for aldehydes, 20 min for ketones). Furthermore, the mechanism of hydrophosphonylation reactions has also been elucidated via H-1 NMR monitoring of reaction.