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

Abstract

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 LnCl3 with 5 equivalents of LiNHPh-(I)Pr2-2,6 in THF generated the heterobimetallic lanthanide-lithium anilido complexes (2,6-(I)Pr2PhNH)5LnLi2(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 ) 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 α-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(1)H NMR monitoring of reaction.

n-BuLi as a Highly Efficient Precatalyst for Hydrophosphonylation of Aldehydes and Unactivated Ketones

“…Quantitative yields were obtained for aromatic aldehydes bearing a substituent at the para- or meta -position of either an electron-donating group, such as CH 3 – ( 1c ) and CH 3 O– ( 1e , 1f ), or an electron-withdrawing group, such as F– ( 1g ), Cl– ( 1i , 1j ), Br– ( 1k ), and NO 2 – ( 1l , 1m ). Different from reactions catalyzed by organolanthanide complexes, the steric effect in this study is not significant. The reactions proceeded smoothly for aldehydes with CH 3 – and Cl– substituents at the ortho- position ( 1b and 1h ).…”

“…The reaction of benzaldehyde with diethyl phosphite was chosen as a model reaction to optimize reaction conditions, and (2,6- i Pr 2 PhNH)Li (0.2 mol %) was selected as the precatalyst, which is equivalent to 0.1 mol % of the aforementioned complex of (2,6- i Pr 2 PhNH) 5 LnLi 2 (THF) 2 in terms of lithium . The reaction proceeded smoothly at rt in neat, and a quantitative yield was achieved within 5 min (Table , entry 1).…”

“…Recently, we reported the synthesis of anionic lanthanide amides (2,6- i Pr 2 PhNH) 5 ­LnLi 2 (THF) 2 (Ln = Sm, Nd, Y) stabilized by simple anilido ligands, which are efficient and easily available precatalysts for hydrophosphonylation reactions. 0.1 mol % of (2,6- i Pr 2 PhNH) 5 ­SmLi 2 (THF) 2 catalyzed a quantitative transformation of a range of both aldehydes and ketones . Since these complexes can be considered as additives of (2,6- i Pr 2 PhNH) 3 Ln and two equivalents of (2,6- i Pr 2 PhNH)Li, we were prompted to explore the role of organic alkali metal compounds in hydrophosphonylation reactions.…”

“…In comparison with known systems, n -BuLi still showed higher activity for ortho -substituted ketones. For example, 4c was converted to 5c in 52% yield within 2 h catalyzed by (2,6- i Pr 2 PhNH) 5 ­SmLi 2 (THF) 2 . On the other hand, the electronic effect of ketones on the hydrophos­phonyla­tion reaction is also obvious.…”

Open-Shell Early Lanthanide Terminal Imides

“…The Nd–N­(amido) distances of 2.312 and 2.344 Å differ marginally. Nevertheless, both are in the range of similar neodymium anilide compounds . The bis­(amido) formation can be rationalized on the basis that single deprotonation of the aniline is favored.…”