Highly Efficient Hydrophosphonylation of Aldehydes and Unactivated Ketones Catalyzed by Methylene‐Linked Pyrrolyl Rare Earth Metal Amido Complexes

Abstract

A series of rare earth metal amido complexes bearing methylene-linked pyrrolyl-amido ligands were prepared through silylamine elimination reactions and displayed high catalytic activities in hydrophosphonylations of aldehydes and unactivated ketones under solvent-free conditions for liquid substrates. Treatment of [(Me(3)Si)(2)N](3)Ln(μ-Cl)Li(THF)(3) with 2-(2,6-Me(2)C(6)H(3)NHCH(2))C(4)H(3)NH (1, 1 equiv) in toluene afforded the corresponding trivalent rare earth metal amides of formula {(μ-η(5):η(1)):η(1)-2-[(2,6-Me(2)C(6)H(3))NCH(2)](C(4)H(3)N)LnN(SiMe(3))(2)}(2) [Ln=Y (2), Nd (3), Sm (4), Dy (5), Yb (6)] in moderate to good yields. All compounds were fully characterized by spectroscopic methods and elemental analyses. The yttrium complex was also characterized by (1)H NMR spectroscopic analyses. The structures of complexes 2, 3, 4, and 6 were determined by single-crystal X-ray analyses. Study of the catalytic activities of the complexes showed that these rare earth metal amido complexes were excellent catalysts for hydrophosphonylations of aldehydes and unactivated ketones. The catalyzed reactions between diethyl phosphite and aldehydes in the presence of the rare earth metal amido complexes (0.1 mol%) afforded the products in high yields (up to 99%) at room temperature in short times of 5 to 10 min. Furthermore, the catalytic addition of diethyl phosphite to unactivated ketones also afforded the products in high yields of up to 99% with employment of low loadings (0.1 to 0.5 mol%) of the rare earth metal amido complexes at room temperature in short times of 20 min. The system works well for a wide range of unactivated aliphatic, aromatic or heteroaromatic ketones, especially for substituted benzophenones, giving the corresponding α-hydroxy diaryl phosphonates in moderate to high yields.

Synthesis and Reactions of α-Hydroxyphosphonates

“…It is worth mentioning that starting from ketones, the accomplishment of the reaction is more challenging than in the cases applying aldehydes. The synthesis of α-alkyl-α-hydroxyphosphonates often requires the use of “exotic” catalysts [ 16 , 17 , 18 , 19 , 20 ], or an excess of a base. Procedures also applicable for the conversion of ketones are marked by an asterisk in Table 1 .…”

Environmentally Benign Syntheses of α-Substituted Phosphonates: Preparation of α-Amino- and α-Hydroxyphosphonates in Water, in Ionic Liquids, and under­ Solvent-Free Conditions

“…79 In a recent communication, Zhou and co-workers reported on synthesis of a series of dinuclear rare earth metal (i.e., yttrium, niobium, samarium, desprosium and ytterbium) amido complexes containing methylene-linked pyrrolylamido ligands and their application in the hydrophosphonylation of aldehydes and unactivated ketones, also under solvent-free conditions. 80 During preliminary experiments, the authors discovered that the reaction of benzaldehyde with diethylphosphite under neat conditions in the presence of 0.1 mol% of 12, a samarium amido complex containing a methylene-linked pyrrolyl-amido ligand, led to the desired α-hydroxyphosphonate in almost quantitative yield in only five minutes at room temperature. In an examination of the protocol's scope, it was shown that both aromatic and aliphatic aldehydes reacted well under solvent-free conditions at room temperature, yielding the desired α-hydroxyphosphonates in good to excellent yields in a reaction time of just five minutes (Table 35).…”

Recent Advances in H-Phosphonate Chemistry. Part 2. Synthesis of C-Phosphonate Derivatives

“…This catalytic system was developed further by combining it with calix [4]pyrrole [61] to form dinuclear trivalent lanthanide amido complexes bearing tetra-anion calix [4]pyrrolyl ligands. Alternatively, the lanthanide catalyst could be combined with methylenelinked pyrrolyl-amino ligands [62] to form dinuclear lanthanide complexes. Both groups of catalysts turned out to be highly efficient for the hydrophosphonylation of aldehydes and inactivated ketones.…”