Highly Reactive SmII Macrocyclic Clusters: Precursors to N2 Reduction

Highly efficient hydrophosphonylation of aldehydes and unactivated ketones catalyzed by methylene-linked pyrrolyl rare earth metal amido complexes

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.

Samarium complexes of a sigma-/pi-pyrrolide/arene based macrocyclic ligand

A bis-pyrrolide macrocyclic ligand [L = trans-calix[2]benzene[2]pyrrole(H)] containing two aromatic phenyl rings in the macrocycle backbone was reacted with SmCl(3)(THF)(3) to afford the corresponding [LSm(III)Cl] (1) complex. Its crystal structure showed the ligand adopting the sigma-bonding mode with the pyrrolide moieties and the pi-bonding with the two aromatic rings. Reaction of 1 with MeLi in THF gave a mixture of two compounds. The major was a C-H activated complex [LSm(III)(THF)] (2a) where the bonding mode of the pyrrolide rings was switched from sigma- to pi- as a result of the deprotonation and metallation of one of the two aromatic rings. The minor component was an unusual [(L)Sm(III)(HL')] (2b) complex containing both a regular ligand and an "N-confused" macrocyclic ligand. The two ligands wrapped the Sm center with the regular ligand adopting a bonding mode similar to 1. The second ligand instead acted as a simple sigma-bonded monodentate ligand, only using one nitrogen atom of one pyrrolide ring. However, this particular pyrrolide moiety has been isomerized by shifting the ring attachment to the macrocycle (N-confused system). In addition, the second pyrrolide ring has been protonated at the nitrogen atom. Complex 2b was obtained as major compound and in analytically pure form by reacting 1 with NaH.