Rare-earth Metal Amides Research Articles

Enantioselective Michael addition of malonates to α,β-unsaturated ketones catalyzed by rare-earth metal amides RE[N(SiMe3)2]3 with phenoxy-functionalized amino alcohol proligands

A combination of rare-earth metal amides RE[N(SiMe3)2]3 and chiral phenoxy-functionalized amino alcohol proligands was developed to realize the enantioselective Michael addition of malonates with unsaturated ketones. The reactions catalyzed by samarium amide Sm[N(SiMe3)2]3 were performed best together with the chiral proligand H3L1 (H3L1 = 2,4-di-tert-butyl-6-((((1S,2R)-2-hydroxy-1,2-diphenylethyl) amino)methyl)phenol) in DCE with good group tolerance, mostly in high to excellent yields (85–98 %) and good to excellent ee values (50− >99 %). The possible mechanism was also proposed.

Enantioselective Michael Addition of Malononitrile to Unsaturated Ketones Catalyzed by Rare-Earth Metal Amides RE[N(SiMe3)2]3 with Phenoxy-Functionalized TsDPEN Ligands.

The catalytic enantioselective Michael addition of α,β-unsaturated ketones with malononitrile was well established using rare-earth metal amides RE[N(SiMe3)2]3 (RE = Y, Eu, Sm, Nd, La) with chiral phenoxy-functionalized TsDPEN ligands. The combination of lanthanum amide La[N(SiMe3)2]3 and chiral TsDPEN ligand H3L1 [H3L1 = N-((1R,2R)-2-((3,5-di-tert-butyl-2-hydroxybenzyl)amino)-1,2-diphenylethyl)-4-methylbenzenesulfonamide] in a 1:1.5 molar ratio was proved to be the optimal partner in THF, which provided the desired β-carbonyl dinitriles in excellent yields and good to high enantioselectivities after 12 h at -15 °C.

Syntheses and structures of bimetallic rare-earth complexes supported by pyrrolyl ligands and their high performance in isoprene polymerization

• A series of the pyrrolyl-ligated bimetallic rare earth metal amido complexes were synthesized and characterized. • Complexes used as catalyst for the polymerization of isoprene. • They were to be highly cis-1,4 selective for isoprene polymerization. The reactions of pyrrole with rare-earth metal amides [(Me 3 Si) 2 N] 3 RE( μ -Cl)Li(THF) 3 produced the bimetallic rare earth metal amido complexes (RE = Y( 1 ), Nd( 2 ), Yb( 3 )) in high yields. X-ray diffraction analysis revealed that the pyrrole was deprotonated with the pyrrolyl ring coordinated to one rare-earth metal in an η 5 mode and the nitrogen atom coordinated to another rare-earth metal in an η 1 modes forming the centrosymmetric structures. Complexes 1 – 3 as precatalysts for isoprene polymerization were investigated. Results showed that except for ytterbium system, all other complexes could initiate effectively the polymerization of isoprene to afford polyisoprene with high conversion, high regio- and stereo-selectivity (1,4- cis selectivity up to 95.2%) in the presence of cocatalysts. A types of pyrrolyl-ligated bimetallic rare earth metal amido complexes were constructed, and their coordinated modes and catalytic activity were studied.

Synthesis, structure and catalytic activity of rare-earth metal complexes derived from chiral phosphoryl-sulfonylamides

A series of rare-earth metal amides derived from (S)-N-(1-(2-(diphenylphosphoryl)phenyl)ethyl)benzenesulfonamide (HL1) and (S)-N-(8-(diphenylphosphoryl)-1,2,3,4-tetrahydronaphthalen-1-ylbenzenesulfonamide(HL2) were prepared, and their catalytic activity for the polymerization of rac-lactide was explored. The amine elimination reactions of Ln[N(SiMe3)2]3 with HL1 or HL2 gave the mono-ligated rare-earth metal amides (L1)Ln[N(SiMe3)2]2 (Ln = Nd (1), Sm (2) and Yb (3)) or bis-ligated rare-earth metal amides (L2)2Ln[N(SiMe3)2] (Ln = Nd (4), Sm (5)) in good yields. All of these complexes were characterized by elemental analyses and X-ray diffraction analyses. Complexes 1–5 are efficient initiators for the ring-opening polymerization of rac-lactide, affording heterotactic-rich polylactides. The ionic radii of the central metals have a significant effect on the catalytic activity.

Rare-Earth Metal Boroxide with Formal Triple Metal–Oxygen Orbital Interaction: Synthesis from B(C 6 F 5 ) 3 ·H 2 O and Radical-Anion Ligated Rare-Earth Metal Amides

Rare-earth metal boroxides are not only rare and of great synthetic challenge but also important theoretically due to their unrevealed bonding characteristics. In this paper, we report the synthesi...

Synthesis, structure and catalytic activity of rare-earth metal amino complexes incorporating imino-functionalized indolyl ligand

The reactions of the imino-functionalized indolyl ligand (HL, L = 3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5N) with the rare-earth metal amides [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 producing different types of rare-earth metal amido complexes were investigated. The reactions of HL with 1 equiv. of [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 generated a series of hetero-nuclear bimetallic rare-earth metal amino complexes {[η1:µ-η2-3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5]RE[N(SiMe3)2]2(µ-Cl)Li(THF)} (RE = Y(1), Sm(2), Gd(3), Er(4), Yb(5)). By extending the reaction time, only the reaction of HL with [(Me3Si)2N]3Gd(µ-Cl)Li(THF)3 gave an unexpected binuclear rare-earth metal complex {[(µ-η5:η1):η1:η1-3-[(Me2N)2-C14H9]-(NCH2CH2-C8H5N)2]Gd2[N(SiMe3)2]3} (6) incorporating a novel polycyclic ligand through C-C and C-N coupling. Treatment of HL with [(Me3Si)2N]3Sm(µ-Cl)Li(THF)3 in a 2:1 ratio generated the bis(indolyl) heteronuclear bimetallic rare-earth metal amino complex {(η1:η1-[µ-η2:η1-3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5]Li[µ-η2:η1-3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5])Sm[N(SiMe3)2]2} (7) in low yield probably due to accompanying with the formation of the complex 2. The above results indicated that reaction conditions play important roles in the formation of different coordination modes of the imino-functionalized indolyl rare-earth metal amido complexes. All new complexes 1−7 are fully characterized including X-ray structural determination. The catalytic activity of complexes 1-7 for the addition of amines to carbodiimides was explored. The results showed that all complexes displayed an excellent activity towards the addition of amines to carbodiimides producing guanidine under solvent-free condition.

Synthesis and characterization of aminophenolate-ligated rare-earth metal amide complexes and their catalytic activity for lactides polymerization

Amine elimination of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with aminophenol H[ON] {H[ON] = 2-(CH2NC5H10)-4,6-tBu2-C6H3OH} in 1:2 molar ratio in THF gave the monometallic rare-earth metal amide complexes [ON]2LnN(SiMe3)2 (Ln = Yb (1), Y (2), Gd (3), Sm (4), Nd (5)) in 57%—73% isolated yields. All these complexes were characterized by elemental analysis. The molecular structures of complexes 1–4 were determined by single crystal X-ray diffraction. These complexes are highly active for l-lactide polymerization to give high molecular weight polymers with unimodal molecular weight distributions. In addition, these complexes can also initiate rac-lactide polymerization with high activity to afford heterotactic-rich polylactides.

Synthesis, characterization and reactivity of rare-earth metal amide complexes supported by pyrrolyl-substituted cyclopentadienyl ligand

Absaact Amine elimination between rare-earth metal tris(amide) complexes Ln [N(SiHMe2)2]3 (THF)x and 1 equiv. of pyrrolyl-substituted cyclopentadienyl ligand C4H4NSiMe2C5Me4H was investigated. Reaction of C4H4NSiMe2C5Me4H and Ln [N(SiHMe2)2]3 (THF)x with small metals afforded the half-sandwich rare-earth metal bis(silylamide) complexes (C4H4NSiMe2C5Me4)Ln [N(SiHMe2)2]2 (Ln = Sc (1), Y (2)), while the same reaction using La [N(SiHMe2)2]3 (THF)2 isolated lanthanum mono-silylamide complex [C5Me4SiMe2N(SiHMe2)2]La [N(SiHMe2)2](C4H4N) (3). These complexes were characterized by elemental analysis and NMR spectroscopy. 1 and 3 were structurally authenticated by single crystal X-ray diffraction. The ternary catalyst systems of 1 or 2/AliBu3/[Ph3C][B(C6F5)4] showed activity towards styrene polymerization to give pure syndio-tactic polystyrenes (rrrr > 99%).

RE[N(SiMe3)2]3-Catalyzed Guanylation/Cyclization of Amino Acid Esters and Carbodiimides.

The example of rare-earth metal-catalyzed guanylation/cyclization of amino acid esters and carbodiimides is well-established, forming 4(3H)-2-alkylaminoquinazolinones in 65-96% yields. The rare-earth metal amides RE[N(TMS)2]3 (RE = Y, Yb, Nd, Sm, La; TMS = SiMe3) showed high activities, and La[N(TMS)2]3 performed best for a wide scope of the substrates.

Intermolecular addition of alcohols to carbodiimides catalyzed by rare-earth metal amides

Various isoureas were obtained in good to excellent yields via the addition reaction using La[N(SiMe3)2]3 as the catalyst.

Stereo-selectivity switchable ROP of rac-β-butyrolactone initiated by salan-ligated rare-earth metal amide complexes: the key role of the substituents on ligand frameworks.

A series of novel salan-ligated rare-earth metal amide complexes were prepared and employed as initiators for the ROP of rac-β-butyrolactone (rac-BBL). Tuning the substituents on the N atoms of the ligand frameworks from aromatic groups to aliphatic groups results in switching tacticity from iso-tactic to syndio-tactic in rac-BBL polymerization.

An efficient asymmetric hydrophosphonylation of unsaturated amides catalyzed by rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with phenoxy-functionalized chiral prolinols

An asymmetric hydrophosphonylation reaction of diethyl phosphite with α,β-unsaturated amides catalyzed by [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with H2Ln ((S)-2,4-R2-6-[[2-(hydroxydiphenylmethyl)pyrrolidin-1-yl]methyl]phenol) was disclosed.

Synthesis, characterization and catalytic activity of rare-earth metal amides incorporating cyclohexyl bridged bis(β-diketiminato) ligands

The bridged bis(β-diketiminato) ligands supported rare-earth amides exhibited high catalytic activity towards the hydrophosphination of β-nitroalkene and α,β-unsaturated carbonyl derivatives with an excellent regioselectivity.

Synthesis and characterization of bridged bis(amidato) rare earth metal amides and their applications in C-N bond formation reactions.

Based on three bisamide proligands H2Ln (n = 1–3) (H2L1 = [(Me3C6H2CONHCH2)2CH2], H2L2 = [(Me3C6H2CONHCH2)2C(CH3)2], H2L3 = [Me3C6H2CONH(CH2)2]2NCH3), eight bis(amidato) trivalent rare-earth metal amides {LnRE[N(TMS)2]}2 (n = 1, RE = La (1), Sm (2), Nd (3), Y (4); n = 2, RE = La (5), Nd (6);n = 3, RE = La (7), Nd (8); TMS = SiMe3) were successfully synthesized by treatment of H2Ln with RE[N(TMS)2]3 in a 1 : 1 molar ratio. Complexes 3, and 5–8 were characterized by single-crystal X-ray diffraction, and NMR characterization was carried out for the La complexes 1, 5, 7 and the Y complex 4. These complexes exhibited high catalytic activities in both the direct amidation of aldehydes and the addition of amines with carbodiimine. It was found that the bis(amidato) rare earth metal amides bearing different linkers have different effects on the transformations and lanthanum and neodymium complexes performed better than others.

Highly Enantioselective Epoxidation of α,β-Unsaturated Ketones Catalyzed by Rare-Earth Amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with Phenoxy-Functionalized Chiral Prolinols

A simple and efficient catalytic enantioselective epoxidation of α,β-unsaturated ketones has been successfully developed, which was catalyzed by rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Yb (1), La (2), Sm (3), Y (4), Lu (5)) in the presence of phenoxy-functionalized chiral prolinols at room temperature using tert-butylhydroperoxide (TBHP) as the oxidant. The combination of an Yb-based amide 1 and a chiral proligand (S)-2,4-di-tert-butyl-6-((2-(hydroxydiphenylmethyl)pyrrolidin-1-yl)methyl)phenol) performed very well, and both the yields and the enantiomeric excess of the chiral epoxides reached up to 99% and 99% ee.

Carboxylation of terminal alkynes with CO2 catalyzed by bis(amidate) rare-earth metal amides

Three novel bis(amidate) rare-earth metal amides were prepared and characterized. Treatment of CO2 with terminal alkynes obtained propiolic acids in high to excellent yields using the highest reactive Nd-based catalyst at ambient pressure.

Synthesis and characterization of bis(amidate) rare-earth metal amides and their application in catalytic addition of amines to carbodiimides

Five bis(amidate) rare-earth metal amides were successfully employed in guanidination, and the Nd-based catalyst showed the highest reactivity.

Reactivity of functionalized indoles with rare-earth metal amides. Synthesis, characterization and catalytic activity of rare-earth metal complexes incorporating indolyl ligands.

The reactivity of several functionalized indoles 2-(RNHCH2)C8H5NH (R = C6H5 (1), (t)Bu (2), 2,6-(i)Pr2C6H3 (3)) with rare-earth metal amides is described. Reactions of 1 or 2 with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Eu, Yb) respectively produced the europium complexes [2-(C6H5N[double bond, length as m-dash]CH)C8H5N]2Eu[N(SiMe3)2] (4) and [2-((t)BuN[double bond, length as m-dash]CH)C8H5N]Eu[N(SiMe3)2]2 (5), and the ytterbium complex [2-((t)BuN[double bond, length as m-dash]CH)C8H5N]2Yb[N(SiMe3)2] (6), containing bidentate anionic indolyl ligands via dehydrogenation of the amine to the imine. In contrast, reactions of the more sterically bulky indole 3 with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 afforded complexes [2-(2,6-(i)Pr2C6H3NCH2)C8H5N]RE[N(SiMe3)2](THF)2 (RE = Yb (7), Y (8), Er (9), Dy (10)) with the deprotonated indolyl ligand. While reactions of 3 with yttrium and ytterbium amides in refluxing toluene respectively gave the complexes [2-(2,6-(i)Pr2C6H3N[double bond, length as m-dash]CH)C8H5N]3Y (11) and [2-(2,6-(i)Pr2C6H3N[double bond, length as m-dash]CH)C8H5N]2Yb(II)(THF)2 (12), along with transformation of the amino group to the imino group, and also with a reduction of Yb(3+) to Yb(2+) in the formation of 12. Reactions of 3 with samarium and neodymium amides provided novel dinuclear complexes {[μ-η(5):η(1):η(1)-2-(2,6-(i)Pr2C6H3NCH2)C8H5N]RE[N(SiMe3)2]}2 (RE = Sm (13), Nd (14)) having indolyl ligands in μ-η(5):η(1):η(1) hapticities. The pathway for the transformation of the amino group to the imino group is proposed on the basis of the experimental results. The new complexes displayed excellent activity in the intramolecular hydroamination of aminoalkenes.

Synthesis and characterization of rare-earth metal complexes supported by a new pentadentate Schiff base and their application in heteroselective polymerization of rac-lactide

Both rare-earth metal salen aryloxides and amides can efficiently initiate the ring-opening polymerization of rac-lactide to give heterotactic-rich polylactides.

Synthesis, structure, and catalytic activity of rare-earth metal amides with a neutral pyrrolyl-functionalized indolyl ligand

The reactions of neutral pyrrolyl-functionalized indole with rare-earth metal amides [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 produced the rare-earth metal complexes [(Me3Si)2N]2RE([η1:µ-η2-3-(2-(N-CH3)C4H3NCH=N-CH2CH2)C8H5N])(µ-Cl)Li(THF) (RE = Er, Y) having indolyl ligand η1 bonded to rare-earth metal ion and η2 bonded to lithium ion. The catalytic activities of these lanthanide amido complexes for addition of terminal alkynes to aromatic nitriles were explored. Results reveal that these complexes displayed a good catalytic activity for the addition reaction under mild conditions.