Lanthanide Amides Research Articles

Synthesis, structure and catalytic activity of alkali metal-free bent-sandwiched lanthanide amido complexes with calix[4]-pyrrolyl ligands

Simple silylamine elimination reactions of calix[4]-pyrrole [R(2)C(C(4)H(2)NH)](4) (R = Me (1), {-(CH(2))(5)-}(0.5) (2)) with 2 equiv. of [(Me(3)Si)(2)N](3)Ln(μ-Cl)Li(THF)(3) (Ln = Nd, Sm, Dy) in reflux toluene, afforded the novel dinuclear alkali metal-free trivalent lanthanide amido complexes (η(5):η(1):η(5):η(1)-R(8)-calix[4]-pyrrolyl){LnN(SiMe(3))(2)}(2) (R = Me, Ln = Nd (3), Sm (4), Dy (5); R = {-(CH(2))(5)-}(0.5), Ln = Nd (6), Sm(7)). The complexes were fully characterized by elemental analyses, spectroscopic analyses and single-crystal X-ray analyses. X-ray diffraction studies showed that each lanthanide metal was supported by bispyrrolyl anions in an η(5) fashion and along with three nitrogen atoms from N(SiMe(3))(2) and two other pyrroyl rings in η(1) modes formed the novel bent-sandwiched lanthanide amido bridged trivalent lanthanide amido complexes, similar to ansa-cyclopentadienyl ligand-supported lanthanide amides with respect to each metal center. The catalytic activities of these organolanthanide complexes as single component l-lactide polymerization catalysts were studied.

Dehydrosilylation of ArNHSiH3 with Ytterbium(II) Amide: Formation of a Dimeric Ytterbium(II) Silanimine Complex

Agostic silanimine complexes: Reaction of [Yb{N(SiMe3)2}2(thf)2] with ArNHSiH3 resulted in the formation of the first lanthanide silanimine complex [{ArNSiH[N(SiMe3)2]}2Yb2] (see picture), having a planar Yb2Si2 core with significant α-(SiH)⋅⋅⋅Yb interactions, as well as the monomeric homoleptic lanthanide(II) amide [{ArNSiH2[N(SiMe3)2]}2Yb], showing β-agostic (SiH)⋅⋅⋅Yb interactions. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Lanthanide Amides [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 Catalyzed Hydrophosphonylation of Aryl Aldehydes

A highly efficient method for the synthesis of α-hydroxy phosphonates via lanthanide amides [(Me(3)Si)(2)N](3)Ln(μ-Cl)Li(THF)(3) catalyzed hydrophosphonylation of aromatic aldehydes was developed. The reactions produced the products in excellent yields in the presence of 0.1 mol % [(Me(3)Si)(2)N](3)La(μ-Cl)Li(THF)(3) at room temperature within 5 min. The existence of LiCl in the catalyst was a key factor affecting the catalytic activity. The mechanism for the process of high efficiency was proposed.

Synthesis and Structural Characterization of Lanthanide Amides Stabilized by an N‐Aryloxo Functionalized β‐Ketoiminate Ligand

AbstractThe synthesis and characterization of dimeric lanthanide amides stabilized by a dianionic N‐aryloxo functionalized β‐ketoiminate ligand are described in this paper. Reactions of 4‐(2‐hydroxy‐5‐tert‐butyl‐phenyl)imino‐2‐pentanone (LH2) with Ln[N(SiMe3)2]3(µ‐Cl)Li(THF)3 in a 1:1 molar ratio in THF gave the dimeric lanthanide amido complexes [LLn{N(SiMe3)2}(THF)]2 [Ln=Nd (1), Sm (2), Yb (3), Y (4)] in good isolated yields. These complexes were characterized by IR spectroscopy, elemental analysis, and 1H NMR spectroscopy in the case of complex 4. The definitive molecular structures of complexes 1, 3, and 4 were determined. It was found that complexes 1 to 4 can initiate the ring‐opening polymerization of L‐lactide.

Lanthanide Amide‐catalyzed Aza‐Henry Reaction of N‐Tosyl Imines with Nitroalkanes

AbstractIn the presence of 10 mol% lanthanide amide [(Me3Si)2N]3Ln(µ‐Cl)Li(THF)3, the aza‐Henry reaction of N‐tosyl imines with nitroalkanes (1:5 molar ratio) could be performed in good yields. The lanthanide amide‐catalyzed aza‐Henry reaction has the features of mild reaction conditions, tolerance of a variety of aromatic aldehyde‐derived imines and nitroalkanes, short time and good chemical yields. A catalytic mechanism for the reaction was also proposed.

Synthesis and characterization of N-aryloxo-functionalized β-ketoiminate rare-earth complexes and their catalytic activity for the polymerization of ɛ-caprolactone

The synthesis and characterization of dimeric rare-earth amides stabilized by a dianionic N-aryloxo functionalized β-ketoiminate ligand are described. Reactions of 4-(2-hydroxy-5-methyl-phenyl) imino-2-pentanone (LH2) with Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 in a 1:1 molar ratio in THF gave the dimeric rare-earth amido complexes [LLn{N(SiMe3)2}(THF)]2 [Ln = Nd (1), Sm (2), Yb (3), Y (4)]. These complexes were well characterized, and the definitive molecular structures of complexes 3 and 4 were determined. It was found that complexes 1–4 can initiate the ring-opening polymerization of ɛ-caprolactone, and the ionic radii of the central metals have significant effect on the catalytic activity.

Lanthanide(II) amide complexes: Efficient initiators for the living polymerization of methyl methacrylate

AbstractLanthanide(II) complexes supported by amido ligands, [(C6H5)(Me3Si)N]2Ln(DME)2 [Ln = Sm (1) or Yb (2); DME = 1,2‐dimethoxyethane] and [(C6H3iPr2‐2,6)(Me3Si)N]2Ln(THF)2 [Ln = Sm (3) or Yb (4); THF = tetrahydrofuran], were found to initiate the polymerization of methyl methacrylate (MMA) as efficient single‐component initiators (in toluene for 3 and 4 and in toluene with a small amount of THF for 1 and 2) to produce syndiotactic polymers. The catalytic behavior was highly dependent on both the amido ligand and the polymerization temperature. Initiators 3 and 4 initiated MMA polymerization over a wide range of temperatures (20°C to −40°C), whereas the polymerization with 1 and 2 proceeded smoothly only at low temperatures (≤0°C). The kinetic behavior and some features of the polymerizations of MMA initiated by 3 and 4 were studied at −40°C. The polymerization rate was first‐order with the monomer concentration. The molar masses of the polymers increased linearly with the increase in the polymer yields, whereas the molar mass distributions remained narrow and unchanged throughout the polymerization; this indicated that these systems had living character. A polymerization mechanism initiated by bimetallic bisenolate formed in situ was proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

C−H and Si−N Bond Oxygenations of a Divalent Ytterbium Amide of the Pyrrolyl-Cyclopentadienyl Ligand

Reaction of Me4C5H-SiMe2-NC4H4 with Yb[N(SiMe3)2]2(THF)2 yielded a new type of ansa-sandwich divalent lanthanide amide (Me4C5-SiMe2-NC4H4)YbN(SiMe3)2 (2), in which the Yb atom is η5-coordinated to both the C5 and C4N rings. 2 rapidly reacted with dioxygen to give a dinuclear trivalent ytterbium species via intramolecular C−H and Si−N bond oxygenation reactions.

Regioselectivity Control in the Metal‐Catalyzed Functionalization of γ‐Allenols, Part 2: Theoretical Study

The gold-, palladium- and lanthanum-catalyzed oxycyclization reactions of azetidin-2-one-tethered gamma-allenol derivatives to a variety of fused enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines have been developed experimentally (Part 1, accompanying paper). The mechanisms of these regiocontrolled metal-catalyzed heterocyclization reactions have now been computationally explored at the DFT level (Part 2). The energies of the reaction intermediates and transition states for different possible pathways have been calculated in various model systems very close to the real system. Additionally, we selected the La[N(SiH(3))(2)](3) complex to simulate the lanthanide amide precatalyst species. The agreement of theoretically predicted and experimentally observed selectivities is very good in all cases.

A Study of Ligand Coordination at Lanthanide and Group 4 Metal Centers by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Reactions of lanthanide amide reagents Ln{N(SiMe3)2}3 (where Ln = Sm, Gd, Ho, or Yb) with amine-bis(phenol) ligands were probed using inert atmosphere matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) (anthracene matrix); the technique rapidly confirms ligand coordination, giving excellent agreement with theoretical isotope patterns for lanthanide(amine-phenolate) fragments. Spectra on isolated lanthanide amine-bis(phenolate) amido complexes are similar to those seen from small scale parallel reactions of metal amides and protonated ligands. Although in all cases molecular ion peaks are not observed, peaks for lanthanide arene complexes, [M + arene]+•, formed in situ, are seen. The lack of molecular ion peak is due to difficulties in ionizing Ln3+ complexes by charge transfer. However, if Nujol is used to disperse the analyte and matrix prior to analysis rather than toluene, arene adducts are not observed. Similar phenol-derived ligands can be reacted with diamagnetic M(NMe2)4 (where M = Ti or Zr), and amine-phenolate complex formation is again confirmed easily by MALDI-TOF MS or LDI-TOF MS (no matrix). These complexes were also characterized by NMR spectroscopy and elemental analysis on isolated samples.

Migration of amide to imine group of lanthanide Schiff base complexes: effect of amido group

The protonolysis of anionic lanthanide amide complexes (THF)LiLn(NPri2)4 with two equiv. of tridentate Schiff base HL (L=3,5-But(2)-2-O-C6H2CH=N-C5H4N) afforded the unanticipated products LiL'2Ln(THF) (L'=3,5-But(2)-2-O-C6H2CH(NPri2)-N-C5H4N; Ln=Y 1, Sm 2 and Yb 3) formed by intramolecular nucleophilic attack of the amide groups at the imine carbon atoms of the original ligand, L. The protonolysis is greatly affected by the amide group. When amine elimination was carried out with a mixture of Ln[N(TMS)2]3(micro-Cl)Li(THF)3 (TMS=SiMe3) and LiN(TMS)2, the expected lanthanide amide complexes with two Schiff base ligands, L2Ln[N(TMS)2] (Ln=Sm 4 and Nd 5), were isolated and no migration of the N(TMS)2 group was observed because of steric hindrance. Complexes 1-5 were well characterized including X-ray structural analyses.

Simple Lanthanide Amides [(Me3Si)2N]3Ln(µ‐Cl)Li(THF)3 as Highly Efficient Catalysts for the Nitroaldol Reaction

AbstractThis contribution is to report the application of simple lanthanide amides [(Me3Si)2N]3Ln(µ‐Cl)Li(THF)3 exhibiting a high activity toward catalyzing Henry reaction of aromatic aldehydes with nitroalkanes to give β‐nitroalcohols or β‐nitroolefins with a very good chemoselectivity by controlling the reaction temperatures and by selecting aromatic aldehydes. It was found that this catalytic system was compatible with a wide range of substrates of aldehydes.

ChemInform Abstract: Preparation and Characteristics of Various Rare Earth Nitrides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

New Chiral Lanthanide Amide Ate Complexes for the Catalysed Synthesis of Scalemic Nitrogen‐Containing Heterocycles

New chiral binaphthylamido yttrium and ytterbium ate complexes with lithium and potassium counterions have been synthesised and characterised. X-ray structures have been obtained for [Li(thf)4][Ln{(R)-C20H12(NC5H9)2}2] (Ln=Yb, Y) and [K(thf)5][Yb{(R)-C20H12(NCH2CMe3)2}2] as isostructural complexes. The efficiency of these complexes for the enantioselective intramolecular hydroamination was examined. [Li(thf)4][Yb{(R)-C20H12(NC5H9)2}2] afforded the highest enantiomeric excess (up to 87 %) for the synthesis of a spiropyrrolidine, while [Li(thf)4][Y{(R)-C20H12(NC5H9)2}2] proved to be slightly more active. The role of the counter cation in the active catalytic species was evidenced by the comparison between lithium and potassium ate complexes. The most active catalyst of this series, [Li(thf)4][Yb{(R)-C20H12(NCH2CMe3)2}2], was successfully used for the cyclisation of aminopentenes with internal double bonds.

ChemInform Abstract: Highly Atom Efficient Guanylation of Both Aromatic and Secondary Amines Catalyzed by Simple Lanthanide Amides.

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Synthesis, Structure, and Diverse Catalytic Activities of [Ethylenebis(indenyl)]lanthanide(III) Amides on N—H and C—H Addition to Carbodiimides and ε‐Caprolactone Polymerization.

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Controlled Syntheses, Characterization, and Reactivity of Neutral and Anionic Lanthanide Amides Supported by Methylene-Linked Bis(phenolate) Ligands

A series of neutral and anionic bis(phenolate) lanthanide amides were synthesized by general metathesis reactions, and their reactivity was explored. Protolytic ligand exchange reactions of MBMPH2 (MBMP = 2,2'-methylene bis(6-tert-butyl-4-methyl-phenolate)) with [Ln{N(TMS)2}2(mu-Cl)(THF)]2 (TMS = SiMe3) afforded the desired bridged bis(phenolate) lanthanide chlorides [(MBMP)Ln(mu-Cl)(THF)2]2 [Ln = Nd (1), Yb (2)] in high isolated yields. These lanthanide chlorides were found to be useful precursors for the synthesis of the corresponding lanthanide derivatives. Reactions of 1 and 2 with 2 equiv of NaN(TMS)2 in THF produced the expected neutral bis(phenolate) lanthanide amido complexes (MBMP)Ln[N(TMS)2](THF)2 [Ln = Nd (3), Yb (4)] in high yields. Whereas the reactions of 1 and 2 with LiN(TMS)2 in a 1:4 molar ratio gave the anionic bis(phenolate) lanthanide amides as discrete ion-pair complexes [Li(THF)4][(MBMP)Ln{N(TMS)2}2] [Ln = Nd (5), Yb (6)] in high isolated yields. Further study revealed that 5 and 6 can also be conveniently synthesized in high yields by the direct reactions of MBMPH2 with [Ln{N(TMS)2}2(mu-Cl)(THF)]2 in a 2:1 molar ratio, and then with 4 equiv of nBuLi. The reactivity of the neutral and anionic bis(phenolate) lanthanide amides was comparatively investigated. It was found that the insertion reactions of carbodiimide into the Ln-N bond of neutral lanthanide amido complexes 3 and 4 gave the anticipated bis(phenolate) lanthanide guanidinate complexes [(mu-O-MBMP)Nd{(iPrN)2CN(TMS)2}]2 (7) and (MBMP)Yb[(iPrN)2CN(TMS)2] (8), respectively, in high yields, whereas the similar reaction of carbodiimide with anionic amido complex 5 provided the unexpected ligand-redistributed products, and the homoleptic ion-pair bis(phenolate) neodymium complex [Li(DME)2(THF)][(MBMP)2Nd(THF)2] (9) was finally isolated as one of the products. Furthermore, the anionic bis(phenolate) lanthanide amides showed higher catalytic activity for the polymerization of epsilon-caprolactone than the neutral ones. All of the complexes were characterized with elemental analysis and IR spectra, and the definitive molecular structures of 1-3 and 5-9 were provided by single-crystal X-ray analyses.

Bis(phosphinimino)methanide Rare Earth Amides: Synthesis, Structure, and Catalysis of Hydroamination/Cyclization, Hydrosilylation, and Sequential Hydroamination/Hydrosilylation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Highly Atom Efficient Guanylation of both Aromatic and Secondary Amines Catalyzed by Simple Lanthanide Amides

It is demonstrated that the cyclopentadienyl-free simple lanthanide amides [(Me(3)Si)(2)N](3)Ln(mu-Cl)Li(THF)(3)(Ln = La, Sm, Eu, Y, Yb) and Ln[N(SiMe(3))(2)]3 (Ln = Y, Yb) are highly efficient catalysts for the guanylation of both aromatic and secondary amines with a high activity under mild conditions. It is found that these catalysts are compatible with a wide range of solvents and substrates.

Synthesis, Structure, and Diverse Catalytic Activities of [Ethylenebis(indenyl)]lanthanide(III) Amides on N−H and C−H Addition to Carbodiimides and ε-Caprolactone Polymerization

The simple silylamine elimination reaction of ethylenebis(indene) with the lanthanide amides [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 produced the [ethylenebis(η5-indenyl)][bis(trimethylsilyl)amido]lanthanide(III) complexes (EBI)LnN(TMS)2 (Ln = Y (1), Sm (2), Yb (3)), which exhibited diverse catalytic activities on the addition of the N−H bond of amines and the C−H bond of terminal alkynes to the carbodiimides and on the ring-opening polymerization of e-caprolactone as well. The new complexes 1 and 2 were fully characterized by spectroscopic methods, elemental analyses, and X-ray crystallographic analyses. This work offers a straightforward, highly atom efficient route for the syntheses of substituted guanidines and propiolamidines, and it represents the first application of readily accessible lanthanocene amides to these reactions.