Lanthanide Amides Research Articles

Lanthanide Amide Complexes Supported by the Bis‐tris(pyrazolyl)borate Ligand Environment

AbstractSynthesis of primary lanthanide amides in the bis‐hydrotris(1‐pyrazolyl)borate ligand environment has been achieved. Salt metathesis of [Dy(Tp)2(OTf)] 1‐Dy (OTf=CF3SO3) with K(N′′) (N′′=N(SiMe3)2) in toluene yielded the [bis(silyl)]amide [Dy(Tp)2(N′′)] 2‐Dy. Complexes 1‐Ln and 2‐Ln were both used to access primary lanthanide amides, where either metathesis of 1‐Ln with K(NHArCF3) (ArCF3=C6H3(CF3)2‐3,5) or protonolysis of 2‐Ln with H2NArCF3 in toluene yielded [Ln(Tp)2(NHArCF3)] 3‐Ln (Ln=Y, Dy). The synthesis of parent amides was also attempted, but the metathesis of 1‐Y with NaNH2 yielded complicated reaction mixtures, but from which the dimeric parent amide [{Y(Tp)2(μ‐NH2)}2] 4‐Y and an ‘ate’‐salt [{Y(Tp)2(μ2‐OTf)(μ3‐OTf)Na(THF)2}2] 5‐Y were isolated. Full characterisation data are presented for all complexes, including the structure determination.

Synthesis of Benzoxazine Functionalized Amine‐Bridged Bis(phenolato) Rare Earth Complexes and Their Application in Ring‐Opening Polymerization of rac‐Lactide

Comprehensive SummaryThe reactivities of benzoxazine functionalized amine bridged bis(phenol)s LnH2 (n = 1—3) with rare earth metal complexes were explored, founding that both the aryl substituents of the ligand and the rare earth metals have profound influences on reaction outcomes. Reactions of L1H2 (R = tBu) with [N(SiMe3)2]3RE(μ‐Cl)Li(THF)3 (RE = La, Nd) afforded the expected rare earth amides L1RE[N(SiMe3)2](THF) (RE = La (1), Nd (2)). However, the similar reaction of L2H2 (R = OMe) and L3H2 (R = Me) with [N(SiMe3)2]3La(μ‐Cl)Li(THF)3 generated the unexpected amine bridged triphenolato lanthanum complexes L2‐NR2La(THF)(μ‐Cl)Li(THF)2 (3) and L3‐NR2La(THF)(μ‐Cl)Li(THF)2 (4), respectively, in which the benzoxazine ring is opened, and a plausible mechanism was proposed. Furthermore, the reactions of L1H2 with [N(SiMe3)2]3RE(μ‐Cl)Li(THF)3 (RE = Y, Yb) produced the unexpected benzoxazine ring‐opened products L1‐HRE(THF) (RE = Y (5), Yb (6)). Further study revealed that the reaction of L1H2 with Cp3Y(THF) in a 1: 1 molar ration in THF gave the corresponding yttrium complex L1YCp·THF (7a), but the benzoxazine ring‐opened product L1‐OCH2PhY(THF) (7b) was formed when 1 equivalent of benzoic alcohol was added. The benzoxazine functionalized amine bridged bis(phenolato) rare earth amides were efficient initiators for the ring‐opening polymerization of rac‐lactide, giving heterotactic polylactide with Pr value up to 0.93.

Six-coordinated dinuclear lanthanide(III) amide complexes: investigation of magnetization relaxation dynamics and their electronic structures.

A series of rare six-coordinated dinuclear Ln(III) complexes [Ln2(μ-Cl)2Cl4Li2(L)2(THF)6] were structurally characterized using a bulky amide ligand (L; Ln = Gd(1), Dy(2) and Y(3)). Detailed magnetic studies disclose that a weak antiferromagnetic coupling exists within 1 (-0.09 cm-1) and 2 (-0.07 cm-1; -2J Hamiltonian). Additionally, this study unveils the importance of the amide ligand at the coordination site of Dy(III), which manifests a slow relaxation of magnetization in the absence of an external magnetic field. This has been rationalized by detailed ab initio calculations as well as the electronic structure determination of 1 and 2.

Cyclic (Alkyl)(amino)carbene Lanthanide Amides: Synthesis, Structure, and Catalytic Selective Hydrosilylation of Alkenes.

The first examples of cyclic (alkyl)(amino)carbene (CAAC) lanthanide (Ln) complexes were synthesized from the reaction of CAAC with Yb[N(SiMe3)2]2 and Eu[N(SiMe3)2]2(THF)2 (THF = tetrahydrofuran). The structures of (CAAC)Yb[N(SiMe3)2]2 (2) and (CAAC)Eu[N(SiMe3)2]2(THF) (3) were determined by X-ray diffraction analysis. Density functional theory calculations of 2 revealed the predominantly ionic bond between the Ln ion and CAAC. Complex 3 enabled catalytic hydrosilylation of aryl- and silylalkenes with primary and secondary silanes in high yields and Markovnikov selectivity.

Lanthanide Silylamide-Catalyzed Synthesis of Pyrano[2,3-b]indol-2-ones.

A lanthanide silylamide-catalyzed tandem reaction of isatins, diethyl phosphite, and 2,3-diarylcyclopropenones has been developed. A series of pyrano[2,3-b]indol-2-ones were synthesized in high yields. The cooperation of the Lewis acidity of the lanthanide center and the Bronsted basicity of the N(SiMe3)2 anion may be the key factor affecting the catalytic activity of lanthanide amides.

Homoleptic Lanthanide Amide Catalysts for Organic Synthesis: Experiment and Theory

Homoleptic lanthanide trisamides provide a simple and highly accessible bridge between organolanthanide chemistry and the synthetic methodology community, and although they have proven to be compet...

Synthesis and characterization of β-diketiminato lanthanide amide complexes and their catalytic activity toward L-lactide polymerization

Amine elimination between lanthanide tris(amide) complexes Ln[N(TMS)2]3(μ-Cl)Li(THF)3 (TMS = SiMe3) and 1 equiv. of β-diketimine [CH3CN(C6H4OMe-o)CHCN(C6H4-iPr2-2,6)CH3]H (BDI-H) in toluene or THF at room temperature afforded β-diketiminato lanthanide bis(amide) complexes (BDI)Ln[N(TMS)2]2 (Ln = Sm (1), Yb (2)) in 86-89% isolated yields, while the same reaction was conducted in toluene at 110 °C gave the unexpected product [(BDI’)SmN(TMS)2]2 (BDI’ = CH3CN(C6H4O-o)C(CH3)CN(C6H4-iPr2-2,6)CH3) (3) in 40% yield. In contrast, treatment of lanthanide tris(amide) complex with a larger metal Nd[N(TMS)2]3(μ-Cl)Li(THF)3 with 1 equiv of BDI-H in toluene, whether at 110 °C or at room temperature, produced exclusively only β-diketiminato neodymium bis(amide) complex (BDI)Nd[N(TMS)2]2 (4). These lanthanide metal complexes were characterized by elemental analysis, and structurally authenticated by single crystal X-ray diffraction. It was found that all these lanthanide amide complexes were active for the ring-opening polymerization of L-lactide.

One-step synthesis of heteroleptic rare-earth amide complexes featuring fluorenyl-tethered N-heterocyclic carbene ligands

Reaction of the fluorenyl-tethered imidazolium bromide salt [9-(C13H9)C2H4N(CH)C2H2N(Me)][Br] (I) with [Y{N(SiMe3)2}3] generated the heteroleptic yttrium complex [Y{(η5-C13H8)C2H4N(κ-C)C2H2N(Me)}(Br){N(SiMe3)2}] (1), which contains an Y centre with a piano-stool geometry and four different donors. The reaction of I with [Nd{N(SiMe3)2}3] led to single crystals of the dimeric Nd complex [Nd{(η5-C13H8)C2H4N(κ-C)C2H2N(Me)}(μ-Br){N(SiMe3)2}]2 (2), likely due to the larger ionic radius of Nd3+. Reactions of I with [La{N(SiMe3)2}3], which contains the larger La3+ ion, demonstrated the formation of multiple products from ligand redistribution, including [La{(η5-C13H8)C2H4N(κ-C)C2H2N(Me)}{N(SiMe3)2}2] (3) and [La{(η5-C13H8)C2H4N(κ-C)C2H2N(Me)}2(Br)] (4).

The importance of the counter-cation in reductive rare-earth metal chemistry: 18-crown-6 instead of 2,2,2-cryptand allows isolation of [YII(NR2)3]1- and ynediolate and enediolate complexes from CO reactions.

The use of 18-crown-6 (18-c-6) in place of 2.2.2-cryptand (crypt) in rare earth amide reduction reactions involving potassium has proven to be crucial in the synthesis of Ln(ii) complexes and isolation of their CO reduction products. The faster speed of crystallization with 18-c-6 appears to be important. Previous studies have shown that reduction of the trivalent amide complexes Ln(NR2)3 (R = SiMe3) with potassium in the presence of 2.2.2-cryptand (crypt) forms the divalent [K(crypt)][LnII(NR2)3] complexes for Ln = Gd, Tb, Dy, and Tm. However, for Ho and Er, the [Ln(NR2)3]1− anions were only isolable with [Rb(crypt)]1+ counter-cations and isolation of the [YII(NR2)3]1− anion was not possible under any of these conditions. We now report that by changing the potassium chelator from crypt to 18-crown-6 (18-c-6), the [Ln(NR2)3]1− anions can be isolated not only for Ln = Gd, Tb, Dy, and Tm, but also for Ho, Er, and Y. Specifically, these anions are isolated as salts of a 1 : 2 potassium : crown sandwich cation, [K(18-c-6)2]1+, i.e. [K(18-c-6)2][Ln(NR2)3]. The [K(18-c-6)2]1+ counter-cation was superior not only in the synthesis, but it also allowed the isolation of crystallographically-characterizable products from reactions of CO with the [Ln(NR2)3]1− anions that were not obtainable from the [K(crypt)]1+ analogs. Reaction of CO with [K(18-c-6)2][Ln(NR2)3], generated in situ, yielded crystals of the ynediolate products, {[(R2N)3Ln]2(μ-OC Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CO)}2−, which crystallized with counter-cations possessing 2 : 3 potassium : crown ratios, i.e.{[K2(18-c-6)3]}2+, for Gd, Dy, Ho. In contrast, reaction of CO with a solution of isolated [K(18-c-6)2][Gd(NR2)3], produced crystals of an enediolate complex isolated with a counter-cation with a 2 : 2 potassium : crown ratio namely [K(18-c-6)]22+ in the complex [K(18-c-6)]2{[(R2N)2Gd2(μ-OCH Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHO)2]}.

Cycloaddition of Aziridine with CO2/CS2 Catalyzed by Amidato Divalent Lanthanide Complexes.

This is the first time that the amidato lanthanide amides ({L nLn[N(SiMe3)2]THF}2 ( n = 1, Ln = Eu (1); n = 2, Ln = Eu (3), Yb (4); HL1 = tBuC6H4CONHC6H3( iPr)2; HL2 = C6H5CONHC6H3( iPr)2) and {L3Eu[N(SiMe3)2]THF}{L32Eu(THF)2} (2) (HL3 = ClC6H4CONHC6H3( iPr)2)) were applied in the cycloaddition reactions of aziridines with carbon dioxide (CO2) or carbon disulfide (CS2) under mild conditions. The corresponding oxazolidinones and thiazolidine-2-thiones were obtained in good to excellent yields with good functional group tolerance.

Lanthanide complexes combined with chiral salen ligands: application in the enantioselective epoxidation reaction of α,β-unsaturated ketones.

Readily available lanthanide amides Ln[N(SiMe3)2]3 (Ln = Nd (1), Sm (2), Eu (3), Yb (4), La (5)), combined with chiral salen ligands H2La ((S,S)-N,N′-di-(3,5-disubstituted-salicylidene)-1,2-cyclohexanediamine) and H2Lb ((S,S)-N,N′-di-(3,5-disubstituted-salicylidene)-1,2-diphenyl-1,2-ethanediamine) were employed in the enantioselective epoxidation of α,β-unsaturated ketones. It was found that the salen–La complex shows the highest efficiency and enantioselectivity. A relatively broad scope of α,β-unsaturated ketones was investigated, and excellent yields (up to 99%) and moderate to good enantioselectivities (37–87%) of the target molecules were achieved.

Synthesis and thermal behavior of [Li(thf)3(μ-Cl)La{N(SiMe3)2}3] and its investigation as spin-coating precursor for lanthanum-based layer formation

The lanthanum(III) complex [Li(thf)3(μ-Cl)La{N(SiMe3)2}3] (3) was obtained by the reaction of LaCl3 with three equiv of Li[N(SiMe3)2]3 in a tetrahydrofuran solution. The molecular structure of 3 in the solid state was characterized by a tetracoordinated anionic lanthanide(III) amide in form of an adduct with LiCl(thf)3 as evidenced by single crystal X-ray structure analysis. In order to study the suitability of 3 as a precursor for the deposition of La2O3/LiLaSiO4 by thin layer deposition techniques, its thermal behavior was investigated by thermogravimetry (TG) and TG-MS-coupled studies. TG studies show a two-step decomposition process, whereby volatile decomposition products can be detected during the second decomposition step. TG measurements under an atmosphere of oxygen produced La2O3. Calcination processes of 3 under ambient atmosphere for 10 h at 1000 °C gave La2O3 and LiLaSiO4, which was confirmed by PXRD studies. Metal-organic 3 was applied as spin-coating precursor for La2O3 thin film formation giving the as-deposited layers nearly crack-free.

NMR spectroscopic study of the adduct formation and reactivity of homoleptic rare earth amides with alkali metal benzyl compounds, and the crystal structures of [Li(TMEDA)2][Nd{N(SiMe3)2}3(CH2Ph)] and [{Li(TMP)}2{Li(Ph)}

An NMR spectroscopic study has been conducted into the reactivity of alkali metal benzyls [M(CH2Ph)], (M = Li, Na, K) with lanthanide tris(amide) complexes [Ln(N″)3] (Ln = Y, Ce, Nd; N″ = N(SiMe3)2) and [Ce(TMP)3] (TMP = 2,2,6,6-tetramethylpiperidide). It was found that for [Ln(N″)3], benzyl adducts [M][Ln(N″)3(CH2Ph)] were initially formed, and the molecular structure for M = Li(TMEDA)2 and Ln = Nd was determined revealing a distorted tetrahedral [Nd(N″)3(CH2Ph)] anion. In all cases, these adduct complexes were unstable, intramolecularly deprotonating a methyl arm of a N″ ligand via benzyl basicity and eliminating toluene to prepare cyclometallated complexes of the form [M][Ln(N″)2{κ2-CH2Si(Me)2N(SiMe3)}]. In parallel studies, reactions of [Li(Ph)] with [Ln(N″)3] (Ln = Ce, Nd) afforded [Li(N″)], whilst for (Ln = Y) adduct formation was observed. [Ce(TMP)3] did not generate any characterisable bimetallic adducts. The reaction of [Li(Ph)] with [Li(TMP)] afforded the hexanuclear [{Li(TMP)}2{Li(μ-Ph)}]2, which features lithium in three different coordination environments.

Synthesis and characterization of lanthanide complexes stabilized by N-aryl substituted β-ketoiminato ligands and their application in the polymerization of rac-lactide

Several lanthanide complexes supported by N-aryl substituted β-ketoiminato ligands were synthesized by the protonolysis reaction. Reactions of 1-phenyl-3-N-(p-methoxyphenylimino)-1-butanone (HL) with Ln[N(SiMe3)2]3 and Ln(OAr)3(THF) (ArO = 2,6-But2-4-MeC6H2O) in a 2:1 M ratio gave mononuclear lanthanide amides L2Ln[N(SiMe3)2] [Ln = Y (1), Sm (2), Nd (3)] and aryloxides L2Ln(OAr) [Ln = Y (4), Nd (5)], respectively, whereas the same reaction with Yb[N(SiMe3)2]3 afforded an unexpected homoleptic ytterbium complex L3Yb (6). The solid-state structures of lanthanide complexes 1–6 were determined by single-crystal X-ray diffraction. It was found that complexes 1–5 can efficiently initiate the ring-opening of rac-lactide in THF to afford hetereotactic-rich polylactides.

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.

Purification of rare earth bis(trifluoromethyl-sulfonyl)amide salts by hydrometallurgy and electrodeposition of neodymium metal using potassium bis(trifluoromethyl-sulfonyl)amide melts

This paper reports a novel bench-scale hydrometallurgical procedure and electrodeposition using potassium bis(trifluoromethyl-sulfonyl)amide (KTFSA) melts for the recovery of rare earth (RE) elements from Nd-Fe-B magnet waste. The investigations were performed at bench scale to assess the potential of a process based on leaching, deironization, and purification of RE amide salts. In the leaching process using 3.4 kg of oxidized Nd-Fe-B and 14.2 L of an aqueous solution of 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide (HTFSA), 83.0% Nd and 0.98% Fe were leached in 13 h, indicating that selective leaching of RE elements was performed at bench scale. Then, KOH or oxidized Nd-Fe-B was used as a precipitation agent in the deironization process and 100.0% Fe was successfully separated from RE components. Moreover, 4.07 kg of purified amide salts (M(TFSA)3, M = Pr, Nd, Dy, B, Al, and trace elements) were recovered from a spray dryer. The electrochemical behavior of Nd(III) in KTFSA melts containing M(TFSA)3 (molar fraction of RE components: xRE = 0.1) was investigated in this study. Electrochemical analysis revealed that the reduction peak of Nd(III) at around +1.0 V vs. K/K+ was due to the following reaction: Nd(III) + 3e− → Nd(0). The diffusion coefficient of Nd(III) was estimated to be 3.14 × 10−10 m2 s−1 at 483 K by semi-differential analysis, which is similar to that of Nd(III) in KTFSA melts containing pure Nd(TFSA)3 salts (xNd = 0.1). The electrodeposition of Nd was performed under potentiostatic conditions of +0.8 V vs. K/K+ at 483 K. The electrodeposits had a fine surface morphology with small metal particles. The electrodeposits were confirmed to be Nd metal in the middle layer analyzed by scanning electron microscopy/energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Finally, we demonstrated the effectiveness of the novel recovery process for practical use by estimating whole material flow.

Synthesis and Characterization of Amidato Divalent Lanthanide Complexes and Their Use in Forming 2,4‐Quinazolidinones from CO2 and 2‐Aminobenzonitriles

AbstractFour amidato divalent lanthanide complexes, {LnLn[N(TMS)2]THF}2 [n = 1, Ln = Eu (1); n = 2, Ln = Eu (3), Yb (4); HL1 = tBuC6H4CONHC6H3(iPr)2; HL2 = C6H5CONHC6H3(iPr)2] and {L3Eu[N(TMS)2]THF}{L32Eu(THF)2} (2) [HL3 = ClC6H4CONHC6H3(iPr)2], were synthesized and extensively characterized. This is the first time that the amidato lanthanide amides 1–4 were used to catalyze the reactions of CO2 and 2‐aminobenzonitriles to form quinazoline‐2,4(1H,3H)‐diones at atmospheric pressure. All the complexes efficiently catalyzed the transformation, with complex 3 showing the highest activity. This catalytic system gave good to excellent yields, and good functional group tolerance. Preliminary studies were conducted to investigate the reaction mechanism.

Heteroleptic lanthanide amide complexes bearing carbon-bridged bis(phenolate) ligands: synthesis, structure and their application in the polymerization of ε-caprolactone

A convenient method for the synthesis of anionic lanthanide amide complexes bearing carbon-bridged bis(phenolate) ligands is described and the catalytic activity of the complexes in the ring-opening polymerization of ε-caprolactone was studied.

Preparation and Some Properties of Nanostructural Rare Earth Nitrides by Using the Reaction of Hydrides with Ammonia

By the use of the thermal decomposition of rare earth (RE) amides to nitrides, the preparation of nanostructural RE nitrides (CeN, PrN, NdN, SmN, GdN, TbN, DyN, HoN and ErN) was extensively studied in search of optimal conditions. In this method, the preparation of amides as an effective precursor for the nitrides was similarly of importance; the amide was here prepared by high-pressure reactions of RE hydrides with ammonia in an autoclave or reactive ball milling of the RE hydrides and ammonia. CeN, PrN, NdN and SmN were successfully prepared by the thermal decomposition of the RE amides or amide-like compounds formed by the reaction of the dihydrides with ammonia, whereas GdN, TbN, DyN, HoN and ErN were not obtained in this way. The dihydrides of gadolinium, terbium, dysprosium, holmium and erbium were generally too stable to react with ammonia to form the amides compared to those of cerium, praseodymium, neodymium and samarium. In the preparation of CeN, PrN and SmN, the amide precursors obtained by the autoclave reaction of the dihydrides with ammonia yielded nanostructural nitrides with higher surface areas (3.9-5.9 m2/g), compared to those obtained by the reactive ball milling method.

Amido rare-earth complexes supported by an ansa bis(amidinate) ligand with a rigid 1,8-naphthalene linker: synthesis, structures and catalytic activity in rac-lactide polymerization and hydrophosphonylation of carbonyl compounds

We report the synthesis of rare-earth amides and their catalytic activity in ROP of lactide.