Lanthanide Alkoxides Research Articles

Synthesis of Rare Earth Metal Complexes Stabilized by Amine Bridged Bis(phenolato) Ligands and Their Performance in the Polymerization of rac-β-Butyrolactone.

A series of rare earth alkoxides bearing amine-bridged bis(phenolato) ligands were synthesized through sequential reactions of RE(C5H5)3(THF) (RE = Y, Lu) or Nd[N(SiMe3)2]3 with bis(phenols) LH2 and CF3CH2OH. Complexes REL(OCH2CF3)(THF)n (1-6) bearing different aryl-substituents were obtained in good yields of 59-70%. They were applied in the ring-opening polymerization (ROP) of rac-β-butyrolactone (rac-BBL), which showed good activity (TOF up to 27,300 h-1), resulting in syndiotactically enriched poly(3-hydroxybutyrate) (PHB) (Pr up to 0.86) with narrow polydispersities (PDI ≤ 1.27). The yttrium complex 3 bearing bulky o-1,1-diphenylethyl substituents outperformed other complexes, suggesting that the smaller ionic radii of metal centers and bulky ortho substituents of ancillary ligands play crucial roles in controlling the activity and stereoselectivity in ROP of rac-BBL. Kinetics of the polymerization of rac-BBL initiated by complex 3 was investigated, which revealed first order dependences on the monomer and initiator concentrations, respectively.

Synthesis of N-Methyl-o-phenylenediamine-Bridged Bis(phenolato) Lanthanide Alkoxides and Their Catalytic Performance for the (Co)Polymerization of rac-Butyrolactone and l-Lactide.

A series of lanthanide alkoxo complexes supported by ONNO salalen ligands were synthesized and characterized. A one-pot reaction of LH2 (L = (2-O-C6H2-tBu2-3,5)CH═N-C6H4-N(CH3)CH2(2-O-C6H2-tBu2-3,5)) with LnCp3(THF) in a 1:1 molar ratio followed by the addition of 1 equiv of ROH (R = Bn, iPr, and CF3CH2), afforded the dimeric lanthanide alkoxo complexes [LLn(μ-OCH2Ph)]2 [Ln = Lu (1), Yb (2), Sm (3), Nd (4)], [L2Yb(μ-OiPr)]2 (5), and [L2Yb(μ-OCH2CF3)]2 (6) in good isolated yields. All these lanthanide complexes were characterized by elemental analysis and FT-IR spectroscopy. In addition, complex 1 has been characterized by NMR spectroscopy. Single-crystal X-ray diffraction analysis of complexes 1, 2, 5, and 6 showed that these lanthanide alkoxo complexes are dimeric in the solid state. Complexes 1-6 showed good activity toward the homopolymerization of rac-butyrolactone (rac-BBL) to give atactic PHB, and ionic radii of central metals have profound influence on the polymerization. The polymerization behavior of l-lactide (l-LA) initiated by complex 2 was also explored. The kinetic study revealed that the polymerizations of rac-BBL and l-LA initiated by salalen lanthanide akoxide are first order for both the monomer and the initiator concentrations. Furthermore, it was found that complexes 1 and 2 showed good activity in the copolymerization of l-LA and rac-BBL, affording gradient copolymers.

Highly heteroselective ring-opening polymerization of rac-lactide initiated by rare-earth alkoxides bearing chiral [NNOO]-type amine-bis(phenolate) ligands

Rare-earth alkoxides [(S)-LM(OiPr)] bearing chiral [NNOO]-type tripodal amine-bridged bis(phenolate) ligands have been successfully synthesized and used as catalysts with high activity for ROP of rac-LA to afford heterotactically enriched polymers.

Mononuclear Dysprosium Alkoxide and Aryloxide Single-Molecule Magnets.

Recent studies have shown that mononuclear lanthanide (Ln) complexes can be high‐performing single‐molecule magnets (SMMs). Recently, there has been an influx of mononuclear Ln alkoxide and aryloxide SMMs, which have provided the necessary geometrical control to improve SMM properties and to allow the intricate relaxation dynamics of Ln SMMs to be studied in detail. Here non‐aqueous Ln alkoxide and aryloxide chemistry applied to the synthesis of low‐coordinate mononuclear Ln SMMs are reviewed. The focus is on mononuclear DyIII alkoxide and aryloxide SMMs with coordination numbers up to eight, covering synthesis, solid‐state structures and magnetic attributes. Brief overviews are also provided of mononuclear TbIII, HoIII, ErIII and YbIII alkoxide and aryloxide SMMs.

Phosphasalalen Rare-Earth Complexes for the Polymerization of rac-Lactide and rac-β-Butyrolactone.

A series of new phosphasalalen pro-ligands, analogues of salalen but with an iminophosphorane replacing the imine functionality, and their corresponding rare-earth alkoxide and siloxide complexes were synthesized. The multinuclear NMR spectra and X-ray diffraction analyses revealed that, for the tert-butoxide and ethoxide complexes, the resulting phosphasalalen rare-earth product was composed of a mononuclear alkoxide and a binuclear complex containing bridged alkoxo and hydroxo groups, while an analogous binuclear complex was isolated as the sole product for the siloxide complex. All the complexes could catalyze the heteroselective ring-opening polymerization (ROP) of rac-lactide (Pr up to 0.77) with high catalytic activities and a controlled polydispersity. Remarkably, the yttrium and lutetium phosphasalalen complexes could also efficiently catalyze the ROP of rac-β-butyrolactone to produce syndiotactic polymers (Pr up to 0.73) while their salalen analogues were inert, revealing the special effects of the iminophosphorane moiety. Detailed end-group analyses and kinetic investigations suggested that the alkoxo-hydroxo-bridged complexes maintained their binuclear structures in the polymerization.

Bipyrrolidine salan alkoxide complexes of lanthanides: synthesis, characterisation, activity in the polymerisation of lactide and mechanistic investigation by DOSY NMR.

Four dimeric lanthanide alkoxide complexes bearing ONNO bipyrrolidine salan ligands (LMeH2/LtBuH2) have been prepared with Nd, Sm and Yb. Depending on the metal and substituents, these complexes adopt varying coordination geometries. While investigating the hydrolytic degradation of these complexes, three dimeric mixed alkoxide/hydroxide and bis-hydroxide products were also prepared, isolated and characterised. Despite paramagnetism, 1H NMR and diffusion ordered spectroscopy (DOSY) allowed additional characterisation alongside elemental and single-crystal X-ray diffraction analyses. These systems were very active for the controlled ring-opening polymerisation (ROP) of rac-lactide (LA), under industrially relevant melt conditions and in solution, yielding complete conversion within 5 minutes at [Ln] : [LA] ratios of up to 3000 : 1 in toluene, and at 80 °C, whilst retaining low dispersities (Đ = 1.1). 1H DOSY NMR spectroscopy was employed to monitor polymer growth from the metal centres in situ, and revealed a dinuclear catalytically active species.

Lanthanide alkoxide complexes stabilized by a novel salen-type Schiff-base ligand: Synthesis, structure, and catalysis for the polymerization of lactide

A series of neutral lanthanide alkoxide complexes stabilized by a new salen-type Schiff-base ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of lactide were explored. Amine elimination reactions of N-methyl-N′,N″-bis(3,5-di-tert-butylsalicylidene)-2,2′-diaminodiethylamine (LH2) with Ln[N(SiMe3)2]3 (Ln = Sm, Nd, La) in a 1:1 M ratio in THF, followed by reactions with 1 equiv of alcohols (tBuOH, EtOH and CH3OCH2CH2OH), produced lanthanide alkoxide complexes LLn(OtBu)(THF) (Ln = Sm (1), Nd (2), La (3)), [LSm(μ-OEt)]2 (4) and [LSm(μ-OCH2CH2OCH3)]2 (5), respectively, whereas the same reaction with Yb[N(SiMe3)2]3 gave an unexpected homoleptic complex L2Yb2(μ-L) (6). X-ray structural determination showed that complexes 1–3 have a THF-solvated monomeric structure, whereas complexes 4–6 have an unsolvated dimeric structure. All lanthanide alkoxide complexes can efficiently initiate the ring-opening polymerization (ROP) of L-LA and rac-LA. The polymerization kinetics of L-LA initiated by complex 1 has been studied in detail and the first-order kinetic dependence on both l-lactide concentration and initiator concentration was found. Furthermore, all complexes showed moderate stereoselectivity for rac-LA polymerization to afford heterotactic-rich polylactides.

Heterobimetallic dinuclear lanthanide alkoxide complexes as acid–base bifunctional catalysts for synthesis of carbamates under solvent-free conditions

Heterobimetallic dinuclear lanthanide alkoxide complexes Ln2Na8(OCH2CH2NMe2)12(OH)2 [Ln: I (Nd), II (Sm), III (Yb) and IV (Y)] were used as efficient acid–base bifunctional catalysts for the synthesis of carbamates and the N-Boc protection of amines.

Heterobimetallic dinuclear lanthanide alkoxide complexes as acid-base difunctional catalysts for transesterification.

A practical lanthanide(III)-catalyzed transesterification of carboxylic esters, weakly reactive carbonates, and much less-reactive ethyl silicate with primary and secondary alcohols was developed. Heterobimetallic dinuclear lanthanide alkoxide complexes [Ln2Na8{(OCH2CH2NMe2)}12(OH)2] (Ln = Nd (I), Sm (II), and Yb (III)) were used as highly active catalysts for this reaction. The mild reaction conditions enabled the transesterification of various substrates to proceed in good to high yield. Efficient activation of transesterification may be endowed by the above complexes as cooperative acid-base difunctional catalysts, which is proposed to be responsible for the higher reactivity in comparison with simple acid/base catalysts.

Enthalpies of formation of europium alkoxides: What lessons can be drawn from them

The synthesis and characterization of two europium alkoxides, Eu(OCH3)2 and Eu(OC2H5)2, were described. For the first time the enthalpies of formation of divalent lanthanide alkoxides were determined by using reaction-solution calorimetry. The values obtained are ΔfH0 [Eu(OCH3)2,cr]=−850.5±5.0kJ/mol and ΔfH0 [Eu(OC2H5)2,cr]=−902.5±5.5kJ/mol, respectively. Since these compounds have a large use as catalysts or catalysts precursors, the first step of the reaction of them with CO2 was addressed, which permits to have an idea of the kind of bond involved in those compounds. Moreover, insertion of CO2 in the europium oxygen bond and formation of metal carboxylate complexes, is in both cases presumably bidentate.

A novel approach to RE–OR bond from in situ reaction of rare earth triflates and sodium alkoxides: A versatile catalyst for living ring-opening polymerization of ε-caprolactone

A series of rare earth triflates (RE(OTf)3, RE = Sc, Y and Lu) were used for the first time as moisture-stable precursors to generate rare earth alkoxide complexes through an in situ reaction with sodium alkoxides (NaOR) in tetrahydrofuran. 1H NMR and 13C NMR results confirmed the fast ligands exchange process and the formation of rare earth–oxygen (RE–OR) bond. The in situ formed catalysts displayed high reactivity toward living ring-opening polymerization (ROP) of ε-caprolactone (CL). For instance, Lu(OTf)3/sodium isopropoxide (NaOiPr)-catalyzed ROP of CL with the [CL]0/[NaOiPr]0/[Lu(OTf)3]0 feeding ratio of 300/3/1 produced poly(ε-caprolactone) (PCL) with controlled molecular weight (Mn,exp = 11.9 kDa vs Mn,theo = 11.8 kDa) and narrow polydispersity (PDI) of 1.08 within 3 min at 25 °C. The kinetic studies and chain extension confirmed the controlled/living nature for the Lu(OTf)3/NaOiPr-catalyzed ROP of CL. In addition, end-functionalized PCLs bearing vinyl or alkynyl group with narrow PDIs were obtained by using functional sodium alkoxides in the presence of Lu(OTf)3. 1H NMR and MALDI-ToF MS analyses of the obtained PCLs clearly indicated the presence of the residue of OR groups at the chain ends. A coordination–insertion polymerization mechanism was proposed including a fast ligand exchange between Lu(OTf)3 and NaOR giving the respective lutetium alkoxide complexes, and a CL insertion into RE–OR bond via acyl-oxygen cleavage.

Synthesis and Characterization of Salalen Lanthanide Complexes and Their Application in the Polymerization of rac-Lactide

A series of neutral lanthanide complexes supported by ONNO Salalen-type ligands were synthesized, and their catalytic activity for the polymerization of rac-lactide (rac-LA) was explored. The amine elimination reactions of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with the ONNO Salalen-type ligand L1H2 (L1 = (2-O-C6H2-But2-3,5)CH═NCH2CH2N(Me)CH2(2-O-C6H2-But2-3,5)) in a 1:1 molar ratio in tetrahydrofuran (THF) gave the neutral lanthanide amides L1Ln[N(SiMe3)2](THF) (Ln = Y (1), Sm (2), Nd (3)). Reaction of the lanthanide amides with benzyl alcohol produces the dimeric lanthanide alkoxo complex (L1LnOCH2Ph)2 (Ln = Y (4), Sm (5)) in high isolated yield. Y[N(SiMe3)2]3(μ-Cl)Li(THF)3 reacted with the Salalen-type ligand L2H2 (L2 = (2-O-C6H2-But2-3,5)CH═NCH2CH2N(Me)CH2{2-O-C6H2-(CPhMe2)2-3,5}) in a 1:l molar ratio in THF also gave the desired yttrium amide, but this complex could not be separated because of its very good solubility even in n-pentane. The proton exchange reactions of L1H2 and L2H2 with (C5H5)3Ln(THF) in a 1:1 molar ratio in THF and then with 1 equiv of benzyl alcohol gave the desired lanthanide alkoxides [L1Ln(OCH2Ph)]2 (Ln = Y (4), Sm (5), Yb (6)) and [L2Y(OCH2Ph)]2 (7), respectively. Complexes 1–7 were well characterized by elemental analyses, IR spectra, X-ray single-crystal structure determination, and NMR spectroscopy in the case of complexes 1, 4, and 7. Complexes 1–3 are isostructural and have a solvated monomeric structure. The coordination geometry around the lanthanide atom can be best described as a distorted trigonal bipyramid. Complexes 4–7 are dimeric species in the solid state. They all contain a Ln2O2 core bridging through the oxygen atoms of the two OCH2Ph groups. Each of the lanthanide atoms is also six-coordinated to form a distorted octahedron. It was found that all the complexes are efficient initiators for the ring-opening polymerization of rac-LA, giving PLA with good heterotacticity (Pr up to 0.85). The observed order of increase in activity is in agreement with the order of the ionic radii, whereas the stereoselectivity is in reverse order. The steric bulkiness of the substituents on the phenol ring has no obvious impact on the rate and stereocontrolability of the polymerizations. The Ln–O species resulted in more controllable polymerization than the corresponding Ln–N species, and complex 4 can initiate rac-LA polymerization in a controlled manner.

Unconventional isomerization of allylic alcohols to allylcarbinols mediated by lanthanide catalysts

We report here the catalytic isomerization of aryl-substituted allylic alcohols mediated by lanthanide alkoxide complexes. The conversion yields allylcarbinols as the products of the olefin isomerization process, but with different olefinic positions than those afforded by typical transition metal catalysts. The average isolated product yields in these reactions are 65–81%. The catalytic cycle and the source of the unusual olefinic positioning are proposed to involve a strong interaction between the Lewis acidic La3+ ion and the substrate hydroxyl group.

Synthesis and Characterization of Amine-Bridged Bis(phenolate)lanthanide Alkoxides and Their Application in the Controlled Polymerization of rac-Lactide and rac-β-Butyrolactone

A series of neutral lanthanide alkoxides supported by an amine-bridged bis(phenolate) ligand were synthesized, and their catalytic behaviors for the polymerization of rac-lactide (LA) and rac-β-butyrolactone (BBL) were explored. The reactions of (C(5)H(5))(3)Ln(THF) with amine-bridged bis(phenol) LH(2) [L = Me(2)NCH(2)CH(2)N{CH(2)-(2-OC(6)H(2)Bu(t)(2)-3,5)}(2)] in a 1:1 molar ratio in THF for 1 h and then with 1 equiv each of 2,2,2-trifluoroethanol, benzyl alcohol, and 2-propanol gave the neutral lanthanide alkoxides LLn(OCH(2)CF(3))(THF) [Ln = Y (1), Yb (2), Er (3), Sm (4)], LY(OCH(2)Ph)(THF) (5), and LY(OPr(i))(THF) (6), respectively. These lanthanide alkoxides are sensitive to moisture, and the yttrium complex [(LY)(2)(μ-OPr(i))(μ-OH)] (7) was also isolated as a byproduct during the synthesis of complex 6. Complexes 1-6 were well characterized by elemental analyses and IR and NMR spectroscopy in the cases of complexes 1 and 4-6. The definitive molecular structures of all of these complexes were determined by single-crystal X-ray analysis. It was found that complexes 1-6 can initiate efficiently the ring-opening polymerization of rac-LA and rac-BBL in a controlled manner. For rac-LA, polymerization gave polymers with very narrow molecular weight distributions (PDI ≤ 1.12) and very high heterotacticity (P(r) up to 0.99). The observed activity-increasing order is in agreement with the order of the ionic radii, whereas the order for stereoselectivity is in the reverse order. For rac-BBL polymerization, the resultant polymers have narrow molecular distributions (PDI ≤ 1.26) and high syndiotacticity (P(r) up to 0.83). It is worth noting that the activity-decreasing order Yb > Er > Y >> Sm is observed for rac-BBL polymerization, which is opposite to the order of ionic radii and to the order of activity for rac-LA polymerization. The ionic radii of lanthanide metals have no obvious effect on the stereoselectivity for rac-BBL polymerization, which is quite different from that for rac-LA polymerization. End-group analysis of the oligomer of rac-BBL suggested that elimination side reactions occurred slowly in these systems, which led to chain cleavage and the formation of crotonate (and carboxy) end groups.

Synthesis of a New Class of Arylsulfonylethylsulfonylmethyloxazolines and Thiazolines

A new class of arylsulfonylethylsulfonylmethyl oxazolines and thiazolines were prepared using multistep, one‐pot methodologies exploiting lanthanide alkoxides and under microwave irradiation. The microwave method provides an excellent approach in a single step with high yields.

Crystal structures and thermal properties of some rare earth alkoxides with tertiary alcohols

Rare earth (RE) alkoxides of Y, La, Pr, and Gd were synthesized using three tertiary alcohols namely 2,3-dimethyl-2-butanol, 2,2-dimethyl-3-ethyl-3-pentanol, and 3-isopropyl-2,4-dimethyl-pentan-3-ol. 1H and 13C NMR, elemental analysis (CHN) and MS were used to characterize the complexes. New crystal structures of dimeric [Y(OCEt2 t Bu)3]2, [La(OCEt2 t Bu)3]2, [Gd(OC i Pr3)3]2, and [La(OC i Pr3)3]2 were solved. Thermal properties of these compounds were studied with TG/SDTA and vacuum sublimation experiments. With all the cations Y, La, Pr, and Gd, the compounds with smallest ligand i PrMe2CO− seem to be the most volatile. The compounds with larger alkoxo ligands have lower volatility but their thermal stability is better. Atomic layer deposition experiments showed that RE oxide thin films could be grown from these alkoxides using water as the oxygen precursor.

Structure of a hepta-nuclear termetallic oxo-alkoxide: Eu3K3TiO2(OBut)11(OMe/OH)(HOBut)

The novel termetallic oxo-methoxo-tert-butoxide Eu3K3TiO2(OBut)11(OMe/OH)(HOBut) (1) has been synthesised and structurally and spectroscopically characterised. Its unusual structure features an Eu3K3O fac-octahedron, capped by a distorted K3TiO tetrahedron on the K3 face. The compound, crystallising in space group P21/n with cell parameters a = 14.44 Å, b = 23.58 Å, c = 21.27 Å and β = 96.18°, is the result of incomplete metathesis between EuCl3 and potassium and titanium tert-butoxides in combination with deliberate hydrolysis and decomposition. It provides one of few examples of termetallic lanthanide alkoxides, as well as of an alkoxide tert-butyl group decomposing into a methyl group.

ChemInform Abstract: Advances in Structurally Characterized Lanthanide Alkoxide, Aryloxide, and Silyloxide Compounds

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.

Advances in Structurally Characterized Lanthanide Alkoxide, Aryloxide, and Silyloxide Compounds

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTAdvances in Structurally Characterized Lanthanide Alkoxide, Aryloxide, and Silyloxide CompoundsTimothy J. Boyle* and Leigh Anna M. OttleyView Author Information Sandia National Laboratories, Advanced Materials Laboratory, 1001 University Boulevard, S.E., Albuquerque, New Mexico 87106* Author to whom correspondences should be addressed. Phone (505) 272-7625 . Fax (505) 272-7336. E-mail [email protected]Cite this: Chem. Rev. 2008, 108, 6, 1896–1917Publication Date (Web):June 11, 2008Publication History Received29 November 2007Published online11 June 2008Published inissue 1 June 2008https://doi.org/10.1021/cr0401063Copyright © 2008 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2295Altmetric-Citations112LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (4 MB) Get e-AlertsSUBJECTS:Chemical structure,Ligands,Metals,Nuclear magnetic resonance spectroscopy,Reaction products Get e-Alerts

Synthesis and Crystal Structure Investigations of Trivalent Rare Earth (Y3+, Nd3+, Er3+) Thienyl‐Substituted Methoxides

AbstractThe synthesis and structural characterization of rare earth alkoxides with thiophene‐based substituents are presented. Monomeric metal thienylmethoxides have been prepared by aminolysis reactions between M[N(SiMe3)2]3 (M = Y3+, Nd3+, Er3+) and the structurally characterized tertiary alcohols HO–C(C4H3S)3 (1) or HO–C(C8H5S2)3 (2). The metal alkoxide derivatives of these thiophene‐substituted alcohols have been isolated as air‐sensitive base adducts, their molecular structures being investigated by single‐crystal X‐ray crystallography. The coordination spheres around the metal centres are distorted trigonal‐bipyramidal for the yttrium thienylmethoxides Y[OC(C4H3S)3]3(thf)2 (3a), {Y[OC(C4H3S)3]3(thf)2}·toluene (3b), Y[OC(C4H3S)3]3(py)2 (4a), {Y[OC(C4H3S)3]3(py)2}·toluene (4b) and Y[OC(C8H5S2)3]3(thf)2 (5). An almost tetrahedral geometry has been detected for Er[OC(C8H5S2)3]3(thf) (9), whereas an approximately octahedral geometry was found for {Nd[OC(C4H3S)3]3(thf)3}·thf (6), {Nd[OC(C8H5S2)3]3(thf)3}·4thf (7) and Er[OC(C4H3S)3]3(thf)3 (8). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)