Lanthanide Bis Research Articles

Structural and Magnetic Studies on Lanthanide Bis(benzoxazol‐2‐yl)methanides

AbstractWe describe the syntheses, solid‐state structures, and magnetic properties of lanthanide(III)‐tris(bis(heterocyclo)methanides) [(THF)M{(NCOC6H4)2CH}3], with M=Tb (1), Dy (2), Ho (3), and Er (4), respectively. The corresponding lanthanide bis(trimethylsilyl)amides have been prepared as starting materials to deprotonate the neutral bis(benzoxazol‐2‐yl)methane ({NCOC6H4}2CH2) at the central methylene bridge to generate the monoanionic ligand. In the course of this investigations the hitherto unknown holmium tris(bis(trimethylsilyl)amide) is communicated in here. X‐ray diffraction data of 1–4 demonstrate an almost planar ligand with metal coordination in an N,N'‐chelating fashion. Different to their d‐metal analogous the magnetic data of the f‐metal complexes presented here show no single‐molecule magnet (SMM) properties.

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.

Electrodeposition of neodymium and dysprosium from organic electrolytes.

A new class of organic electrolytes has been developed for the electrodeposition of rare-earth metals at room temperature. These electrolytes consist of a rare-earth bis(trifluoromethylsulfonyl)imide or chloride salt and a borohydride salt, dissolved in the ether solvents 1,2-dimethoxyethane or 2-methyltetrahydrofuran. In these electrolytes, a soluble lanthanide(iii) borohydride complex [Ln(BH4)4]- is formed, which allows for the electrodeposition of neodymium- or dysprosium-containing layers. The electrochemistry of these electrolytes was characterized by cyclic voltammetry. The deposits were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray fluorescence (EDX) and X-ray photoelectron spectroscopy (XPS), and the results suggest the presence of metallic neodymium and dysprosium.

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...

Selecting Quantum-Chemical Methods for Lanthanide-Containing Molecules: A Balance between Accuracy and Efficiency.

An analysis of how different density functionals, basis sets, and relativistic approximations affect the computed properties of lanthanide-containing molecules allows one to determine which method provides the highest accuracy. Historically, many different density functional methods have been employed to perform calculations on lanthanide complexes and so herein is a detailed analysis of how different methodological combinations change the computed properties of three different families of lanthanide-bearing species: lanthanide diatomic molecules (fluorides and oxides) and their dissociation energies; larger, molecular complexes and their geometries; and lanthanide bis(2-ethylhexyl)phosphate structures and their separation free energies among the lanthanide series. The B3LYP/Sapporo/Douglas-Kroll-Hess (DKH) method was shown to most accurately reproduce dissociation energies calculated at the CCSDT(Q) level of theory with a mean absolute deviation of 1.3 kcal/mol. For the calculations of larger, molecular complexes, the TPSSh/Sapporo/DKH method led to the smallest deviation from experimentally refined crystal structures. Finally, this same method led to calculated separation factors for lanthanide bis(2-ethylhexyl)phosphate structures that matched very closely with experimental values.

Iodinated Metallacrowns: Toward Combined Bimodal Near-Infrared and X-Ray Contrast Imaging Agents.

Multimodal probes capable of combining imaging modalities within a single molecule are in high demand today as they can provide information at both molecular and anatomical levels. Herein, a study was conducted on a series of gallium(III)/lanthanide(III) bis(12-MC-4) metallacrowns (MCs) with the general composition {Ln[12-MCGa III N(shi) -4]}2 (iph)4 (Ln-Ix , x=0, 4, 8, 12), where shi and iph are salicylhydroximate and isophthalate ligands, respectively, or their iodinated derivatives. For Yb-Ix , the attenuation in X-ray computed tomography (XCT) imaging and near-infrared (NIR) luminescence properties can be finely tuned by controlled structural modifications based on iodo groups. Solutions of Yb-Ix appear to be 22-40 times more efficient as XCT agents in comparison to the commercially available iobitridol, while providing an intense emission signal in the NIR range with total quantum yields up to 8.6 %, which are among the highest values reported so far. Therefore, these molecules are promising potential bimodal agents for combined NIR luminescence and XCT imaging.

Voltammetric investigation of some lanthanides in neutral ligand-ionic liquid

The ionic liquids having wide electrochemical window and extended cathodic stability were invariably made up of strongly hydrophobic polynucler organic ions. Such hydrophobic ionic liquids were found to be unsuitable for the electrodeposition of actinides and lanthanides due to the poor solubility of actinide or lanthanide salts in these ionic liquids. To enhance the solubility of rare earth salts and recover the lanthanides by electrodeposition, a neutral ligand-ionic liquid (NLIL) containing lanthanide bis(trifluoromethanesulphonyl)imide salt (Ln = Eu, Nd and Dy) and dihexyloctanamide (DHOA) ligand has been prepared and the spectroscopic and electrochemical behavior of the lanthanide (III) ion present in NLIL was investigated by FTIR, visible spectroscopy and cyclic voltammetry respectively. The stoichiometry of Ln(III) to DHOA in NLIL was determined from the cyclic voltammograms recorded at different Ln to DHOA mole ratios. The diffusion coefficient of [Ln(DHOA)3]3+ in NLIL was determined and they are of the order 10−8 cm2/s. The possible application of neutral ligand-ionic liquids for the dissolution of rare earth oxides followed by the electrodeposition of rare earths from NLIL has been explored.

Lanthanide bis(borohydride) complexes coordinated by tetradentate phenoxide ligand: Synthesis, structure, and catalytic activity in ring-opening polymerization of rac-lactide and ε-caprolactone

New lanthanide bis(borohydride) complexes coordinated by monoanionic tetradentate phenoxide ligand [(C5H4NCH2)2NCH2(3,5-tBu2C6H2O)]Ln(BH4)2 [Ln = Y (1), Nd (2), Sm (3)] were synthesized by the reactions of Ln(BH4)3(THF)3 with an equimolar amount of the lithium phenoxide [(C5H4NCH2)2NCH2(3,5-tBu2C6H2O)Li] in THF at 60 °C. The complexes were isolated after recrystallization from toluene in 75, 64, and 69% yields, respectively. X-ray analysis revealed that in 1 the phenoxide ligand is tetradentate, while two borohydride groups are coordinated to the Y3+ ion in a κ3-fashion. Compounds 1–3 initiate ring-opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL) and racemic lactide (rac-LA) in toluene at 25 °C. The obtained polylactides are characterized by atactic structures Pr = 0.54–0.58, and rather narrow polydispersities (Mw/Mn = 1.1–1.5). For ɛ-caprolactone polymerization, the resulting polymers have moderate polydispersities (Mw/Mn = 1.4–2.4) and molecular weights (6.2–54.1·103).

Ligand-Field Energy Splitting in Lanthanide-Based Single-Molecule Magnets by NMR Spectroscopy

A method for the experimental determination of ligand-field (LF) energy splitting in mononuclear lanthanide complexes, based purely on variable-temperature NMR spectroscopy, was developed. The application of this method in an isostructural series of anionic lanthanide bis(cyclooctatetraenide) double-decker compounds bearing large rigid substituents is demonstrated. Using the three-nuclei plot approach devised by Reilley, the isostructurality of the compound series and the identical orientation of the magnetic main axis of all Ln3+ ions in the series Tb3+ to Tm3+ are demonstrated. Measurement of the 2H NMR spectra of partially deuterated analogues of the complexes permitted determination of the axial magnetic susceptibility anisotropies χax for all five ions in the temperature range from 185 to 335 K. For this purpose, analysis of the hyperfine shifts was combined with structural models derived from density functional theory calculations. In a final step, the temperature dependence of the χax values was used for determination of the three axial LF parameters, adapting a method employed previously for phthalocyanine-based systems. The temperature dependence dictated by the LF parameters determined by this NMR-based approach is compared to the results of recently published ab initio calculations of the system, indicating reasonable agreement of both methods. For all ions except Dy3+, the NMR method determines the same mJ ground state as the calculations and the order and energies of the excited states match well. However, the sign of the magnetic anisotropy of the dysprosium complex in the temperature range evaluated here is not correctly predicted by the published calculations but can be described accurately by the NMR approach. This shows that our experimental method for determination of the LF parameters is an ideal complementation to other theoretical and experimental methods.

Isomorphous rare-earth bis[bis(2,6-diisopropylphenyl)phosphate] complexes and their self-assembly into two-dimensional frameworks by intramolecular hydrogen bonds.

The crystal structures of rare-earth diaryl- or dialkylphosphate derivatives are poorly explored. Crystals of bis[bis(2,6-diisopropylphenyl)phosphato-κO]chloridotetrakis(methanol-κO)neodymium methanol disolvate, [Nd(C24H34O4P)Cl(CH4O)4]·2CH3OH, (1), and of the lutetium, [Lu(C24H34O4P)Cl(CH4O)4]·2CH3OH, (2), and yttrium, [Y(C24H34O4P)Cl(CH4O)4]·2CH3OH, (3), analogues have been obtained by reactions between lithium bis(2,6-diisopropylphenyl)phosphate and LnCl3(H2O)6 (in a 2:1 ratio) in methanol. Compounds (1)-(3) crystallize in the C2/c space group. Their crystal structures are isomorphous. The molecule possesses C2 symmetry with a twofold crystallographic axis passing through the Ln and Cl atoms. The bis(2,6-diisopropylphenyl)phosphate ligands all display a κ1O-monodentate coordination mode. The coordination polyhedron for the metal atom [coordination number (CN) = 7] is a distorted pentagonal bipyramid. Each [Ln{O2P(O-2,6-iPr2C6H3)2}2Cl(CH3OH)4] molecular unit exhibits two intramolecular O-H...O hydrogen bonds, forming six-membered rings, and two intramolecular O-H...Cl interactions, forming four-membered rings. Intermolecular O-H...O hydrogen bonds connect each unit via four noncoordinating methanol molecules with four other units, forming a two-dimensional hydrogen-bond network. Crystals of bis[bis(2,6-diisopropylphenyl)phosphato-κO]tetrakis(methanol-κO)(nitrato-κ2O,O')neodymium methanol disolvate, [Nd(C24H34O4P)(NO3)(CH4O)4]·2CH3OH, (4), have been obtained in an analogous manner from NdCl3(H2O)6. Compound (4) also crystalizes in the C2/c space group. Its crystal structure is similar to those of (1)-(3). The κ2O,O'-bidentate nitrate anion is disordered over a twofold axis, being located nearly on it. Half of the molecule is crystallographically unique (CNNd = 8). Unlike (1)-(3), complex (4) exhibits disorder of all three methanol molecules, one isopropyl group of the phosphate ligand and the NO3- ligand. The structure of (4) displays intra- and intermolecular O-H...O hydrogen bonds similar to those in (1)-(3). Compounds (1)-(4) represent the first reported mononuclear bis[bis(diaryl/dialkyl)phosphate] rare-earth complexes.

Synthesis and Structural Characterization of Homo‐ and Heterometallic Li and Li/Ln Disiloxanediolate Complexes

A series of new homo‐ and heterometallic lithium and lithium/lanthanide disiloxanediolate complexes were prepared and fully characterized. Three new adducts of dilithium tetraphenyldisiloxanediolate, [(Ph2SiOLi)2O] (2), with simple Lewis bases (Et2O, THF, DME) were prepared by treatment of Ph2Si(OH)OSiPh2(OH) (1) with 2 equiv. of n‐butyllithium in the respective donor solvent. This way the adducts [{Ph2SiOLi(Et2O)}2O]2 (3), [{Ph2SiOLi(THF)}2O]2 (4), and [{Ph4Si2O(OLi)2}2(DME)3]∞ (5a) were obtained in a straightforward manner and in nearly quantitative yields. Treatment of anhydrous lanthanide(III) chlorides LnCl3 (Ln = Tb, Lu) with 2 equiv. of 2 in THF afforded the new lanthanide(III) bis(disiloxanediolate) complexes [{(Ph2SiO)2O}2{Li(THF)2}2]TbCl (6) and [{(Ph2SiO)2O}2{Li(THF)2}2]LuCl (7) in high yields. Similar reactions of LnCl3 (Ln = Ce, Nd) with 3 equiv. of 2 provided the heterometallic Li/Ln tris(disiloxanediolate) complexes [{(Ph2SiO)2O}3{Li(DME)}2{Li(THF)}]Ce (8) and [{(Ph2SiO)2O}3{Li(DME)}{Li(Et2O)}{Li(THF)}]Nd (9). All title compounds were structurally characterized through single‐crystal X‐ray diffraction.

Bis(salicylato)borate as Versatile Sensitizer for Highly Luminescent Lanthanide Oxoborates from the Ultraviolet to Near Infrared with 4f and 5d Participation of the Lanthanides

Several lanthanide bis(salicylato)borate (BSBs) compounds were synthesized from anhydrous lanthanide chlorides and pyridine (py). The reactions start with the formation of small complexes, as indicated by [ErCl2(py)4(BSB)], on to 1D polymers 1∞[Ln(BSB)3(py)2] (Ln = Y, La–Nd, Sm) with a reduced py content. As the lanthanide radii contract along the lanthanide (Ln) series, the formation of 2D networks of the constitution 2∞[Ln(BSB)3(py)] (Ln = Sm, Eu, Tb, Dy, Er) is observed with the further release of py. The coordination polymers exhibit intense photoluminescence from the UV to the near‐infrared (NIR) region through lanthanide‐specific 4f–4f emission for the Nd3+, Sm3+, Eu3+, Tb3+, and Dy3+ species. The emission is remarkable for the Dy3+ (yellow‐white) and Nd3+ (NIR) species owing to the sensitizer effects of the [BSB]– anion, which shows energy transfer to most Ln ions. For the Ce3+ species, the participation of 5d states is observed and produces parity‐allowed broadband 5d–4f emission. The bis(salicylato)borate ligand shows fluorescence in the UV with a short lifetime of only 2 ns, which makes the energy transfer in the other Ln compounds remarkable and marks it as versatile sensitizer for these metal ions.

Systematic Structural Elucidation for the Protonated Form of Rare Earth Bis(porphyrinato) Double-Decker Complexes: Direct Structural Evidence of the Location of the Attached Proton.

Direct structural evidence of the presence and location of the attached proton in the protonated form of rare earth bis(porphyrinato) double-decker complexes is obtained from an X-ray diffraction study of single crystals for a series of protonated forms of bis(tetraphenylporphyrinato) complexes [M(III)(tpp)(tppH)] (M = Tb, Y, Sm, Nd, and La). When CHCl3 is used as a solvent for crystallization of the complexes, their nondisordered molecular structures are obtained and the attached proton is identified on one of the eight nitrogen atoms. Use of other solvents affords another type of crystal, in which the position of the proton is disordered and thus the molecular structure is averaged. La complex also affords the disordered average structure even when CHCl3 is used for crystallization. A variable-temperature diffraction study for the Tb complex reveals that the dynamics of the proton in the nondisordered crystal is restricted.

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 optical limiting properties of new lanthanide bis- and tris-phthalocyanines

This manuscript reports on syntheses of new multi-decker phthalocyanines, namely: bis-{2,3,9,10,16,10,16,17,23,24-octa(4-tertbutylphenoxy) phthalocyaninato} cerium(III) (2), tris-{2,3,9,10,16,10,16,17,23,24-octa(4-tertbutylphenoxy) phthalocyaninato} dicerium(III) (4) and bis-{2,3,9,10,16,10,16,17,23,24-octa(4-tertbutylphenoxy) phthalocyaninato} gadolinium(III) (5). Complex 4 which is a tris phthalocyanine showed better nonlinear optical behavior in solution than 2 which is a bis phthalocyanine, both containing the same central metal, Ce. All the three molecules possess good optical limiting properties judged by the limiting threshold values which ranged from 0.04 to 0.09 J cm−2 with complex 5 embedded in thin films, showing the lowest value of 0.04 J cm−2. Furthermore, nonlinear optical processes responsible for reverse saturable absorption data are investigated.

Homoleptic Divalent Dialkyl Lanthanide-Catalyzed Cross-Dehydrocoupling of Silanes and Amines

The rare-earth bis(alkyl) compound Sm{C(SiHMe2)3}2THF2 (1b) is prepared by the reaction of samarium(II) iodide and 2 equiv of KC(SiHMe2)3. This synthesis is similar to that of previously reported Yb{C(SiHMe2)3}2THF2 (1a), and compounds 1a,b are isostructural. Reactions of 1b and 1 or 2 equiv of B(C6F5)3 afford SmC(SiHMe2)3HB(C6F5)3THF2 (2b) or Sm{HB(C6F5)3}2THF2 (3b), respectively, and 1,3-disilacyclobutane {Me2Si-C(SiHMe2)2}2 as a byproduct. Bands from 2300 to 2400 cm–1 assigned to νBH in the IR spectra and highly paramagnetically shifted signals in the 11B NMR spectra of 2b and 3b provided evidence for Sm-coordinated HB(C6F5)3. Compounds 1a,b react with the bulky N-heterocyclic carbene (NHC) 1,3-di-tert-butylimidazol-2-ylidene (ImtBu) to displace both THF ligands and give three-coordinate monoadducts Ln{C(SiHMe2)3}2ImtBu (Ln = Yb (4a), Sm (4b)). Complexes 4a,b catalyze cross-dehydrocoupling of organosilanes with primary and secondary amines at room temperature to give silazanes and H2, whereas 1a,b are ...

Bis(amido) rare-earth complexes coordinated by tridentate amidinate ligand: synthesis, structure and catalytic activity in the polymerization of isoprene and rac-lactide

Rare-earth bis(amides) {2-[Ph2Р(O)]C6H4NC(tBu)N(2,6-Me2C6H3)}Ln(N(SiMe3)2)2 (Ln = Y, Nd, La) coordinated by tridentate amidinate ligand were synthesized, structurally characterized and evaluated as catalysts for isoprene and rac-lactide polymerizations.

A monometallic lanthanide bis(methanediide) single molecule magnet with a large energy barrier and complex spin relaxation behaviour.

We report a dysprosium(iii) bis(methanediide) single molecule magnet (SMM) where stabilisation of the highly magnetic states and suppression of mixing of opposite magnetic projections is imposed by a linear arrangement of negatively-charged donor atoms supported by weak neutral donors. Treatment of [Ln(BIPMTMS)(BIPMTMSH)] [Ln = Dy, 1Dy; Y, 1Y; BIPMTMS = {C(PPh2NSiMe3)2}2-; BIPMTMSH = {HC(PPh2NSiMe3)2}-] with benzyl potassium/18-crown-6 ether (18C6) in THF afforded [Ln(BIPMTMS)2][K(18C6)(THF)2] [Ln = Dy, 2Dy; Y, 2Y]. AC magnetic measurements of 2Dy in zero DC field show temperature- and frequency-dependent SMM behaviour. Orbach relaxation dominates at high temperature, but at lower temperatures a second-order Raman process dominates. Complex 2Dy exhibits two thermally activated energy barriers (U eff) of 721 and 813 K, the largest U eff values for any monometallic dysprosium(iii) complex. Dilution experiments confirm the molecular origin of this phenomenon. Complex 2Dy has rich magnetic dynamics; field-cooled (FC)/zero-field cooled (ZFC) susceptibility measurements show a clear divergence at 16 K, meaning the magnetic observables are out-of-equilibrium below this temperature, however the maximum in ZFC, which conventionally defines the blocking temperature, T B, is found at 10 K. Magnetic hysteresis is also observed in 10% 2Dy@2Y at these temperatures. Ab initio calculations suggest the lowest three Kramers doublets of the ground 6H15/2 multiplet of 2Dy are essentially pure, well-isolated |±15/2, |±13/2 and |±11/2 states quantised along the C[double bond, length as m-dash]Dy[double bond, length as m-dash]C axis. Thermal relaxation occurs via the 4th and 5th doublets, verified experimentally for the first time, and calculated U eff values of 742 and 810 K compare very well to experimental magnetism and luminescence data. This work validates a design strategy towards realising high-temperature SMMs and produces unusual spin relaxation behaviour where the magnetic observables are out-of-equilibrium some 6 K above the formal blocking temperature.

Syntheses of bimetallic rare-earth bis(cyclopentadienyl) derivatives supported by bridged bis(guanidinate) ligands and their catalytic property for the hydrophosphonylation of aldehydes

Some bimetallic rare earth bis(cyclopentadienyl) derivatives supported by bridged bis(guanidinate) ligands {(C5H5)2RE[(RN)2CN(CH2)2]}2 [R = iPr, RE = Yb(1), Er(2), Y(3); R = Cy, RE = Yb(4)] and {(CH3C5H4)2Sm[(iPrN)2CN(CH2)2]}2 (5) were prepared by the reaction of lithium guanidinate {Li[(RN)2CN(CH2)2]}2 (R = iPr, Cy) with (C5H5)2RECl (RE = Yb, Er, Y) or (CH3C5H4)2SmCl in a 1:2 M ratio in THF. Complexes 1–5 were confirmed by elemental analyses, IR spectra and NMR spectroscopy (for complex 3). The molecular structures of complexes 1–3 and 5 were provided by X-ray structure diffraction, which indicated that these complexes have similar dinuclear solid state structure. The rare-earth ion in these complexes is bonded to two η5-cyclopentadienyl rings and one chelating guanidinate ligand. It was found that these rare-earth metal complexes are efficient catalysts for the hydrophosphonylation of various aldehydes, to generate α-hydroxyphosphonates in high yields under mild reaction conditions.

Synthesis and structural characterization of new bis(alkynylamidinato)lanthanide(III)-amides

Four new unsolvated lanthanide bis(alkynylamidinato) amide complexes [c-C3H5–CC–C(NR)2]2LnN(SiMe3)2 (2: Ln = Ce, R = iPr; 3: Ln = Ce, R = Cy; 4: Ln = Nd, R = Cy; 5: Ln = Ho, R = Cy) have been prepared in moderate to good isolated yields (37–67%) via three-component reactions between anhydrous LnCl3 (Ln = Ce, Nd, Ho), Li[c-C3H5–CC–C(NR)2]- (1a: R = iPr, 1b: R = Cy) and KN(SiMe3)2 in a 1:2:1 M ratio in THF. The same compounds were also accessible by amination of the previously reported lanthanide bis(amidinate) chloro precursors [c-C3H5–CC–C(NR)2]2Ln(μ-Cl)2] and [c-C3H5–CC–C(NR)2]2Ho(μ-Cl)2Li(THF)(Et2O) with KN(SiMe3)2. However, this synthetic protocol gave significantly lower yields of 2–5 (17–42%). The molecular structures of 4 and 5 have been authenticated through single-crystal X-ray diffraction. An initial catalytic study showed that the new complexes cannot be reliably employed as precatalysts for hydroamination/cyclization reactions.