Chiral Benzamidinate Ligands in Rare‐Earth‐Metal Coordination Chemistry

The treatment of the recently reported potassium salt (S)‐N,N′‐bis‐(1‐phenylethyl)benzamidinate ((S)‐KPEBA) and its racemic isomer (rac‐KPEBA) with anhydrous lanthanide trichlorides (Ln=Sm, Er, Yb, Lu) afforded mostly chiral complexes. The tris(amidinate) complex [{(S)‐PEBA}₃Sm], bis(amidinate) complexes [{Ln(PEBA)₂(μ‐Cl)}₂] (Ln=Sm, Er, Yb, Lu), and mono(amidinate) compounds [Ln(PEBA)(Cl)₂(thf)_n] (Ln=Sm, Yb, Lu) were isolated and structurally characterized. As a result of steric effects, the homoleptic 3:1 complexes of the smaller lanthanide atoms Yb and Lu were not accessible. Furthermore, chiral bis(amidinate)–amido complexes [{(S)‐PEBA}₂Ln{N(SiMe₃)₂}] (Ln=Y, Lu) were synthesized by an amine‐elimination reaction and salt metathesis. All of these chiral bis‐ and tris(amidinate) complexes had additional axial chirality and they all crystallized as diastereomerically pure compounds. By using rac‐PEBA as a ligand, an achiral meso arrangement of the ligands was observed. The catalytic activities and enantioselectivities of [{(S)‐PEBA}₂Ln{N(SiMe₃)₂}] (Ln=Y, Lu) were investigated in hydroamination/cyclization reactions. A clear dependence of the rate of reaction and enantioselectivity on the ionic radius was observed, which showed higher reaction rates but poorer enantioselectivities for the yttrium compound.     

Rare‐Earth‐Metal Nitridophosphates through High‐Pressure Metathesis

Developing a synthetic method to target an broad spectrum of unknown phases can lead to fascinating discoveries. The preparation of the first rare‐earth‐metal nitridophosphate LiNdP₄N₈ is reported. High‐pressure solid‐state metathesis between LiPN₂ and NdF₃ was employed to yield a highly crystalline product. The in situ formed LiF is believed to act both as the thermodynamic driving force and as a flux to aiding single‐crystal formation in dimensions suitable for crystal structure analysis. Magnetic properties stemming from Nd³⁺ ions were measured by SQUID magnetometry. LiNdP₄N₈ serves as a model system for the exploration of rare‐earth‐metal nitridophosphates that may even be expanded to transition metals. High‐pressure metathesis enables the systematic study of these uncharted regions of nitride‐based materials with unprecedented properties.     

Molecular Rare‐Earth‐Metal Hydrides in Non‐Cyclopentadienyl Environments

Molecular hydrides of the rare‐earth metals play an important role as homogeneous catalysts and as counterparts of solid‐state interstitial hydrides. Structurally well‐characterized non‐metallocene‐type hydride complexes allow the study of elementary reactions that occur at rare‐earth‐metal centers and of catalytic reactions involving bonds between rare‐earth metals and hydrides. In addition to neutral hydrides, cationic derivatives have now become available.     

Rare‐Earth Nanoparticles with Enhanced Upconversion Emission and Suppressed Rare‐Earth‐Ion Leakage

Upconversion emissions from rare‐earth nanoparticles have attracted much interest as potential biolabels, for which small particle size and high emission intensity are both desired. Herein we report a facile way to achieve NaYF₄:Yb,Er@CaF₂ nanoparticles (NPs) with a small size (10–13 nm) and highly enhanced (ca. 300 times) upconversion emission compared with the pristine NPs. The CaF₂ shell protects the rare‐earth ions from leaking, when the nanoparticles are exposed to buffer solution, and ensures biological safety for the potential bioprobe applications. With the upconversion emission from NaYF₄:Yb,Er@CaF₂ NPs, HeLa cells were imaged with low background interference.     

Rare‐Earth‐Metal Dialkynyl Dimethyl Aluminates

A new class of rare‐earth‐metal alkynyl complexes has been prepared. The reactions of the tris(tetramethylaluminate)s of lanthanum, praseodymium, samarium, yttrium, holmium, and thulium, [Ln(AlMe₄)₃], with phenylacetylene afforded compounds [Ln{(μ‐C?CPh)₂AlMe₂}₃] (Ln=La ( 1 ), Pr ( 2 ), Sm ( 3 ), Y ( 4 ), Ho ( 5 ), Tm ( 6 )). All of these compounds have been characterized by NMR spectroscopy, X‐ray crystallography, and by elemental analysis. NMR spectroscopic studies of the series of para‐ magnetic compounds [Ln(AlMe₄)₃] and [Ln{(μ‐C?CPh)₂AlMe₂}₃] have also been performed.     

Water‐Free Rare‐Earth‐Metal Ionic Liquids/Ionic Liquid Crystals Based on Hexanitratolanthanate(III) Anion

The hexanitratolanthanate anion (La(NO₃)₆^3?) is an interesting symmetric anion suitable to construct the component of water‐free rare‐earth‐metal ionic liquids. The syntheses and structural characterization of eleven lanthanum nitrate complexes, [C_nmim]₃[La(NO₃)₆] (n=1, 2, 4, 6, 8, 12, 14, 16, 18), including 1,3‐dimethylimidazolium hexanitratolanthanate ([C₁mim]₃[La(NO₃)₆], 1 ), 1‐ethyl‐3‐methylimidazolium hexanitratolanthanate ([C₂mim]₃[La(NO₃)₆], 2 ), 1‐butyl‐3‐methylimidazolium hexanitratolanthanate ([C₄mim]₃[La(NO₃)₆], 3 ), 1‐isobutyl‐3‐methylimidazolium hexanetratolanthanate ([isoC₄mim]₃[La(NO₃)₆], 4 ), 1‐methyl‐3‐(3′‐methylbutyl)imidazolium hexanitratolanthanate ([MC₄mim]₃[La(NO₃)₆], 5 ), 1‐hexyl‐3‐methylimidazolium hexanitratolanthanate ([C₆mim]₃[La(NO₃)₆], 6 ), 1‐methyl‐3‐octylimidazolium hexanitratolanthanate ([C₈mim]₃[La(NO₃)₆], 7 ), 1‐dodecyl‐3‐methylimidazolium hexanitratolanthanate ([C₁₂mim]₃[La(NO₃)₆], 8 ), 1‐methyl‐3‐tetradecylimidazolium hexanitratolanthanate ([C₁₄mim]₃[La‐(NO₃)₆], 9 ), 1‐hexadecyl‐3‐methylimid‐azolium hexanitratolanthanum ([C₁₆dmim]₃[La(NO₃)₆], 10 ), and 1‐methyl‐3‐octadecylimidazolium hexanitratolanthanate ([C₁₈mim]₃[La(NO₃)₆], 11 ) are reported. All new compounds were characterized by ¹H and ¹³C NMR, and IR spectroscopy as well as elemental analysis. The crystal structure of compound 1 was determined by using single‐crystal X‐ray diffraction, giving the following crystallographic information: monoclinic; P2₁/c; a=15.3170 (3), b=14.2340 (2), c=13.8954(2) Å; β=94.3453(15)°, V=3020.80(9) ų, Z=4, ρ=1.764 g cm^?3. The coordination polyhedron around the lanthanum ion is rationalized by six nitrate anions with twelve oxygen atoms. No hydrogen‐bonding network or water molecule was found in 1 . The thermodynamic stability of the new complexes was investigated by using thermogravimetric analysis (TGA). The water‐free hexanitratolanthanate ionic liquids are thermal and moisture stable. Four complexes, namely complexes 8 – 11 , were found to be ionic liquid crystals by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). They all present smectic A liquid‐crystalline phase.     

Rare‐Earth‐Metal–Hydrocarbyl Complexes Bearing Linked Cyclopentadienyl or Fluorenyl Ligands: Synthesis,Catalyzed Styrene Polymerization,and Structure–Reactivity Relationship

A series of rare‐earth‐metal–hydrocarbyl complexes bearing N‐type functionalized cyclopentadienyl (Cp) and fluorenyl (Flu) ligands were facilely synthesized. Treatment of [Y(CH₂SiMe₃)₃(thf)₂] with equimolar amount of the electron‐donating aminophenyl‐Cp ligand C₅Me₄H‐C₆H₄‐o‐NMe₂ afforded the corresponding binuclear monoalkyl complex [({C₅Me₄‐C₆H₄‐o‐NMe(μ‐CH₂)}Y{CH₂SiMe₃})₂] ( 1 a ) via alkyl abstraction and C? H activation of the NMe₂ group. The lutetium bis(allyl) complex [(C₅Me₄‐C₆H₄‐o‐NMe₂)Lu(η³‐C₃H₅)₂] ( 2 b ), which contained an electron‐donating aminophenyl‐Cp ligand, was isolated from the sequential metathesis reactions of LuCl₃ with (C₅Me₄‐C₆H₄‐o‐NMe₂)Li (1 equiv) and C₃H₅MgCl (2 equiv). Following a similar procedure, the yttrium‐ and scandium–bis(allyl) complexes, [(C₅Me₄‐C₅H₄N)Ln(η³‐C₃H₅)₂] (Ln=Y ( 3 a ), Sc ( 3 b )), which also contained electron‐withdrawing pyridyl‐Cp ligands, were also obtained selectively. Deprotonation of the bulky pyridyl‐Flu ligand (C₁₃H₉‐C₅H₄N) by [Ln(CH₂SiMe₃)₃(thf)₂] generated the rare‐earth‐metal–dialkyl complexes, [(η³‐C₁₃H₈‐C₅H₄N)Ln(CH₂SiMe₃)₂(thf)] (Ln=Y ( 4 a ), Sc ( 4 b ), Lu ( 4 c )), in which an unusual asymmetric η³‐allyl bonding mode of Flu moiety was observed. Switching to the bidentate yttrium–trisalkyl complex [Y(CH₂C₆H₄‐o‐NMe₂)₃], the same reaction conditions afforded the corresponding yttrium bis(aminobenzyl) complex [(η³‐C₁₃H₈‐C₅H₄N)Y(CH₂C₆H₄‐o‐NMe₂)₂] ( 5 ). Complexes 1 – 5 were fully characterized by ¹H and ¹³C NMR and X‐ray spectroscopy, and by elemental analysis. In the presence of both [Ph₃C][B(C₆F₅)₄] and AliBu₃, the electron‐donating aminophenyl‐Cp‐based complexes 1 and 2 did not show any activity towards styrene polymerization. In striking contrast, upon activation with [Ph₃C][B(C₆F₅)₄] only, the electron‐withdrawing pyridyl‐Cp‐based complexes 3 , in particular scandium complex 3 b , exhibited outstanding activitiy to give perfectly syndiotactic (rrrr >99 %) polystyrene, whereas their bulky pyridyl‐Flu analogues ( 4 and 5 ) in combination with [Ph₃C][B(C₆F₅)₄] and AliBu₃ displayed much‐lower activity to afford syndiotactic‐enriched polystyrene.     

Rare‐Earth Oxide Nanostructures: Rules of Rare‐Earth Nitrate Thermolysis in Octadecylamine

The decomposed regularity of rare‐earth nitrates in octadecylamine (ODA) is discussed. The experimental results show that these nitrates can be divided into four types. For rare‐earth nitrates with larger RE³⁺ ions (RE=rare earth, La, Pr, Nd, Sm, Eu, Gd), the decomposed products exhibited platelike nanostructures. For those with smaller RE³⁺ ions (RE=Y, Dy, Ho, Er, Tm, Yb), the decomposed products exhibited beltlike nanostructures. For terbium nitrate with a middle RE³⁺ ion, the decomposed product exhibited a rodlike nanostructure. The corresponding rare‐earth oxides, with the same morphologies as their precursors, could be obtained when these decomposed products were calcined. For cerium nitrate, which showed the greatest differences, flowerlike cerium oxide could be obtained directly from decomposition of the nitrate without further calcination. This regularity is explained on the basis of the lanthanide contraction. Owing to their differences in electron configuration, ionic radius, and crystal structure, such a nitrate family therefore shows different thermolysis properties. In addition, the potential application of these as‐obtained rare‐earth oxides as catalysts and luminescent materials was investigated. The advantages of this method for rare‐earth oxides includes simplicity, high yield, low cost, and ease of scale‐up, which are of great importance for their industrial applications.     

Rare‐Earth‐Metal Methyl,Amide, and Imide Complexes Supported by a Superbulky Scorpionate Ligand

The reaction of monomeric [(Tp^tBu,Me)LuMe₂] (Tp^tBu,Me=tris(3‐Me‐5‐tBu‐pyrazolyl)borate) with primary aliphatic amines H₂NR (R=tBu, Ad=adamantyl) led to lutetium methyl primary amide complexes [(Tp^tBu,Me)LuMe(NHR)], the solid‐state structures of which were determined by XRD analyses. The mixed methyl/tetramethylaluminate compounds [(Tp^tBu,Me)LnMe({μ₂‐Me}AlMe₃)] (Ln=Y, Ho) reacted selectively and in high yield with H₂NR, according to methane elimination, to afford heterobimetallic complexes: [(Tp^tBu,Me)Ln({μ₂‐Me}AlMe₂)(μ₂‐NR)] (Ln=Y, Ho). X‐ray structure analyses revealed that the monomeric alkylaluminum‐supported imide complexes were isostructural, featuring bridging methyl and imido ligands. Deeper insight into the fluxional behavior in solution was gained by ¹H and ¹³C NMR spectroscopic studies at variable temperatures and ¹H–⁸⁹Y HSQC NMR spectroscopy. Treatment of [(Tp^tBu,Me)LnMe(AlMe₄)] with H₂NtBu gave dimethyl compounds [(Tp^tBu,Me)LnMe₂] as minor side products for the mid‐sized metals yttrium and holmium and in high yield for the smaller lutetium. Preparative‐scale amounts of complexes [(Tp^tBu,Me)LnMe₂] (Ln=Y, Ho, Lu) were made accessible through aluminate cleavage of [(Tp^tBu,Me)LnMe(AlMe₄)] with N,N,N′,N′‐tetramethylethylenediamine (tmeda). The solid‐state structures of [(Tp^tBu,Me)HoMe(AlMe₄)] and [(Tp^tBu,Me)HoMe₂] were analyzed by XRD.     

Highly Isoselective Coordination Polymerization of ortho‐Methoxystyrene with β‐Diketiminato Rare‐Earth‐Metal Precursors

Stereoselective coordination/insertion polymerization of the polar ortho‐methoxystyrene has been achieved for the first time by using the cationic β‐diketiminato rare‐earth‐metal species. High activity and excellent isoselectivity (mmmm>99 %) were acheived. The unmasked Lewis‐basic methoxy group does not poison the Lewis‐acidic metal center, but instead activates the polymerization through σ‐π chelation to the active species together with the vinyl group, thus lower the coordination and activation energies as compared with those of styrene derivatives lacking the methoxy group.     

Syntheses and Structures of New Rare‐Earth Metal Tetracyanidoborates

Six new rare‐earth metal tetracyanidoborates were prepared and characterized by single‐crystal X‐ray diffraction. Crystals of these salts contain co‐crystallized solvent molecules, such as water, acetone, ethanol, or diethyl ether. In [La(EtOH)₃(H₂O)₂{B(CN)₄}₃] ( 1 ), [La(EtOH)(H₂O)₄{B(CN)₄}₃] · Et₂O ( 2 ), and [Y(EtOH)(H₂O)₄{B(CN)₄}₃] · EtOH ( 6 ) the tetracyanidoborate anions are all or in part bonded to the RE³⁺ ions, whereas in [Pr(H₂O)₉][B(CN)₄]₃ · (CH₃)₂CO ( 3 ), [Er(H₂O)₈][B(CN)₄]₃ · (CH₃)₂CO ( 4 ), and [Lu(EtOH)(H₂O)₇][B(CN)₄]₃ · EtOH · 0.5H₂O ( 5 ) the [B(CN)₄]^– anions are not coordinated to the central metal atoms. Only in 1 , one of the three crystallographically independent [B(CN)₄]^– anions acts as a bridging ligand.     

Dinuclear Rare‐Earth Metal Alkyl Complexes Supported by Indolyl Ligands in μ‐η2:η1:η1 Hapticities and their High Catalytic Activity for Isoprene 1,4‐cis‐Polymerization

Two series of new dinuclear rare‐earth metal alkyl complexes supported by indolyl ligands in novel μ‐η²:η¹:η¹ hapticities are synthesized and characterized. Treatment of [RE(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of 3‐(tBuN?CH)C₈H₅NH ( L₁ ) in THF gives the dinuclear rare‐earth metal alkyl complexes trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH(CH₂SiMe₃)}Ind)RE(thf)(CH₂SiMe₃)]₂ (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L₁ is deprotonated by the metal alkyl species and the imino C?N group is transferred to the amido group by alkyl CH₂SiMe₃ insertion, affording a new dianionic ligand that bridges two metal alkyl units in μ‐η²:η¹:η¹ bonding modes, forming the dinuclear rare‐earth metal alkyl complexes. When L₁ is reduced to 3‐(tBuNHCH₂)C₈H₅NH ( L₂ ), the reaction of [Yb(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of L₂ in THF, interestingly, generated the trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (major) and cis‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (minor) complexes. The catalytic activities of these dinuclear rare‐earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio‐ and stereoselectivities for isoprene 1,4‐cis‐polymerization.