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.     

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.     

Dual Functionalization of White Phosphorus: Formation,Characterization, and Reactivity of Rare‐Earth‐Metal Cyclo‐P3 Complexes

The [3+1] fragmentation reaction of rare‐earth metallacyclopentadienes 1 a – c with 0.5 equivalents of P₄ affords a series of rare‐earth metal cyclo‐P₃ complexes 2 a – c and a phospholyl anion 3. 2 a – c demonstrate an unusual η³ coordination mode with one P−P bond featuring partial π‐bonding character. 2 a – c are the first cyclo‐P₃ complexes of rare‐earth metals, and also the first organo‐substituted polyphosphides in the category of Group 3 and f‐block elements. Rare‐earth metallacyclopentadienes play a dual role in the combination of aromatization and Diels–Alder reaction. Compounds 2 a – c can coordinate to one or two [W(CO)₅] units, yielding 4 a – c or 5 c , respectively. Furthermore, oxidation of 2 a with p ‐benzoquinone produces its corresponding phospholyllithium and regenerated P₄.     

Solid‐State NMR and DFT Studies on the Formation of Well‐Defined Silica‐Supported Tantallaaziridines: From Synthesis to Catalytic Application

Single‐site, well‐defined, silica‐supported tantallaaziridine intermediates [≡Si‐O‐Ta(η²‐NRCH₂)(NMe₂)₂] [R=Me ( 2 ), Ph ( 3 )] were prepared from silica‐supported tetrakis(dimethylamido)tantalum [≡Si‐O‐Ta(NMe₂)₄] ( 1 ) and fully characterized by FTIR spectroscopy, elemental analysis, and ¹H,¹³C HETCOR and DQ TQ solid‐state (SS) NMR spectroscopy. The formation mechanism, by β‐H abstraction, was investigated by SS NMR spectroscopy and supported by DFT calculations. The C?H activation of the dimethylamide ligand is favored for R=Ph. The results from catalytic testing in the hydroaminoalkylation of alkenes were consistent with the N‐alkyl aryl amine substrates being more efficient than N‐dialkyl amines.     

Rare‐Earth‐Metal Methylidene Complexes

Transition‐metal carbene complexes have been known for about 50 years and widely applied as reagents and catalysts in organic transformations. In contrast, the carbene chemistry of the rare‐earth metals is much less developed, but has attracted the research interest in the recent years. In this field rare‐earth‐metal alkylidene, especially methylidene, compounds are an emerging class of compounds with a high synthetic potential for organometallic chemistry and maybe in the future also for organic chemistry.     

Catalytic Selective Dihydrosilylation of Internal Alkynes Enabled by Rare‐Earth Ate Complex

Hydrosilylation of alkynes generally yield vinylsilanes, which are inert to the further hydrosilylation because of the steric effects. Reported here is the first successful dihydrosilylation of aryl‐ and silyl‐substituted internal alkynes enabled by a rare‐earth ate complex to yield geminal bis‐ and tris(silanes), respectively. The lanthanum bis(amido) ate complex supported by an ene‐diamido ligand proved to be the ideal catalyst for this unprecedented transformation, while the same series of yttrium and samarium alkyl and samarium bis(amido) ate complexes exhibited poor activity and selectivity, indicating significant effects of the ionic size and ate structure of the rare‐earth catalysts.     

Simultaneous Chain‐Growth and Step‐Growth Polymerization of Methoxystyrenes by Rare‐Earth Catalysts

The simultaneous chain‐growth and step‐growth polymerization of a monomer is of great interest and importance because it can produce unique macromolecules which are difficult to prepare by other means. However, such a transformation is usually difficult to achieve in one polymerization system because chain‐growth polymerization and step‐growth polymerization proceed by different reaction mechanisms. Reported here is the simultaneous chain‐growth and step‐growth polymerization of para‐ and meta‐methoxystyrenes catalyzed by half‐sandwich rare‐earth alkyl complexes, and the step‐growth polymerization proceeds by the C?H polyaddition of anisyl units to vinyl groups. This unprecedented transformation affords a new family of macromolecules containing unique alternating anisole‐ethylene sequences. In contrast to para‐ and meta‐methoxystyrenes, ortho‐methoxystyrene exclusively undergo syndiospecific, living chain‐growth polymerization by continuous C=C bond insertion to give perfect syndiotactic poly(ortho‐methoxystyrene) with high molecular weight and narrow polydispersity (rrrr >99 %, M_n up to 280 kg mol^?1, M_w/M_n <1.10).     

Dimeric Rare‐Earth BINOLate Complexes: Activation of 1,4‐Benzoquinone through Lewis Acid Promoted Potential Shifts

Reaction of p‐benzoquinone (BQ) with a series of rare‐earth metal/alkali metal/1,1′‐BINOLate (REMB) complexes (RE: La, Ce, Pr, Nd; M: Li) results in the largest recorded shift in reduction potential observed for BQ upon complexation. In the case of cerium, the formation of a 2:1 Ce/BQ complex shifts the two‐electron reduction of BQ by greater than or equal to 1.6 V to a more favorable potential. Reactivity investigations were extended to other RE^III (RE=La, Pr, Nd) complexes where the resulting highly electron‐deficient quinone ligands afforded isolation of the first lanthanide quinhydrone‐type charge‐transfer complexes. The large reduction‐potential shift associated with the formation of 2:1 Ce/BQ complexes illustrate the potential of Ce complexes to function both as a Lewis acid and an electron source in redox chemistry and organic‐substrate activation.     

Structural Study of Alkaline‐Earth Metal Heterocycles Supported by Triazole‐based Sulfur Ligands

The alkaline earth metal complex [Mg{4,5‐(P(S)Ph₂)₂}₂tz}₂(thf)₄] ( 2 ) and the bimetallic complexes, [M{4,5‐(P(S)Ph₂)₂}₂tz}₂(thf)]₂ [M = Ca ( 3 ), Sr ( 4 ), Ba ( 5 )], [SrI{4,5‐(P(S)Ph₂)₂tz}₂(thf)₃]₂ ( 6 ), and [{BaI(4,5‐(P(S)Ph₂)₂tz)}₂(thf)₇] ( 7 ) were prepared in good yields from the metathesis reactions of the potassium salt of 4,5‐bis(diphenylthiophosphoranyl)‐1,2,3‐triazole [H{4,5‐(P(S)Ph₂)₂tz}] ( 1 ) and MI₂ (M = Ca, Sr, Ba), whereas the tetrametallic magnesium hydroxide [Mg₂(μ‐OH){4,5‐(P(S)Ph₂)₂}₂tz}₃]₂ ( 8 ) was obtained as the hydrolysis product from the starting material (MgnBuCl) and 1 . The NMR study of 2 – 8 in solution suggests the formation of solvated species in CD₃OD‐d4, whereas for 4 , 5 , and 6 a fluxional behavior is observed in CD₂Cl₂. The structural analyses of 3 – 5 , 6 , and 7 in solid state reveal in all cases a central core defined by M₂N₄ heterocycle bearing M–S bonding. The degree of aggregation observed for these compounds depends significantly on the size of the metal atom as well as on the metal‐ligand molar ratio employed for each reaction.     

Molecular Polyarsenides of the Rare‐Earth Elements

Reduction of [Cp*Fe(η⁵‐As₅)] with [Cp′′₂Sm(thf)] (Cp′′=η⁵‐1,3‐(tBu)₂C₅H₃) under various conditions led to [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] and [(Cp′′₂Sm)₂As₇(Cp*Fe)]. Both compounds are the first polyarsenides of the rare‐earth metals. [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] is also the first d/f‐triple decker sandwich complex with a purely inorganic planar middle deck. The central As₄^2? unit is isolobal with the 6π‐aromatic cyclobutadiene dianion (CH)₄^2?. [(Cp′′₂Sm)₂As₇(Cp*Fe)] contains an As₇^3? cage, which has a norbornadiene‐like structure with two short As?As bonds in the scaffold. DFT calculations confirm all the structural observations. The As?As bond order inside the cyclo As₄ ligand in [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] was estimated to be in between an As?As single bond and a formally aromatic As₄^2? system.     

Engineered Anisotropic Fluids of Rare‐Earth Nanomaterials

The self‐assembly of inorganic nanoparticles into well‐ordered structures in the absence of solvents is generally hindered by van der Waals forces, leading to random aggregates between them. To address the problem, we functionalized rigid rare‐earth (RE) nanoparticles with a layer of flexible polymers by electrostatic complexation. Consequently, an ordered and solvent‐free liquid crystal (LC) state of RE nanoparticles was realized. The RE nanomaterials including nanospheres, nanorods, nanodiscs, microprisms, and nanowires all show a typical nematic LC phase with one‐dimensional orientational order, while their microstructures strongly depend on the particles’ shape and size. Interestingly, the solvent‐free thermotropic LCs possess an extremely wide temperature range from ?40 °C to 200 °C. The intrinsic ordering and fluidity endow anisotropic luminescence properties in the system of shearing‐aligned RE LCs, offering potential applications in anisotropic optical micro‐devices.     

Pore‐Environment Engineering with Multiple Metal Sites in Rare‐Earth Porphyrinic Metal–Organic Frameworks

Multi‐component metal–organic frameworks (MOFs) with precisely controlled pore environments are highly desired owing to their potential applications in gas adsorption, separation, cooperative catalysis, and biomimetics. A series of multi‐component MOFs, namely PCN‐900(RE), were constructed from a combination of tetratopic porphyrinic linkers, linear linkers, and rare‐earth hexanuclear clusters (RE₆) under the guidance of thermodynamics. These MOFs exhibit high surface areas (up to 2523 cm² g^?1) and unlimited tunability by modification of metal nodes and/or linker components. Post‐synthetic exchange of linear linkers and metalation of two organic linkers were realized, allowing the incorporation of a wide range of functional moieties. Two different metal sites were sequentially placed on the linear linker and the tetratopic porphyrinic linker, respectively, giving rise to an ideal platform for heterogeneous catalysis.     

Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare‐Earth Complexes: Non‐Redox Oxygen Atom Transfer

The preferential substitution of oxo ligands over alkyl ones of rare‐earth complexes is commonly considered as “impossible” due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare‐earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln‐oxo bond, but also protect the highly reactive Ln‐alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non‐redox rare‐earth‐mediated oxygen atom transfer from ketones to CS₂ and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare‐earth oxo complexes.     

Cationic Allyl Complexes of the Rare‐Earth Metals: Synthesis,Structural Characterization,and 1,3‐Butadiene Polymerization Catalysis

Monocationic bis‐allyl complexes [Ln(η³‐C₃H₅)₂(thf)₃]⁺[B(C₆X₅)₄]^? (Ln=Y, La, Nd; X=H, F) and dicationic mono‐allyl complexes of yttrium and the early lanthanides [Ln(η³‐C₃H₅)(thf)₆]²⁺[BPh₄]₂^? (Ln=La, Nd) were prepared by protonolysis of the tris‐allyl complexes [Ln(η³‐C₃H₅)₃(diox)] (Ln=Y, La, Ce, Pr, Nd, Sm; diox=1,4‐dioxane) isolated as a 1,4‐dioxane‐bridged dimer (Ln=Ce) or THF adducts [Ln(η³‐C₃H₅)₃(thf)₂] (Ln=Ce, Pr). Allyl abstraction from the neutral tris‐allyl complex by a Lewis acid, ER₃ (Al(CH₂SiMe₃)₃, BPh₃) gave the ion pair [Ln(η³‐C₃H₅)₂(thf)₃]⁺[ER₃(η¹‐CH₂CH?CH₂)]^? (Ln=Y, La; ER₃=Al(CH₂SiMe₃)₃, BPh₃). Benzophenone inserts into the La? C_allyl bond of [La(η³‐C₃H₅)₂(thf)₃]⁺[BPh₄]^? to form the alkoxy complex [La{OCPh₂(CH₂CH?CH₂)}₂(thf)₃]⁺[BPh₄]^?. The monocationic half‐sandwich complexes [Ln(η⁵‐C₅Me₄SiMe₃)(η³‐C₃H₅)(thf)₂]⁺[B(C₆X₅)₄]^? (Ln=Y, La; X=H, F) were synthesized from the neutral precursors [Ln(η⁵‐C₅Me₄SiMe₃)(η³‐C₃H₅)₂(thf)] by protonolysis. For 1,3‐butadiene polymerization catalysis, the yttrium‐based systems were more active than the corresponding lanthanum or neodymium homologues, giving polybutadiene with approximately 90 % 1,4‐cis stereoselectivity.     

The Reduction of Rare‐Earth Metal Halides with Unlike Metals – Wöhler's Metallothermic Reduction

Rare‐earth halides may be reduced by rare‐earth metals (conproportionation) and, as an alternative, by unlike metals such as alkali or alkaline‐earth metals, a route first established for the production of rare‐earth metals. It has great power for exploratory research subject to enhanced reactivity at lower temperatures and the formation of alkali halide flux for crystal growth. A large number of new compounds, ternary and higher, salt‐like and (semi‐)metallic including interstitially stabilized cluster compounds has been synthesized and characterized during the last decades.     

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.     

Homometallic Rare‐Earth Metal Phosphinidene Clusters: Synthesis and Reactivity

Two new trinuclear μ₃‐bridged rare‐earth metal phosphinidene complexes, [{L(Ln)(μ‐Me)}₃(μ₃‐Me)(μ₃‐PPh)] (L=[PhC(NC₆H₄iPr₂‐2,6)₂]^?, Ln=Y ( 2 a ), Lu ( 2 b )), were synthesized through methane elimination of the corresponding carbene precursors with phenylphosphine. Heating a toluene solution of 2 at 120 °C leads to an unprecedented ortho C? H bond activation of the PhP ligand to form the bridged phosphinidene/phenyl complexes. Reactions of 2 with ketones, thione, or isothiocyanate show clear phospha‐Wittig chemistry, giving the corresponding organic phosphinidenation products and oxide (sulfide) complexes. Reaction of 2 with CS₂ leads to the formation of novel trinuclear rare‐earth metal thione dianion clusters, for which a possible pathway was determined by DFT calculation.     

Co‐syndiospecific Alternating Copolymerization of Functionalized Propylenes and Styrene by Rare‐Earth Catalysts

The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of functional polymers, but studies toward this goal have met with only limited success to date. Now, the co‐syndiospecific alternating copolymerization of methoxyphenyl‐ and N,N‐dimethylaminophenyl‐functionalized propylenes with styrene by half‐sandwich rare‐earth catalysts is reported. This reaction efficiently afforded the corresponding functionalized propylene‐alt‐styrene copolymers with a perfect alternating sequence and excellent co‐syndiotacticity (rrrr >99 %), thus constituting the first example of co‐stereospecific alternating copolymerization of polar and non‐polar olefins.