Scandium Complexes Research Articles

Access to Disentangled Ultrahigh Molecular Weight Polyethylene via a Binuclear Synergic Effect

AbstractDisentangled ultrahigh molecular weight polyethylene (dis‐UHMWPE) has excellent processability but can be achieved under extreme conditions. Herein, we report ethylene polymerization with the binuclear half‐sandwich scandium complexes C1‐Sc2 and C2‐Sc2 to afford UHMWPE. C1‐Sc2 bearing a short linker shows higher activity and gives higher molecular weight PEs than C2‐Sc2 containing a flexible spacer and the mononuclear Sc1. Strikingly, all UHMWPEs isolated from C1‐Sc2 under broad temperature range (25–120 °C) and wide ethylene pressures (2–13 bar) feature very low degree of entanglement as proved by rheological test, DSC annealing study and SEM. These dis‐UHMWPEs are facilely mediated solid‐state‐process at 130 °C and their tensile strength and modulus reach up to 149.2 MPa and 1.5 GPa, respectively. DFT simulations reveal that the formation of dis‐UHMWPE is attributed to the binuclear synergic effect and the agostic interaction between the active center and the growing chain.

Access to Disentangled Ultrahigh Molecular Weight Polyethylene via a Binuclear Synergic Effect.

Disentangled ultrahigh molecular weight polyethylene (dis-UHMWPE) has excellent processability but can be achieved under extreme conditions. Herein, we report ethylene polymerization with the binuclear half-sandwich scandium complexes C1-Sc2 and C2-Sc2 to afford UHMWPE. C1-Sc2 bearing a short linker shows higher activity and gives higher molecular weight PEs than C2-Sc2 containing a flexible spacer and the mononuclear Sc1 . Strikingly, all UHMWPEs isolated from C1-Sc2 under broad temperature range (25-120 °C) and wide ethylene pressures (2-13 bar) feature very low degree of entanglement as proved by rheological test, DSC annealing study and SEM. These dis-UHMWPEs are facilely mediated solid-state-process at 130 °C and their tensile strength and modulus reach up to 149.2 MPa and 1.5 GPa, respectively. DFT simulations reveal that the formation of dis-UHMWPE is attributed to the binuclear synergic effect and the agostic interaction between the active center and the growing chain.

Synthesis of an Arenide Scandium Complex Accompanied by Reductively Induced C–H Activation

Synthesis of an Arenide Scandium Complex Accompanied by Reductively Induced C–H Activation

Synthesis of syndiotactic polystyrene—Polyisobutylene graft copolymers by cationic half‐sandwich scandium complex

AbstractSyndiotactic polystyrene is a high strength engineering plastic, and polyisobutylene is an excellent elastomers. In order to combine the advantages of syndiotactic polystyrene and polyisobutylene, isobutylene was achieved to graft onto the crystalline syndiotactic polystyrene, forming graft copolymers, under half sandwich scandium complex [(C5Me4SiMe3)Sc(CH2SiMe3)2THF]/[Ph3C][B(C6F5)4] after the application of syndiotactic copolymers of styrene and 4‐isopropenylstyrene with pendant double bonds. Grafted copolymers based on crystalline polystyrene and rubbery polyisobutylene block have both high Tm (270°C) and low Tg (−67°C), meanwhile, these materials have relative good mechanical properties.

Coordination Polymerization of Renewable (E)‐4,8‐Dimethyl‐1,3,7‐Nonatriene by Rare‐Earth Metal Catalysts

Comprehensive SummaryCoordination polymerization of renewable (E)‐4,8‐dimethyl‐1,3,7‐nonatriene (DMNT) has been performed using pyridyl‐methylene‐ fluorenyl scandium complex 1, half‐sandwich scandium complex 2, diiminophosphinato rare‐earth metal complexes 3a—3c and 4a—4b, bis(phosphino)carbazolide yttrium complex 5 and β‐diketiminato yttrium complex 6. Fluorenyl scandium complexes 1 and 2, activated by [Ph3C][B(C6F5)4] and AliBu3, are moderately active and show perfect 1,2‐regioselective (1,2 > 99%). Conversely, asymmetric diiminophophinato complexes 3a—3c promote the DMNT polymerization to produce high trans‐1,4 regulated products with the activity trend: Sc < Lu < Y. Complexes 4—6 are virtually inactive for the DMNT polymerization although they are highly active in isoprene polymerization. A diblock copolymer bearing 3,4‐polyisoprene block and trans‐1,4‐poly(DMNT) block is obtained using complex 3c in one‐pot reaction. Hydrogenation of trans‐1,4‐poly(DMNT) affords an elastomer with a Tg of –10°C. The epoxidation reaction of trans‐1,4‐poly(DMNT) with 3‐chloroperbenzoic acid transfers the pendant double bonds in the cis configuration into the epoxy groups.

New luminescent 10-oxybenzoquinolate complexes of rare earth metals

A series of Sc, Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm and Yb complexes with oxybenzoquinoline ligands (BQ) was synthesized by the reactions of 10-hydroxybenzo[h]quinoline with cyclopentadienides or tris(trimethylsilyl)amides of rare earth metals. The structure, as well as the photo- and electroluminescent (PL, EL) properties of these complexes in solutions and solid state were studied. In solutions, complexes of sodium and lanthanides exhibit double peaked ligand-centered PL of enol and keto forms of BQ with a quantum yield of 1%–8%. In the solid state the complexes of Sm, Eu, Ho, Nd, Er, and Yb along with the ligand-centered PL also exhibit a moderate-intensity metal-centered PL which is characteristic of the corresponding Ln3+ ions. Sc(BQ)3 complex shows bright green EL which has intensity comparable to the best results observed for scandium complexes with other organic ligands.

An Asymmetric Intramolecular Rauhut-Currier Reaction Initiated by Chiral Selenolate-BINOL Complexes

This work reports the new method of Rauhut-Currier reaction (RC) with the use of lithium selenolates, which provided up to 80% yield in a non-asymmetric IRC reaction. Therefore, our paper involves the search for an efficient chiral additive in the asymmetric version. The influence of various reaction parameters, such as solvent, additives, temperature, and time, was examined. The results for the non-asymmetric version were significantly higher with the presence of water, but surprisingly different observations were obtained in the asymmetric version. Here, the chiral scandium complex with tertiary amine played an important role. The reaction carried out in the presence of chiral complexes gave the expected product with up to 60% yield and up to 70% ee.

The Synthesis and Structure of a Scandium Nitrate Hydroxy-Bridged Dimeric Complex Supported by Bipyridyl Ligands.

The current discussion on whether scandium, yttrium and lanthanum should represent Group 3 in the Periodic Table or whether lutetium should replace lanthanum in the group has prompted us to further explore the structural chemistry of the Group 3 elements and compare the coordination numbers and coordination geometries adopted. The steric and electronic properties of the coordinated ligands have a major influence on the structures adopted. We report the synthesis and crystal structure determination of an unusual dinuclear scandium complex [(bipy)(NO3)2Sc(µ-OH)2Sc(NO3)2(bipy)] obtained by the reaction of hydrated scandium nitrate with 2,2′-bipyridyl (bipy) in either ethanol or nitromethane. The crystal structure of the complex shows that the scandium centers are eight coordinate, and the structure obtained contrasts with related complexes found in the lanthanide series [Ln(bipy)2(NO3)3] and [Ln(phen)2(NO3)3] (phen = phenanthroline) and in [M(terpy)(NO3)3] (M = Sc, Er–Lu), where these complexes are all mononuclear.

Synthesis of pyrrolidinyl-ethylene fluorenyl rare-earth metal complexes and catalysis for 2-vinylpyridine polymerization

The metathesis reaction between pyrrolidinyl-ethylene fluorenyl lithium salts with in situ prepared cationic rare-earth metal dialkyl species [Ln(CH2SiMe3)2(THF)x][BPh4] afford efficiently the corresponding constrained-geometry complexes L1Ln(CH2SiMe3)2 (L1 = FluCH2CH2NC4H8, Ln = Y (1a), Lu (1b), Sc (1c)) and L2Ln(CH2SiMe3)2 (L2 = (2,7-di-tert-butyl)FluCH2CH2NC4H8, Ln = Y (2a), Lu (2b), Sc (2c)) in good yields. All these complexes were characterized by NMR spectroscopy, and the solid-state molecular structure of yttrium complex 1a was defined with single-crystal X-ray diffraction analysis. The catalytic performance of these complexes towards 2-vinylpyridine polymerization was investigated, where these complexes alone can efficiently promote the polymerization of 2-vinylpyridine giving isotactic poly(2-vinylpyridine). Upon the activation with [Ph3C][B(C6F5)4], the yttrium and lutetium complexes also afford isotactic poly(2-vinylpyridine), while the scandium complexes produce syndiotactic poly(2-vinylpyridine).

Non-radioactive scandium oxide receiving out of uranium ISR solutions

The task of the research was to study and determine an effective method for the preparation of non-radioactive scandium compounds from uranium In-Situ Recovery (ISR) solutions. The widespread use of scandium is restrained by the high price due to its small production volumes, low content in the raw materials (scandium is a scattered element and does not form its own deposits), as well as the complexity of technological schemes for its extraction. Scandium receiving out of uranium reverses ISR solutions technological scheme was experimental tested, including sorption on MTS 9580 (Purolite’s production) ion exchanger with recurrent ballast impurities desorption and receiving concentrate that contains scandium. New radiation cleaning technological sequencing based on different solubility of radioactive elements and scandium in carbonate solutions, that accompanied by insoluble macro components complex formation, that contains in deactivated scandium concentrate and allows to get scandium oxide with desired component maintenance more than 94 % and less than 0,3 kilobecquerels/kg specific activity level was developed. The developed technology is based on the ability to form soluble carbonate complexes of scandium and radioactive elements, while the main macro components of the concentrate - ferrum, aluminum, calcium, silicon and others under the conditions of carbonation of the concentrate are inert or form insoluble compounds. Optimal radioactive impurity removing from concentrate conditions and scandium leaching from deactivated residue of scandium and macro impurity were studied and identified in laboratory conditions and during pilot tests.

Влияние катамина АБ на комплексообразование скандия с пирокатехиновым фиолетовым

Regularities of the complex formation of scandium with catechol violet in the presence of the cationic surfactant catamine AB in aqueous solutions are considered. The optimum pH interval of scandium complexation with the reagent in systems with and without catamine AB has been determined. The absorption spectra of pyrocatechin vio- let and its complexes with scandium in the double system and in the catamin AB presence at different pH values and surfactant concentrations were taken. The ratio of metal ion and reagent in the forming complex in double and triple systems has been established by methods of saturation and isomolar series. Calibration graphs were constructed, molar light absorption coefficients were calculated, and conditional stability constants of scandium complexes with pyrocate- chin violet were determined by the Babko method.

Synthesis and characterisation of an enantiomerically pure scandium pentadienyl complex and its application in the polymerisation of rac-lactide

The alkyl-functionalised scandium complex [(pdl*SiMe2NtBu)Sc(thf)(CH2SiMe3)] (2) was synthesised in enantiomerically pure form and characterised by NMR spectroscopy and X-ray diffraction analysis. Complex 2 features a chiral constrained geometry ligand derived from the natural compound (1R)-(-)-myrtenal, in which the pentadienyl (pdl*) fragment coordinates in η3:η2-allyl-en fashion to the scandium atom. Compound 2 catalyses the polymerisation of rac-lactide at 30 °C and 50 °C yielding amorphous poly(lactide) with slightly heterotactic enchainment (Pm = 0.36 and 0.37). In agreement with the data obtained from GPC and DSC measurements, a chain-end control mechanism is proposed with fast chain propagation relative to the initiation, which leads to broad molecular weight distributions (Đ ≈ 1.80) and higher than expected molecular weights. Furthermore, chain transfer processes are observed, but only small amounts of transesterification and racemisation occur. Kinetic studies reveal a second-order dependence in rac-lactide (monomer) concentration and a first-order dependence in the concentration of catalyst 2.

Crystalline sulfur-functionalized poly(α-olefin) synthesized by scandium-catalyzed coordination polymerization

Combined with organoborate, the scandium complex catalyzed monomers to produce a series of syndiotactic sulfur-functionalized poly(α-olefin)s (rrrr of up to 0.95) which formed crystalline materials with a Tm of up to 91 °C.

Preparation of Group 3 Metal Sulfur Monoxide Complexes via Oxidation of Metal Atoms using SOF2 in Cryogenic Matrixes

AbstractSide‐on sulfur monoxide complexes of scandium, yttrium, and lanthanum difluorides [MF2(η2‐SO)] were prepared via oxidation of metal atoms by SOF2 in cryogenic matrixes. The structures of these SO complexes are determined by characteristic infrared absorptions as well as isotopic frequency ratios, and the assignments are further supported by density functional theory calculations. A doublet ground state with nonplanar Cs symmetry was established for all the complexes with side‐on SO ligands. The S−O bond lengths as well as the S−O stretching vibrational frequencies approach those of SO−, suggesting that the group 3 metal MF2(η2‐SO) complexes can be considered as (MF2)+(SO)−. Consistent with this notion, the interaction between MF2 and SO is mainly ionic with SO negatively charged by about −0.60 e, and the unpaired electron is located in the SO 3π orbital that is antibonding in character. It is highly exothermic to form MF2(η2‐SO) mediated by a single fluorine transfer MF(SOF) intermediate from the reactions of SOF2 and metal atoms. The absence of group 3 metal sulfur monoxide complexes using SO2F2 as a precursor is because the resulting complexes would require a metal center with the oxidation state higher than III.

Synthesis and Structure Diversity of Half‐Sandwich Rare Earth Dialkynyl Complexes

AbstractHalf‐sandwich rare‐earth dialkynyl complexes are of much interest in both structure and reactivity but have remained much underexplored to date. Here we report the synthesis and transformation of a new family of half‐sandwich dialkynyl complexes bearing the C5Me4SiMe3 ligand, which exhibited diverse structural features depending on metal ion size, alkyne substituent and with or without THF coordination. The acid‐base reactions between half‐sandwich rare earth dialkyl complexes (C5Me4SiMe3)Ln(CH2SiMe3)2(THF) (Ln=Sc, Y, Lu) and two equivalents of terminal alkynes such as phenylacetylene and trimethylsilylacetylene in THF generally gave the corresponding THF‐coordinated monomeric rare earth dialkynyl complexes, which upon recrystallization from toluene yielded further aggregated alkynyl complexes with partial or full dissociation of the THF ligands. In the case of phenylacetylene, trimeric yttrium and lutetium hexaalkynyl complexes were formed, in which each pair of the metal atoms was bridged by two alkynyl ligands in solid state but the alkynyl ligands underwent rapid site exchange in toluene solution. In the case of trimethylsilylacetylene with yttrium and lutetium, dimeric tetraalkynyl complexes bearing two terminal and two bridging alkynyl ligands were obtained from toluene. In contrast, recrystallization of the scandium trimethylsilylacetylide complex from toluene induced alkynyl coupling and yielded dimeric scandium complex with one butatrienediyl and two alkynyl bridging ligands. Upon dissolution in THF, all the aggregated alkynyl/butatrienediyl complexes were rapidly reconverted to the monomeric dialkynyl complexes as a result of THF coordination to the rare earth metal atoms.

EXTRACTION CONCENTRATING OF SCANDIUM (III) IN COMPLEX FORM WITH 2-HYDROXY-5-T-BUTYLPHENOL-4-METOXYAZOBENZENE AND ITS DETERMINATION BY ATOMIC-ABSORPTION SPECTROMETRY

Complexation of scandium 2-hydroxy-5-T-butylphenol-4-metoxyazobenzene (HR) was studied by atomic-absorption and spectrophotometric methods. Optimum conditions of formation and extraction of the complex were found. Maximum light absorbance of a complex in n-butanol is in the range of 470÷480 nm. Molar absorption coefficient equals to (2.2–3.0).104. Stability constant of scandium in n-butanol is л=2.8·1010. Selective and sensitive techniques of extraction-atomic absorption determination of scandium in soils were developed

Direct Synthesis of Functional Thermoplastic Elastomer with Excellent Mechanical Properties by Scandium-Catalyzed Copolymerization of Ethylene and Fluorostyrenes.

Herein, we report copolymerizations of ethylene (E) and ortho-/meta-/para-fluorostyrenes (SF =oFS/mFS/pFS) by using quinolyl methylene fluorenyl scandium complex (Flu-CH2 -Qu)Sc(CH2 SiMe3 )2 . The copolymerizations proceed in a controlled fashion to afford copolymers composed of "soft" ethylene-fluorostyurene (E-SF ) random segments (Tg =-22.2-5.1 °C) and "hard" crystalline ethylene-ethylene (E-E) segments (Tm =42.3-130.2 °C). The copolymers behave like thermoplastic elastomers at room temperature by showing high stress values up to 39.5 MPa under elongation-at-break above 774 % with elastic recovery over 75 %. The excellent mechanical properties are mainly attributed to the microphase separation of the nanoscale crystalline E-E domain from the amorphous E-SF copolymer matrix proved by AFM, WAXD and SAXS. The mechanism investigation by the density functional theory (DFT) simulation reveals that the steric bulky and electron-withdrawing ligand of the catalytic precursor prefers E propagation to generate long E-E segments, while the incorporation of SF is thermodynamic control.

Direct Synthesis of Functional Thermoplastic Elastomer with Excellent Mechanical Properties by Scandium‐Catalyzed Copolymerization of Ethylene and Fluorostyrenes

AbstractHerein, we report copolymerizations of ethylene (E) and ortho‐/meta‐/para‐fluorostyrenes (SF=oFS/mFS/pFS) by using quinolyl methylene fluorenyl scandium complex (Flu‐CH2‐Qu)Sc(CH2SiMe3)2. The copolymerizations proceed in a controlled fashion to afford copolymers composed of “soft” ethylene‐fluorostyurene (E–SF) random segments (Tg=−22.2–5.1 °C) and “hard” crystalline ethylene–ethylene (E–E) segments (Tm=42.3–130.2 °C). The copolymers behave like thermoplastic elastomers at room temperature by showing high stress values up to 39.5 MPa under elongation‐at‐break above 774 % with elastic recovery over 75 %. The excellent mechanical properties are mainly attributed to the microphase separation of the nanoscale crystalline E–E domain from the amorphous E–SF copolymer matrix proved by AFM, WAXD and SAXS. The mechanism investigation by the density functional theory (DFT) simulation reveals that the steric bulky and electron‐withdrawing ligand of the catalytic precursor prefers E propagation to generate long E–E segments, while the incorporation of SF is thermodynamic control.

Alkyl scandium complexes coordinated by dianionic O,N,N- and O,N,O-ligands derived from Schiff bases

The reactions of imino phenols 3,5-But2-2-HOC6H2CH=NX (X = 8-C9H6N, 2-MeO-5-MeC6H3 and 2-PhOC6H4) with Sc(CH2SiMe3)3(THF)2 in toluene proceed with silane elimination and reductive alkylation of the CN group affording dimeric base-free monoalkyl scandium complexes. X-ray analysis of the two complexes revealed their dimeric structures due to μ-bridging amidophenolato dianions. The complexes catalyze hydrophosphination of styrene, phenylacetylene and tolane with Ph2PH as well as dehydrogenative coupling of anisole with hydrosilanes.

An Ylidic Cp and its Scandium Complexes in Equilibrium

An Ylidic Cp and its Scandium Complexes in Equilibrium