Rare-earth Metal Catalysts Research Articles

Terpolymerization of Ethylene with Hexene and Styrene Derivatives by Half-Sandwich Scandium Catalyst.

The terpolymerization of ethylene with hexene and styrene derivatives was achieved with a rare earth metal catalyst (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2 to prepare functional polyethylene. The catalyst system exhibited high activity in the terpolymerization of ethylene with hexene and amine-substituted styrene, affording terpolymers a moderate molecular weight and a unimodal molecular weight distribution. In addition, the comonomer content of the terpolymers can be controlled by changing the feeding ratio of monomers. The aliphatic region of the 13C NMR spectra reveals that the structural units of the comonomers are separately incorporated into the polyethylene backbone. Terpolymers containing styrene derivatives exhibit enhanced tensile strength and significantly improve hydrophilic properties.

Polar Molecules Regulating the Regio- and Stereoselectivity of Polymerization of Conjugated Dienes Catalyzed by CGC-Type Rare-Earth Metal Catalysts.

Herein, a concise, effective, and scalable strategy is reported that the introduction of polar molecules (PMs) (e.g., anisole (PhOMe), phenetole (PhOEt), 2-methoxynaphthalene (NaphOMe), thioanisole (PhSMe), and N,N-dimethylaniline (PhNMe2)) as continuously coordinated neutral ligand of cationic active species in situ generated from the constrain-geometry-configuration-type rare-earth metal complexes A-F/AliBu3/[Ph3C][B(C6F5)4] ternary systems can easily switch the regio- and stereoselectivity of the polymerization of conjugated dienes (CDs, including 2-subsituted CDs such as isoprene (IP) and myrcene (MY), 1,2-disubstituted CD ocimene (OC), and 1-substituted polar CD 1-(para-methoxyphenyl)-1,3-butadiene (p-MOPB)) from poor selectivities to high selectivities (for IP and MY: 3,4-selectivity up to 99%; for OC: trans-1,2-selectivity up to 93% (mm up to 90%); for p-MOPB: 3,4-syndioselectivity (3,4- up to 99%, rrrr up to 96%)). DFT calculations explain the continuous coordination roles of PMs on the regulation of the regio- and stereoselectivity of the polymerization of CDs. In comparison with the traditional strategies, this strategy by adding some common PMs is easier and more convenient, decreasing the synthetic cost and complex operation of new metal catalyst and cocatalyst. Such regio- and stereoselective regulation method by using PMs is not reported for the coordination polymerization of olefins catalyzed by rare-earth metal and early transition metal complexes.

Polar comonomers regulate and control the copolymerization of conjugated dienes and methoxystyrenes catalyzed by a CGC-type rare-earth metal catalyst

A new strategy utilizing the continuous coordination of heteroatoms of polar comonomers realized the regulation and controllability of the regioselectivity, Mn, Mw/Mn and living nature of the copolymerization of polar olefins and conjugated dienes.

Regio- and Stereoselective Polymerization of Bio-based Ocimene by Rare-Earth Metal Catalysts

Regio- and Stereoselective Polymerization of Bio-based Ocimene by Rare-Earth Metal Catalysts

Unraveling the Electron Transfer Effect of Single-Metal Ce-N4 Sites via Mesopore-Coupling for Boosted Oxygen Reduction Activity.

The development of cerium (Ce) single-atom (SA) electrocatalysts for oxygen reduction reaction (ORR) with high active-site utilization and intrinsic activity has become popular recently but remains challenging. Inspired by an interesting phenomenon that pore-coupling with single-metal cerium sites can accelerate the electron transfer predicted by density functional theory calculations, here, a facile strategy is reported for directional design of a highly active and stable Ce SA catalyst (Ce SA/MC) by the coupling of single-metal Ce-N4 sites and mesopores in nanocarbon via pore-confinement-pyrolysis of Ce/phenanthroline complexes combined with controlling the formation of Ce oxides. This catalyst delivers a comparable ORR catalytic activity with a half-wave potential of 0.845V versus RHE to the Pt/C catalyst. Also, a Ce SA/MC-based zinc-air battery (ZAB) has exhibited a higher energy density (924Wh kgZn -1 ) and better long-term cycling durability than a Pt/C-based ZAB. This proposed strategy may open a door for designing efficient rare-earth metal catalysts with single-metal sites coupling with porous structures for next-generation energy devices.

Flexible Coordination of the Bis(amino-oxazoline) Ligand in Rare-Earth Metal Complexes: Synthesis, Structure, and Their Reactivity and Polymerization Performance.

Mononuclear rare-earth metal alkyl complexes supported by tetradentate dianionic bis(amino-oxazoline) ligands have been synthesized, and their reactivity toward small molecules and catalytic performance on ring-opening polymerization have been studied. Treatment of Ln(CH2SiMe3)3(THF)2 (Ln = Sc, Y; THF = tetrahydrofuran) with the bis(amino-oxazoline) proligand H2L afforded the corresponding rare-earth metal monoalkyl complexes L-Ln(CH2SiMe3)(THF)x (Ln = Sc, x = 0 (1); Ln = Y, x = 1 (2)). The isopropyl-substituted Sc alkyl complex L'-Sc(CH2SiMe3) (3) and the analogue Y silylamide complex L-Y[N(SiHMe2)2] (4) have been prepared by a similar method. Complexes 1 and 2 were stable in solution at room temperature but transformed gradually at elevated temperature to give a nucleophilic addition product for Sc (5) and an oxazoline ring-opened dimeric complex for Y (6). Reactions of 1 with elemental sulfur and selenium each led to insertion of one chalcogen into the Sc-C bond, and the corresponding six-coordinate mononuclear chalcogenolate complexes L-Sc(ECH2SiMe3)(THF) (E = S (7), Se (8)) were isolated. Treatment of 1 with an equimolar amount of aniline yielded the Sc anilide complex L-Sc(NHC6H5) (9), whereas the reaction of 1 with [NHEt3][BPh4] afforded the Sc ion-pair [L-Sc][BPh4] (10), which upon recrystallization led to formation of a THF-solvated product [L-Sc(THF)][BPh4] (11). Single-crystal X-ray diffraction analyses of complexes 1-3, 7-9, and 11 revealed the flexible coordination capability of the tetradentate bis(amino-oxazoline) ligand of upholding a mononuclear metal center via a torsion of the diaminobiphenyl axis. Complexes 1-4 were active catalysts for initiating the ring-opening polymerization of rac-lactide with good activity (TOF up to 3204 h-1) and heteroselectivity (Pr = 0.65-0.71). This study highlights the applicability of the well-defined tetradentate bis(amino-oxazoline) ligands for mononuclear rare-earth metal complexation and shed light on the new potential of rare-earth metal catalysts bearing this type of easily derivatizable polydentate ligand.

PNP-Ligated Rare-Earth Metal Catalysts for Efficient Polymerization of Isoprene

The tridentate PNP ligand-supported rare-earth metal complexes, i.e., bis[o-diphenylphosphinophenyl]amido-Re-bis[o-dimethylaminobenzyl], [(Ph2P-o-C6H4)2N]Re[(CH2-o-Me2N(C6H4))2]: (Re = Y, 1; Nd, 2; Gd, 3) were applied to isoprene polymerization. When activated with borate activator ([PhMe2NH][B(C6F5)4] (NH-BARF), catalysts 1 and 3 exhibited excellent catalytic efficiency in aromatic media, produced very-high to ultrahigh molecular weight (Mw over 130 × 104 g/moL) polyisoprene rubber (PIR), and the obtained PIR contained over 98% cis-1,4 head-to-tail repeating unites. In most cases, the borate-activated polymerization reaction proceeded in a quasi-living pattern (PDI = 1.2–1.5) under controlled monomer conversion; whereas, activated with the commercially available modified methylaluminoxane (MMAO3A) in aliphatic hydrocarbon media, complexes 1, 2 and 3 all showed high catalytic efficiency, produced high molecular weight PIR with narrow molecular weight distribution (PDI ≤ 2.0) and high cis-1,4 head-to tail repeating unites in the range of 91–95%. Thus, the catalyst systems that consisted of 1, 2 and 3/MMAO3A, are closely relevant to the current industrial polybutadiene rubber (PBR) and PIR production processes.

(Digital Presentation) Carbon Aerogel Platinum-Praseodymium Oxide Nanocatalyst for Methanol Oxidation in 0.5 M Sulfuric Acid

Electrooxidation of methanol is an essential topic in developing direct methanol fuel cells, and numerous catalyst materials have been studied for this application. 1–3 Among other materials, the platinum-based composite catalysts containing rare earth metal oxides on various support materials have shown promising properties for methanol oxidation and implementation for direct methanol fuel cells.1–3 In this study, platinum-praseodymium oxide nanocatalyst on carbon aerogel support for methanol oxidation was synthesized. The material was electrochemically characterized using rotating disk electrode, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy methods. X-ray diffraction, specific surface area measurements, thermogravimetric analysis, and high-resolution scanning electron microscopy with energy dispersive X-ray analysis were used to determine the physical properties of the material.The catalyst was synthesized by depositing platinum4 on a pyrolyzed organic aerogel doped with Pr(NO3)3 5,6. Synthesized nanocatalyst material contained 21 wt% of Pt and 20 wt% of PrOx. This material has micro-mesoporous structure with surface area of 230 m2 g−1, micropore area of 70 m2 g−1, total pore volume of 0.62 cm3 g−1 and micropore volume of 0.032 cm3 g−1. Pt and PrOx particles were uniformly dispersed on the supporting carbon aerogel-derived material.Electrochemical measurements showed that the studied material has an electrochemically active surface area of 54 mPt 2 gPt −1, which is noticeably higher than that for commercial Pt-Vulcan catalyst (17 mPt 2 gPt −1) and comparable with similar composite catalyst materials containing rare earth metal oxides (from 45 mPt 2 gPt −1 up to 61 mPt 2 gPt −1).3 For methanol electrooxidation the synthesized material showed high current density peaks in both anodic (310 A gPt −1) and cathodic (240 A gPt −1) potential sweeps. These current densities are higher than measured for commercial Pt-Vulcan catalyst (for the peaks in both anodic (178 A gPt −1) and cathodic (167 A gPt −1) potential sweeps). Furthermore, the synthesized material demonstrated the ability of preserving higher catalytic activity (0.33 A gPt −1) than the commercial Pt-Vulcan catalyst (0.07 A gPt −1) after working on a fixed potential of ‒0.2 V vs RHE for an extended period of time (30 min). While these results outstand the catalytic activity of some similar catalyst materials containing praseodymium,1,7,8 higher current densities on both cathodic and anodic potential sweep have been measured with Pt-PrOx catalyst deposited on carbon black Vulcan XC-72R.3 These characteristics show good suitability of the developed nanocatalyst for methanol oxidation in direct methanol fuel cells.This study shows the potential of nanocatalysts containing rare earth metal oxides and catalyst on the carbon aerogel support for methanol electrooxidation. These materials could be further investigated for the electrooxidation for ethanol or other organic fuels. Acknowlegements This work was supported by the EU through the European Regional Development Fund TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), the Estonian Energy Technology Program: SLOKT10209T “Nanomaterials – research and applications (NAMUR)” project 3.2.0304.12-0397and Personal Research Grant PRG676. References Z. Tang and G. Lu, J. Power Sources, 162, 1067–1072 (2006).P. Valk et al., J. Electrochem. Soc., 165, F315–F323 (2018).P. Valk et al., J. Electrochem. Soc., 166, F1062 (2019).C. Galeano et al., J. Am. Chem. Soc., 134, 20457–20465 (2012).K. Kreek, M. Kulp, M. Uibu, A. Mere, and M. Koel, Oil Shale, 31, 185–194 (2014).K. Kreek et al., J. Non-Cryst. Solids, 404, 43–48 (2014).A. O. Neto et al., J. Alloys Compd., 476, 288–291 (2009).L. Chen, J. Hu, and J. S. Foord, Phys. Status Solidi A, 209, 1792–1796 (2012).

Living 3,4-Isoselective (Co)polymerization of Biobased β-Farnesene Catalyzed by Phosphine-Functionalized Fluorenyl Rare-Earth Metal Catalysts

With an objective to reduce petrochemical dependency, synthesis of biobased polymers from renewable feedstocks has been widely investigated. In this study, we report that living and highly 3,4-isoselective polymerization of the biobased monomer β-farnesene (100% 3,4-, >99% mmmm) can be realized at room temperature using a phosphine-functionalized fluorenyl-ligated yttrium catalytic system with ultrahigh activity. Detailed investigations suggested that the coordinated phosphine group plays a pivotal role in the high regio- and stereoselectivity of 1-Y-catalyzed β-farnesene polymerization, and the density functional density (DFT) calculation offered important insights into the 3,4-isoselectivity. Additionally, block copolymers featuring rigid 3,4-isospecific polyisoprene blocks and amorphous 3,4-isospecific polyfarnesene blocks were successfully prepared. The morphology and mechanical properties of these elastomeric copolymers were studied by using atomic force microscopy and stress–strain experiments, respectively.

CeO2-Based Heterogeneous Catalysts in Dry Reforming Methane and Steam Reforming Methane: A Short Review

Transitioning to lower carbon energy and environment sustainability requires a reduction in greenhouse gases such as carbon dioxide (CO2) and methane (CH4) that contribute to global warming. One of the most actively studied rare earth metal catalysts is cerium oxide (CeO2) which produces remarkable improvements in catalysts in dry reforming methane. This paper reviews the management of CO2 emissions and the recent advent and trends in bimetallic catalyst development utilizing CeO2 in dry reforming methane (DRM) and steam reforming methane (SRM) from 2015 to 2021 as a way to reduce greenhouse gas emissions. This paper focus on the identification of key trends in catalyst preparation using CeO2 and the effectiveness of the catalysts formulated.

Synthesis of functional polyethylene via scandium catalysted copolymerization of ethylene with triphenylamine- or carbazole-substituted styrene derivatives

The copolymerization of ethylene with triphenylamine or carbazole substituted styrene derivatives was achieved to prepared functional polyethylene with pendant triphenylamine or carbazole groups using a rare earth metal catalyst (C5Me4SiMe3)Sc(CH2SiMe3)2(THF). The catalyst system showed high activity for the copolymerization of ethylene with triphenylamine or carbazole substituted styrene derivatives, affording copolymers with moderate molecular weight and narrow molecular weight distribution. In addition, the content of styrene derivatives in the copolymers can be adjusted by changing the feeding amount. Inspection of the aliphatic region of the 13C NMR spectrum reveal the random or pseudo-random sequence structure of the copolymers. Representative photophysical properties such as UV–vis absorption and fluorescence spectroscopy of the copolymers with different content have been characterized.

DMAO-activated Rare-earth Metal Catalysts for Styrene and Its Derivative Polymerization

The catalytic performance of rare-earth metal dialkyl complexes in combination with DMAO (dry methylaluminoxane) is explored. In the presence of 60 equivalents of DMAO, the half-sandwich complex (C13H8CH2Ph)Sc(CH2SiMe3)2(THF) (1) is inert for styrene polymerization, but (C5Me4Ph)Sc(CH2C6H4NMe2-o)2 (2) converts 18% styrene into syndiotactic polystyrene. Under the same conditions, the constrained-geometry configuration sandium complex (C13H8CH2Py)Sc(CH2SiMe3)2 (3a) displays extremely high catalytic activity (> 6420 kg·molSc−1 h−1) and perfect syndiospecific (rrrr > 99%) for styrene polymerization, and, in contrast, its lutetium (3b) and yttrium (3c) analogues are nearly inactive. Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization, it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene, 4-methylthiostyrene, 4-fluorostyrene, 4-dimethylhydrosilylstyrene, alkyne-susbstituted styrenes and 4-methylstyrene. In addition, the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass transition at 80 °C and 4 bar ethylene pressures. On increasing styrene feed amount from 20 to 60 mmol, the styrene content slight increases from 48.2 mol% to 53.8 mol%, but the polymerization activity is obviously promoted from 240 to 532 kg molSc–1·h–1.

Rare-earth metal catalysts for high-pressure synthesis of rare diamonds

The combination of the unique properties of diamond and the prospects for its high-technology applications urges the search for new solvents–catalysts for the synthesis of diamonds with rare and unusual properties. Here we report the synthesis of diamond from melts of 15 rare-earth metals (REM) at 7.8 GPa and 1800–2100 °C. The boundary conditions for diamond crystallization and the optimal parameters for single crystal diamond synthesis are determined. Depending on the REM catalyst, diamond crystallizes in the form of cube–octahedrons, octahedrons and specific crystals bound by tetragon–trioctahedron and trigon–trioctahedron faces. The synthesized diamonds are nitrogen-free and belong to the rare type II, indicating that the rare-earth metals act as both solvent–catalysts and nitrogen getters. It is found that the REM catalysts enable synthesis of diamond doped with group IV elements with formation of impurity–vacancy color centers, promising for the emerging quantum technologies. Our study demonstrates a new field of application of rare-earth metals.

CePMo 12 O 40 / TiO 2 catalysts for photocatalytic oxidation of methane to value‐added organic oxygenates

Methane is the main component of natural gas. The effective activation of C-H bond of methane to synthesize value-added compounds under mild conditions is attractive. Compared to the most investigated noble metal catalysts (such as Au, Pd, and Rh), rare earth metal catalysts possess stronger oxidizing activity. Herein, we report the first synthesis of Ce cation-based phosphomolybdic salt (CePMo12O40) with a simple milling method. Furthermore, CePMo12O40-based TiO2 catalyst (CePMo/TiO2) exhibited excellent catalytic performance for selective conversion of methane, achieving high yield (5618.5 μmol/gcat) of organic oxygenates (CH3OOH, HCOOH, and HCHO) using O2 as an oxidant in water at 150°C under 1.5G sunlight irradiation for 2 hours. It was found that the yield of total produced organic oxygenates over CePMo/TiO2 is 119% larger with 1.5G sunlight light irradiation than that without the light irradiation. In addition, the introduction of CePMo into TiO2 increased its photocatalytic activity for organic oxygenates by 11%. The isotope-labeling evaluation revealed that both H2O and O2 participated the oxidation of methane into CH3OOH, HCOOH, and HCHO. This work provides the first example of rare earth POM-based photocatalysts for conversion of methane into liquid oxygenates.

Syndiospecific coordination (Co)polymerization of carbazole-substituted styrene derivatives using the scandium catalyst system

Perfect syndiospecific polymerization of carbazole-substituted styrene derivatives was achieved using a rare-earth metal catalyst. Also copolymerization of FSt with styrene afforded copolymers with gradient sequence distributions and easily tunable incorporation rate.

Asymmetric epoxidation of α,β-unsaturated ketones catalyzed by rare-earth metal amides RE[N(SiMe3)2]3with chiral TADDOL ligands

The first application of rare-earth metal catalyst combined with TADDOLs in the asymmetric epoxidation of α,β-unsaturated ketones is disclosed.

Highly Syndioselective Coordination (Co)Polymerization of para-Chlorostyrene

Chlorostyrene is difficult to polymerize due to its electron-withdrawing chlorine substituent. Herein, we report the polymerization of para-chlorostyrene (pCS) using rare-earth metal catalysts (Flu...

Cis-1,4-Polymerization of isoprene catalyzed by rare-earth metal amido complexes supported by 2-t-butylimino- or 2-amino-functionalized indolyl ligand

Aiming at developing highly efficient and more conveniently treated rare-earth metal catalyst systems, the performance of a series of the rare-earth metal amido complexes bearing 2-t-butylimino- or 2-amino-functionalized indolyl ligands as precatalysts toward isoprene polymerization was investigated. Under the activation of borate activator [Ph3C][B(C6F5)4] and AlR3, the monomeric bis(amido) complexes [2-(tBuN = CH)C8H5N]RE[N(SiMe3)2]2 (RE = Er (1), Y (2), Sm (3), Nd (4)) and the dinuclear complex {[µ-η5:η1:η1-2-(2,6-iPr2C6H3NCH2)C8H5N]Nd[N(SiMe3)2]}2 (5) exhibit different catalytic activities and cis-1,4-selectivities for isoprene polymerization depending on cocatalysts of aluminum alkyls, central rare-earth metals and the solvents. Among them, the homogeneous ternary system Nd complex 4 or 5/ [Ph3C][B(C6F5)4]/AliBu3 could very efficiently catalyze polymerization of isoprene under the relatively mild conditions to afford the cis-1,4-polyisoprenes (up to 98.3%) with high number-average molecular weights and narrow to moderate molecular weight distributions.

Rare-earth metal catalysts for alkene hydrosilylation

Rare-earth metal catalyzed hydrosilylation of alkenes has emerged as a powerful and selective strategy for the synthesis of organosilanes. This transformation can offer distinctive catalytic sequences and reaction patterns from other catalysts because of the high electropositivity and lack of oxidative-addition process of rare-earth metal. This review summarizes the rare-earth metal catalysts for hydrosilylation of alkene according to the type of ligands. The synthesis and structure of rare-earth metal catalysts, the substrate scope as well as some preliminary structure-activity relationship and mechanism are discussed.

Highly active rare-earth metal catalysts for heteroselective ring-opening polymerization of racemic lactide

Rare-earth metal complexes usually exhibit high activities in the ring-opening polymerization (ROP) of lactide, yet only a few scandium complexes have shown satisfactory activity. Herein, we report the synthesis of a series of chiral anilido-oxazoline-supported scandium and yttrium complexes that exhibit high activity in the ROP of racemic lactide (rac-LA). Complexes La-f-Ln(CH2SiMe3)2THF (La-f = 2-(2,6-R2PhN)-phenyl-4-(S)-R'-oxazoline; for 1a-f: L = La-f, Ln = Sc; for 2a-d: L = La-d, Ln = Y) were synthesized via the convenient one-pot reaction of Ln(CH2SiMe3)3(THF)2 (Ln = Sc, Y) with the corresponding proligands. The crystal structures of 1a, 1d, 1e, and 1f were isostructural, adopting a distorted trigonal bipyramidal configuration. Sc complexes 1 showed outstanding activity in the ROP of rac-LA with heteroselectivity. TOFs of up to 720 h-1 and 2910 h-1 were obtained in THF at room temperature and toluene at 60 °C, respectively. To our knowledge, these are the highest activities reported for Sc systems. Y complexes 2 showed higher activity and heteroselectivity than the Sc complexes, with TOFs of up to 1176 h-1 in THF at room temperature. Compared with the ortho-substituent on the anilido moiety, the bulky substituent at the chiral center of the oxazoline ring had a greater effect on controlling the heteroselectivity.