Novel polymerization catalysts and hydride clusters from rare-earth metal dialkyls

Bis(phosphinophenyl)amido-Ligated Binuclear Rare-Earth Metal Complexes for Highly cis-1,4-Selective Polymerization of 1,3-Conjugated Dienes

A series of binuclear rare-earth metal complexes based on the ligands containing bis(phosphinophenyl)amido-PNP unit are successfully synthesized. All the ligands and the corresponding binuclear complexes are fully characterized by NMR spectra (1H, 13C, and 31P). In conjunction with [Ph3C][B(C6F5)4], all the binuclear complexes exhibited high catalytic activity and high cis-1,4-selectivity (>99%) toward the polymerization of 1,3-conjugated dienes (isoprene, β-myrcene and β-farnesene) with excellent livingness at room temperature or even 80 °C.

Multi-electron redox reactivity of a samarium(ii) hydrido complex

Well-defined low-valent molecular rare-earth metal hydrides are rare, and limited to Yb2+ and Eu2+ centers. Here, we report the first example of the divalent samarium(ii) hydrido complex [(CpAr5)SmII(μ-H)(DABCO)]2 (4) (CpAr5 = C5Ar5, Ar = 3,5-iPr2-C6H3; DABCO = 1,4-diazabicyclooctane) supported by a super-bulky penta-arylcyclopentadienyl ligand, resulting from the hydrogenolysis of the samarium(ii) alkyl complex [(CpAr5)SmII{CH(SiMe3)2}(DABCO)] (3). Complex 4 exhibits multi-electron redox reactivity toward a variety of substrates. Exposure of complex 4 to CO2 results in the formation of the trivalent samarium(iii) mixed-bis-formate/carbonate complex [(CpAr5)SmIII(μ-η2:η1-O2CH)(μ-η2:η2-CO3)(μ-η1:η1-O2CH)SmIII(CpAr5)(DABCO)] (8), mediated by hydride insertion and reductive disproportionation reactions. Complex 4 shows four-electron reduction toward four equivalents of CS2 to afford the trivalent samarium(iii) bis-trithiocarbonate complex [(CpAr5)SmIII(μ-η2:η2-CS3)(DABCO)]2 (9). A mechanistic study of the formation of complex 8 was carried out using DFT calculations.

Synthesis of bis(oxazoline)-based rare-earth metal complexes and their catalytic performance in the polymerization of isoprene and polar ortho-methoxystyrene

A series of bis(oxazoline) rare-earth metal dialkyl complexes [(L)Ln(CH2SiMe3)2(THF)n] (L = L1 (dimethyl-substituted bis(oxazoline) ligand), Ln = Y (1-Y), Lu (1-Lu), Sc (1-Sc), n = 1; L = L2 (phenyl-substituted bis(oxazoline) ligand), Ln = Y (2-Y), Lu (2-Lu), Sc (2-Sc), n = 2) was successfully prepared. NMR spectroscopy and X-ray diffraction indicated that all the complexes ligated with a C2 symmetric bis(oxazoline) and two trimethylsilylmethyl ligands. In the presence of borate and triisobutyl aluminium, these complexes exhibited high catalytic activity for the polymerization of isoprene, yielding the polymer with high cis-1,4-regularity (up to 99.9%) and high molecular weight. Moreover, these ternary catalytic systems also served as efficient initiators for the polymerization of polar ortho-methoxystyrene. However, atactic polymers in all the cases were isolated despite the C2 symmetric geometry of bis(oxazoline) ligands.

Theoretical investigations of 2-vinylpyridine stereoselective polymerization catalyzed by cationic yttrium complexes with different ancillary ligands

The polymerization mechanism of 2-vinylpyridine catalyzed by cationic yttrium complexes with diverse ancillary ligands, specifically [L1Y(CH2SiMe3)(THF)]+ [L1 = (2,6-Et2C6H3)NC(Me)CHC(Me)N(2,6-Et2C6H3)] (Y-1), [L2Y(CH2SiMe3)(THF)]+ [L2 = (2,6-Cl2C6H3)NC(Me)CHC(Me)N(2,6-Cl2C6H3)] (Y-2), and [L3Y(CH2SiMe3)(THF)]+ [L3 = (2,6-C6H5)NC(Me)CHC(Me)N(2,6-iPr2C6H3)] (Y-3), was studied using density functional theory (DFT) calculations. Having achieved an agreement between theory and experiment, it is found that isotactic selectivity induced by Y-1 or Y-2 results from a combination of smaller deformation of the catalyst and stronger electronic effects. Conversely, the Y-3 complex exhibits comparable energy barriers for proceeding via either isotactic or syndiotactic pathways, aligning with the production of atactic polymers as seen experimentally. To examine the steric effects on the kinetic and thermodynamic properties, a computational model of an analogue complex [L4Y(CH2SiMe3)(THF)]+ [L4 = (2,6-Cl2C6H3)NC(Me)CHC(Me)N(iPr2C6H3)] (Y-4), featuring increased steric hindrance, was analyzed. Distortion-interaction and topographic steric map analyses further affirmed that steric hindrance significantly influences stereoselectivity. A direct relationship was identified between the energy barriers of isotactic insertion transition states and the bulkiness of ancillary ligands; greater distortion energy of the catalyst correlates with higher barriers for isotactic polymerization. These findings enhance the mechanistic comprehension of 2-vinylpyridine polymerization and are expected to contribute valuable insights for the improvement of catalytic polymerization systems of 2-vinylpyridine.

Origins of Ligand-Controlled Stereoselective Polymerization of ortho-Methoxystyrene by Rare-Earth Catalysts: A Theoretical Perspective

The stereoselective polymerization of polar vinyl monomers has recently received much attention due to their excellent physicochemical properties. Over the past decade, breakthroughs have been achieved in this field by rare-earth catalysts. However, the mechanistic origins of those stereoselective polymerizations still remain unclear. Herein, stereoselective polymerization of ortho-methoxystyrene (oMOS) by several representative rare-earth catalysts bearing different ligands (i.e., η5-C5Me5, pyridinyl-methylene-fluorenyl, quinolyl-anilido, β-diketiminato) were systematically investigated by density functional theory (DFT) calculations. After achieving agreement between the calculations and experiments, we focused on discussing the role of ligands in controlling stereoselectivity. Our results reveal that the stereoregularity of oMOS polymerization is mainly controlled by the steric effect of the catalyst-monomer structures. Specifically, the type of ligand influences the orientation and configuration of the inserting monomer, thereby affecting the tacticity of the polymers. In the cases of η5-C5Me5-, pyridinyl-methylene-fluorenyl, and quinolyl-anilido-ligated yttrium catalysts, we observe consistent insertion directions and alternating insertion sides of oMOS monomers, leading to syndiotactic selectivity. The opposite insertion directions and the alternating insertion sides of oMOS monomers were observed in the case of the β-diketiminato yttrium catalyst, leading to isotactic selectivity. These findings reported here offer valuable insights into the role of ligands in controlling stereoselectivity in rare-earth catalyzed coordination polymerization of polar vinyl monomers, thus providing guidance for the rational design of new ligands for stereospecific polymerization of polar monomers in the future.

Frustrated Lewis Pair-Type Reactivity of Intermolecular Rare-Earth Aryloxide and N-Heterocyclic Carbene/Olefin Combinations

This work reports the cooperative reactivity of rare-earth aryloxide complexes with N-heterocyclic carbene (NHC) or N-heterocyclic olefin (NHO), showcasing their synergistic effect on the activation of H2 and diverse organic substrates. Reactions of RE(OAr)3 (RE=La, Sm, and Y; Ar=2,6-tBu2-C6H3) with unsaturated NHC ItBu (:C[N(R)CH]2, R=tBu) isolated abnormally bound RE metal NHC complexes RE/aNHC. In contrast, no metal-NHO adducts were formed when RE(OAr)3 were treated with NHO (R2C=C[N(R)C(R)]2, R=CH3). Both RE/aNHC and RE/NHO Lewis pairs enabled cooperative H2 activation. Furthermore, RE(OAr)3 were found to catalyze the hydrogenation of the exocyclic C=C double bond of NHO under mild conditions. Moreover, treatment of the La/aNHC complex with benzaldehyde produced a La/C4 1,2-addition product. The La/NHO Lewis pair could react with (trimethylsilyl)diazomethane and α, β-conjugated imine, affording an isocyanotrimethylsilyl lanthanum amide complex and a La/C 1,4-addition product, respectively.

Synthesis and Reactivity of Discrete Europium(II) Hydride Complexes

The bulky β-diketiminate ligand frameworks [BDIDCHP]- and [BDIDipp/Ar]- (BDI=[HC{C(Me)2N-Dipp/Ar}2]- (Dipp=2,6-diisopropylphenyl (Dipp); Ar=2,6-dicyclohexylphyenyl (DCHP) or 2,4,6-tricyclohexylphyenyl (TCHP)) have been developed for the kinetic stabilisation of the first europium (II) hydride complexes, [(BDIDCHP)Eu(μ-H)]2, [(BDIDipp/DCHP)Eu(μ-H)]2 and [(BDIDipp/TCHP)Eu(μ-H)]2, respectively. These complexes represent the first step beyond the current lanthanide(II) hydrides that are all based on ytterbium. Tuning the steric profile of β-diketiminate ligands from a symmetrical to unsymmetrical disposition, enhanced solubility and stability in the solution-state. This provides the first opportunity to study the structure and bonding of these novel Eu(II) hydride complexes crystallographically, spectroscopically and computationally, with their preliminary reactivity investigated.

Synthesis of Mechanically Robust Very High Molecular Weight Polyisoprene Particle Brushes by Atom Transfer Radical Polymerization

Linear polyisoprene (PI) and SiO2-g-PI particle brushes were synthesized by both conventional and activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). The morphology and solution state study on the particle brushes by transmission electron microscopy (TEM) and dynamic light scattering (DLS) confirmed the successful grafting of PI ligands on the silica surface. The presence of nanoparticle clusters suggests low grafting density (associated with the limited initiation efficiency of ARGET for PI). Nevertheless, particle brushes with very high molecular weights, Mn > 300,000, were prepared, which significantly improved the dispersion of silica nanoparticles and also contributed to excellent mechanical performance. The reinforcing effects of SiO2 nanofillers and very high molecular weight PI ligands were investigated by dynamic mechanical analysis (DMA) as well as computational simulation for the cured linear PI homopolymer/SiO2-g-PI particle brush bulk films.

Regio- and Diastereoselective Annulation of α,β-Unsaturated Aldimines with Alkenes via Allylic C(sp3)-H Activation by Rare-Earth Catalysts

The [3 + 2] or [4 + 2] annulation of α,β-unsaturated aldimines with alkenes via β'- or γ-allylic C(sp3)-H activation is, in principle, an atom-efficient route for the synthesis of five- or six-membered-ring cycloalkylamines, which are important structural motifs in numerous natural products, bioactive molecules, and pharmaceuticals. However, such a transformation has remained undeveloped to date probably due to the lack of suitable catalysts. We report herein for the first time the regio- and diastereoselective [3 + 2] and [4 + 2] annulations of α,β-unsaturated imines with alkenes via allylic C(sp3)-H activation by half-sandwich rare-earth catalysts having different metal ion sizes. The reaction of α-methyl-substituted α,β-unsaturated aldimines with alkenes by a C5Me4SiMe3-ligated scandium catalyst took place in a trans-diastereoselective [3 + 2] annulation fashion via C(sp3)-H activation at the α-methyl group (β'-position), exclusively affording alkylidene-functionalized cyclopentylamines with excellent trans-diastereoselectivity. In contrast, the reaction of β-methyl-substituted α,β-unsaturated aldimines with alkenes by a C5Me5-ligated cerium catalyst proceeded in a cis-diastereoselective [4 + 2] annulation fashion via γ-allylic C(sp3)-H activation, selectively yielding multisubstituted 2-cyclohexenylamines with excellent cis-diastereoselectivity. The mechanistic details of these transformations have been elucidated by deuterium-labeling experiments, kinetic isotope effect studies, and the isolation and transformations of key reaction intermediates. This work offers an efficient and selective protocol for the synthesis of a new family of cycloalkylamine derivatives, featuring 100% atom efficiency, high regio- and diastereoselectivity, broad substrate scope, and an unprecedented reaction mechanism.

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.

Divergent Synthesis of Multi-Substituted Aminotetralins via [4+2] Annulation of Aldimines with Alkenes by Rare-Earth-Catalyzed Benzylic C(sp3 )-H Activation

The search for efficient and selective methods for the divergent synthesis of multi-substituted aminotetralins is of much interest and importance. We report herein for the first time the diastereoselective [4+2] annulation of 2-methyl aromatic aldimines with alkenes via benzylic C(sp3 )-H activation by half-sandwich rare-earth catalysts, which constitutes an efficient route for the divergent synthesis of both trans and cis diastereoisomers of multi-substituted 1-aminotetralin derivatives from readily accessible aldimines and alkenes. The use of a scandium catalyst bearing a sterically demanding cyclopentadienyl ligand such as C5 Me4 SiMe3 or C5 Me5 exclusively afforded the trans-selective annulation products in the reaction of aldimines with styrenes and aliphatic alkenes. In contrast, the analogous yttrium catalyst, whose metal ion size is larger than that of scandium, yielded the cis-selective annulation products. This protocol features 100 % atom-efficiency, excellent diastereoselectivity, broad substrate scope, and good functional group compatibility. The reaction mechanisms have been elucidated by kinetic isotope effect (KIE) experiments and the isolation and transformations of some key reaction intermediates.

Stabilization of Pr4+ in Silicates─High-Pressure Synthesis of PrSi3O8 and Pr2Si7O18

The reaction between PrO2 and SiO2 was investigated at various pressure points up to 29 GPa in a diamond anvil cell using laser heating and in situ single-crystal structure analysis. The pressure points at 5 and 10 GPa produced Pr2III(Si2O7), whereas Pr4IIISi3O12 and Pr2IV(O2)O3 were obtained at 15 GPa. Pr4IIISi3O12 can be interpreted as a high-pressure modification of the still unknown orthosilicate Pr4III(SiO4)3. PrIVSi3O8 and Pr2IVSi7O18 that contain praseodymium in its rare + IV oxidation state were identified at 29 GPa. After the pressure was released from the reaction chamber, the Pr(IV) silicates could be recovered, indicating that they are metastable at ambient pressure. Density functional theory calculations of the electronic structure corroborate the oxidation state of praseodymium in both PrIVSi3O8 and Pr2IVSi7O18. Both silicates are the first structurally characterized representatives of Pr4+-containing salts with oxoanions. All three silicates contain condensed networks of [SiO6] octahedra which is unprecedented in the rich chemistry of lanthanoid silicates.

Rare-earth metal ethylene and ethyne complexes

Guanidinate homometallic rare-earth ethyl complexes [LLn(μ2-η1:η2-Et)(Et)]2 (Ln = Y(1-Y), Lu(1-Lu)) and heterobimetallic rare-earth ethyl complexes LLn(Et)(μ2-η1:η2-Et)(μ2-η1-Et)(AlEt2) (Ln = Y(2-Y), Lu(2-Lu)) have been synthesized by the treatment of LLn(CH2C6H4NMe2-o)2 (L = (PhCH2)2NC(NC6H3iPr2-2,6)2) with different equivalents of AlEt3 in toluene at ambient temperature. Interestingly, the unprecedented rare-earth ethyne complex [LY(μ2-η1-Et)2(AlEt)]2(μ4-η1:η1:η2:η2-C2H2) (3-Y) containing a [C2H2]4- unit was afforded from 2-Y. The formation mechanism study on 3-Y was carried out by DFT calculations. Furthermore, the nature of the bonding of 3-Y was also revealed by NBO analysis. The reactions of LLn(CH2 C6H4NMe2-o)2 (Ln = Y, Lu) with AlEt3 (4 equiv.) in toluene at 50 °C produced firstly the non-Cp rare-earth ethylene complex LY(μ3-η1:η1:η2-C2H4)[(μ2-η1-Et)(AlEt2)(μ2-η1-Et)2(AlEt)] (4-Y), and the Y/Al ethyl complex LY[(μ2-η1-Et)2(AlEt2)]2 (5-Y) as an intermediate of 4-Y was isolated from the reaction of LY(CH2C6H4NMe2-o)2 with AlEt3 (4 equiv.) in toluene at -10 °C.

High-Efficiency Mono-Cyclopentadienyl Titanium and Rare-Earth Metal Catalysts for the Production of Syndiotactic Polystyrene

Syndiotactic polystyrene (SPS) refers to a type of thermoplastic material with phenyl substituents that are alternately chirally attached on both sides of an aliphatic macromolecular main chain. Owing to its excellent physical and mechanical properties, as well as its chemical stability, high transparency, and electrical insulation characteristics, SPS is used in a wide variety of technical fields. SPS is commonly produced via the stereoselective transition metal-catalyzed coordination polymerization method mediated by stereospecific catalysts, which consists of anionic mono-cyclopentadienyl derivative η5-coordinated single active metal centers (referred to as "mono-Cp'-M"), with active center metals involving Group 4 transition metals (with an emphasis on titanium) and rare-earth (RE) metals of the periodic table. In this context, the use of mono-cyclopentadienyl titanocene (mono-Cp'Ti) catalysts and mono-cyclopentadienyl rare-earth metal (mono-Cp'RE) metallocene catalysts for the syndiospecific polymerization of styrene is discussed. The effects of the mono-cyclopentadienyl ligand structure, cationic active metal types, and cocatalysts on the activity and syndiospecificity of mono-Cp' metallocene catalysts are briefly surveyed.

Diastereo- and Enantioselective Hydrophosphination of Cyclopropenes under Lanthanocene Catalysis

The asymmetric hydrophosphination of cyclopropenes with phosphines is of much interest and importance, but has remained hardly explored to date probably because of the lack of suitable catalysts. We report here the diastereo- and enantioselective hydrophosphination of 3,3-disubstituted cyclopropenes with phosphines by a chiral lanthanocene catalyst bearing the C2 -symmetric 5,6-dioxy-4,7-trans-dialkyl-substituted tetrahydroindenyl ligands. This protocol offers a selective and efficient route for the synthesis of a new family of chiral phosphinocyclopropane derivatives, featuring 100 % atom efficiency, good diastereo- and enantioselectivity, broad substrate scope, and no need for a directing group.

Enantioselective Synthesis of 1-Aminoindanes via [3 + 2] Annulation of Aldimines with Alkenes by Scandium-Catalyzed C-H Activation

Multisubstituted chiral 1-aminoindanes are important components in many pharmaceuticals and bioactive molecules. Therefore, the development of efficient and selective methods for the synthesis of chiral 1-aminoindanes is of great interest and importance. In principle, the asymmetric [3 + 2] annulation of aldimines with alkenes through C-H activation is the most atom-efficient and straightforward route for the construction of chiral 1-aminoindanes, but such a transformation has remained undeveloped to date probably due to the lack of suitable catalysts. Herein, we report for the first time the enantioselective [3 + 2] annulation of a wide range of aromatic aldimines and alkenes via ortho-C(sp2)-H activation by chiral half-sandwich scandium catalysts, which provides a straightforward route for the synthesis of multisubstituted chiral 1-aminoindanes. This protocol features 100% atom-efficiency, broad functional group compatibility, and high regio-, diastereo-, and enantioselectivity (up to >19:1 dr and 99:1 er). Remarkably, by fine-tuning the sterics of the chiral ligand around the catalyst metal center, the diastereodivergent asymmetric [3 + 2] annulation of aldimines and styrenes has been achieved with a high level of diastereo- and enantioselectivity, offering an efficient method for the synthesis of both the trans and cis diastereomers of a novel class of chiral 1-aminoindane derivatives containing two contiguous stereocenters from the same set of starting materials. Moreover, the asymmetric [3 + 2] annulation of aldimines with aliphatic α-olefins, norbornene, and 1,3-dienes has also been achieved.

Monodentate Alkoxy/Aryloxy Anchored Yttrium Dihydrides; Anticipated Outcomes and Surprises

The synthesis, characterization, and solid-state structure of bulky alkoxy- and aryloxy-supported yttrium polynuclear hydrides are reported. Hydrogenolysis of the supertrityl alkoxy anchored yttrium dialkyl, Y(OTr*)(CH₂SiMe₃)₂(THF)₂ (1) (Tr* = tris(3,5-di-tert-butylphenyl)methyl), resulted in the clean conversion to the tetranuclear dihydride, [Y(OTr*)H₂(THF)]₄ (1a). X-ray analysis revealed a highly symmetrical structure (4̅ site symmetry) with the four Y atoms located on the corners of a compressed tetrahedron, each bonded to an OTr* and tetrahydrofuran (THF) ligand and the cluster held together by four face-capping, μ₃-H, and four edge-bridging, μ₂-H, hydrides. DFT calculations on the full system with and without THF, but also on model systems, clearly show that the structural preference for complex 1a is controlled by the presence and coordination of THF molecules. Contrary to the exclusive formation of the tetranuclear dihydride, hydrogenolysis of the bulky aryloxy yttrium dialkyl, Y(OAr*)(CH₂SiMe₃)₂(THF)₂ (2) (Ar* = 3,5-di-tert-butylphenyl) gave a mixture of the analogous tetranuclear 2a and trinuclear, [Y₃(OAr*)₄H₅(THF)₄], polyhydride, 2b. Similar results, i.e., a mixture of tetra-/tri-nuclear products, were obtained from hydrogenolysis of the even bulkier Y(OAr^Ad2,Me)(CH₂SiMe₃)₂(THF)₂ compound. Experimental conditions were established to optimize the production of either the tetra- or trinuclear products. X-ray structure of 2b revealed a triangular array of three yttrium atoms with two face-capping μ₃-H and three edge-bridging μ₂-H hydrides, with one yttrium bonded to two aryloxy ligands while the other two have a complement of one aryloxy and two THF ligands; the solid-state structure is close to being C₂ symmetric, with the C₂ axis running through the unique Y and unique μ₂-H hydride. As opposed to 2a, which shows distinct ¹H NMR resonances for μ₃/ μ₂-H (δ = 5.83/6.35 ppm, respectively), no hydride signals for 2b were observed at room temperature, indicating hydride exchange on the NMR time scale. Their presence and assignment were secured at -40 °C from ¹H SST (spin saturation) experiment.

Cationic Half-Sandwich Tetrahydrofluorenyl Rare-Earth Metal Complexes as Stable Single-Site Catalysts for (Co)Polymerization of Styrene and Butadiene

As indenyl-derivates, the tetrahydrofluorenyl ligands had an expanded "wingspan" with considerable steric hindrance. In this text, the rare-earth metal complexes bearing tetrahydrofluorenyl ligands have been synthesized and fully characterized by NMR (¹H and ¹³C) and X-ray diffraction analyses. Upon the activation by [Ph₃C][B(C₆F₅)₄], all the scandium complexes exhibited excellent catalytic activity for highly syndioselective polymerization of styrene with a narrow molecular weight distribution (M_w/M_n < 2.0), suggesting the beneficial influence of tetrahydrofluorenyl ligands in stabilizing the single-site active species during the polymerization. Moreover, the scandium-based catalytic systems also promoted the 1,4-regular polymerization of butadiene and its copolymerization with styrene, affording diblock copolymers featuring a highly syndiotactic polystyrene block and a 1,4-specific PBD block. The kinetics investigation revealed the huge gap in TMS-Sc-catalyzed polymerization reactivity ratios (r_BD/r_St > 300) between butadiene and styrene, and this further proved the block structure of styrene-butadiene copolymers. The morphology and mechanical property of the selected diblock copolymer were, respectively, investigated by atomic force microscopy and stress-strain experiments.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

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.

Rare-earth-metal half-sandwich complexes incorporating methyl, methylidene, and hydrido ligands

Complexes Cp*₃Ln₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ (Ln = Y, Dy; Cp* = C₅Me₅) are formed via elimination of CH₄ and C₂H₄ from the respective trinuclear polymethyl complexes [Cp*Ln(μ₂-CH₃)₂]₃, involving the methyl/methylidene complex Cp*₃Ln₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-CH₃)(thf)₂ as an intermediate. Compound Cp*₃Y₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ displays "Schrock-type" nucleophilic carbene reactivity, converting ketones into the corresponding terminal alkenes. Treatment of Cp*₃Y₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ with [D₄]methanol proved accessibility of all small-group functionalities as indicated by the simultaneous formation of deuterated HD and deuterated methanes CH₃D and CH₂D₂.

Synthesis of allylanilines via scandium-catalysed benzylic C(sp3)-H alkenylation with alkynes

The ortho-selective benzylic C(sp³)-H alkenylation of 2-methyl tertiary anilines with internal alkynes has been achieved for the first time by using a half-sandwich scandium catalyst. This protocol provides a straightforward route for the synthesis of a new family of 2-allylaniline derivatives, featuring broad substrate scope, 100% atom-efficiency, high yields, and high chemo-, regio-, and stereoselectivity.

π-Carbazolyl supported bis(alkyl) complexes of Sc, Y and La for α-olefin polymerization and hydrogenation

A series of new half-sandwich bis(alkyl) rare-earth metal complexes coordinated by a sterically demanding 1,3,6,8-tetra-tert-butyl-carbazol-9-yl ligand [tBu₄Carb]La(CH₂C₆H₅)₂(THF) (1-La), [tBu₄Carb]Ln(o-NMe₂C₆H₄CH₂)₂ (Ln = Sc (2-Sc), Y (2-Y), La (2-La), [tBu₄Carb]Ln(CH₂SiMe₃)₂(THF) (Ln = Sc (3-Sc), Y (3-Y)), were synthesized. 1-La, 2-La, and 2-Y were prepared by an alkane elimination protocol, while 2-Sc, 3-Sc, and 3-Y became accessible only when salt metathesis reactions of tBu₄CarbK with R₂Ln(THF)_n⁺[BPh₄]^- were employed. X-ray analysis revealed that in all complexes the carbazolyl ligand exhibits π-coordination with metal ions. 2-Sc and 3-Sc when activated with [Ph₃C][B(C₆F₅)₄] demonstrate excellent activity in α-olefin (octene-1, nonene-1, decene-1 and 1,1-diphenyl-but-1-ene) polymerization. When H₂ was used as a chain transfer agent (1 bar, rt) in the presence of 3-Sc/[Ph₃C][B(C₆F₅)₄] or 2-Y, 2-La olefin hydrogenation occurred with quantitative conversion.

CO, CO2 and CS2 activation by divalent ytterbium hydrido complexes

Treatment of a divalent ytterbium hydride complex [(Tp^Ad,iPr)Yb(H)(THF)] (Tp^Ad,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) (1) with CO, CO₂ and CS₂ resulted in the formation of a divalent ytterbium ethenediolate complex [(Tp^Ad,iPr)Yb]₂(cis-OCHCHO) (2), a formate complex [(Tp^Ad,iPr)Yb(κ²-O₂CH)(THF)] (3), and a trivalent ytterbium ethenetetrathiolate complex [(Tp^Ad,iPr)Yb^III]₂(C₂S₄) (4), respectively. DFT calculations were carried out to elucidate the reaction profiles of complexes 3 and 4.

Rare-Earth-Metal Complexes Bearing an Iminodibenzyl-PNP Pincer Ligand: Synthesis and Reactivity toward 3,4-Selective Polymerization of 1,3-Dienes

A PNP-pincer ligand provides a versatile ligation framework, which is highly useful in organometallic chemistry and catalytic chemistry. In this work, by a de novo strategy, a simple and efficient synthetic pathway, has been developed to prepare the new iminodibenzyl-based PNP pincer proligand ^imin-RPNP(Li or H) (R = isopropyl, phenyl). By employing salt metathesis or direct alkyl elimination, we successfully synthesized a series of iminodibenzyl-PNP rare-earth-metal (Ln = Sc, Y, Dy, Ho, Er, Tm, Lu) complexes and characterized them by NMR and X-ray diffraction analyses. Upon addition of a borate and triisobutylaluminum (TIBA), the rare-earth-metal complexes 2-Y, 2-Dy, 2-Ho, 2-Er, and 2-Tm bearing the ^imin-PhPNP ligand exhibited unexpectedly high 3,4-selectivity (up to 95%) for the polymerization of 1,3-dienes (isoprene and myrcene); in particular, the chosen yttrium complex 2-Y promoted the 1,3-diene polymerization in a living manner. A computational study suggested that the sterically congested configuration around the metal center imposed by the ^imin-RPNP ligand might be the main reason for this unusual selectivity.

Recent progress in rare-earth metal-catalyzed sp2 and sp3 C–H functionalization to construct C–C and C–heteroelement bonds

The review presents rare-earth metal-catalyzed C(sp2/sp3)–H functionalization accessing C–C/C–heteroatom bonds and olefin (co)polymerization, highlighting substrate scope, mechanistic realization, and origin of site-, enantio-/diastereo-selectivity.

Amido-trihydroquinoline ligated rare-earth metal complexes for polymerization of isoprene

In combination with a borate, the amido-trihydroquinoline ligated rare-earth metal complexes (Ln = Y, Lu) showed moderate catalytic activities for isoprene polymerization to generate 1,4-enriched polyisoprenes.

Yttrium tris(trimethylsilylmethyl) complexes grafted onto MCM-48 mesoporous silica nanoparticles

A series of tris(trimethylsilylmethyl) yttrium donor adduct complexes was synthesized and fully characterized by X-ray diffraction, ¹H/¹³C/²⁹Si/³¹P/⁸⁹Y heteronuclear NMR and FTIR spectroscopies as well as elemental analyses. Treatment of Y(CH₂SiMe₃)₃(thf)_x with various donors Do led to complete (Do = TMEDA, DMAP) and partial displacement of THF (Do = NHC^iPr, DMPE). Exceptionally large ⁸⁹Y NMR shifts to low field were observed for the new complexes. Complexes Y(CH₂SiMe₃)₃(tmeda) and Y(CH₂SiMe₃)₃(dmpe)(thf) were chosen to perform surface organometallic chemistry, due to a comparatively higher thermal stability and the availability of the ³¹P nucleus as a spectroscopic probe, respectively. Mesoporous nanoparticles of the MCM-48-type were synthesized and used as a 3^rd generation silica support. The parent and hybrid materials were characterized using X-ray powder diffraction, solid-state-NMR spectroscopy, DRIFTS, elemental analyses, N₂-physisorption, and scanning electron microscopy (SEM). The presence of surface-bound yttrium alkyl moieties was further proven by the reaction with carbon dioxide. Quantification of the surface silanol population by means of HN(SiHMe₂)₂-promoted surface silylation is shown to be superior to titration with lithium alkyl LiCH₂SiMe₃.

Regio- and Diastereoselective [3+2] Annulation of Aliphatic Aldimines with Alkenes by Scandium-Catalyzed β-C(sp3 )-H Activation

Here we report for the first time the regio- and diastereoselective [3+2] annulation of a wide range of aliphatic aldimines with alkenes via the activation of an unactivated β-C(sp³ )-H bond by half-sandwich scandium catalysts. This protocol offers a straightforward and atom-efficient route for the synthesis of a new family of multi-substituted aminocyclopentane derivatives from easily accessible aliphatic aldimines and alkenes. The annulation of aldimines with styrenes exclusively afforded the 5-aryl-trans-substituted 1-aminocyclopentane derivatives with excellent diastereoselectivity through the 2,1-insertion of a styrene unit. The annulation of aldimines with aliphatic alkenes selectively gave the 4-alkyl-trans-substituted 1-aminocyclopentane products in a 1,2-insertion fashion. A catalytic amount of an appropriate amine such as adamantylamine (AdNH₂ ) or dibenzylamine (Bn₂ NH) showed significant effects on the catalyst activity and stereoselectivity.