Group 3 metal catalysts for ethylene and α-olefin polymerization

Half-Sandwich Cerium and Lanthanum Dialkyl Complexes: Synthesis, Structure, and Reactivity Studies

Cerium and lanthanum dialkyl complexes [η5-1,2,4-(Me3C)3C5H2]Ln(CH2C6H4-o-NMe2)2 (Ln = Ce 1 and La 2), supported by a tri-tert-butylcyclopentadienyl ligand, have been successfully synthesized. Studies demonstrate that these complexes possess diverse reactivity toward various small molecules. For example, the reaction of complexes 1 and 2 with diphenyl dichalcogenides PhEEPh (E = S, Se) results in the formation of lanthanide thiolates [(η5-1,2,4-(Me3C)3C5H2)Ln(SPh)(μ-SPh)]2 (Ln = Ce 3 and La 4) and selenolates [(η5-1,2,4-(Me3C)3C5H2)Ln(SePh)(μ-SePh)]2 (Ln = Ce 5 and La 6), concomitantly releasing PhE(CH2C6H4-o-NMe2). Furthermore, complexes 1 and 2, upon reaction with dibenzyl disulfide, yield tetranuclear rare-earth metallomacrocyclic compounds {[(η5-1,2,4-(Me3C)3C5H2)Ln(μ-SCH2C6H5)]2(μ-η3:η3-SCHC6H5)}2 (Ln = Ce 7 and La 8). This reaction may involve a process of σ-bond metathesis and C-H activation. While the reaction of 1 and 2 with dibenzyl diselenide in the presence of LiCH2C6H4-o-NMe2 leads to the formation of lanthanide-lithium selenido clusters [(η5-1,2,4-(Me3C)3C5H2)La(μ-SeCH2C6H5)]3(μ3-Se)[μ3-SeLi(THF)3] (Ln = Ce 9 and La 10). Meanwhile, lanthanide selenido clusters [(η5-1,2,4-(Me3C)3C5H2)La(μ-SeCH2C6H4-o-NMe2)]4(μ3-Se)2 (Ln = Ce 11 and La 12) can be obtained by treating 1 and 2 with elemental selenium in a 1:2 molar ratio. Additionally, the treatment of 1 and 2 with benzoxazole generates ring-opening/C-C coupling/C-N coupling products {(η5-1,2,4-(Me3C)3C5H2)La[μ-OC6H4-o-N═CHN(CH(CH2C6H4-o-NMe2)2C6H4-o-O]}2 (Ln = Ce 13 and La 14). All new compounds were characterized by various spectroscopic methods, and their solid-state structures were confirmed by single-crystal X-ray diffraction analyses.

Highly Active Immobilized Catalyst for Ethylene Polymerization: Neutral Single Site Y(III) Complex Bearing Bulky Silylallyl Ligand

Exploring the surface organometallic chemistry on silica of highly electrophilic yttrium complexes is a relatively uncommon endeavor, particularly when focusing on tris-alkyl complexes characterized by Y-C σ-alkyl bonds. A drawback with this class of complexes once grafted on silica, is the frequent occurrence of alkyl transfer by ring opening of siloxane groups, resulting in a mixture of species. Herein, we employed a more stable homoleptic yttrium allyl complex bearing bulky η3-1,3-bis(trimethylsilyl)allyl ligand to limit this transfer reaction. This strategy has been validated by comparing the reactivity between [Y{ η3-1,3-C3H3(SiMe3)2}3] and [Y(o-CH2PhNMe2)3] with SiO2-700, where the undesired alkyl transfer reaction occurred for [Y(o-CH2PhNMe2)3] leading to a bipodal [(≡SiO)2Y(o-CH2PhNMe2)] as major surface species, 2, while [Y{ η 3-1,3-C3H3(SiMe3)2}3] resulted selectively in a monopodal species, [(≡SiO)Y{η3-1,3-C3H3(SiMe3)2}2], 1. The materials obtained were characterized by DRIFT, solid state NMR, mass balance analysis and EXAFS. Catalyst 1 showed high activity compared to 2 in ethylene polymerization. The catalytic performance of this neutral catalyst 1 was extended to pre-industrial scale in the presence of hydrogen and 1-hexene. An unprecedented activity, up to 7400 gPE gcat -1 h-1 was obtained even with very low concentration of scavenger AliBu3 (TIBA/Y=1.2). The obtained HDPE exhibited desired spherical particle morphology with broad molar mass distribution.

Rare-Earth Metallocenes for Polymerization of Olefins and Conjugated Dienes: From Fundamental Studies to Olefin Block Copolymers

The various steps in the mechanism of olefin polymerizations mediated by neutral rare-earth metallocene complexes are discussed. The complexes are either trivalent hydride and alkyl rare-earth compounds or divalent metallocenes that are activated by the monomer via an oxidation step. The stereospecific polymerizations of conjugated dienes based on the association of a cationic metallocene complex and an alkylaluminum and the polymerization mechanism based on monomer insertion into an aluminum-carbon bond are also discussed. The exploitation of metallocene complexes for the copolymerization of olefins with conjugated dienes is the subject of a third part of this review. The synthesis of new elastomers called ethylene butadiene rubber (EBR) is highlighted. Finally, the use of rare-earth metallocenes in macromolecular engineering is detailed. This includes the synthesis of functional polyolefins and block copolymers including thermoplastic elastomers.

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.

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.

Synthesis of rare-earth metal complexes with a morpholine-functionalized β-diketiminato ligand and their catalytic activities towards C–O and C–N bond formation

Unusual tridentate β-diketiminato rare-earth metal chlorides LRECl(µ-Cl)2Li(THF)2 (RE = Y (1a), Yb (1b), Lu (1c); L = MeC(NDipp)CHC(Me)N(CH2)2NC4H8O; Dipp = 2,6-iPr2C6H3) and the corresponding dialkyl complexes LRE(CH2SiMe3)2 (RE = Y...

Rare-earth-metallocene alkylaluminates trigger distinct tetrahydrofuran activation

Thermal treatment of Cp*2YMe(thf) (Cp* = C5Me5), obtained from Cp*2Y(AlMe4) via donor-induced AlMe3 cleavage, in THF resulted in the concomitant formation of vinyl oxide Cp*2Y(OC2H3)(thf) and 2-ethylene-tetrahydrofuranyl complex Cp*2Y(2-C2H4-OC4H7) via the release of methane. In stark contrast, dissolving Cp*2La(AlMe4) in THF/n-hexane led to the quantitative formation of AlMe3-stabilized 2-tetrahydrofuranyl complex Cp*2La(2-AlMe3-OC4H7), with methane elimination.

Ln(ii) alkyl complexes: from elusive exotics to catalytic applications

The synthesis, structures and reactivity of isolable Ln^II (Ln = Sm, Eu, Yb) alkyl complexes are discussed. The application of Ln^II alkyl derivatives in a variety of catalytic reactions is considered as well.

Precisely regulating the acidity of mesoporous silica on the catalytic performance of 1-decene oligomerization

Optimization of the acidity of Al-MCM-41 catalysts to improve the catalytic performance of 1-decene oligomerization.

Gas-Phase Thermochemistry of MX3 and M2X6 (M = Sc, Y; X = F, Cl, Br, I) from a Composite Reaction-Based Approach: Homolytic versus Heterolytic Cleavage

A domain-based local-pair natural-orbital coupled-cluster approach with single, double, and improved linear-scaling perturbative triple correction via an iterative algorithm, DLPNO-CCSD(T₁), was applied within the framework of the Feller-Peterson-Dixon approach to derive gas-phase heats of formation of scandium and yttrium trihalides and their dimers via a set of homolytic and heterolytic dissociation reactions. All predicted heats of formation moderately depend on the reaction type with the most and least negative values obtained for homolytic and heterolytic dissociation, respectively. The basis set size dependence, as well as the influence of static correlation effects not covered by the standard (DLPNO-)CCSD(T) approach, suggests that exploitation of the heterolytic dissociation reactions with the formation of M³⁺ and X^- ions leads to the most robust heats of formation. The gas-phase formation enthalpies ΔH_f°(0 K)/ΔH_f°(298.15 K) and absolute entropies S°(298.15 K) were obtained for the first time for the Sc₂F₆, Sc₂Br₆, and Sc₂I₆ species. For ScBr₃, ScI₃, Sc₂Cl₆, and Y₂Cl₆, we suggest a reexamination of the experimental heats of formation available in the literature. For other compounds, the predicted values were found to be in good agreement with the experimental estimates. Extracted MX₃ (M = Sc, Y; X = F, Cl, Br, and I) 0 K atomization enthalpies indicate weaker bonding when moving from fluorine to iodine and from yttrium to scandium. Likewise, the stability of yttrium trihalide dimers degrades when going from fluorine to iodine. Respective scandium trihalide dimers are less stable, with 0 K dimer dissociation energy decreasing in the row fluorine - chlorine - bromine ≈ iodine. Correlation of the (n - 1)s²p⁶ electrons on bromine and iodine, inclusion of zero-point energy, relativistic effects, and the effective-core-potential correction as well as amelioration of the DLPNO localization inaccuracy are shown to be of similar magnitude, which is critical if accurate heats of formation are a goal.

Rare-earth metal-promoted (double) C–H-bond activation of a lutidinyl-functionalized alkoxy ligand: formation of [ONC] pincer-type ligands and implications for isoprene polymerization

Steric pressure enforces the formation of dianionic and trianionic pincer-type ligands involving a rare alkylidene moiety in the latter case.

Ln(ii) and Ca(ii) NCsp3N pincer type diarylmethanido complexes – promising catalysts for C–C and C–E (E = Si, P, N, S) bond formation

The first examples of Ln(ii) (Ln = Yb, Sm) and Ca [NC_sp3N] pincer type diarylmethanido complexes were synthesized and successfully used as efficient and selective precatalyst for intermolecular C–C and C–E bond formation.

Half-sandwich rare-earth metal complexes bearing a C5Me4-C6H4-o-CH2NMe2 ligand: synthesis, characterization and catalytic properties for isoprene, 1-hexene and MMA polymerization

A new ortho-dimethylaminomethylphenyl-tetramethylcyclopentadienyl ligand C₅Me₄H-C₆H₄-o-CH₂NMe₂ (HL) and a series of rare-earth metal complexes bearing this ligand were synthesized. Of these complexes, two binuclear alkyl complexes [(C₅Me₄-C₆H₄-o-CH₂N(Me)CH₂-μ)Ln(CH₂SiMe₃)]₂ (Ln = Sc (1a) and Y (1b)) were obtained from the alkane elimination reaction of the free ligand with Ln(CH₂SiMe₃)₃(THF)₂, followed by an intramolecular C-H activation process of a NMe group in the ligand with a CH₂SiMe₃ group, two binuclear dichloro complexes (C₅Me₄-C₆H₄-o-CH₂NMe₂)₂Y₂Cl₄[LiCl(THF)₂] (2a) and [(C₅Me₄-C₆H₄-o-CH₂NMe₂)LuCl(μ-Cl)]₂ (2b) were synthesized by the reaction of anhydrous yttrium or lutetium trichloride with the lithium salt of the ligand LiL, and the binuclear bis(borohydrido) complexes [(C₅Me₄-C₆H₄-o-CH₂NMe₂)Ln(μ-BH₄)BH₄]₂ (Ln = Sm (3a) and Nd (3b)) were synthesized by the reaction of Ln(BH₄)₃(THF)₃ (Ln = Sm and Nd) with the lithium salt of the ligand. The molecular structures of all complexes 1a, 1b, 2a, 2b, 3a and 3b were determined by single-crystal X-ray crystallography. Upon activation with AlR₃/Ph₃CB(C₆F₅)₄, MAO or MMAO, the binuclear alkyl complexes 1a and 1b show good catalytic activity for isoprene cis-1,4 enriched regioselective polymerization and moderate catalytic activity for 1-hexene polymerization. Complexes 3a and 3b were studied as catalysts for methyl methacrylate polymerization reaction under different conditions and were found to show moderate to high catalytic activity.

Constrained geometry scandium permethylindenyl complexes for the ring-opening polymerisation of l- and rac-lactide

The synthesis and characterisation of constrained geometry scandium permethylindenyl chloride, aryloxide and borohydride complexes ^Me₂SB(^tBuN,I*)Sc(Cl)(THF) (1), ^Me₂SB(^tBuN,I*)Sc(O-2,6-ⁱPr-C₆H₃)(THF) (2), ^Me₂SB(^tBuN,I*)Sc(O-2,4-^tBu-C₆H₃)(THF) (3) and ^Me₂SB(^tBuN,I*)Sc(BH₄)(THF) (4) are reported. The activity of complexes 1-4 as initiators for the ring-opening polymerisation (ROP) of l- and rac-lactide is presented. The ROP of l- and rac-lactide using complexes 2 and 3 show first-order dependence on monomer concentration, and produced isotactic polylactide (PLA) and moderately heterotactic PLA (P_r = 0.68-0.72), respectively. Good agreement between experimental and theoretical molecular weights of PLA (M_n) and relatively narrow dispersities (M_w/M_n < 1.20) were obtained. Complex 4 showed higher activity for ROP of l- and rac-lactide than 2 or 3, with second-order dependence on monomer concentrations. However, poorly controlled molecular weights and lower heteroselectivity (P_r = 0.61-0.67) were observed. The effect of temperature and catalyst concentration for the ROP of l-lactide using 2 and 3 was also studied.

Yttrium dialkyl supported by a silaamidinate ligand: synthesis, structure and catalysis on cyclotrimerization of isocyanates

A four-coordinate yttrium dialkyl complex with a sterically demanding silaamidinate ligand exhibited high activity and excellent functional group tolerance for the catalysis of isocyanate cyclotrimerization.

Rare-earth metal bis(aminobenzyl) complexes supported by pyrrolyl-functionalized arylamide ligands: synthesis, characterization and styrene polymerization performance

Acid–base reaction between Ln(CH₂C₆H₄NMe₂-o)₃ and 2,5-Me₂C₄H₂NCH₂SiMe₂NHC₆H₄R (R = H, (HL1); R = Cl-p, (HL2) in 1 : 1 molar ratio gave L₁Ln(CH₂C₆H₄NMe₂-o)₂ (Ln = Sc (1), La (2), Lu (3) and L₂Ln(CH₂C₆H₄NMe₂-o)₂ (Ln = Sc (4), La (5), Lu (6). The catalyst systems of 2 or 5/[Ph₃C][B(C₆F₅)₄] were active for syndio-specific styrene polymerization.

Controlled iso-specific polymerization of 2-vinylpyridine catalyzed by arylamide-ligated rare-earth metal aminobenzyl complexes

Arylamide rare-earth metal aminobenzyl complexes were employed as highly active catalysts for iso-specific polymerization of 2-vinylpyridine.

Cis-1,4-Polymerization of Isoprene by 1,3-Bis(oxazolinymethylidene)isoindoline-Ligated Rare-Earth Metal Dialkyl Complexes

A series of novel chiral nonmetallocene pincer-type rare-earth metal dialkyl complexes bearing the chiral monoanionic tridentate C₂-symmetric 1,3-bis(oxazolinymethylidene)isoindoline (BOXMI-H) ligand (BOXMI)Ln(CH₂SiMe₃)₂ 1⁻3 (1: Ln = Sc, yield = 57%; 2: Ln = Lu, yield = 55%; 3: Ln = Y, yield = 62%) have been prepared in moderate yields via the acid-base reaction between the BOXMI ligand and rare-earth metal tri(trimethylsilylmethyl) complexes. The X-ray diffractions show that both of the complexes 1 and 2 contain one BOXMI ligand and two trimethylsilylmethyl ligands, adopting a distorted trigonal bipyramidal configuration. In the presence of a cocatalyst such as borate and AlR₃, these complexes 1⁻3 exhibit high activities of up to 6.8 × 10⁴ (g of polymer)/(molLn h) and high cis-1,4 selectivities of up to 97% in the polymerization of isoprene in toluene, yielding the cis-1,4-polyisoprenes with heavy molecular weights (Mn of up to 710,000 g/mol) and bimodal molecular weight distributions (Mw/Mn = 2.0⁻4.5).