Aluminum Effects in the Syndiospecific Copolymerization of Styrene with Ethylene by Cationic Fluorenyl Scandium Alkyl Catalysts

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.

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.

Syndiospecific Copolymerization of Styrene with para-Methoxystyrene Catalyzed by Functionalized Fluorenyl-Ligated Rare-Earth Metal Complexes

The development of efficient catalysts for the copolymerization of nonpolar monomers with polar monomers remains a great challenging task in polymer synthesis. A one-pot reaction of anhydrous LnCl₃ with pyridyl-methylene-functionalized octamethylfluorenyl lithium OctFlu-CH₂PyLi in a 1:1 molar ratio, followed by alkylation with 2 equiv of LiCH₂SiMe₃ in THF afforded the fluorenyl-ligated rare-earth metal bis(alkyl) complexes (OctFlu-CH₂Py)Ln(CH₂SiMe₃)₂(THF) [Ln = Sc (1), Y (2)]. Both complexes were isolated as neutral species and were characterized by NMR spectrum and elemental analysis. Complex 2 was subjected to single-crystal X-ray diffraction, which showed that the whole modified fluorenyl ligand was coordinated to Y³⁺ in the η⁵/κ¹ mode to form a constrained geometry configuration. In the presence of excess AlⁱBu₃, and on activation with 1 equiv of [Ph₃C][B(C₆F₅)₄] in toluene, complexes 1 and 2 became active for both styrene (St) and para-methoxystyrene (pMOS) polymerization, giving polymers with high syndiotacticity (rrrr > 99%) without solvent extraction. Moreover, the ternary catalyst system composed of complex 2/AlⁱBu₃/[Ph₃C][B(C₆F₅)₄] was highly effective for the syndiospecific copolymerization of styrene with pMOS, producing random copolymers with high molecular weights and narrow molecular weight distributions. The contents of pMOS in the copolymers could be easily tuned in a wide range (11-93 mol %) by simply changing the pMOS-to-St feed ratios.

Scandium, titanium and vanadium complexes supported by PCP-type pincer ligands: synthesis, structure, and styrene polymerization activity

A series of first-row early transition metal dialkyl complexes bearing pincer ligands [(POCOP)M(CH₂SiMe₃)₂] (POCOP: (2,6-(^tBu₂PO)₂-C₆H₃); 1-Sc: M = Sc; 1-Ti: M = Ti; 1-V: M = V) and [(PCP)M(CH₂SiMe₃)₂] (PCP: (2,6-(^tBu₂PCH₂)₂-C₆H₃); 2-Sc: M = Sc; 2-Ti: M = Ti) have been synthesized. These dialkyl complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy, and solution magnetic susceptibility (Evans method) analyses appropriately. All the complexes exhibited square pyramidal geometries with different extents of distortion. The activities of these complexes were further explored in styrene polymerization, in which combinations of scandium complexes (1-Sc or 2-Sc) with [Ph₃C][B(C₆F₅)₄] were found to be active catalytic systems for highly syndiospecific (>99% rrrr) polymerization of styrene. Meanwhile, the Ti(III) complexes 1-Ti and 2-Ti showed rather low activity in styrene polymerization, which stands in sharp contrast to those in previous reports involving Ti(III) catalysts bearing cyclopentadienyl derivative ligands.

Access to Derivatizable Octahydrofluorenyl Ligand: Half-Sandwich Rare-Earth Metal Complexes for Highly Syndiospecific (Co)Polymerization of Styrene

A simple and facile synthetic pathway for accessing new derivatizable bulky-demanding octahydrofluorenyl (OHF) ligands has been developed, and a series of half-sandwich rare-earth metal (Sc, Y, Lu) complexes bearing the OHF ancillary ligands have been synthesized. In conjunction with a borate, the OHF-ligated Sc complexes exhibited high catalytic activity for styrene (co)polymerization to afford polymers with highly syndiotactic polystyrene sequence (>99% rrrr).

Scandium bis(trimethylsilyl)methyl complexes revisited: extending the 45Sc NMR chemical shift range and a new structural motif of Li[CH(SiMe3)2]

Depending on the molar ratio employed, the reaction of ScCl₃(thf)₃ with Li[CH(SiMe₃)₂] afforded the bis and tris(alkyl) ate complexes [Sc{CH(SiMe₃)₂}₂(μ-Cl)₂Li(thf)₂]₂ and Sc[CH(SiMe₃)₂]₃(μ-Cl)Li(thf)₃, respectively, in moderate yields. Treatment of these mixed alkyl/chlorido complexes with MeLi gave the mixed alkyl complexes [Sc{CH(SiMe₃)₂}₂(μ-Me)₂Li(thf)₂]₂ and Sc[CH(SiMe₃)₂]₃(μ-Me)Li(thf)₃. Aiming at homoleptic {Sc[CH(SiMe₃)₂]₃} both of the mixed [CH(SiMe₃)₂]/Me complexes were treated with AlMe₃. Although LiAlMe₄ separation occurred, aluminium complex Al[CH(SiMe₃)₂]Me₂(thf) was the only isolable crystalline complex. Ate complexes [Sc{CH(SiMe₃)₂}₂(μ-Me)₂Li(thf)₂]₂ and [Sc(CH₂SiMe₃)₄][Li(thf)₄] revealed the maximum downfield ⁴⁵Sc NMR chemical shifts of 888.0 and 933.4 ppm, respectively, reported to date. The synthesis of putative {Sc[CH(SiMe₃)₂]₃} was also attempted via the aryloxide route applying complexes Sc(OC₆H₂tBu₂-2,6-Me-4)₃ and [Sc(OC₆H₃iPr₂-2,6)₃]₂ along with Li[CH(SiMe₃)₂] but the outcome was inconclusive. Instead, a cyclic octamer was found for Li[CH(SiMe₃)₂] in the solid state.

Unprecedentedly High Activity and/or High Regio-/Stereoselectivity of Fluorenyl-Based CGC Allyl-Type η3:η1-tert-Butyl(dimethylfluorenylsilyl)amido Ligated Rare Earth Metal Monoalkyl Complexes in Olefin Polymerization

A series of fluorenyl-based constrained-geometry-configuration (CGC) allyl-type rare earth metal monoalkyl complexes bearing the divalent anionic η3:η1-tert-butyl(dimethylfluorenylsilyl)amido (η3:η1-FluSiMe2NtBu) ligand (η3:η1-FluSiMe2NtBu)Ln(CH2SiMe3)(THF)2 (1-3) have been synthesized via the alkane elimination reaction between the FluHSiMe2NHtBu ligand and rare earth metal tri(trimethylsilylmethyl) complexes Ln(CH2SiMe3)3(THF)n. Their structures are characterized by means of NMR spectrum, elemental analyses, and X-ray diffraction. These complexes 1-3 are isostructural and isomorphous, and each of them adopts a distorted-trigonal-bipyramidal configuration containing one η3:η1-FluSiMe2NtBu ligand, one CH2SiMe3 ligand, and two THF molecules. Unlike traditional CGC allyl-type rare earth metal complexes showing no or low activity and regio-/stereoselectivity in styrene or MMA polymerization, these complexes 1-3 exhibit high catalytic activities and/or high regio-/stereoselectivities in the cis-1,4-polymerization of isoprene and myrcene or in the syndiotactic polymerization of styrene under the aid of different activators (borate or borane) and AlR3. The in situ 1H NMR spectra suggest that the exchanges of chelating ligands such as alkyl groups and divalent anionic η3:η1-FluSiMe2NtBu ligands between rare earth metal centers and Al centers result in the formation of a heterobimetallic tetraalkylaluminate complex R2Al(μ-R)2Ln(R)(μ-R)2AlR2, which is activated by activators to form a divalent cationic species [Ln(μ-R)2AlR2]2+ as a catalytically active species in the coordination-insertion polymerization of olefins.

Sequence-controlled ethylene/styrene copolymerization catalyzed by scandium complexes

Sequence controlled E/St copolymerization was achieved by tuning the electrophilicity of scandium center and the steric around it, isolating multi-block, random, “pseudo random” and alternating E/St copolymers.

Highly syndioselective coordination (co)polymerization of isopropenylstyrene

Coordination (co)polymerization of para-isopropenylstyrene (pIPSt) and meta-isopropenylstyrene (mIPSt), initiated by scandium (Sc) based catalysts, afforded new type of products, bearing pendant isopropenyl groups with perfect syndiotacity (rrrr > 99%).

A displacement-type fluorescent probe reveals active species in the coordinative polymerization of olefins

The correct identification of active species is an important prerequisite to study the mechanism of coordinative polymerization of olefins, which can afford important theoretical guidance for the design and synthesis of new organometallic catalysts and high-performance polyolefin materials.

Engineering of Syndiotactic and Isotactic Polystyrene-Based Copolymers via Stereoselective Catalytic Polymerization

This contribution presents an updated overview of the different copolymers containing stereoregular polystyrene blocks. Special emphasis is placed on syndiospecific and isospecific copolymerization of styrene with co-monomers (ethylene and α-olefins, conjugated and non-conjugated dienes, styrene derivatives, etc.). The catalytic systems involved are described and the polymerization mechanisms are discussed. Alternative approaches (simultaneous, living, chain-transfer and graft copolymerization) and the resulting detailed structures and characteristics of the copolymers are also reported.

Copolymerization of propylene with styrene and ethylene by a THF-containing half-sandwich scandium catalyst: efficient synthesis of polyolefins with a controllable styrene content

A novel family of multi-block propylene–styrene copolymers with syndiotactic styrene–styrene blocks and random propylene–ethylene–styrene terpolymers with a broad composition range were obtained by using (C₅Me₄SiMe₃)Sc(CH₂SiMe₃)₂(THF).

1,4-Specific copolymerization of 1,3-cyclohexadiene with isoprene and their terpolymerization with styrene by cationic half-sandwich fluorenyl rare-earth metal alkyl catalysts

1,4-Copolymerization of 1,3-cyclohexadiene with isoprene and terpolymerization with styrene have been achieved by cationic half-sandwich fluorenyl rare-earth metal species.

DFT study on 1,7-octadiene polymerization catalyzed by a non-bridged half-titanocene system

For (η⁵-C₅Me₅)TiCl₂(O-2,6-ⁱPr₂C₆H₃)/MAO system, the selectivity of repeated insertion and intramolecular cyclization of 1,7-octadiene were explored in detail by DFT method.

Tandem vinyl insertion-/ring-opening metathesis copolymerization with ansa-6-[2-(dimesitylboryl)-phenyl]pyrid-2-ylamido zirconium complexes: role of trialkylaluminum and MAO

Activation of Zr-bisalkyl complexes containing the η⁵-tetramethylcyclopentadienyl-6-[2-(dimesitylboryl)phenyl]pyrid-2-ylamido motif with MAO offers access to poly(ethylene)-co-poly(norbornene) with ROMP-derived sequences.

Mono(boratabenzene) rare-earth metal dialkyl complexes: synthesis, structure and catalytic behaviors for styrene polymerization

Four mono(boratabenzene) rare-earth metal dialkyl complexes, [(3,5-Me2-C5H3BR)Ln(CH2SiMe3)2(THF)] (1: R = NEt2, Ln = Sc; 2: R = NEt2, Ln = Lu; 3: R = Ph, Ln = Sc; 4: R = Ph, Ln = Lu), were synthesized efficiently via a one-pot strategy with Li[3,5-Me2-C5H3BR] (R = NEt2, Ph), LnCl3(THF)x (Ln = Sc, x = 3; Ln = Lu, x = 0), and LiCH2SiMe3. The solid-state structures of 1 and 2 were determined by single-crystal X-ray diffraction. Variable-temperature NMR studies indicated that the energy barrier for the rotation of aminoboratabenzene in 1 (ΔG‡ ≈ 71 kJ mol−1) is higher than that of phenylboratabenzene in 3 (ΔG‡ ≈ 59 kJ mol−1). These mono(boratabenzene) rare-earth metal dialkyl complexes’ catalytic behaviors for styrene polymerization were investigated, and found that mono(boratabenzene) scandium dialkyl complexes show high catalytic activities for syndiotactic polymerization upon activation with cocatalysts.