Allylansa-Lanthanidocenes: Single-Component, Single-Site Catalysts for Controlled Syndiospecific Styrene and Styrene–Ethylene (Co)Polymerization

Trianionic Carbocyclic NCN Pincer Ligand: Coordination Chemistry and Reactivity Studies

(BCHT-NCN)H3 (1) [1,6-bis(methylene(bis-2,6-diisopropylaniline)(benzo)cycloheptatriene)] was synthesized by nucleophilic substitution treating 1,6-bis(methylenebromide)(benzo)cycloheptatriene with 2 equiv of Li[2,6-iPr2C6H3NH], Li[Dipp-NH]. Triple deprotonation of (BCHT-NCN)H3 (1) using n-BuLi yields the deprotonation product [(BCHT-NCN)Li3] (2), which crystallizes as a dimer [{[BCHT-NCN]Li3(Et2O)2}2] (2)2. Coordination compounds of the trianionic pincer ligand were obtained with SnCl2, YCl3(THF)3.5, and HfCl4(THF)2: [(BCHT-NCN)SnLi] (3), [(BCHT-NCN)Y(THF)2] (4), [(BCHT-NCN)HfCl2][Li(THF)4] (5), respectively. A hafnium hydride complex [(BCHT-NCN)HfH(HBEt3)][K(Et2O)2] (6) was isolated after reaction of 5 with K[HBEt3]. A MeNHC substitution product [(BCHT-NCN)HfCl(MeNHC)] (7) was synthesized treating compound 5 with MeNHC at rt. Following an n-BuLi reaction of 7 gives an alkyl complex [(BCHT-NCN)Hf(n-Bu)(MeNHC)] (8). Thermolysis of 7 yields the isomerization product [(BCHT-NCN#)HfCl(MeNHC)] (9), which was transferred into a methyl complex [(BCHT-NCN#)HfMe(MeNHC)] (10) upon treatment with MeMgBr. Hydride abstraction from complex 9 leads to a cationic complex [(BCHT-NCN+)HfCl(MeNHC)][Al(OtBuF)4] (11).

Divalent ansa-Octaphenyllanthanocenes: Synthesis, Structures, and EuII Luminescence

Reductive dimerization of fulvenes using low-valent metal precursors is a straightforward one-step approach to access ethylene-bridged metallocenes. This process has so far mainly been employed with fulvenes carrying one or two substituents in the exocyclic position. In this work, a new synthesis of the unsubstituted exocyclic 1,2,3,4-tetraphenylfulvene (1), its full structural characterization by NMR spectroscopy and single-crystal X-ray diffraction, as well as some photophysical properties and its first use in reductive dimerization are described. This fulvene reacted with different lanthanoid metals in thf to provide the divalent ansa-octaphenylmetallocenes [Ln(C5Ph4CH2)2(thf)n] (Ln = Sm, n = 2 (2); Ln = Eu, n = 2 (3); and Ln = Yb, n = 1 (4)). These complexes were characterized by X-ray diffraction, laser desorption/ionization time of flight mass spectrometry, and, in the case of Sm and Yb, multinuclear NMR spectroscopy, showing the influence of the ansa-bridge on solution and solid-state structures compared to previously reported unbridged metallocenes. Furthermore, the luminescence properties of the Eu ansa complex 3 were studied in solution and the solid state, revealing significant differences with the known octa- and deca-phenyleuropocenes, [Eu(C5Ph4H)2(dme)] and [Eu(C5Ph5)2].

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.

Neodymium catalysts for polymerization of dienes, vinyl monomers, and ε-caprolactone

This review discusses various neodymium catalysts for stereospecific polymerization of dienes, vinyl monomers, and ε-caprolactone.

Synthesis and Characterization of Syndiotactic Polystyrene-Polyethylene Block Copolymer

The direct synthesis of syndiotactic polystyrene-block-polyethylene copolymer (sPS-b-PE) with a diblock structure has been achieved. The synthetic strategy consists of the sequential stereocontrolled polymerization of styrene and ethylene in the presence of a single catalytic system: cyclopentadienyltitanium(IV) trichloride activated by modified methylaluminoxane (CpTiCl₃/MMAO). The reaction conditions suitable for affording the partially living polymerization of these monomers were identified, and the resulting copolymer, purified from contaminant homopolymers, was fully characterized. Gel permeation chromatography coupled with two-dimensional NMR spectroscopy COSY, HSQC, and DOSY confirmed the block nature of the obtained polymer, whose thermal behaviour and thin film morphology were also investigated by differential scanning calorimetry, powder wide angle x-ray diffraction, and atomic force microscopy.

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.

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.

Copolymerization of ethylene with styrene catalyzed by a scandium catalyst

The pseudo-random copolymers of ethylene and styrene can also be generated by a rare-earth metal based catalyst system.

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.

Conformationally dynamic titanium and zirconium cationic complexes of bis(naphthoxy)pyridine ligands: structure, "oscillation" and olefin polymerization catalysis

Discrete ionic complexes {ONO^SiMe₂tBu}M(CH₂Ph)((η⁶-Ph)CH₂B(C₆F₅)₃) (M = Ti, 2-Ti; Zr, 2-Zr) have been prepared from the parent neutral dibenzyl precursors and B(C₆F₅)₃. Also, a neutral dichloro complex {ONO^SiMe₂tBu}ZrCl₂(Me₂NH) (3) was synthesized by the reaction of a proligand {ONO^SiMe₂tBu}H₂ (1-H2) with (Me₂N)₂ZrCl₂(DME). The compounds were characterized by NMR spectroscopy and X-ray crystallography (for 2-Zr and 3). In the solid state, both 2-Zr and 3 feature meso-like binding of the ligand. VT NMR studies of 2-Ti and 2-Zr revealed that the former species dissociates in solution to form an outer-sphere ion pair (OSIP) that features a complicated dynamic behavior, while the latter compound retains an inner-sphere ion pair (ISIP) structure that interconverts between C_s-symmetric (meso-like) and C₁-symmetric (rac-like) conformations. The mechanism of this interconversion was assessed by DFT calculations and the corresponding barrier for the straightforward interconversion was calculated ().

Highly Active and Isospecific Styrene Polymerization Catalyzed by Zirconium Complexes Bearing Aryl-substituted [OSSO]-Type Bis(phenolate) Ligands

[OSSO]-type dibenzyl zirconium(IV) complexes 9 and 10 possessing aryl substituents ortho to the phenoxide moieties (ortho substituents, phenyl and 2,6-dimethylphenyl (Dmp)) were synthesized and characterized. Upon activation with dMAO (dried methylaluminoxane), complex 9 was found to promote highly isospecific styrene polymerizations ([mm] = 97.5%–99%) with high molecular weights M_w up to 181,000 g·mmol⁻¹. When the Dmp-substituted pre-catalyst 10/dMAO system was used, the highest activity, over 7700 g·mmol(10)⁻¹·h⁻¹, was recorded involving the formation of precisely isospecific polystyrenes of [mm] more than 99%.

Differences in the cyclometalation reactivity of bisphosphinimine-supported organo-rare earth complexes

A novel yttrium complex [L_nY(CH₂SiMe₃)₂] is resistant to cyclometalation, while samarium variants undergo C–H activation, forming unique cyclometalated motifs.

Recent progress in the chemical modification of syndiotactic polystyrene

This review provides a snapshot of recent progress in the chemical modification of syndiotactic polystyrene.

Homopolymerization of ethylene, 1-hexene, styrene and copolymerization of styrene with 1,3-cyclohexadiene using (η⁵-tetramethylcyclopentadienyl)dimethylsilyl(N-Ar')amido-TiCl₂/MAO (Ar'=6-(2-(diethylboryl)phenyl)pyrid-2-yl, biphen-3-yl)

The propensity of a half-sandwich (η⁵-tetramethylcyclopentadienyl) dimethylsilylamido Ti(IV)-based catalyst bearing an auxiliary diethylboryl-protected pyridyl moiety (Ti-8), activated by methylaluminoxane (MAO) to homopolymerize α-olefins such as ethylene, 1-hexene and styrene as well as to copolymerize styrene with 1,3-cyclo-hexadiene is described. The reactivity of Ti-8 was investigated in comparison to a 6-(2-(diethylboryl)phenyl)pyrid-2-yl-free analogue (Ti-3).