Post-metallocenes in the industrial production of polyolefins

Mechanistic details of ethylene polymerization reaction using methallyl nickel(ii) catalysts

We present a mechanistic study of the ligand functionalization of bulky boron co-activators on neutral methallyl Ni(ii) catalysts for polyethylene production. This provides a blueprint for the development and design of catalysts with a high degree of tunability in a more efficient way.

Bis(pentalene)dititanium chemistry: C–H, C–X and H–H bond activation

Formation of an agostic hydrogen by protonation of a “tucked-in” bis(pentalene)ditanium complex.

Ethylene/propylene copolymerization catalyzed by half-titanocenes containing monodentate anionic nitrogen ligands: effect of ligands on catalytic behaviour and structure of copolymers

Ethylene–propylene copolymers with high molecular weight, nearly random sequence distribution and high propylene content could be synthesized by a novel T6/TIBA/MMAO catalytic system.

Use of Vanadium Complexes Bearing Naphthalene-Bridged Nitrogen-Sulfonate Ligands as Catalysts for Copolymerization of Ethylene and Propylene

Vanadium complexes bearing naphthalene-bridged nitrogen-sulfonate ligand ([ê²(N,O)-8-(PhN)-1-naphthalenesulfonato]VOCl (1a) and [ê²(N,O)-8-(PhN)-1-naphthalenesulfonato]VCl₂ (1b)) were synthesized. Activated by ethylaluminium sesquichloride (EASC) and in the presence of ethyl trichloroacetate (ETCA) as reactivator, complexes 1a and 1b showed activities of up to 39.1 kg polymer (mol V)⁻¹ h⁻¹, affording the copolymers with high molecular weights (M_w up to 28 × 10⁴) and narrow molecular weight distributions (M_w/M_n ~ 3.0) as well as high propylene incorporation of up to 49.4%. Compared to the traditional VOCl₃ system, these complexes exhibited higher propylene incorporation ability and higher catalytic activities especially at high polymerization temperatures of 50 °C and above. Determined by DSC and ¹³C NMR, the copolymers obtained with 1a and 1b had more random structures than that with the VOCl₃ system.

Polyolefins, a Success Story

This paper reports the principal discoveries which have played a major role in the polyolefin field and have positioned polyolefins as the most produced plastics. The early development of polyolefins covering the production of LDPE (Low density polyethylene) at ICI (Imperial Chemical Industries) and the discovery of Phillips or Ziegler-Natta catalysts are highlighted in the first section. In the second part, the impact of the implementation of molecular catalysts on the research in polyolefins is discussed together with the most recent advances leading to high-performance tailor-made resins.

Synthesis and Characterization of Constrained Geometry Oxygen and Sulphur Functionalized Cyclopentadienylchromium Complexes and Their Use in Catalysis for Olefin Polymerization

A series of constrained geometry O-functionalized cyclopentadienylchromium complexes (1–6) and a S-functionalized cyclopentadienylchromium complex (7) were first synthesized, characterized, and tested as catalyst precursors for the olefin polymerization. In the presence of MAO, the complexes exhibited high catalytic activity for the polymerization of ethylene. It is shown that ligand variations can have a substantial effect on catalyst activity and stability. The effect of Al/Cr ratio on catalytic activity was also studied.

Ultra-high molecular weight elastomeric polyethylene using an electronically and sterically enhanced nickel catalyst

Highly active para-t-Bu-containing 1,2-bis(imino)acenaphthene-Ni(ii) catalysts are disclosed which afford hyper-branched PEs with M_w's up to 3.1 × 10⁶ g mol⁻¹; high tensile strength, excellent shape fixity as well as high elongation at break are a feature.

On the binding modes of metal NHC complexes with DNA secondary structures: implications for therapy and imaging

This perspective review aims at providing an overview of the most representative examples of bioactive metal NHC complexes reacting with nucleic acidsviadifferent binding modes.

Synthesis, structure and reactivity of guanidinate rare earth metal bis(o-aminobenzyl) complexes

A series of guanidinate rare-earth dialkyl complexes were synthesized. Their reactivity towards small molecules has been disclosed.

Avoiding leaching of silica supported metallocenes in slurry phase ethylene homopolymerization

Leaching of (n-BuCp)₂ZrCl₂/MAO catalyst from silica supports has been studied in slurry phase ethylene homopolymerisation by changing i) the polymerization protocol, ii) aluminum alkyl scavengers and iii) by adding butylated hydroxytoluene (BHT-H) along with aluminum alkyl scavengers.

Metal-catalyzed reductive coupling of olefin-derived nucleophiles: Reinventing carbonyl addition

α-Olefins are the most abundant petrochemical feedstock beyond alkanes, yet their use in commodity chemical manufacture is largely focused on polymerization and hydroformylation. The development of byproduct-free catalytic C-C bond-forming reactions that convert olefins to value-added products remains an important objective. Here, we review catalytic intermolecular reductive couplings of unactivated and activated olefin-derived nucleophiles with carbonyl partners. These processes represent an alternative to the longstanding use of stoichiometric organometallic reagents in carbonyl addition.

Insight into Oxide-Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

Reaction of (TBBP)AlMe⋅THF with [Cp*₂ Zr(Me)OH] gave [(TBBP)Al(THF)-O-Zr(Me)Cp*₂ ] (TBBP=3,3',5,5'-tetra-tBu-2,2'-biphenolato). Reaction of [DIPPnacnacAl(Me)-O-Zr(Me)Cp₂ ] with [PhMe₂ NH]⁺ [B(C₆ F₅ )₄ ]^- gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)-O-Zr(THF)Cp₂ ]⁺ [B(C₆ F₅ )₄ ]^- (DIPPnacnac=HC[(Me)C=N(2,6-iPr₂ -C₆ H₃ )]₂ ). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40-47 kcal mol^-1 ) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six-membered-ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal-Me-C angle that prevents synchronized bond-breaking and making. A more-likely pathway is dissociation of the Al-O-Zr complex into an aluminate and the active polymerization catalyst [Cp*₂ ZrMe]⁺ .