Metallocene Catalysts

Abstract

Metallocene catalysts are useful for the polymerization of olefins and copolymerization of ethene or propene with cyclic olefins, styrene, and polar vinyl monomers. These catalysts contain two components such as a metallocene or half‐sandwich complex of transition metals and an organoaluminum compound, methylaluminoxane (MAO), or a perfluorinated boron aromatic compound. Most polymerization active metallocenes contain zirconium or titanium as transition metal but also hafnium, chromium, scandium, or others. The use of metallocene catalysts and their modifications has widely increased the synthetic and technical possibilities in more precisely controlling the polymer composition, polymer structure, tacticity, and other special properties. They allow the synthesis of polyolefins with short‐ or long‐chain branches, different tacticities and stereoregularities, copolymers with high‐compositional uniformity, new norbornene or styrene copolymers, and polyolefin composite materials in a purity that cannot be obtained by Ziegler–Natta catalysts. Today, industries mainly produce metallocene‐based linear low‐density polyethylene (LLDPE) and ethene/propene (EPM and EPDM) copolymers. These polyolefins show a higher growing rate than similar polymers obtained by conventional catalysts. The single‐site character of metallocene/MAO or other metallocene/borate catalysts has led to a better understanding of the mechanism of olefin polymerization.

Tutorial on the Role of Cyclopentadienyl Ligands in the Discovery of Molecular Complexes of the Rare-Earth and Actinide Metals in New Oxidation States

“…One of the key ligands that has supported this development is the cyclopentadienyl ligand. From the early involvement of the (C 5 H 5 ) − ligand in the discovery of the first organometallic sandwich compound, ferrocene, (C 5 H 5 ) 2 Fe, to the highly substituted cyclopentadienyl variants that led to sophisticated catalysts, the cyclopentadienyl ligand has been of central importance in organometallic chemistry . Although extensive efforts have been made to develop ancillary ligands beyond cyclopentadienyl in the “postmetallocene era”, cyclopentadienyl ligands continue to make significant contributions.…”

Octahedral Zirconium Salan Catalysts for Olefin Polymerization: Substituent and Solvent Effects on Structure and Dynamics

“…14 Extending the approach to post-metallocenes, we now report an in-depth analysis of seven Zr-Salan complexes (Scheme 1), differing in the ortho-substituent (R 1 ) on the phenoxy-amine ring. These complexes mirror the broad tuning range in propene polymerization in this catalyst class, ranging from slow and living (1,4) to very highly active (2, 3, 7), from highly isotactic selective (1, 7) to poorly isotactic selective (2) to chain-end controlled syndiotactic selective (3), and from (very) low (1−6) to high molar mass capability (7). 38,39 The synthesis of complexes 4 and 6 is detailed in the Supporting Information.…”

“…Whether a C 6 D 5 Cl solvent molecule occupies the "vacant" site cannot be directly inferred from NMR data but is confirmed by X-ray analysis on a single crystal of 3 + FF (vide infra). NMR structural analysis of 3 + FF generated in C 7 D 8 is more complex because 1 H NMR resonances of the benzyl moiety are not detected, likely as a result of σ-bond metathesis (SBM) with the deuterated solvent leading to a fully deuterated benzyl ligand. 49 Generating 3 + FF in C 7 H 8 , isolating it by precipitation with npentane, and redissolving it in C 7 D 8 at 233 K, allows to observe aromatic benzyl resonances at chemical shifts similar to those in C 6 D 5 Cl (Figure S21).…”

“…In contrast, for both complex S1 and Figure 6). For 8 + MM , a complex analogous to 4 + MM but having an OMe substituent in para position of the phenolate rings and a Zr−Me instead of a Zr−Bn moiety, previously shown to adopt the MM geometry based on 19 F, 1 H HOESY NMR data and DFT calculations, δ C2 and δ C2′ are observed at 42.7 ppm and at 37.6 ppm, respectively, allowing to exclude anisotropic effects originating from the benzyl ligand. Thus, 13 C NMR chemical shifts of C 2 and C 2 ′, easily measurable NMR parameters, may indeed discriminate FF from MM/FM geometries.…”

Role of Solvent Coordination on the Structure and Dynamics of ansa-Zirconocenium Ion Pairs in Aromatic Hydrocarbons

“…Since the pioneering discoveries by Brintzinger and Kaminsky, indenyl-based group IV ansa -metallocenes , have emerged as one of the most studied and systematically engineered classes of catalysts for stereoselective homogeneous olefin polymerization. − Under the promise of industrially relevant enhanced productivity at high reaction temperatures, these organometallic species underwent intense optimization aimed at rationalizing the correlation between molecular descriptors and the catalytic performance . This search culminated recently with the development of ultrarigid triptycene-based systems, affording isotactic polypropylene at 120 °C with high productivities .…”