Ligands for olefin polymerization

Fluorinated ligands have often been employed in olefin polymerization. Fluorine substituents on the aromatic ring in well-refined Kaminsky-type metallocence catalysts for olefin polymerization play an important role in controlling the activity of the catalysts, molecular weight, tacticity, and molecular weight distribution of the polymers [28]. The catalyst (67), 

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With these features in mind, we envisioned a new family of macrocyclic ligands for olefin polymerization catalysis (Fig. 9) [131, 132], We utilized macrocycles as the ligand framework and installed the catalytic metal center in the core of the macrocycles. Appropriate intra-annular binding sites are introduced into cyclophane framework that not only match the coordination geometry of a chosen metal but also provide the appropriate electronic donation to metal center. The cyclophane framework would provide a microenvironment to shield the catalytic center from all angles, but leaving two cis coordination sites open in the front one for monomer coordination and the other for the growing polymer chain. This could potentially protect the catalytic center and prevent it from decomposition or vulnerable side reactions. 

Matsui, S. Mitani, M. Saito, J. Tohi, Y Makio, H. Matsukawa, N. Takagi, Y. et al. A family of zirconium complexes having two phenoxy-imine chelate ligands for olefin polymerization. J. Am. 

Ni catalysts for olefin polymerization incorporating a-iminocarboxamide ligands are activated by the formation of borane-carbonyl adducts (153).542 Structure/reactivity relationships are similar to Brookhart s dimine catalysts. 

The above achievements depend highly on both the recent advances in rational catalyst design with the aid of computational science represented by DFT calculations and the wide range of catalyst design possibilities that are afforded by FI catalysts. These possibilities are derived from the readily varied steric and electronic properties of the phenoxy-imine ligands. It is expected that future research on FI catalysts will provide opportunities to produce additional polyolefin-based materials with unique microstructures and a chance to study catalysis and mechanisms for olefin polymerization. 

In contrast to the free-radical polymerizations, there have been relatively few studies on transition metal catalysed polymerization reactions in water. This is largely due to the fact that the early transition metal catalysts used commercially for the polymerization of olefins tend to be very water-sensitive. However, with the development of late transition metal catalysts for olefin polymerizations, water is beginning to be exploited as a medium for this type of polymerization reaction. For example, cationic Pd(II)-bisphosphine complexes have been found to be active catalysts for olefin-CO copolymerization [21]. Solubility of the catalyst in water is achieved by using a sulfonated phosphine ligand (Figure 10.5) as described in Chapter 5. 

Cationic transition metal amide complexes have been investigated in part because of their potential in catalysis p irticularly for olefin polymerization. Much of this work has concerned polydentate amido, linked cyclopentadienyl-amido or delocalized nitrogen centred bidentate ligands (see later). However, the structures of a small number of cationic complexes containing monodentate amido ligands have been determined. These include... 

Fig. 12.5 Symyx high-throughput primary screen, in which arrays of metal-ligand combinations are rapidly surveyed for olefin polymerization activity. In this example, a 1-octene primary screen was used to discover a new amide ether-based hafnium catalyst.

Fig. 6 Typical metallocene catalysts for olefin polymerization containing a C2-symmetric ligand (left) and a Cs-symmetric ligand (right)...

Fig. 5-18i,13 has been followed in recent years by studies of early transition metal-carboranes as catalysts for olefin polymerization.14 In these applications, the metalla-carborane species resemble their metallocene-based analogues however, there are other areas, such as the construction of new types of electronic, magnetic, and optical materials, in which the unique structural and other characteristics of metalla-carboranes may be put to use. Venus flytrap linked-dicarbollide ligands such as that shown encapsulating a Co3+ ion in Fig. 5-18f have been prepared as a possible way to bind radiotransition metals to tumor-associated monoclonal antibodies for purposes of diagnosis and therapy.15... 

Bulky amido groups as ancillary ligands have been used as alternative to the Cp rings for the stabilization of a wide range of alkyltitanium derivatives and group 4 metal diamido dialkyl complexes are receiving special attention as potential catalysts for olefin polymerizations. 

Mono-Cp titanium derivatives show reactivity as catalyst precursors for olefin polymerizations, particularly for the polymerization of styrene and functionalized monomers. A review highlighting the developments in the design and applications of non-metallocene complexes, including mono-Cp derivatives, as catalyst systems for a-olefin polymerization has appeared.440 Titanium complexes bearing Cp in addition to chloro ligands and activated by aluminum... 

Metallocene derivatives are the most extensively studied class of homogeneous catalysts for the polymerization of olefins. Less saturated and less hindered mono-Gp group 4 metal species of the type [Cp MR2]+ (Cp denotes Cp or a substituted cyclopentadienyl ring) may also behave as useful catalysts or initiators for olefin polymerization. Catalysts for syndiospecific polymerization of styrene based on mono-Cp titanium derivatives with different substituents on the Gp ligand and with various types of tetraphenylborates have been examined. A good relationship between the... 

A monograph including complexes with Cp-amido ligands has recently been published.676 The role of the group 4 Cp-amido derivatives as catalyst precursors for olefin polymerization has been reviewed.677 A review highlighting the... 

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