Non-metallocene catalysts

The most successful examples of commercialized non-metallocene catalysts are the constrained geometry complexes such as (29) developed at Dow and Exxon.109-112 The open nature of the titanium center favors co-monomer uptake. Hence, o-oleflns such as propene, 1-butene, 1-hexene... 

Other anionic nitrogen-containing ligands which have been examined in the search for new non-metallocene catalysts include macrocyclic porphyrins and tetraazaannulenes. However, activities with these catalysts are low. 

Stereoselective propylene polymerization with non-metallocene catalysts... 

This section focuses on group 4 metallocenes, which have been the most widely and thoroughly investigated among the homogeneous alkene-polymerization catalysts. These will also serve as useful reference standards in the following discussions regarding non-metallocene catalysts. 

Non-metallocene catalysts have attracted much attention recently.These catalysts generally contain oxygen and/ or nitrogen (and sometimes sulfur and phosphorous) as ligating atoms, and those heteroatoms are often incorporated into a chelate ligand structure. These catalyst precursors often take an octahedral configuration, providing... 

Sudhakar, P. and Sundararajan, G. (2005) Tuning the reactivity of N, O.O.O-non-metallocene catalysts for a-olefin polymerization issues related to ligand symmetry and derivatization. Macromol. Rapid Commun., 26, 1854. 

Two communications on propene polymerization by non-metallocene catalysts that include DFT/MM calculations have been recently published [60, 61]. They deal with group 4 bidentate non-cyclopentadienyl complexes. In the first communication [60], the topic addressed is the fact that a C2-symmetric precatalyst of titanium leads to a syndiotactic polymer, contrary to observations of metallocene catalysts. The chirality at the metal center is found to play a key role in the stereocontrol of the process. The second communication [61] addresses the fact that a C2-symmetric precatalyst of zirconium very similar to the previous one produces an isotactic polymer, finds out that it is due to a complicated concourse of synergic steric and electronic effects, and emphasizes the key role that serendipity still plays in the design of new catalysts. 

Transfer to A1 was reported to be operative with several non-metallocene catalysts. It is the only chain-release mechanism operative with the diamido complexes MCl2 ArN(CH2) NAr catalysts, as well as with the mono-and tris(benzamidinate) catalysts, since no olefinic resonances were observed in the H or 13C NMR spectra of these polymers.275 276 This chain-release reaction is also dominant with bis(phenoxy-imine)zirconium cat-... 

A unique example of non metallocenic catalyst [(DADMB)YMe], [(DADMB) = 2,2 -bis(/er -butyldimethylsilylamido)-6,6 -dimethyldiphenyl], was recently reported [13]. It was assumed that the methyl complex first reacts with the silane to give a small concentration of a monomeric highly reactive hydride (Scheme 2). The yttrium hydride was not detected by NMR spectroscopy, probably because its concentration is very low. Nevertheless, precipitation of the insoluble yttrium dimer [(DADMB)YH]2 occurred at the end of the reaction. The bulky ligand... 

Two non-metallocene catalysts tor the formation of ethylene-propylene block copolymers. 

Capacchione, C. Proto, A. EbeUng, H. MtUhaupt, R. Moller, K. Manivannan, R. Spaniol, T. P. Okuda, J. Non-metallocene catalysts for the styrene polymerization Isospecific gronp 4 metal bis(phenolate) catalysts. J. Mol. Catal. A Chem. 2004, 213,137-140. 

Table 7 shows examples of polymers obtained by non-metallocene catalysts. Independent of the catalyst used, the polysilanes obtained are inhomogeneous and control of structure and molecular weights remains difficult. Most promising... 

Abstract Metallocene complexes that serve as stereoselective olefin polymerization catalysts are described. The polymerization of propylene, styrene, methyl methacrylate, 1,3-dienes, non-conjugated dienes and cycloolefins is discussed. The stereochemistry of monomer insertion is governed by the chiral steric environment of catalysts derived from a ligand structure (catalytic-site control) or a chiral center in the polymer chain (chain-end control). The mechanism of formation of isotactic and syndiotactic polymers in each monomer and catalyst is explained. Non-metallocene catalysts for stereospecific polymerization are also mentioned. 

It has been shown that a variety of metallocene complexes serve as effective homogeneous, stereoselective polymerization catalysts. They achieve imprece-dented polymers that could not be produced by traditional catalysts. Many examples of non-metallocene catalysts have also been studied. In industry, however, conventional heterogeneous catalyst systems are still major processes for the production of polyolefins. 

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