Post-metallocene catalyst
From Wikipedia, the free encyclopedia
A post-metallocene catalyst is a kind of catalyst for olefin polymerization. "Post-metallocene" refers to the generation of catalysts following Kaminsky catalysts, which are metallocene catalysts discovered in 1980 by Walter Kaminsky, and have been predominant in the olefin polymerization catalyst area for the past quarter century. The first post-metallocene catalysts appeared in the late 1990s.
Most post-metallocene catalysts are homogeneous single-site systems, so their catalytic properties can be controlled by modification of the structure of the catalyst. A large number of studies have been conducted by academia and industry to construct high-performance post-metallocene catalysts based on new concepts.
Most post-metallocene catalysts have been made by using early transition metals. However, late transition metal complexes such as nickel, palladium, and iron complexes have also been reported as good catalysts for olefin polymerization by Maurice S. Brookhart, Robert H. Grubbs, Vernon Gibson and others. A salicylimine catalyst system based on zirconium, developed by Terunori Fujita and Geoff Coates provides extremely high activity for ethylene polymerization, and can produce some novel polypropylene structures.
Despite intensive research and development of these systems, very few have been successfully commercialised due to their complex synthesis and relative fragility compared to metallocene catalysts. The presence of (highly toxic) aniline units in the majority of active salicylimine species effectively precludes their use in several major markets for polyethylene.
[edit] References
1) L. K. Johnson, C. K. Killian, M. Brookhart, J. Am. Chem. Soc., 117, 6414 (1995).
2) C. Wang, S. Friedrich, T. R. Younkin, R. T. Li, R. H. Grubbs, D. A. Bansleben, M. W. Day, Organometallics, 17, 3149 (1998).
3) S. Matsui, Y. Tohi, M. Mitani, J. Saito, H. Makio, H. Tanaka, M. Nitabaru, T. Nakano, T, Fujita, Chem. Lett., 1065 (1999).
