Is the metallocene (3-THF-CH₂-Cp)₂ZrCl₂ a better catalyst than the corresponding 2-THF derivative for olefin polymerisation? A molecular modelling study

Abstract

Semi-empirical, ab initio and density functional calculations performed on the active intermediates (2-THF-CH₂-Cp)₂Zr⁺-CH₃ and (3-THF-CH₂-Cp)₂Zr⁺-CH₃ indicate that the former is more stable as an intra-molecular complex by up to 21.6 kcal mol^–1 and is, therefore, a less efficient catalyst for olefin polymerisation.

References

1. BP Patent No: EP 608054. In a laboratory scale experiment it was found that 1.9 mg (4.1 × 10^–3 mmol) of the catalyst (2-THF-CH₂-Cp)₂ZrCl₂ in the presence of MAO in toluene (100 ml, 0.41 M) at an ethylene pressure of 4 psig shows no polymerisation activity at room temperature—addition of Cp₂ZrCl₂ to the mixture, however, restored immediate polymerisation activity. In comparison, the catalyst (3-THF-CH₂-Cp)₂ZrCl₂ gave 9.25 g h^–1 of the polymer, under similar experimental conditions.
2. A. Anderson, H. G. Cordes, J. Herwig, W. Kaminsky, A. Merk, R. Mottweiler, J. H. Sinn and H. J. Vollmer, Angew. Chem., Int. Ed. Engl., 1976, 15, 630.
3. P. C. Mohring and N. J. Colville, J. Organomet. Chem., 1994, 479, 1.
4. M. J. S. Dewar and W. Thiel, J. Am. Chem. Soc., 1977, 99, 4899.
5. SPARTAN version 5.0, Wavefunction Inc., 18401 Von Karman Ave., Suite 370, Irvine, CA 92612, USA.
6. GAUSSIAN94 Revision D.3, M. J. Frisch et al., Gaussian Inc., Pittsburgh, PA, 1995.
7. J. S. Binkley, J. A. Pople and W. J. Hehre, J. Am. Chem. Soc., 1980, 102, 939.
8. P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 270.
9. A. D. Becke, Phys. Rev. A, 1988, 38, 3098.
10. C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785.
11. Y. Qian, G. Li, W. Chen, B. Li and X. Lin, J. Organomet. Chem., 1989, 373, 185.