π-Stacking as a control element in the (2-PhInd)2Zr elastomeric polypropylene catalyst

Journal of the American Chemical Society

Volumn 118, Issue 44, 1996, Pages 10908-10909

  Pietsch, M A ^a   Rappe A K ^a  

^a Immunology and Pathology   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

POLYPROPYLENE;

ARTICLE; CRYSTALLIZATION; DRUG STRUCTURE;

EID: 0029820172     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja960293p     Document Type: Article

References (27)

1. Karasz. F. E.; Mac Night, W. J. Macromolecules 1968, 1, 537.
2. Brintzinger, H. H.; Fischer, C; Mülhaupt, R.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
3. Chien, J. C. W.; Llinas, G. H.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Atwood, J. L.; Bott, S. G. J. Am. Chem. Soc. 1991, 113, 8569. Llinas, G. H.; Dong, S.-H.; Mallin, D. T.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Chien, J. C. W. Macromolecules 1992, 25, 1242. Chien, J. C. W.; Sugimoto, R. J. Polym. Sci., Part A: Polym. Chem. 1991, 29, 459. Chien, J. C. W.; Gong, B. M. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 1747. Gauthier, W. J.; Collins, S. Macromolecules 1995, 28, 3779.
4. Chien, J. C. W.; Llinas, G. H.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Atwood, J. L.; Bott, S. G. J. Am. Chem. Soc. 1991, 113, 8569. Llinas, G. H.; Dong, S.-H.; Mallin, D. T.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Chien, J. C. W. Macromolecules 1992, 25, 1242. Chien, J. C. W.; Sugimoto, R. J. Polym. Sci., Part A: Polym. Chem. 1991, 29, 459. Chien, J. C. W.; Gong, B. M. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 1747. Gauthier, W. J.; Collins, S. Macromolecules 1995, 28, 3779.
5. Chien, J. C. W.; Llinas, G. H.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Atwood, J. L.; Bott, S. G. J. Am. Chem. Soc. 1991, 113, 8569. Llinas, G. H.; Dong, S.-H.; Mallin, D. T.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Chien, J. C. W. Macromolecules 1992, 25, 1242. Chien, J. C. W.; Sugimoto, R. J. Polym. Sci., Part A: Polym. Chem. 1991, 29, 459. Chien, J. C. W.; Gong, B. M. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 1747. Gauthier, W. J.; Collins, S. Macromolecules 1995, 28, 3779.
6. Chien, J. C. W.; Llinas, G. H.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Atwood, J. L.; Bott, S. G. J. Am. Chem. Soc. 1991, 113, 8569. Llinas, G. H.; Dong, S.-H.; Mallin, D. T.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Chien, J. C. W. Macromolecules 1992, 25, 1242. Chien, J. C. W.; Sugimoto, R. J. Polym. Sci., Part A: Polym. Chem. 1991, 29, 459. Chien, J. C. W.; Gong, B. M. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 1747. Gauthier, W. J.; Collins, S. Macromolecules 1995, 28, 3779.
7. Chien, J. C. W.; Llinas, G. H.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Atwood, J. L.; Bott, S. G. J. Am. Chem. Soc. 1991, 113, 8569. Llinas, G. H.; Dong, S.-H.; Mallin, D. T.; Rausch, M. D.; Lin, G.-Y.; Winter, H. H.; Chien, J. C. W. Macromolecules 1992, 25, 1242. Chien, J. C. W.; Sugimoto, R. J. Polym. Sci., Part A: Polym. Chem. 1991, 29, 459. Chien, J. C. W.; Gong, B. M. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 1747. Gauthier, W. J.; Collins, S. Macromolecules 1995, 28, 3779.
8. Coates, G. W.; Waymouth, R. M. Science 1995, 207, 217.
9. Almenningen, A.; Bastlansen, O.; Fernholt, L.; Cyvin, B. N.; Cyvin, S. J.; Samdal, S. J. Mol. Struct. 1985, 128, 59.
10. Haaland, A. Acc. Chem. Res. 1979, 12, 415.
11. Rappé, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard, W. A., III; Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024.
12. Consistent with the published UFF force field, electrostatic interactions were not included in the present study. Calculations were carried out with the MCM suite of programs (Skiff, W. M.; Ramachandran. S.; Pietsch, M. A.; McGaughey, G. B.; Rappé, A. K. Unpublished Results). For reference, the barrier for biphenyl rotation in UFF is 4.5 kcal/mol compared to the 1-2 kcal/mol found experimentally. The barrier to rotation for the 2-phenylindenyl ligand in UFF is 0.6 kcal/mol.
13. For both systems, the conformation coordinate was chosen to be the rotation of the Ph-Cp(centroid)-Cp(centroid)-Ph dihedral angle ø (see Figure 1a). ø was constrained in 5° increments, while the rest of the geometry was allowed to optimize. The methyl was used to simulate solvent, counterion, or alkane. Since the conformational equilibrium rather than the insertion transition state was studied, it is important to have the fourth coordination site occupied but not necessarily by propylene.
14. Four minima were actually found, corresponding to two symmetry equivalent meso and two symmetry equivalent rac conformations.
15. The transition state was verified as having one negative frequency. In addition, walking along the imaginary mode in both directions produced the respective minima.
16. Because of their accessable π-cloud, aromatic substituents can participate in stablizing or attractive interactions with other aromatic substituents. These interactions are called π-stacking. Due to the dispersive nature of the interaction, it is largely orientation invariant with both perpendicular, and parallel, orientations observed and nearly isoenergetic with binding energies of roughly 2 kcal/mol.
17. 2 was optimized using the UFF force field. Two minima were found. The meso (ø = 23°) is 3.1 kcal/mol less stable than the rac conformation (ø = 119°). Since the rac confromation is prefered over the meso conformation, only isotactic polypropylene would be formed by a catalyst generated from this precursor if the catalyst were catalytically active.
18. Castonguay, L. A.; Rappé, A. K.; Casewit, C. J. J. Am. Chem. Soc. 1991, 113, 7177. Hunter, C. A.; Singh, J.; Thornton, J. M. J. Mol. Biol. 1991, 218, 837. Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1990, 93, 5893. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1993, 97, 3937. Nagy, J.; Smith, V. H., Jr.; Weaver, D. F. J. Phys. Chem. 1995, 99, 13868.
19. Castonguay, L. A.; Rappé, A. K.; Casewit, C. J. J. Am. Chem. Soc. 1991, 113, 7177. Hunter, C. A.; Singh, J.; Thornton, J. M. J. Mol. Biol. 1991, 218, 837. Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1990, 93, 5893. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1993, 97, 3937. Nagy, J.; Smith, V. H., Jr.; Weaver, D. F. J. Phys. Chem. 1995, 99, 13868.
20. Castonguay, L. A.; Rappé, A. K.; Casewit, C. J. J. Am. Chem. Soc. 1991, 113, 7177. Hunter, C. A.; Singh, J.; Thornton, J. M. J. Mol. Biol. 1991, 218, 837. Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1990, 93, 5893. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1993, 97, 3937. Nagy, J.; Smith, V. H., Jr.; Weaver, D. F. J. Phys. Chem. 1995, 99, 13868.
21. Castonguay, L. A.; Rappé, A. K.; Casewit, C. J. J. Am. Chem. Soc. 1991, 113, 7177. Hunter, C. A.; Singh, J.; Thornton, J. M. J. Mol. Biol. 1991, 218, 837. Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1990, 93, 5893. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1993, 97, 3937. Nagy, J.; Smith, V. H., Jr.; Weaver, D. F. J. Phys. Chem. 1995, 99, 13868.
22. Castonguay, L. A.; Rappé, A. K.; Casewit, C. J. J. Am. Chem. Soc. 1991, 113, 7177. Hunter, C. A.; Singh, J.; Thornton, J. M. J. Mol. Biol. 1991, 218, 837. Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1990, 93, 5893. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1993, 97, 3937. Nagy, J.; Smith, V. H., Jr.; Weaver, D. F. J. Phys. Chem. 1995, 99, 13868.
23. Castonguay, L. A.; Rappé, A. K.; Casewit, C. J. J. Am. Chem. Soc. 1991, 113, 7177. Hunter, C. A.; Singh, J.; Thornton, J. M. J. Mol. Biol. 1991, 218, 837. Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1990, 93, 5893. Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Chem. Phys. 1993, 97, 3937. Nagy, J.; Smith, V. H., Jr.; Weaver, D. F. J. Phys. Chem. 1995, 99, 13868.
24. The special nature of this π-π interaction can be seen from UFF studies of the parent bis(indenyl) and 2-tert-butyl complexes. The barrier for converting between the nearly isoenergetic meso and rac conformations (computed energy difference of 0.3 kcal/mol) was found to be only 1.2 kcal/mol (with respect to the more stable rac conformation) for the parent complex. For the 2-tert-butyl complex, the meso and rac conformations only differ by 0.2 kcal/mol but the steric congestion due to the tert-butyl group in both rac and meso conformations will prevent either from being viable catalysts (Supporting Information gives molecular structure pictures).
25. Computed and X-ray (in parentheses) distances were found to be quite similar: The average Zr-C(Cp) distance is 2.538 (2.506) and 2.542 (2.512) Å for the meso conformation and 2.548 (2.502) and 2.546 (2.502) A for the rac conformation. The Zr-Cl distances in the meso conformation are 2.42 (2.47) and 2.43 (2.49) Å. The Zr-Cl distances in the rac conformation are 2.42 (2.49) and 2.43 (2.49) Å. The distances between the indenyl ligands and the phenyl groups are 1.47 (1.48) and 1.49 (1.49) Å for the meso conformation and 1.48 (1.48) and 1.47 (1.48) Å for the rac conformation. The dihedral angles φ and φ′ are 27° (3°) and -27° (12°) for the meso and -19° (-11°) and -27° (-4°) for the rac conformations.
26. 2 symmetric. To be consistant with the meso conformation, φ and φ′ correspond to the front and back dihedral angle, respectively. The corresponding dihedral angles for the bottom back and top front are -27° and -19°, respectively.
27. Hauptman, E.; Waymouth, R. M. J. Am. Chem. Soc. 1995, 117, 11586.