Relative reaction rates of olefin substrates with ruthenium(II) carbene metathesis initiators

Organometallics

Volumn 17, Issue 12, 1998, Pages 2484-2489

  Ulman, Michael ^a   Grubbs, Robert H ^a  

^a California Institute of Technology   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000681082     PISSN: 02767333     EISSN: None     Source Type: Journal    
DOI: 10.1021/om9710172     Document Type: Article

References (26)

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2. For several reviews see: (a) Grubbs, R. H.; Tumas, W. Science 1989, 243, 907.
3. (b) Schrock, R. R. Acc. Chem. Res. 1990, 23, 158.
4. (c) Stelzer, F. J. Macromol. Sci., Pure Appl. Chem. 1996, A33, 941.
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10. Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996, 118, 100.
11. Herrison, J. L.; Chauvin, Y. Makromol. Chem. 1970, 141, 161.
12. 2, or benzylidene, Ru=CHPh.
13. Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15, 1518.
14. Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1997, 119, 3887.
15. 2 so as to orient the phenyl group opposite the crowded metal center, not adjacent as it actually turned out. (14) These two phosphines are sterically similar but electronically different. Their similar activity in quenching the intermediate which bulkier phosphines could not stabilize supports steric factors as being more significant than electronic effects. For a review of the steric and electronic properties of phosphines, see: Tolman, C. A. Chem. Rev. 1977, 77, 313.
16. HH = 8.0 Hz).
17. A reviewer suggested that the predominance of the 2,4-metallacycle can also be attributed to competing steric and electronic effects. We have observed that carbene initiators reacting with 2-hexene result in ethylidene formation, rather than butylidene, while terminal olefins do not kinetically form the methylidene. Thus, as the reviewer suggested, a steric effect places the bulk away from the metal center while electronic effects favor alkyl substituents adjacent to the metal.
18. (a) Randall, M. L.; Tallarico, J. A.; Snapper, M. L. J. Am. Chem. Soc. 1995, 117, 9610.
19. (b) Schneider, M. F.; Blechert, S. Angew. Chem. Int. Ed. Engl. 1996, 35, 411.
20. (c) Snapper, M. L.; Tallanco, J. A..; Randall, M. L. J. Am. Chem. Soc. 1997, 119, 1478.
21. (d) Tallarico, J. A.; Bonitatebus, P. J.; Snapper, M. L. J. Am. Chem. Soc., 1997, 119, 7157.
22. Reference 16a addressed the potential mechanism for this process where polycyclobutene is first formed by ROMP and subsequently depolymerized and metathesized with the terminal olefin to form the ring-opened cross-metathesis product. However, when those authors treated polycyclobutene with the carbene and terminal olefin, they only obtained 15% of the expected product while treating the cyclobutene with carbene and terminal olefin produced 80% yields by GC. Thus it is very unlikely that polymerization is a significant pathway toward the products of ring-opening cross-metathesis while the mechanism in Scheme 4 is consistent with the results.
23. For a brief discussion of secondary kinetic isotope effects, see for example: Lowry, T. H.; Richardson, K. S. Mechanism and Theory in Organic Chemistry, 3rd ed.; Harper and Row: New York, 1987; pp 238-240.
24. Lee, J. B.; Ott, K. C.; Grubbs, R. H. J. Am. Chem. Soc. 1982, 104, 7491.
25. Brown, H. C.; Okamoto, Y. J. Am. Chem. Soc. 1958, 80, 4979.
26. Shiner, V. S., Jr.; Verbanic, C. J. J. Am. Chem. Soc. 1957, 79, 373.