1. Modeling of Ru and Fe based olefin metathesis Michael T. Feldmann Richard P. Muller William A. Goddard, III Materials and Process Simulation Center, Caltech Olefin metathesis is an important reaction for many chemical processes including polymerization. It has been shown that the Grubbs ruthenium-based catalyst is very efficient at olefin metathesis with high functional group tolerance. It has been so successful that we would quickly deplete the world of its supply of ruthenium if we were to use it for all its applications. Looking at related elements that have a higher natural abundance leads to iron. Iron should have similar electronic behavior which could lead to a successful iron based olefin metathesis catalyst. The mechanism of the ruthenium-based Grubbs catalyst of the formula L 2 X 2 Ru=CHR has been examined. Experimentally it has been shown that L=PCy 3,P i Pr 3, X=Cl, and R=CHPh 2 produce an effective catalyst. When X=Cl and R=H in our theoretical study, L was varied from a simple phosphine to a carbene and an sp 2 nitrogen donating ligand. Understanding gained from this mechanism has allowed for possible performance enhancement of the ruthenium- based catalyst. In addition, the iron-based analog is showing promise as the ligand effects are being understood and tuned to the needs of the iron-based reaction pathway. Acknowledgements: NSF-Che

2. What is olefin metathesis? What is the reactive intermediate?

3. Why should anyone care about olefin metathesis? Ring closing metathesis (RCM) Ring opening metathesis polymerization (ROMP) [1] Acyclic diene metathesis (ADMET)

4. What do we know about the Grubbs catalyst? Ring-closing kinetics: [2] Addition of CuCl or CuCl 2 speed up reaction (Cu acts as a phosphine scavenger) Structure of starting catalyst: [2][3][4] Activity for various ligands: [2] X=> Cl>Br>>I L=> PCy 3 >P i Pr 3 >PCy 2 Ph>P i Pr 2 Ph>>PPh 3 X tends to be small and electronegative L tends to have large cone angle and be electron donating

5. Scheme 1: L-dissociation

6. Scheme 2: olefin-association [2][5]

7. Scheme 2b: olefin-association

8. Reaction pathway (Ru: X=Cl, L=PH 3 )

9. Reaction pathway (b) (Ru: X=Cl, L=PH 3 )

10. Ru catalyst: X=Cl L=

11. [6]

12. Why is using Ru not ideal? Ruthenium is scarce. If we were to use the Ru-based Grubbs catalyst for all the applications it is suited for we would soon deplete the world’s supply of ruthenium. Why not just use Fe? Iron-based Grubbs catalysts don’t work. Iron tends to be high spin.

13. Fe catalyst: X=Cl L=PH 3 (triplet surface)

14. Fe catalyst: X=Cl L= (triplet surface)

15. Fe catalyst: X=Cl L= (triplet surface)

16. Conclusions Scheme 1 is the supported mechanism Mixed “L”-ligand systems look promising High spin state of iron may be a major issue Strong electron donors remedy some of the high spin state issues for the iron-based catalyst

17. Acknowledgements: National Science Foundation References: 1.) J.A. Tallarico, P.J. Bonitatebus,Jr., M.L. Snapper, J. Am. Chem. Soc., 1997, 119, 7157-7158. 2.) E.L. Dias, S.T. Nguyen, R.H. Grubbs, J. Am. Chem. Soc., 1997, 119, 3887-3897. 3.) Z. Wu, S.T. Nguyen, R. Grubbs, J.W. Ziller, J. Am. Chem. Soc., 1995, 117, 5503-5511. 4.) P. Schwab, R. Grubbs, J.W. Ziller, J. Am. Chem. Soc., 1996, 118, 100-110. 5.) O.M. Aagaard, R.J. Meier, F. Buda, J. Am. Chem. Soc., 1998, 120, 7174-7182. 6.) T. Weskamp, W.C. Schattenmann, M. Spiegler, W.A. Herrmann, Angew. Chem. Int. Ed. 1998, 37, 2490-2493.