View
4
Download
0
Category
Preview:
Citation preview
A General Model for Selectivityin Olefin Cross Metathesis
R.H. Grubbs, JACS ASAP.
Bryan Wakefield @ Wipf Group 1 8/30/03
Common Metathesis Catalysts
Bryan Wakefield @ Wipf Group 2 8/30/03
Examples of Metathesis
• Ring OpeningMetathesisPolymerization
• Ring ClosingMetathesis
Angew. Chem. Int.Ed. 2003, 42, 1900
Bryan Wakefield @ Wipf Group 3 8/30/03
Examples of Metathesis Cont.
• Ring Opening/RingClosing Metathesis
• Cross Metathesis
Bryan Wakefield @ Wipf Group 4 8/30/03
Cross Metathesis(CM)• The mutual exchange of
alkylidene fragmentsbetween two olefinspromoted by metal-carbene complexes
• There are 3 majorvariations on this theme: a)CM, b) Ring Opening CMand c) intermolecularenyne metathesis
Bryan Wakefield @ Wipf Group 5 8/30/03
Metathesis Mechanism
Bryan Wakefield @ Wipf Group 6 8/30/03
Problems with CM
• Not a large driving force unlike ROMP orRCM
• Low product selectivity, mixtures ofhomodimers or polymers can be formed
• Poor Stereoselectivity in the producedolefin.
• Lack of a model that predicts selectivity.
Bryan Wakefield @ Wipf Group 7 8/30/03
Classification of Olefins for CM
Bryan Wakefield @ Wipf Group 8 8/30/03
CM with Two Type 1 Olefins
Bryan Wakefield @ Wipf Group 9 8/30/03
General CM of Type 1 andType 2/3 Olefins
Bryan Wakefield @ Wipf Group 10 8/30/03
Results of CM of Type 1 andType 2/3 Olefins
Bryan Wakefield @ Wipf Group 11 8/30/03
Results of CM of Type 2 andType 3 Olefins
Bryan Wakefield @ Wipf Group 12 8/30/03
Application of Guidelines
Bryan Wakefield @ Wipf Group 13 8/30/03
Three Component CM
Bryan Wakefield @ Wipf Group 14 8/30/03
Conclusions
• There is now a classification of olefins that allowsfor some predictive abilities in CM.
• These classifications are based on rate ofhomodimerization and can be influenced by stericand electronic effects as well as protection ofalcohols.
• More work needs to be done to develop a modelthat is more quantitative and less qualitative
Bryan Wakefield @ Wipf Group 15 8/30/03
Recommended