A General Model for Selectivityin Olefin Cross Metathesis

R.H. Grubbs, JACS ASAP.

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Common Metathesis Catalysts

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Examples of Metathesis

• Ring OpeningMetathesisPolymerization

• Ring ClosingMetathesis

Angew. Chem. Int.Ed. 2003, 42, 1900

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Examples of Metathesis Cont.

• Ring Opening/RingClosing Metathesis

• Cross Metathesis

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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

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Metathesis Mechanism

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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.

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Classification of Olefins for CM

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CM with Two Type 1 Olefins

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General CM of Type 1 andType 2/3 Olefins

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Results of CM of Type 1 andType 2/3 Olefins

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Results of CM of Type 2 andType 3 Olefins

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Application of Guidelines

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Three Component CM

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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

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