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Impact of Ethylene on Efficiency and Stereocontrol in Olefin Metathesis: When to Add It, When to Remove It, and When to Avoid It

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Angewandte Chemie International Edition
Authors:
Amir H. Hoveyda
Amir H. Hoveyda
Amir H. Hoveyda
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Zhenxing Liu at Boston College
Zhenxing Liu
Can Qin
Can Qin
Can Qin
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Tobias Koengeter
Tobias Koengeter
Tobias Koengeter
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Abstract and Figures

Ethylene is the byproduct of olefin metathesis reactions that involve one or more terminal alkenes. Its volatility is one reason why many cross‐metathesis or ring‐closing metathesis processes, which are reversible transformations, are efficient. However, because ethylene can be converted to a methylidene complex, which is a highly reactive but relatively unstable species, its concentration can impact olefin metathesis in other ways. In some cases, introducing excess ethylene can increase reaction rate owing to faster catalyst initiation. Ethylene and a derived methylidene complex can also advantageously inhibit substrate or product homocoupling, and/or divert a less selective pathway. In other instances, a methylidene's low stability and high activity may lead to erosion of efficiency and/or kinetic selectivity, making it preferable that ethylene is removed while being generated. If methylidene decomposition is so fast that there is little or no product formation, it is best that ethylene and methylidene complex formation is avoided altogether. This is accomplished by the use of di‐ or trisubstituted alkenes in stereoretentive processes, which includes adopting methylene capping strategy. Here, we analyze the different scenarios through which ethylene and the involvement of methylidene complexes can be manipulated and managed so that an olefin metathesis reaction may occur more efficiently and/or more stereoselectively.
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Olefin Metathesis
Impact of Ethylene on Efficiency and Stereocontrol in
Olefin Metathesis:When to Add It, When to Remove It,
and When to Avoid It
Amir H. Hoveyda,* Zhenxing Liu, Can Qin, Tobias Koengeter,and Yucheng Mu
Angewandte
Chemie
Keywords:
cross-metathesis ·ethylene ·
methylidene complexes ·
olefin metathesis ·
ring-closing
metathesis
A
ngewandte
Chemie
Minireviews
How to cite: Angew.Chem. Int. Ed. 2020,59,22324–22348
International Edition: doi.org/10.1002/anie.202010205
German Edition: doi.org/10.1002/ange.202010205
22324 T2020 Wiley-VCH GmbH Angew.Chem. Int. Ed. 2020,59,22324 –22348
... The resulting ester (±)-18 was then treated with various metathesis catalysts in the presence of ethylene. 18 Unfortunately, olen metathesis stopped aer the ring opening step, with the only product being amino ester (±)-19 (Scheme 6). The most efficient catalyst was G-1, but all four catalysts provided the product in good yields. ...
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  • Jan 2019
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