Titanium-Catalyzed Vinylic and Allylic CF Bond Activation--Scope, Limitations and Mechanistic Insight

The hydrodefluorination (HDF) of fluoroalkenes in the presence of a variety of titanium catalysts was studied with respect to scope, selectivity, and mechanism. Optimization revealed that the catalyst requires low steric bulk and high electron density; secondary silanes serve as the preferred hydrid...

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Bibliographic Details
Published in:Chemistry : a European journal 2012-08, Vol.18 (34), p.10701
Main Authors: Kuehnel, Moritz F, Holstein, Philipp, Kliche, Meike, Kruger, Juliane, Matthies, Stefan, Nitsch, Dominik, Schutt, Joseph, Sparenberg, Michael, Lentz, Dieter
Format: Article
Language:English
Subjects:
Chemistry
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Summary:The hydrodefluorination (HDF) of fluoroalkenes in the presence of a variety of titanium catalysts was studied with respect to scope, selectivity, and mechanism. Optimization revealed that the catalyst requires low steric bulk and high electron density; secondary silanes serve as the preferred hydride source. A broad range of substrates yield partially fluorinated alkenes, such as previously unknown (Z)-1,2-(difluorovinyl)ferrocene. Mechanistic studies indicate a titanium(III) hydride as the active species, which forms a titanium(III) fluoride by H/F exchange with the substrate. The HDF step can follow both an insertion/elimination and a σ-bond metathesis mechanism; the E/Z selectivity is controlled by the substrate. The catalysts' ineffieciency towards fluoroallenes was rationalized by studying their reactivity towards Group6 hydride complexes.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201201125