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Titanium‐Catalyzed Vinylic and Allylic CF Bond Activation—Scope, Limitations and Mechanistic Insight
Author(s) -
Kuehnel Moritz F.,
Holstein Philipp,
Kliche Meike,
Krüger Juliane,
Matthies Stefan,
Nitsch Dominik,
Schutt Joseph,
Sparenberg Michael,
Lentz Dieter
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201201125
Subject(s) - chemistry , catalysis , hydride , allylic rearrangement , metathesis , silanes , steric effects , reactivity (psychology) , selectivity , combinatorial chemistry , titanium , substrate (aquarium) , photochemistry , organic chemistry , medicinal chemistry , polymerization , hydrogen , silane , medicine , polymer , alternative medicine , oceanography , pathology , geology
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 Group 6 hydride complexes.