Titanium-catalyzed vinylic and allylic C-F 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 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.
Institut für Chemie und Biochemie-Anorganische Chemie, Freie Universität Berlin, Fabeckstr. 34-36, 14195 Berlin, Germany.
Moritz F
MF
Kuehnel
Philipp
P
Holstein
Meike
M
Kliche
Juliane
J
Krüger
Stefan
S
Matthies
Dominik
D
Nitsch
Joseph
J
Schutt
Michael
M
Sparenberg
Dieter
D
Lentz