Selective Copper Complex-Catalyzed Hydrodefluorination of Fluoroalkenes and Allyl Fluorides: A Tale of Two Mechanisms

The
transition to more economically friendly small-chain fluorinated
groups is leading to a resurgence in the synthesis and reactivity
of fluoroalkenes. One versatile method to obtain a variety of commercially
relevant hydrofluoroalkenes involves the catalytic hydrodefluorination
(HDF) of fluoroalkenes using silanes. In this work it is shown that
copper hydride complexes of tertiary phosphorus ligands (L) can be
tuned to achieve selective multiple HDF of fluoroalkenes. In one example,
HDF of the hexafluoropropene dimer affords a single isomer of heptafluoro-2-methylpentene
in which five fluorines have been selectively replaced with hydrogens.
DFT computational studies suggest a distinct HDF mechanisms for L2CuH (bidentate or bulky monodentate phosphines) and L3CuH (small cone angle monodentate phosphines) catalysts, allowing
for stereocontrol of the HDF of trifluoroethylene.