Synthesis, Characterization, and Reactivity of Palladium Fluoroenolate Complexes

Cross-coupling
reactions of aryl groups with α-fluoro carbonyl
compounds catalyzed by palladium complexes have been reported, but
palladium fluoroenolate intermediates relevant to such reactions have
not been isolated or even detected previously. We report the synthesis,
structural characterization, and reactivity of a series of C-bound
arylpalladium fluoroenolate complexes ligated by monophosphines and
bisphosphines. DPPF-ligated arylpalladium fluoroenolate complexes
(DPPF = 1,1-bis­(diphenylphosphino)-ferrocene) derived from a monofluoroester,
a difluoroester, difluoroamides, and difluoroacetonitrile underwent
reductive elimination in high yields. Reductive elimination was faster
from complexes containing less electron-withdrawing fluoroenolate
groups and longer Pd–C­(enolate) bonds than from complexes containing
more electron-withdrawing fluoroenolate groups and shorter Pd–C­(enolate)
bonds. The rates of reductive elimination from these C-bound fluoroenolate
complexes were significantly faster than those of the analogous trifluoromethyl
complexes.