Synthesis, Characterization, and Reactivity of Palladium Fluoroenolate Complexes
Cross-coupling reactions of aryl groups with a-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. DPPFligated 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) bond lengths than from complexes containing more electron-withdrawing fluoroenolate groups and shorter Pd-C(enolate) bond lengths. The rates of reductive elimination from these Cbound fluoroenolate complexes were significantly faster than those of the analogous trifluoromethyl complexes.
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