Perfluoroalkyl Cobalt(III) Fluoride and Bis(perfluoroalkyl) Complexes: Catalytic Fluorination and Selective Difluorocarbene Formation

Four
perfluoroalkyl cobalt­(III) fluoride complexes have been synthesized
and characterized by elemental analysis, multinuclear NMR spectroscopy,
X-ray crystallography, and powder X-ray diffraction. The remarkable
cobalt fluoride 19F NMR chemical shifts (−716 to
−759 ppm) were studied computationally, and the contributing
paramagnetic and diamagnetic factors were extracted. Additionally,
the complexes were shown to be active in the catalytic fluorination
of p-toluoyl chloride. Furthermore, two examples
of cobalt­(III) bis­(perfluoroalkyl)­complexes were synthesized and their
reactivity studied. Interestingly, abstraction of a fluoride ion from
these complexes led to selective formation of cobalt difluorocarbene
complexes derived from the trifluoromethyl ligand. These electrophilic
difluorocarbenes were shown to undergo insertion into the remaining
perfluoroalkyl fragment, demonstrating the elongation of a perfluoroalkyl
chain arising from a difluorocarbene insertion on a cobalt metal center.
The reactions of both the fluoride and bis­(perfluoroalkyl) complexes
provide insight into the potential catalytic applications of these
model systems to form small fluorinated molecules as well as fluoropolymers.