Effect of anchoring group and valent of cobalt center on the competitive cleavage of C–F or C–H bond activation

Treatment of CoMe(PMe3)4 with 2,6-difluorobenzophenone imine and 2,6-difluorobenzophenone resulted in C–H bond activation complex, [Co(2-C6H4)-(CNH)-(2′,6″-F2C6H3)(PMe3)3] (2), and C–F bond activation complex [Co(Me)(F)(2-(6-FC6H3)-(CO)-C6H5)(PMe3)2] (3) respectively. Using Co(PMe3)4 instead of CoMe(PMe3)4 the C–F activation Co(І) complex [Co(2-(6-FC6H3)-(CNH)-C6H5)(PMe3)3] (1), was obtained by the reaction of Co(PMe3)4 with 2,6-difluorobenzophenone imine. In the case of mono-fluorinated aromatic ketone, the reaction of CoMe(PMe3)4 with 2,4′-difluorobenzophenone afforded only C–H bond activation complex, [Co(2-(4-FC6H3)-(CO)-(2′-FC6H4)(PMe3)3] (4) in comparison with the C–F activation in the di-fluorinated aromatic ketone 2,6-difluorobenzophenone system. The crystal structures of complexes 1, 3 and 4 were determined by X-ray diffraction. The proposed mechanisms were discussed.

The C–F or C–H bond of difluorobenzophenone can not be activated by Co(PMe3)4, while the C–F or C–H bond of the difluorobenzophenone can be activated by CoMe(PMe3)4. Both Co(PMe3)4 and CoMe(PMe3)4 can activate the C–F or C–H bond with the better anchoring group (CNH) instead of the ketone group. The Co-methyl group is beneficial for the C–H activation because of the thermodynamic contribution of evolution of methane. Increasing the subsituted fluoroatoms in phenyl ring is advantageous to the C–F bond activation. The proposed mechanisms were discussed.Figure optionsDownload as PowerPoint slide