Selective C-F/C-H bond activation of fluoroarenes by cobalt complex supported with phosphine ligands.

The reactions of pentafluoropyridine C5NF5, hexafluorobenzene C6F6, and perfluoronaphthalene C10F8 with cobalt(0) complex, Co(PMe3)4, were investigated. The Co(I) complexes (4-C5NF4)Co(PMe3)3 (1), (C6F5)Co(PMe3)3 (2), (C10F7)Co(PMe3)3 (3), (4-C5NF4)Co(PMe3)4 (4) and (C10F7)Co(PMe3)4 (6) were obtained by selective activation of the C–F bonds. The reactions of 1 and 2 with CO afforded dicarbonyl cobalt(I) complexes (4-C5NF4)Co(CO)2(PMe3)2 (7), (C6F5)Co(CO)2(PMe3)2 (8). Under similar reaction conditions, 2 as a C–H bond activation product was obtained from the reaction of pentafluorobenzene, C6F5H, with Co(PMe3)4. The byproducts, hydrodefluorination product 1,2,4,5-C6F4H2 and F2PMe3 from the reaction of C6F5H and Co(PMe3)4 were also observed. The reaction mechanism of C6F5H with Co(PMe3)4 is proposed and partly-experimentally verified. The reaction of C6F5H with Co(PMe3)4 under 1 bar of CO at room temperature afforded hydrido dicarbonyl cobalt(II) complex (C6F5)Co(H)(CO)2(PMe3)2 (11). Treatment of the mixtures of C6F5H/Co(PMe3)4 with hexachlorobenzene, C6Cl6, resulted in (C6F5)CoCl(PMe3)3 (12) via C–H bond cleavage with the hydrodechlorination product pentachlorobenzene, C6Cl5H, and 1,2,4,5-tetrachlorobenzene, C6Cl4H2. The structures of complexes 1, 2, 6, 7, 8, 11 and 12 were determined by X-ray diffraction.