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

Abstract

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.