Structural and synthetic insights into sodium‐mediated‐ferration of fluoroarenes

Exploiting chemical cooperation between Na and Fe(II) within the bimetallic base [dioxane ⋅ NaFe(HMDS) ₃] (I), (dioxane=1,4-dioxane, HMDS=N(SiMe ₃) ₂) the selective ferration of fluorobenzene, 1-fluoronaphthalene, 1,4-difluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1-bromo-3,5-difluorobenzene, 3-fluoroanisole and 3,5-difluoroanisole has been realized, affording sodium ferrates [dioxane ⋅ Na(HMDS)(2-F-C ₆H ₄)Fe(HMDS)] _∞ (1), [dioxane ⋅ Na(HMDS)(2-F-C ₁₀H ₆)Fe(HMDS)] _∞ (2), [dioxane ⋅ {Na(HMDS)(2,5-F ₂-C ₆H ₃)Fe(HMDS)} ₂] _∞ (3), [dioxane ⋅ {Na(HMDS)(2,3,6-F ₃-C ₆H ₂)Fe(HMDS)} ₂] _∞ (4), [(dioxane) _1.5 ⋅ Na(HMDS)(2,4,6-F ₃-C ₆H ₂)Fe(HMDS)] ₂ (5), [(dioxane) _1.5 ⋅ {Na(HMDS)(4-Br-2,6-F ₂-C ₆H ₂)Fe(HMDS) ₂] (6), [{(dioxane) ₂ ⋅ Na ₂Fe(HMDS) ₂(2-methoxy-6-F-C ₆H ₃)} ⁺{Fe(HMDS) ₃} ⁻] _∞ (7) and [dioxane ⋅ {Na(HMDS)(4-methoxy-2,6-F ₂-C ₆H ₂)Fe(HMDS)} ₂] _∞ (8), respectively. Reactions take place under mild reaction conditions, with excellent control of the selectivity and no competing C−F bond activation is observed. Showcasing complex polymeric arrangements in some cases, the structures of compounds 1–8 have been determined by X-ray crystallographic studies. In all cases, the Fe(II) centers occupy the position in the relevant fluoroarene that was previously filled by a proton, confirming that these metallations are actually ferration processes whereas the Na atoms prefer to form Na⋅⋅⋅F dative interactions. Compounds 1–8 are thermally stable and do not undergo benzyne formation (through NaF elimination) and their formation contrasts with the inertness of Fe(HMDS) ₂ which fails to act as a base to metallate fluoroarenes.