Coordination chemistry of perhalogenated cyclopentadienes and alkynes. Part 30. New high-yield syntheses of monochloroferrocene and 1,2,3,4,5-pentachloroferrocene. Molecular structures of 1,2-dichloroferrocene and 1,2,3-trichloroferrocene

Lithiation of ferrocene with KOtBu and tBuLi in tetrahydrofuran at −78 °C, followed by treatment with hexachloroethane gives monochloroferrocene 1 in essentially quantitative yield. Lithiation of 1 with 1.2 equiv. lithium tetramethylpiperidide (LiTMP) in THF and chlorination with C2Cl6 gives 1,2-dichloroferrocene 2 contaminated with 1 and ferrocene. Treatment of this mixture with a tenfold excess of LiTMP and C2Cl6 yields after workup 1,2,3,4,5-pentachloroferrocene 3 in 29% yield based on ferrocene. Alternatively, from this mixture of 1 and 2 1,2,3-trichloroferrocene 4 and 1,2,3,4-tetrachloroferrocene 5 can be prepared in a stepwise fashion with yields of 40% and 46%, respectively. The molecular structures of 2 and 4 have been determined by X-ray diffraction and prove the postulated regiochemistry.