Synthesis of ferrocenyl-1,2-diketones and related compounds: Crystal and molecular structures of 1,2-diferrocenylethanedione and 1-ferrocenyl-2-(4-biphenylyl) ethanedione

Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C₅H₅)Fe(C₅H₄)] can be prepared by oxidation of acylferrocenes FcCOCH₂R or, more efficiently, by oxidation of the isomeric ketones FcCH₂COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH₂PPh₃)⁺I^- via the acylated salts [FcCH(COR)PPh₃]⁺I^-. The haloacylferocenes FcCOCCl_xH_3-x (x = 1, 2, 3, of which the x = 2 example is synthetically equivalent to a diketone) are synthesized by Friedel-Crafts acylation of ferrocene using CCl_xH_3-xCOCl/AlCl₃, but the reaction proceeds via two parallel pathways, one giving the normal acyl derivatives FcCOCCl_xH_3-x and the other giving the reduced products FcCOCCl_x-1H_4-x. Two diketones FcCOCOFc 3b and FcCOCOC₆H₄Ph 3c have been structurally characterised by single-crystal X-ray diffraction.