The formation and reactions of (η 5-carboxycyclopentadienyl)dicarbonylcobalt

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A reaction between sodium cyclopentadienide and dimethyl carbonate in THF solution produces sodium carbomethoxycyclopentadienide in high yield. The analogous carbethoxy derivative can also be readily prepared starting with diethyl carbonate. Carbomethoxycyclopentadienylthallium has been prepared by cracking carbomethoxycyclopentadiene dimer and passing the unstable monomer into an aqueous mixture of thallium(I) chloride and potassium hydroxide. Reactions of these reagents with mixtures of dicobalt octacarbonyl and iodine in THF solution afford moderate yields of the respective products (η 5-carbomethoxycyclopentadienyl)dicarbonylcobalt and (η 5-carbethoxycyclopentadienyl)dicarbonylcobalt. (η 5-Carboxycyclopentadienyl)dicarbonylcobalt is obtained in 67–74% yield by treatment of either ester with potassium hydroxide in aqueous ethanol followed by acidification. A reaction between this acid and oxalyl chloride in benzene solution produces (η 5-chloroformylcyclopentadienyl)dicarbonylcobalt in 67% yield, and the latter reacts readily with ammonia and with aniline to form the respective amide and anilide derivatives. The acid chloride also reacts with ferrocene and aluminum chloride under Friedel-Crafts conditions to afford the bimetallic product (η 5-ferrocenoylcyclopentadienyl)dicarbonylcobalt. The IR and 1H NMR spectra of these new functionally-substituted derivatives of (η 5-cyclopentadienyl)dicarbonylcobalt are discussed.