Thermal properties and reactions towards nucleophiles of an iron complex displaying an acetyl and a pyruvoyl ligands

Thermal evolution at 4 °C of the structurally characterized cis(CO)₄FeC(O)C(O)CH₃]C(O)CH₃] (1(2)) gives rise to the cis(CO)₄FeC(O)CH₃]₂ (1(3)) which, probably owing to synthetic problems, has never been described in the literature. By reaction with anionic nucleophiles (Nu⁻), 1(2) affords anionic trifunctionalized metallalactones {(CO)₃FeC(O)CH₃]C(O)C(CH₃)(Nu)OC⁷(O);(Fe-C⁷)]}⁻ (3) formed by addition of the nucleophile reagent on the β carbon of the pyruvoyl moiety followed by the cyclization of this ligand on a terminal carbonyl of the complex. Anions 3 are characterized by ¹H and ¹³C NMR and by X-ray diffraction for the complex with Nu = C(H)(CO₂C₂H₅)₂. Complexes 3 are also prepared by reaction of CH₃Li with the neutral metallalactones (CO)₄FeC(O)C(CH₃)(Nu)OC⁷(O);Fe-⁷C] (2). The results of this study shed light on the reaction of cyclization of a pyruvoyl ligand as they clearly show that the presence of a second ligand (for example CO₂R) with a labile OR group is not required to perform the formation of the metallalactone ring and then that the observed reaction has no connection with organic chain-ring transformations.