Electrochemical activation of acyl ligands in organometals. ESR studies of acetyl- and benzoyliron(III) complexes

The anodic oxidation of two series of acyliron(II) complexes, the neutral CpFe(CO)₂COR(I) and the anionic CpFe(CO)(CN)COR^? (II) where R = CH₃ and C₆H₅, are examined in acetonitrile solutions. The cyclic voltammograms of II are reversible, whereas those of I are irreversible even at sweep rates as high as 10 V s^?1. The neutral CpFe^III (CO)(CN)COCH₃ radical is sufficiently stable at 20°C to examine its ESR spectrum, as well as the kinetics and mechanism of thermal decomposition to afford acetone in high yields. However the cation-radical CpFe^III(CO)₂COCH⁺₃ from I is too reactive to observe directly, and it undergoes rapid solvolytic substitution in the presence of ethanol to afford ethyl acetate. The distinction between neutral and cationic acyliron(III) radicals is discussed in the context of acyl activation of organometals by electrochemical methods.