Application of the Rotating Photoelectrode to the Detection of an Organotransition-Metal Intermediate. Photoelectrochemical Detection of (η⁵-C₅H₅)Fe(CH₃CN)3⁺

Photolysis of CpFe(η⁶-p-xyl)⁺(p-xyl = p-xylene) in acetonitrile at-40 °C results in an intensely purple solution that contains the CpFe(CH₃CN)₃ion. Allowing this purple solution to warm to room temperature results in the formation of the previously reported photoproducts: ferrocene and Fe(CH₃CN)₆²⁺. The cyclic voltammogram of CpFe(CH₃CN)₃⁺ exhibits one irreversible oxidation E_{p, a}= +0.64 V vs. Ag/AgCl which is cyclopentadienyl ligand centered. Anodic photocurrents due to the CpFe(CH₃CN)₃⁺ cation were detected at room temperature via the photolysis of acetonitrile solutions of CpFe(η⁶-arene)⁺(arene = p-xylene, 9-cinnamylidenefluorene) through a rotating photoelectrode (RPE). A decrease in the photocurrent with increased rate of RPE rotation is observed for arene = 9-cinnamylidenefluorene, but for arene = p-xylene, the photocurrent was independent of rotation rate. These observations are explained in terms of the differences in the molar absorptivity of the two compounds.