Sono-electrochemistry: the oxidation of bis(cyclopentadienyl)molybdenum dichloride

Abstract

The oxidation of [Mo(cp)₂Cl₂](cp =η-C₅H₅) in acetonitrile solution at platinum electrodes has been studied. In the absence of ultrasound a simple one-electron oxidation with a half-wave potential of +0.5V (vs. saturated calomel electrode) is observed together with a much smaller wave with a half-wave potential of +1.05 V. In the presence of ultrasound the first wave involves the passage of greater than one electron per molecule of electroactive species and the second wave disappears. The mechanism in equations (i)–(iii) is proposed to explain the observations, where the chemical (c.)(e. = electrochemical) and the disp. (disproportionation) steps are promoted by ultrasound.

e. step [Mo(cp)₂Cl₂]– e^–→[Mo(cp)₂Cl₂]⁺(i), c. step [Mo(cp)₂Cl₂]⁺+ MeCN → Cl·+[Mo(cp)₂Cl(MeCN)]⁺(ii), disp. step [Mo(cp)₂Cl₂]⁺+[Mo(cp)₂Cl(MeCN)]⁺→[Mo(cp)₂Cl(MeCN)]²⁺+[Mo(cp)₂Cl₂](iii)