Oxidatively induced M–C bond cleavage reactions of Cp*Ir(Me2SO)Me2 and Cp*Rh(Me2SO)Me2 (Cp* = η5-C5Me5)

Abstract

Electrochemical and chemical oxidation of Cp*Ir(Me₂SO)Me₂ (1; Cp* = η⁵-C₅Me₅) in Me₂SO lead to the formation of methane and traces of ethene (ratio ca. 20 ∶ 1) as well as Cp*Ir(Me₂SO)₂Me⁺. Labeling studies indicate that three of the methane hydrogen atoms arise from the iridium-bonded methyl, while the fourth appears to arise from adventitious water. By contrast, oxidation of the rhodium analog Cp*Rh(Me₂SO)Me₂ gave only ethane and Cp*Rh(Me₂SO)₂Me⁺. Quantitative derivative cyclic voltammetry (DCV) showed that the disappearance of electrode-generated 1˙⁺ follows a rate law that is second order with respect to Ir. The Rh analog 6˙⁺ reacted at rates too great to be measured by DCV under these conditions. Possible mechanisms for these reactions are discussed, and particular attention is paid to the reactivity differences between Rh and Ir. Convenient new syntheses of Cp*Ir(Me₂SO)Me₂ and Cp*Rh(Me₂SO)Me₂, as well as X-ray structure determinations of these compounds and of Cp*Ir(Me₂SO)₂Me⁺, are reported.