Electrocatalytic oxidation of styrene by a high valent ruthenium porphyrin cation radical

A sterically-hindered carbonylruthenium(II) porphyrin RuII(CO)(TMP) (where TMP=meso-tetramesitylporphyrinato dianion) has been synthesized. Chemical oxidation of RuII(CO)(TMP) by m-chloroperbenzoic acid (m-CPBA) gives the dioxoruthenium(VI) porphyrin (RuVI(O)2TMP). Cyclic voltammograms show that RuVI(O)2TMP is reversibly oxidized at E1/2=+1.24 V in CH2Cl2. Thin-layer absorption spectra for oxidation of RuVI(O)2TMP at +1.32 V indicates that the product is a porphyrin cation radical (RuVI(O)2TMP+). Electrogenerated RuVI(O)2TMP+ reacts selectively with styrene to give phenylacetaldehyde (96%) and benzaldehyde (4%). We report the first case of styrene oxidation by high valent ruthenium porphyrin under electrochemical conditions. An electrocatalytic oxidation reaction scheme is proposed.