Rhodium porphyrins electrochemical oxidation

The electrooxidation of Rh(III) porphyrins is relatively straightforward and consists for the most part of two successive one-electron transfers, both of which involve the porphyrin 7r-ring system. An assignment of the electron-transfer site has often been made on the basis of ESR and/or UV-visible spectra of the singly oxidized products. Other types of rhodium porphyrins, which have been electrochemically examined include [(TPP)Rh(L)2] Cl and (TPP)Rh(L)Cl, where L = NMe2, both of which were proposed to form a dimeric Rh(II) species after an initial one-electron... 

An alternative route used in organometallic chemistry is the reaction of low valent organometallic derivatives with alkyl (aryl) halides. The two electron oxidative addition of alkyl (aryl) halides or cyclopropane derivatives to metalloporphyrins such as [M (Por)] leads to metal alkyl (aryl) o-bonded porphyrins of cobalt " rhodium and iridium ° (Scheme 2). Substitution of aryl and vinyl halides by electrochemically generated iron(I) porphyrins also leads to o-bonded Fe complexes ... 

Di(porphyrinato)rhodium(II) [Rh(Por)]2 described by OgoshP Wayland , Coil-man, and Kadish are the only known metalloporphyrin dimers containing one single metal-metal bond. Oxidative cleavage (Eq. 24) or thermal homolytic cleavage (Eq. 25) of the Rh-H bond of Rh(OEP)H can produce the [Rh(OEP)]2 dimer The Rh" dimer may also be formed by electrochemical reduction of some Rh" porphyrin complexes (See Sect. D III 4). 

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