Iridium complexes electrochemical oxidation

Other oxidizing agents which can convert Cu(II)G4 to Cu(III)G4 include S2082- and IrCle2". The IrC 2" reaction is quantitative under suitable conditions and was used to help prove that Cu(III)-peptide complexes could be formed and characterized in aqueous solutions (9). Electrochemical oxidation is more efficient and avoids the need to remove the iridium complexes. The Cu(III)-peptide complexes have now been characterized by ... 

The irreversible electrochemical oxidation of [Ir(X)(CO)(PR3)2] (X = Cl, Br, I PR3 = PPh3, PPh2Et, PPhEt2, PEt3) on rotating Pt electrodes in Bu4NC104/CH2Cl2 reportedly proceeds at diffusion-controlled rates. In the redox addition process, atom transferability predominates over complex redox properties. Evidence indicates that the insoluble product of the one-electron oxidation of [Ir(X)(CO)(PR3)2] is a dimeric iridium(II) complex with an iridium-iridium bond.96... 

The same electrochemical oxidation, carried out on the iridium complexes [Ir2(CO)4(PZ )](R4N) (R = Bu or Pr), gave dark conducting materials that analyzed as [Ir2(CO)4(PZ )](R4N)0 5 (193). Conductivity measurements for the latter species gave values that are 1000 times higher than the values found for the most conducting unoxidized precursor (the Me4N+ salt of the iridium complex). 

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 ... 

Once electrochemically or chemically activated, this complex undergoes a stepwise loss of four electrons and four protons, producing an intermediate reactive species able to oxidizes water. Unfortunately, the blue dimer loses its catalytic efficiency after few cycles, due to the degradation of the organic ligands. However, its discovery paved the way to the development of a variety of molecular water oxidation catalysts, most of them still based on ruthenium centers, but also on iridium, as well as on earth abundant and cheap metals, such as manganese, iron, and cobalt. " ... 

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