Germanium porphyrins potentials

TABLE 12. Reduction potentials of porphyrin-iron carbonyl complexes of germanium and tin in CH2CI2 with TBA(PF<5), 0.1 M, on Au electrodes vs SCEa... 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

The lack of adequate experimental data on chelates of germanium, boron, titanium, and vanadium prevents a similar comparison for these elements however, their high ionic potentials do indicate that they should form stable chelates. Vanadium does occur naturally in the very stable vanadium porphyrin complex. For similar reasons, molybdenum and tin are not discussed further. 

The oxidation of M(Por)Fe(CO)4 is irreversible in the sense that there are no coupled peaks associated with reduction of [M(Por)Fe(CO)4]. Similar voltammograms were obtained for the six M(Por)Fe(CO)4 complexes and peak potentials for the single irreversible oxidation at an Au electrode are listed in Table 19. As expected, the OEP complexes are easier to oxidize than the TpTP and TmTP complexes. Also, with a given porphyrin ligand the oxidation is easier for the Ge complex than for the Sn complex. This is due to the higher electronegativity of the germanium ion. 

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