Germanium—cobalt bonds

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. 

In summary, the four chemical systems described in this paper demonstrate the versatility and selectivity of electrochemical methods for synthesis and characterization of metal-carbon a-bonded metalloporphyrins. The described rhodium and cobalt systems demonstrate significant differences with respect to their formation, stability and to some extend, reactivity of the low valent species. On the other hand, properties of the electroche-mically generated mono-alkyl or mono-aryl germanium and silicon systems are similar to each other. 

Silicon and germanium hydrides react with cobalt, manganese and rhenium carbonyls affording complexes having a silicon (or germanium)-metal bond. These reactions, described previously for inactive compounds have been used in the synthesis of optically active silyl and germyl-transition metals ... 

AICI3 and SnCl4 cleave the germanium-cobalt bond. In the case of SnCl, the trichlorostannyl derivative can be isolated. 

Another reactivity pattern of the carbene analogues 1 and 2 with cyclopenta-dienyl metal carbonyls was established with Co(Cp)(CO)2. As can be concluded from Eq. (8), carbon monoxide is smoothly eliminated and the cobalt atom in Co(Cp)(CO) bonds to a germanium or tin atom. 

The above method has been used for the synthesis of metal alkyl (or aryl) o-bonded porphyrins of iron , cobalt rhodium titanium iridium gallium indium thallium, silicon germanium " " and tin ... 

Electronic absorption spectra for o-bonded complexes of cobalt rhodium , thal-lium silicon germanium °), and tin are characteristic of regular porphyrins. 

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