Germanium-carbon bonds

That the carbon—metal or carbon—metalloid bonds are preserved at all in these reactions is quite surprising. With tetramethylgermanes, for example, this free radical reaction must be a 24 step process. The success in preserving carbon-germanium bonds must arise from very rapid molecular vibrational, rotational, and translational relaxation processes occurring on the cryogenically cooled surfaces such that the energy from the extremely exothermic reaction is smoothly dissipated. 

Lewis acid-mediated cycloaddition reactions of allylgermane have been reported. Thus, [3-1-2] cycloaddition of a-keto ester to allylgermane occurred under the influence of tin(IV) chloride to afford germyl-substituted tetrahydrofurans stereoselectively (Scheme 11.13) [26]. Because the carbon-germanium bond is weaker than the carbon-silicon bond, yields of the cycloadducts were lower than those of the corresponding silicon analog ]27]. 

The existence of a germanium-carbon pjr-pjr double bond in the intermediate complex is likely. The intermediate was not isolated as such, but as its dimer. Compounds containing a carbon-germanium double bond were prepared by Satg6 and coworkers59, like the fluorenylidenedimethylgermanium, where stabilization arises from change transfer in the aromatic system. 

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. 

Table II. Half-wave and Peak Potentials for Metal-Carbon c-bonded Germanium and...

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. 

The germabenzene species 15 reacts in two different fashions with a variety of substrates to give cylcoaddition products (Scheme 7).30 With MesCNO and 2,3-dimethylbutadiene, 15 behaves similarly to a compound with a single Ge-C double bond, whereas in reactions with styrene and phenylacetylene, 15 behaves as a 1-germabuta-l,3-diene to give Diels-Alder-type adducts. The germanium-carbon doubly bonded species 23 reacts with nitriles in several different ways, including as a 1,2-dipolar species with Bu CN, as a 1,4-dipolar species with PhCN, and as a base with various /3-functionalized nitriles (Scheme 8). 

Organogermanes R, GeX (X = H, MeO, Cl, Br) do not react with antimony(V) fluoride/carbon, but allyl —germanium bond breaking occurs under mild conditions (24 h at 25 C in diethyl ether), and in high yields (80-85%), leading to the corresponding fluorogermanes.101... 

Germanium-carbon multiple bonds, formation, 3, 709 Germanium-chalcogen bonds, reactivity, 3, 745 Germanium complexes with alkali metal bonds, 3, 748 with Isis // -arcnc chromium heteroatoms, 5, 340 with chromium carbonyls, 5, 208 coupling reactions, 3, 711 with CpMoCO, 5, 463... 

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