Germyl radicals

The H and 13C CIDNP studies have shown that not only the sulfone 14, but also the sulfmic ester 15, is generated as cage products from the phenyl/p-toluenesulfonyl radical pair during the thermal decomposition of phenylazo aryl sulfone (13)54 (Scheme 2). The cross-termination of arenesulfonyl and triethylgermyl radicals was found to occur exclusively via the formation of germyl sulfinate, ArS(0)0GeEt333. 

The development of sophisticated new experimental techniques during the last decade has made possible the isolation of stable representatives of the free radical species featuring an nnpaired electron on the heavier group 14 elements, that is, silyl, germyl, and stannyl radicals. This great progress in the isolation of the stable radicals opens unprecedented possibilities for their structural characterization in the crystalline form, which in tnrn enables the direct comparison of the fundamental differences and similarities between the solntion and solid state strnctnres of the free radical species. " ... 

The first solution ESR spectra of the transient radicals were observed in 1969 and 1972. Silyl radicals see refs. 121a,c. Germyl radicals see ref 121a. Stannyl radicals ref. 97. 

Acyltriphenylgermanes react photochemically with styrene to form 2 + n2 and 2 + jj2 + jj2 adducts47. The yields of the two adducts 25 and 26 are ca 40% and ca 20%, respectively. The presence of GePh3 in both products indicates that addition takes place before the germyl and acyl radical pair diffuse apart (reaction 31). 

Germyl enol ethers react with perfluoroalkyl iodides under Et3B initiation to give a-pcrfluoroalkyl ketones. The intermediate radical adduct decomposes readily via /1-elimination and provides the a-perfluoroalkyl ketone and a trialkylgermanyl radical as a chain carrier (Scheme 12) [32]. 

As with silicon hydrides, the reaction of atoms or radicals with germanium hydrides is the key step for the majority of reactions forming germyl radicals. However, kinetic data for the reactions of organic radicals with germanium hydrides in solution are limited to carbon- and oxygen-centered radicals. 

Transient digermene 86 was postulated as possible intermediate in the reaction of 1,2-dichlorodigermacyclobutane 87 with Mg/MgBr2 in the presence of an alkene, leading to the bicyclic compound 8878 [Eq. (17)]. However, an electron transfer reaction with the intermediate formation of a germyl radical is also a possibility.78 Similarly, transient 1,2-digermacyclobu-... 

A range of addition reactions of (TMS)3GeH with alkynes, alkenes, ketones, azines, and quinones has been studied using EPR. In addition, synthetic studies of hydrogermylation of alkynes have shown that the reaction proceeds regio- and stereo-selectively, whereas reactions with alkenes do not take place (presumably owing to the reversibility of the germyl radical addition) (Scheme 29). 

Germanium and silicon hydrides should be even more selective toward alkoxyl radicals relative to carbon radicals. Indeed, while silicon hydrides react rapidly with alkoxyl radicals, reactions with carbon radicals are too slow to propagate chains. The rapid addition of silyl and germyl radicals to C—O bonds is a possible complicating reaction. 

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