Alkylsilver compounds

Silver 2//-hexafluoroisobutyrate, (CF3)2CHC02Ag, in pyridine solution at room temperature, or in acetonitrile or dimethylformamide (dmf) at 40-50° C, loses carbon dioxide to form l//-hexafluoroisopropylsilver, (CF3)2CHAg. The alkylsilver compound was characterized spectroscopically without isolation (23). 

Two plausible mechanistic pathways have been proposed for the thermal decomposition of alkylsilver compounds either a radically-mediated cleavage of the carbon-silver bond or a process by which the breaking of the silver-carbon bond and formation of the carbon-carbon bond are concerted. Mechanistic studies by Whitesides and coworkers in which the product ratios obtained for the thermal process... 

The addition of lithium bromide significantly increases the thermal stability of alkylsilver compounds.14 Westmijze and coworkers found that the reaction of n-butylmagnesium bromide, for example, with AgBr2LiBr gave a solution of butylsilver that was stable up to — 10°C, which is in stark contrast to the species obtained from the reaction with silver bromide alone, which decomposes at — 60°C. This marked stabilization of the alkylsilver compounds allowed for the first meaningful use of these reagents in intermolecular reactions. 

A number of simple alkylsilver compounds have been found to react with enynylsulfinates via a 1,5 addition to give substituted butatrienes in excellent yield (Scheme 1.5).15 Interestingly, a different outcome was obtained for alkylcopper compounds, which underwent 1,3 addition to the enynylsulfinates. 

Kauffmann and coworkers have described the reaction of alkylsilver compounds with cyclohexenone (Scheme 1.6).29 It was found that the alkylsilver derivatives reacted preferentially, and in some cases exclusively, in the (3 position. A significant amount of 3-methylcyclohex-2-enol was observed for the reaction of Me2AgMgBr, which has been attributed to the elimination and subsequent reaction of silver(I) hydride. Silver(I) hydride has been observed in the gas-phase fragmentation of other organosilver compounds.30... 

In comparison to the corresponding alkylsilver compounds, the perfluoroalkylsilver derivatives are significantly more stable and are able to participate in chemistry not... 

An anionic active centre can be transformed to a radical centre by peroxy-alkyl halides [244] or by molecular oxygen [245], It appears, however, that the most elegant way so far was found by the British workers [246,247], They make use of the decomposition of unstable alkylsilver compounds generated from alkyllead salts and silver halides. The transformation thus proceeds in two steps. In the first step, a suitable Pb-containing end group is formed on the macroanion... 

The use of organozinc compounds to prepare alkylsilver species was attempted as early as 1859. Success in synthesizing alkylsilver compounds, however, was not achieved until 1941 when Semerano and Riccoboni found that tetraalkyllead could be used as a starting material (equation 1). 

The first, unsuccessful, attempts to prepare alkylsilver compounds were made as early as 1859 by Buckton5a and 1861 by Wanklyn and Carius5b. The reaction of silver chloride with diethylzinc yielded only metallic silver, and a mixture of ethylene, ethane and butane. Due to their low thermal stability alkylsilver compounds were entirely unknown until 1941, when Semerano and Riccoboni6 reported the formation of some alkylsilver complexes by the reaction of silver nitrate with tetraalkyllead in alcoholic solution at low temperatures (equation 1). The yellow to brown precipitates of the formula RAg (R = methyl, ethyl, propyl) were stable at —80 °C for several hours, but upon warming to room temperature rapid decomposition took place with formation of metallic silver and... 

Other transmetallation reactions of silver halides or their complexes with phosphine ligands (e.g. [AgIP(Bu-w)3]) with alkylhthium and alkylmagnesium reagents confirm the fleeting stability of the alkylsilver compounds. In each case the composition of the AgR intermediates has been derived from the analysis of the products formed in their thermal decomposition. So far, representatives of the class of simple alkylsilver complexes have not been isolated in pure form. 

However, some interesting alkylsilver compounds, where the organic group is a di- or tri-substituted anionic (sp3)C ligand, have been reported. 

Alkenylsilver compounds are more thermally stable than alkylsilver compounds. This has allowed the isolation of a few genuine representatives of this class of compounds. 

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