Stannyls decomposition

On the other hand, the corresponding tin precursor (63) undergoes smooth cycloaddition with a wide variety of aldehydes to produce the desired methylene-tetrahydrofnran in good yields [32, 33]. Thus prenylaldehyde reacts with (63) to give cleanly the cycloadduct (64), whereas the reaction with the silyl precursor (1) yields only decomposition products (Scheme 2.20) [31]. This smooth cycloaddition is attributed to the improved reactivity of the stannyl ether (65) towards the 7t-allyl ligand. Although the reactions of (63) with aldehydes are quite robust, the use of a tin reagent as precursor for TMM presents drawbacks such as cost, stability, toxicity, and difficult purification of products. 

In comparison to other vinylic compounds , the vinyl proton in 1-alkenyl carbamates, deprotonation has a very high kinetic acidity . After protection of the 4-hydroxy group in the homoaldol products by silylation, deprotonation (w-BuLi, TMEDA, diethyl ether or THF) of enol carbamate 384 is complete at —78 °C (equation 103), and the resulting vinyUithium 385 can be kept at this temperature without decomposition for several hours. Stannylation , silylation , methoxycarbonylation (with methyl chloroformate) ... 

Chemical properties of silyl-, germyl-, and stannyl triazenes have not been studied very systematically so far. Most of the known compounds are air stable and sensitive to hydrolysis. Thermostability of triazenes of type 18a (R = organyl) is strikingly high, and these can often be heated above 150°C without decomposition. On the other hand, the known triazenes of type 18c (R = aryl) decompose slowly at room temperature. Triazenes of type 18b, 18d, and 18e are even more thermolabile and can be prepared only if triazene substituents are quite bulky [e.g., f-Bu3 SiN3H(Sir-Bu3) is stable above 150°C]. For more details of triazene thermolysis, which occurs mainly with N2 elimination, see Section II,C. 

Potassium trialkyl- and triarylstannates are air and moisture sensitive. They are thermally instable, leading to R3Sn—SnR3, which is known to catalyse the decomposition of stannyl anions. They must be handled and stored in an inert atmosphere (nitrogen or argon) by normal vacuum line techniques. For a prolonged storage, it is desirable to store the substance at low temperatures (below -40°). 

Both the catalysed and uncatalysed decompositions can be stopped by a radical inhibitor such as 2,6-di-t-butylphenol, but after a period the inhibitor is consumed and the decomposition recommences. If an alkyl halide or alkyne is added to the system, the evolution of hydrogen is quenched, and the substrates show the reactions which are characteristic of stannyl radicals. 

The photolytic decomposition of benzyltin hydrides is a promising source of stannylenes which has not yet been exploited. In THF at 293 K, the benzyl and stannyl radicals which are formed interact to give toluene quantitatively and (Me2Sn) , presumably via monomeric Me2Sn , but in a THF matrix at 4 K, the radicals recombine to give back the hydride.9... 

The reaction of stannylated dicyclopentadiene (111) with methyllithium gave dicyclopentadiene (113) and cyclopentadienyllithium (114) even at -78 C. ° The intermediate can be trapped by addition of iron(ll) chloride to give intermediate (115), which then cleaves off cyclopentadiene ftom one of the two dicyclopentadiene ligands in a rDA process to give (116) as the isolated product. It therefore appears that the rDA decomposition is only partially blocked by trapping with iron(II) chloride. 

Stannylated azines have been widely used for cross-coupling. Al-Oxides of tri(n-butyl)stannylated pyridine, quinoline, and isoquinoline and tti(n-butyl)stannylated N-methiodides of pyridine and quinoline have been coupled with heteroaryl halides (Scheme 61). The use of tosylate as a counterion for the quatemized salts 149 and 150 minimized decomposition of the stannane whereas iodide anion promotes destannyla-tion.f ... 

Complexes of internal alkynes of general formula Pd(7] -alkyne)(PR3)2 or Pd( 7 -alkyne)(diphos) have been reported, often prepared in the course of palladium-catalyzed reactions and other processes. Thus, most of them have been synthesized by decomposition of Pd(ii) complexes in the presence of the alkyne as shown in Equations (20) and (21). Insertion into a Pd-E bond and reductive elimination generates the silylated or stannylated alkene and Pd(0), which is trapped by the alkyne in excess. 

Stannane is toxic and is intermediate between silane and germane in its chemical properties it is unattacked by dilute acids and alkalis, but is decomposed by concentrated acid or alkali. It is a powerful reducing agent, and is rapidly decomposed by solutions of transitional metal salts. Stannane and hydrogen chloride evolve hydrogen to form stannyl chloride, HsSnCl, which is very unstable, undergoing noticeable decomposition, even at —70°. (Contrast H3GeCl stable at 20°C and HsSiCl stable at 200°C.)... 

Trimethylgermanyl perrhenate is also a colorless crystalline solid, mp 108°C, sublimes at 115—125°C/1.5 Torr (25). Trimethyl-stannyl perrhenate is a colorless crystalline powder, mp 213°C (decomposition) (28). Their preparation follows similar protocols. 

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