Sensitizers stannylene

Frequencies assigned to the fundamental vibrations of the triatomic germylenes, stannylenes and plumbylenes are collected in Table 7 together with corresponding data on triatomic silylenes for comparison. The vibrational frequencies are sensitive to the environment of the molecule. Therefore, the most precise frequency values measured under each type of condition used (in the gas phase and in different low-temperature inert matrices) by different spectroscopic methods are shown in the table for each of the CAs. Nonfundamental frequencies of triatomic and observed frequencies of polyatomic germylenes, stannylenes and plumbylenes are listed in the text. 

Very few reactions have been reported for organostannylene and plum-bylene complexes. The complexes are generally air sensitive, but less so than the parent divalent stannylenes or plumbylenes. Triphenylphosphine fails to displace the terminal stannylene in the complex shown in Eq. (54). 

A) in hydrocarbon solutions, NMR spectra indicated a monomer dimer equilibrium with the energy of dissociation = 12.8kcalmol (equation 109). From an electron diffraction study, [(Mes Si)2CH]2 Sn in the gas phase has a V-shaped monomeric stmcture, with C Sn = 97(2)°. The related stannylene (77) is monomeric in the solid state, with the shortest Sn- - -Sn distance of 7.4 A. The dark-red air- and moistnre-sensitive componnd (77) exists in a dimer monomer eqnUibrium in solntion. Two crystal modifications of [2,4,6-(F3C)3C6H2]2Sn have been reported one is monomeric and the other is a weakly associated dimer with a Sn-Sn distance of 3.639(1) A. There are Sn F interactions (eqna-tion 110). 

Stannylenes have also been prepared with tt-ligands related to the cyclopentadienyl gronp these inclnde 1,3-diborolenyl, 1,2-azaborolenyl, and diazastannocene species, e g. (94)-(96). Other 7r-complexes of Sn which have been obtained inclnde carboranyl derivatives, e.g. (97), and the very air-sensitive arene derivatives [( -R2C6H4)SnCl AlCl4] (R = H or Me) and [(j7 -C6H6)Sn(AlCl4)2] PhH (98). ... 

Stannyl radicals R3Sn can be identified by ESR spectroscopy, but there is no equivalent sensitive and selective technique for observing the transient simple (singlet) stannylenes, R2Sn . Their formation usually has to be inferred from their reactions, and it is not always unambiguous as to whether monomeric R2Sn has existed as a kinetically free entity the same problem of course occurs with the carbenes R2C . 

The organostannylenes are yellow to red solids which are sensitive to air and to moisture, and bis[2,4,6-tris(trifluoromethyl)phenyl]stannylene (21-10) has been shown to react with triplet oxygen to give the cyclic tristannoxane.56... 

Alkylation requires more vigorous conditions. These reactions were originally performed on the stannylene acetal with the alkylating reagent in DMF at elevated temperatures, 45 °C for methyl iodide or 100 °C for benzyl bromide. It was then discovered that the presence of added nucleophiles markedly accelerates the reactions so that alkylation of dibutylstannylene acetals in benzene, which were very slow at reflux with benzyl bromide alone, occur at a reasonable speed at reflux in the presence of added tetra-butylammonium halides. Many other nucleophiles are also effective, including A-methylimidazole and cesium fluoride. Cesium fluoride has been used mainly in DMF and the combination of an added nucleophile with a polar aprotic solvent allows benzylation with benzyl bromide to occur efficiently at room temperature. If the stannylene acetal is a 1,2-D-stannylene acetal derivative of a carbohydrate and the electrophile is a carbohydrate-derived triflate, oligosaccharide synthesis can be achieved. More recently, both formation of the stannylene acetal and alkylation in the presence of tetrabutylammonium iodide have been performed under microwave irradiation excellent yields have been obtained in <0.5 h and the short reaction times allow the use of more sensitive reagents (Scheme 5.1.10). ... 

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