Silene

Some years ago we proposed divalent organosilicon compounds as reaction intermediates. More recently, in other studies, it seemed quite probable that the reaction of silacyclopentadienes under suitable Diels- 

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Silene EF stocks contain 2.4, 3.8, and 5.0 parts of diethylene glycol, respectively. 

Pulsation dampeners or intake or diseharge sileneers to be supplied. 

Returning now to the reaetions in the seheme it ean be seen that earbenes and silenes... 

Direct spectroscopic studies and calculations of cyclic silylene-to-silene and germylene-to-germene interconversions 99IZV2027. 

This fundamental discovery dramatically affected the whole chemistry of main-group elements. Subsequently, a series of new compounds with silicon element multiple bonds has been introduced. Within only a few years, stable silenes (silaethenes with a Si = C double bond) [8-11], silaimines Si = N [12-14], and silaphosphenes Si = P [15] were synthesized. As a pacemaker, silicon chemistry has exerted a strong influence on further areas of main-group chemistry a variety of stable molecules with Ge = Ge [16], P = P [17], As = As [18], P = C and P = C [19-22] bonds were subsequently isolated, and systems with cumulated double bonds P = C = P [23-25] are also known today. 

During recent years, fascinating developments have occurred in the area of r 2-silene complexes, which opened up to totally new chemistry. Some of the highlights will be presented in this section. The first investigations of coordination compounds of silenes were carried out by means of matrix isolation techniques at very low temperatures. In particular, photochemical methods proved to be most effective... 

Brook, Adrian, G., and Brook, Michael, A., The Chemistry of Silenes. 

Compound 59a underwent intermolecular reactions characteristic of silenes (Scheme 19). Water added instantly across the Si=C double bond of the I -silaallene is expected to give vinylhydroxysilane 65 in 71% yield, and methanol was added... 

Mori M (2005) Synthesis and Reactivity of Zirconium-Silene Complexes. 10 41-62... 

Unstable compounds with double-bonded silicon and germanium atoms (silenes, silanones, germanones, germathiones)... 

The first successful stabilization of a silene, Me2Si=CH2 [117], in an argon matrix was achieved in experiments on the vacuum pyrolysis of 1,1-dimethylsilacyclobutane [118] (Mal tsev et al., 1976b). The IR spectra of the silene [117] and some of its deuterated analogues have been recorded... 

A first attempt in argon matrices to stabilize silenes H2Si=CH2 and Cl2Si=CH2, which do not have multiatomic substituents at the silicon atom. 

Matrix IR spectra of various silenes are important analytical features and allow detection of these intermediates in very complex reaction mixtures. Thus, the vibrational frequencies of Me2Si=CH2 were used in the study of the pyrolysis mechanism of allyltrimethylsilane [120] (Mal tsev et al., 1983). It was found that two pathways occur simultaneously for this reaction (Scheme 6). On the one hand, thermal destruction of the silane [120] results in formation of propylene and silene [117] (retroene reaction) on the other hand, homolytic cleavage of the Si—C bond leads to the generation of free allyl and trimethylsilyl radicals. While both the silene [117] and allyl radical [115] were stabilized and detected in the argon matrix, the radical SiMc3 was unstable under the pyrolysis conditions and decomposed to form low-molecular products. 

The IR spectrum of another silene homologue, trimethylsilaethene [121], Me2Si=CHMe, was recorded after matrix stabilization of the products of... 

UV photolysis (Chapman et al., 1976 Chedekel et al., 1976) and vacuum pyrolysis (Mal tsev et al., 1980) of trimethylsilyldiazomethane [122]. The silene formation occurred as a result of fast isomerization of the primary reaction product, excited singlet trimethylsilylcarbene [123] (the ground state of this carbene is triplet). When the gas-phase reaction mixture was diluted with inert gas (helium) singlet-triplet conversion took place due to intermolecular collisions and loss of excitation. As a result the final products [124] of formal dimerization of the triplet carbene [123] were obtained. 

Nowadays silenes are well-known intermediates. A number of studies have been carried out to obtain more complex molecules having Si=C double bonds. Thus, an attempt has been made to generate and stabilize in a matrix 1,1-dimethyl-l-silabuta-l,3-diene [125], which can be formed as a primary product of pyrolysis of diallyldimethylsilane [126] (Korolev et al., 1985). However, when thermolysis was carried out at 750-800°C the absorptions of only two stable molecules, propene and 1,1-dimethylsilacyclobut-2-ene [127], were observed in the matrix IR spectra of the reaction products. At temperatures above 800°C both silane [126] and silacyclobutene [127] gave low-molecular hydrocarbons, methane, acetylene, ethylene and methylacetylene. A comparison of relative intensities of the IR... 

A number of relatively stable silenes with bulky substituents are known at present, but stable silanones have not been isolated till now. Their instability, like that of silenes, is caused by a kinetic factor, according to various calculations. Thus, cyclooligomerization of silanones should proceed with zero activation barrier (Kudo and Nagase, 1985). 

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