Silicon compounds double bonded

Silenes with a wide range of structures have been synthesized over the years, from the simplest possible compound, H2Si=CH2, which has a transient existence, to species that contain four complex groups attached to the ends of the silicon-carbon double bond, e.g., (Me3Si)MesSi=C... 

Silicon-Oxygen Double Bond Compounds (Silanones)... 

In the previous reviews,1 la,d f syntheses of many examples of transient silicon-oxygen double bond compounds such as MeHSi=0, Me2Si=0, H2Si=0 (2), (H0)HSi=0 (silanoic acid), and (H0)2Si=0 (silicic acid) have been described, and they are reportedly isolated as stable species in the low temperature matrices. However, the stabilization of this extremely reactive double bond species is very difficult, and no stable example of silanone (RR/Si=0) has been isolated until now even by the methods of thermodynamic or kinetic stabilization. 

On the other hand, Driess et al. have succeeded in the synthesis and isolation of a stable silicon-arsenic double bond compound (13), the first stable arsasi-lene (arsanilidenesilane),19 and they found that the arsasilene 13 undergoes ready... 

Silicon-Selenium and Silicon-Tellurium Double Bond Compounds... 

Compounds containing the silicon-carbon double bond have been prepared (Scheme 85) and derivatives of silabenzene and germabenzene have been characterized (Section 1.20.13). Methyllithium and n -butyllithium will alkylate the silole (126) showing the ring silicon to be the site for nucleophilic attack. The reaction is quantitative and no silole anion (127) was detected (Scheme 205) (8lJOM(2l8)C2l). 

At the same time, advances in the field of organosilicon chemistry have also been incredibly large2. Characterization of unstable species such as divalent silylenes or compounds with silicon-containing double bonds were successfully achieved for many compounds. Advances in the field of siloxanes and other polymeric materials are also remarkable. 

Formation from silenes and silicon-heteroatom double-bond compounds... 

Among the silicon-chalcogen double-bond compounds, the silicon-sulfur doubly-bonded compounds (silanethiones) are considered to be easier to synthesize, since it has been predicted by the theoretical calculations that a silicon-sulfur double bond is thermodynamically and kinetically more stable than a silicon-oxygen double bond (silanone)13,14. According to the calculations, the lower polarization of Si=S compared to Si=0 should lead to a lower reactivity of Si=S. In addition, H2Si=S (1) is calculated to be by 8.9 kcal mol-1 more stable than its divalent isomer, H(HS)Si , whereas H2Si=0 (2) is by 2.4 kcal mol-1 less stable than H(HO)Si . 

As mentioned in this chapter, in recent years much progress has been made in the chemistry of silicon-chalcogen multiple bonds. For silicon-sulfur doubly-bonded compounds, we have now several isolated examples, both kinetically stabilized and thermodynamically stabilized. Furthermore, there have been reports of the synthesis and characterization of stable compounds with silicon-nitrogen double bonds (i.e. silanimines or iminosilanes) as well as their heavier group 15 element analogues such as phosphasilenes and arsasilenes. 

In this case, no product arising from the reaction of the silicon-carbon double-bonded intermediate with methanol can be observed at all. However, on prolonged irradiation of the solution two products, 1,1-dimethyl-2,3-benzo-5-trimethylsilyl-l-silacycIopentene (48) and 1-methoxy-dimethylsilyl-l-trimethylsilyl-2-phenylethane are obtained in 17 and 7% yield, in addition to the (Z)- and (E)-isomers (15 and 12% yield). The formation of the latter compound can best be understood by the transient formation of a silacyclopropane followed by reaction with methanol (98). The mechanism for the production of 48 in the prolonged irradiation of PhCH=CHSiMe2SiMe3 is not fully understood but is tentatively given in Scheme 16. 

As mentioned before, carbon and silicon mostly differ in their ability to from multiple p,-p, bonds E=Y with suitable partners (E = C, Si Y = element of group 14 to 16 ). While the p orbital overlap in compounds >C=Y is sufficient to yield stable multiple bonded species, this overlap is strongly reduced in the case of silicon (classical double bond rule of Pitzer and Mulliken). Consequently, under comparable conditions the equivalents of many unsaturated monomeric compounds of carbon, such as H2C=CH2, R2C=0 or CO2 are silicon single bonded polymeric products, e g. polysilanes (-H2Si-SiH2-)n, silicones (-R2Si-0-) and silicon dioxide (Si02)n... 

No silanones 71, i.e. compounds with silicon-oxygen double bonds, have been isolated yet either neat or even in dilute solution, but matrix-isolation techniques have recently allowed their direct observation. Consequently, most of our experimental knowledge of silanone properties still originates in studies on transients19. Theory, being a primary source of reliable fundamental information, is therefore extremely valuable to the study of these species. 

The simplest molecules with silicon-oxygen double bonds are SiO and Si02146,214. The calculated bond lengths are 1.494 A in SiO214a (experimental 1.51 A214b) and 1.484 A in Si02 which is calculated to be linear2143. Similar results were reported for these compounds in Reference 146. 

The first compelling evidence that a silene (a compound containing a silicon-carbon double bond) could exist was provided by Gusel nikov and Flowers in 1967 from results of the thermolysis of dimethylsilacyclobutane26 (equation 16). Thus, it is not surprising that... 

Photolysis of cyclic silicon-selenium ring systems (analogs of D3, (Me2SiO)3) apparently generated compounds with silicon-selenium double bonds these were trapped with hexamethylcyclotrisiloxane to yield the two-atom insertion products158 (equation 100). 

VIII. THE SILICON-PHOSPHORUS DOUBLE BOND, SILICON-PHOSPHORUS ) COMPOUNDS AND SILYL-PHOSPHORUS RADICALS. 1383... 

Notable advances in the last decade are isolation of kinetically stabilized silicon-containing double-bonded species. As we have seen already, a variety of sterically bulky substituents have been utilized to stabilize silicon-centered reactive intermediates. This kinetic stabilization is the key issue also to isolate silicon double-bonded species. For example, the synthesis of isolable silicon analog of benzene and other aromatic compounds has been a target for a long time. One example is shown below for the generation of transient silabenezene. ... 

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