Silanones structure

FIGURE 16. Schematic illustrations of (a) inserted and (b) silanone structures on Si(100)-2 x 1 surface... 

A recent study of the photolysis of simple diazoalkanes 314 or diazirines 315, compounds known to lead to the formation of silenes under inert conditions, led, in oxygen-doped argon matrices, via the silene 316 to the siladioxirane 317. While previously postulated as an intermediate in silene oxidations, this is important experimental evidence for this intermediate. Continued photolysis of the system led to a compound identified as the silanone-formaldehyde complex 318, which on further irradiation led to the silanol-aldehyde 319. The latter compound itself underwent further photochemical oxidation leading to the silanediol 320160. The reactions are summarized in Scheme 58. Detailed infrared studies, including the use of isotopes, and calculations, were used to establish the structures of the compounds. 

Fig. 7.4. The experimental evidence of the formation of the complexes comprising silanone group and CO molecule, obtained by the optical and IR methods. The calculated structure for model of this complex is given in the same figure.

All this is equally related to the spatial structure of the Sia(-0-Si =)2 groups that serve as building blocks for the silanone groups. 

The silanone groups (=Si-0)2Si = O were experimentally detected on the surface of mechanically activated silica in Ref. [52], Most likely, this was the first experimental evidence for the stabilization of silanone groups in the silica structure. Then the method for their preparation from SC on the surface of thermo chemically activated silica (RSi) was developed [18,79,80] (see reactions 8-10 in Table 7.3). 

Silanone groups easily undergo the addition to unsaturated molecules (reactions 6-9) to form the corresponding cyclic structures [86,87], According to the results of quantum-chemical calculations, in these reactions, comparatively stable ( 10kcal/mol) intermolecular complexes are formed, which then yield the final products. The silicon atom of the silanone group mainly participates in complex formation. 

High-temperature heating of the hydrated silicon samples is accompanied by the decomposition of hydroxyl groups and formation of the reactive cyclic structures (=Si-0-)2Si < 02> Si(-0-Si=)2. Their concentration is equal to 10l3cm-2 [4,72]. These groups can also form through the combination (condensation) of two silanone groups ... 

Keywords Silanols / Structure / Synthesis / Silanone / Steric Hindrance... 

The potential energy surface for the head-to-tail dimerization of silanone (equation 25) was also studied137. The fascinating structure of the product 33 was discussed in Section IV.C.2.b. The dimerization is calculated to be highly exothermic (109.4 kcal mol-1 at... 

Relative to carbon, silicon has a much smaller tendency to form compounds of coordination number less than four, such as silenes, silanones or silicenium ions, but a pronounced capacity for the enlargement of the coordination sphere. Complex formation by silicon tetrafluoride was first observed1 early in the nineteenth century, when Gay-Lussac and Davy reported the formation of the adduct SiF4 2NH3. A hexacoordinate cationic complex, Si(acac)3 HCI2 was described by Dilthey2 in 1903, and represented a new structural type for the element. 

Summary l-[2,6-bis(dimethylaminomethyl)phenyl]silenes (2a-d) were prepared by treatment of the (dichloromethyl)oligosilanes R (Me3Si)2Si-CHCl2 la-d (a R = Me b R = teri-Bu c R = Ph d R = Me3Si) with 2,6-bis(dimethylaminomethyl)phenyl-lithium and were characterized by NMR studies and (in part) by X-ray structural analyses as well as by their reactions with water to give silanols. Treatment of 2a-d with benzaldehyde produced 2,2-bis(trimethylsilyl)styrene (4) and a silanone polymer as the expected products. For the reaction of 2a and 2c with benzaldehyde, an interesting side reaction was observed leading to the 2-oxa-1-sila-1,2,3,4-tetrahydro-naphthalenes 6a and 6c, respectively. 

Figure 5.1. Structures of silanone oxide (3a), siladioxirane (4a) and the transition state for ring closure as computed at the MP2(full)/6-31G(d) and GVB/6-31 G(d) (in brackets) levels of theory. All data are taken from reference [27].

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