1,4-Disilabenzene, hexamethyl

The pyrolysis of ds-hexamethyl-l,4-dihydrodisilabenzene yields hexamethyl-1,4-disilabenzene, which was characterized by trapping experiments but attempts at its matrix isolation failed319. The trans isomer is unreactive under the same conditions. In the absence of trapping agents, two products were obtained, a disilanorbornadiene and a bismethylenesilacyclopentene (equation 147). A complicated scheme for their formation... 

Of the (276)-(277) structures, the 1,3-isomer (276a) is the most stable. The calculation of ISE also shows that the 1,3-isomer possesses a greater value for the energy of aromatic stabilization (see the values of R). The preparation of hexamethyl-l,4-disilabenzene has been reported (82-JA6884). According to ab initio calculations on 1,4-disilabenzene (277) and its isomers (278)-(280) (85JOM51), structure (277) is more stable than its valence isomers (278) (by 5.9 kcal/mol, 3-21G //STO-3G) and (280) (by... 

The stabilization of a silicon-containing arene has not as yet been achieved. Nevertheless, silabenzene (7), 1-silatoluene (8) and hexamethyl-l,4-disilabenzene (9) have all been generated as transients.42"47 Both silabenzene and 1-silatoluene are stable when condensed in argon matrices. The UV spectrum exhibits three bands at 212, 272 and 320 nm expected for a jr-perturbed benzene. In its photoelectron spectrum, the lowest ionization energies are at 8.0, 9.3 and 11.3 eV (cfcalculated values derived by SCF methods of 8.2, 9.2 and 11.5 eV).48... 

Although the fundamental breakthrough in the field of silaaromatics resulted from their successful pyrolytic generation as described below, a few photochemical approaches are known as well. Trapping with alcohols, oxygen or acetylenes produced evidence that the photolysis of the precursor 78 yields hexamethyl-l,4-disilabenzene (79) as the initial transient product (equation 147)314. 

The photochemical precursor for transient hexamethyl-l,4-disilabenzene, 78, can also be used in pyrolysis with similar results314. 

It is very likely that the thermal interconversion between silaaromatics and their Dewar isomers is facile. The ultimate transformation products from pyrolytically produced hexamethyl-l,4-disilabenzene have been accounted for by a scheme in which isomerization to the Dewar form represents the first step319. 

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