Silaanthracenes

Evidence for the formation of 34 (R = Ph) was provided by neutralization reionization mass spectrometry and more directly by the matrix isolation and spectroscopic investigations on 34 (R = Ph) in an argon matrix at 12 K. The UV spectrum of 34 (R = Ph) exhibits characteristic bands at X = 364, 386, 404, 420, 440, 470 and 502 nm, resembling those of the electronic spectrum of anthracene, but with the expected bathochromic shifts. If one irradiates into the maximum at X = 502 nm, all bands shown in the spectrum disappear completely within 5 minutes. The vanishing of these characteristic bands can again be explained by the photoisomerization of silaanthracene 34 (R = Ph) to the corresponding Dewar valence isomer. 

In the same way pyrolysis of unsubstituted dihydrosilaanthracene 33 (R = H) formed the parent silaanthracene 34 (R = H), which likewise could be photoisomerized into the corresponding Dewar silaanthracenes46. 

Silaanthracenes turned out to be also available by the 254 nm photolysis of the appropriate dihydrosilaanthracenes in rigid hydrocarbon glass at 77 K47. 

The flash photolysis of several 9,10-dihydrosilaanthracene derivatives 72 in argon matrices led to the detection of 9-silaanthracenes, 73, characterized by their UV spectra38 (equation 9). 

Jutzi, P. Massenspektrometrischer Nachweis des 9-methyl-9-silaanthracen-ions. J. Organometal. Chem. 16, 71—72 (1969). 

IfMRjRa = SiMe2 for (XIII), the derivative would be 9.9-dimethyl-9,10-dihydro-9-silaanthracene or, according to the Ring Index rules, 5,5-dimethyl-5,10-dihydrodibenzo[i,e]silicin. ... 

Data for the silaanthracene derivative (XLIVe) are harder to evaluate. The i<(SiH) shifts from 2110 cm in 9,9-dimethyl-9-silaanthracene to 2010 cm in the anion, and the T(SiH) shifts from 4.43 to < 3.78 ppm in the PMR spectrum (183). These observations may be consistent with buildup of negative charge at the heteroatom which could result from electron delocalization into the d orbitals on silicon. 

The UV spectra of all the metalloanthracene derivatives have been published. The longwave absorption maxima of 9-boraanthracene anion and 9-arsaanthracene are similar to anthracene, and 9-silaanthracene exhibits a UV spectrum similar to that of 9-fluorenyllithium (183). The spectrum of 9-mesityl-9-boraanthracene was qualitatively explained by... 

Ionized silaarenes, silaallenes and silabutadienes have been suggested to be formed by mechanistically not always fully understood processes. It may suffice to list, out of many examples, the following few cases HC1 loss from ionized halogen-substituted 9,10-dihydro-9-silaanthracenes 211 is believed to yield the silaanthracenium cation radical 212 (reaction 82)113. 

Silaanthracene derivatives can be obtained by means of metallated precursor compounds. For instance, the bis-Grignard compound of bis(o-chlorophenyl)methane (356) forms with chloromethylmethyldichlorosilane (357) 9-chloromethyl-9-methyl-9,10-dihydro-9-silaanthracene (358) (equations 161)185. In a related manner, the dilithio... 

Markel and Schlosser reported the synthesis of the substituted silabenzene 3 which was stable in solution up to 170 K . Kinetic stabilization by bulky substituents led to the isolation in an argon matrix of 9, R = MesSi or -PrMe2Si by Jutzi, Maier and coworkers 9, R = -PrMe2Si was stable up to 90 K even without an argon cage . In 1991 Maia-and coworkers isolated and characterized spectroscopically in the gas phase and in an argon matrix at 12 K the 9-silaanthracenes, 10, R = H, Ph . Most recently, Okazaki and coworkers reported the synthesis and isolation of 2-silanaphthalene (1), the first silaben-zenoid compound which is a stable crystalline material even at room temperature. ... 

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