Intramolecular Rearrangements of Silenes. 3. From 2,5-Bis(1-methyl-1-silacyclobut-1-yl)-p-xylene to 1,2,4,5-Tetrahydro-1,1,4,4-tetramethyl-1,4-disiladicyclobuta- [a,d]benzene. The First
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- 作者：L. E. Gusel'nikov ; V. V. Volkova ; E. N. Buravtseva ; A. S. Redchin ; N. Auner ; B. Herrschaft ; B. Solouki ; G. Tsantes ; Y. E. Ovchinnikov ; S. A. Pogozhikh ; F. M. Dolgushin ; and V. V. Negrebetsky
- 刊名：Organometallics
- 出版年：2002
- 出版时间：March 18, 2002
- 年：2002
- 卷：21
- 期：6
- 页码：1101 - 1110
- 全文大小：189K
- 年卷期：v.21,no.6(March 18, 2002)
- ISSN：1520-6041
文摘
Low-pressure pyrolysis of 2,5-bis(1,1-dimethyl-1-silacyclobut-1-yl)-p-xylene (1) results inthe formation of 1,2,4,5-tetrahydro-1,1,4,4-tetramethyl-1,4-disiladicyclobuta[a,d]benzene (2),here named as the butterfly compound and representing the first silacyclobutene diannelated[a,d]benzene. Both compounds, 1 and 2, were characterized by NMR, IR, and MS methods;furthermore, the molecular structures were determined by single-crystal X-ray diffractionanalysis. Density functional and ab initio calculations prove that the difference in the benzenecarbon-carbon bond lengths in 2 results primarily from substituent effects and is not causedby ring strain effects. Forming strongly bent silicon-carbon bonds, silicon decreases theamount of strain in the model compounds, in the 1-silacyclobut-2-ene 10 by 8.3 kcal/moland in the 1,4-disiladicyclobuta[a,d]benzene 15 by 19.0 kcal mol-1, compared to the analogoushydrocarbons. The total strain energy is additive, depending on the number of annelatedrings. The photoelectron spectrum of the butterfly compound exhibits three isolated bandsat low energy. The ground state of the radical cation 
ges/entities/Xtilde.gif">(2Ag) at 8.15 eV and the first exitedstate Ã(2Ag) at 8.7 eV arises from ges/gifchars/pi.gif" BORDER=0 >-electron ionization at the benzene molecule center. Thecalculated values with 8.35 and 8.82 eV are in agreement with the experimental verticalionization energies.