Transient 1,1-Dimethyl-1-germene, (CH3)2Ge=CH2. Gas-Phase Pyrolytic Generation and EIMS, Matrix Isolation FTIR, and Theoretical Studies

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• 作者：Valery N. Khabashesku ; Konstantin N. Kudin ; Josef Tamá ; s ; Sergei E. Boganov ; John L. Margrave ; and Oleg M. Nefedov
• 刊名：Journal of the American Chemical Society
• 出版年：1998
• 出版时间：May 27, 1998
• 年：1998
• 卷：120
• 期：20
• 页码：5005 - 5016
• 全文大小：172K
• 年卷期：v.120,no.20(May 27, 1998)
• ISSN：1520-5126

文摘

Vacuum pyrolyses of 1,1-dimethyl-1-germa-3-thietane(2) and1,1,3,3-tetramethyl-1-germacyclobutane(3) most likely proceed with the formation of the sametransient species, 1,1-dimethyl-1-germene (1),detectedboth in the gas phase by electron impact mass spectrometry (EIMS) andin argon solid matrixes at 12 K byFourier transform infrared (FTIR) spectroscopy. The production ofmethylgermylene (6) in the reactionsstudiedhas also been suggested, probably as a result of secondaryisomerization of 1 into methylethylgermylene(8)and subsequently to 1-methyl-1-germacyclopropane (9),and further dissociation of 9 at highertemperatures,in agreement with the theoretical consideration of the suggestedmechanism. Full vibrational assignments forthe IR spectra of 1 and 6 have been proposed onthe basis of ab initio and density functional theorycalculationsof the harmonic vibrational frequencies and infrared intensities, andof literature data on related molecules.The assignment of a high-intensity IR band at 847.3cm^-1 to a Ge=C stretching vibration coupledwith theCH₃ rocking mode in 1 has also been supported bythe calculation of potential energy distribution in theinternal coordinates and by the observed splitting of this band due tonatural isotopic abundance of germanium,being in accord with the B3LYP-calculated⁷⁰Ge/⁷²Ge/⁷⁴Ge/⁷⁶Geisotopic frequency shifts in 1. Thecalculatedforce constant for the Ge=C bond in 1 confirms a nature of this bond and yields an estimated bond orderto be somewhat lower than the Si=C -bond order in1,1-dimethyl-1-silene (4).