%0 Journal Article %1 Lichtblau.1995 %A Lichtblau, Alexander %A Ehlend, Anja %A Hausen, H.-D. %A Kaim, Wolfgang. %D 1995 %J Chemische Berichte %K bistriisopropylsilyl crystal dihydropyrazine dihydropyrazine;disilylated dihydropyrazine;mol disilylated electron exchange exchange;fullerene hindrance steric structure %N 8 %P 745--750 %R 10.1002/cber.19951280802 %T N,N'-Disilylated 1,4-dihydropyrazines: Organosilyl substitution reactions, structural effects of steric hindrance, and electron exchange with C60 %V 128 %X Organosilyl exchange reactions of the extremely electron-rich and formally antiarom. 1,4-bis(trimethylsilyl)-substituted 1,4-dihydropyrazine I (R = Me, R' = H) with Ph3SiCl or Me5Si2Cl yielded 2 and 3 with triarylsilyl and disilanyl substituents. At d = 4.53 in CDCl3 compd. 3 shows a particularly high-field shifted 1H NMR resonance for the 1,4-dihydropyrazine protons. In contrast to the planar ring arrangement of 1,4-bis(triisopropylsilyl)-1,4-dihydropyrazine 4, the crystal structure detn. of the 2,5-dimethylated analog I R = iPr, R' = 2,5-Me2 (5) as obtained by reductive silylation exhibits a pronounced boat conformation of the heterocycle due to steric repulsion between the substituents, the closest H...H (CH3/CH) contact being 211 pm. Despite the sizeable structural differences between 4 and 5 both compds. are reversibly oxidized at very neg. potentials, at -0.90 and -0.85 V vs. Fc+/0, resp. Apparently the electrochem. behavior of this class of compds. is detd. primarily by the configuration at the N centers and less by the ring conformation. 4 Reacts with C60 under EPR-detectable electron exchange to afford 4+.bul. and C60-.bul.. The radical cation 4+.bul. generated sep. via oxidn. with I was characterized by low-temp. UV/visible and ENDOR spectroscopy. An ENDOR spectrum revealing silylalkyl coupling was also obtained for the related radical cation of reversibly oxidizable 1,1'-bis(tert-butyldimethylsilyl)-1,1',4,4'-bipyridylidene (8). on SciFinder(R)

@article{Lichtblau.1995, abstract = {Organosilyl exchange reactions of the extremely electron-rich and formally antiarom. 1,4-bis(trimethylsilyl)-substituted 1,4-dihydropyrazine I (R = Me, R' = H) with Ph3SiCl or Me5Si2Cl yielded 2 and 3 with triarylsilyl and disilanyl substituents. At \textgreek{d} = 4.53 in CDCl3 compd. 3 shows a particularly high-field shifted 1H NMR resonance for the 1,4-dihydropyrazine protons. In contrast to the planar ring arrangement of 1,4-bis(triisopropylsilyl)-1,4-dihydropyrazine 4, the crystal structure detn. of the 2,5-dimethylated analog I [R = iPr, R' = 2,5-Me2 (5)] as obtained by reductive silylation exhibits a pronounced boat conformation of the heterocycle due to steric repulsion between the substituents, the closest H...H (CH3/CH) contact being 211 pm. Despite the sizeable structural differences between 4 and 5 both compds. are reversibly oxidized at very neg. potentials, at -0.90 and -0.85 V vs. Fc+/0, resp. Apparently the electrochem. behavior of this class of compds. is detd. primarily by the configuration at the N centers and less by the ring conformation. 4 Reacts with C60 under EPR-detectable electron exchange to afford 4+.bul. and C60-.bul.. The radical cation 4+.bul. generated sep. via oxidn. with I was characterized by low-temp. UV/visible and ENDOR spectroscopy. An ENDOR spectrum revealing silylalkyl coupling was also obtained for the related radical cation of reversibly oxidizable 1,1'-bis(tert-butyldimethylsilyl)-1,1',4,4'-bipyridylidene (8). [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Lichtblau, Alexander and Ehlend, Anja and Hausen, H.-D. and Kaim, Wolfgang.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/2c1c20bf55980116fba8a043e7e7ed4a4/huebleriac}, doi = {10.1002/cber.19951280802}, interhash = {ad54cbb21f97878c194e7b7d47d2b673}, intrahash = {c1c20bf55980116fba8a043e7e7ed4a4}, issn = {0009-2940}, journal = {Chemische Berichte}, keywords = {bistriisopropylsilyl crystal dihydropyrazine dihydropyrazine;disilylated dihydropyrazine;mol disilylated electron exchange exchange;fullerene hindrance steric structure}, number = 8, pages = {745--750}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {N,N'-Disilylated 1,4-dihydropyrazines: Organosilyl substitution reactions, structural effects of steric hindrance, and electron exchange with C60}, volume = 128, year = 1995 }