ISSN:
0009-2940
Keywords:
Silicon compounds
;
Hydrogen-hydrogen contacts
;
Radicals
;
ENDOR spectroscopy
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Organosilyl exchange reactions of the extremely electronrich and formally “antiaromatic” 1,4-bis(trimethylsilyl)-substituted 1,4-dihydropyrazine 1 with Ph3SiCl or Me5Si2Cl yielded the new compounds 2 and 3 with triarylsilyl and disilanyl substituents. At δ = 4.53 in CDCl3 compound 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 determination of the 2,5-dimethylated analogue 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 compounds are reversibly oxidized at very negative potentials, at -0.90 and -0.85 V vs. Fc+/0, respectively, It appears that the electrochemical behavior of this class of compounds is determined ***primarly by the configuration at the nitrogen centers and less by the ring conformation. Compound 4 reacts with C60 under EPR-detectable electron exchange to afford 4+* and C-*60. The radical cation 4+* generated separately via oxidation with iodine was characterized by low-temperature UV/Vis 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).
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19951280802
