V. V. Negrebetsky, P. Taylor, E. P. Kramarova
Apr 1, 2008
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0
Influential Citations
19
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Journal
Journal of Organometallic Chemistry
Abstract
Abstract The novel compounds, N -(trifluorosilylmethyl)-[ N -( S )-(1-phenylethyl)]-acetamide ( 1a ) and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine ( 1b ) have been prepared from the corresponding NH-compounds using ClCH 2 SiCl 3 /Et 3 N or ClCH 2 SiCl 3 /(Me 3 Si) 2 NH followed by methanolysis or hydrolysis of the reaction mixture in the presence of Lewis bases, and then BF 3 etherate. Potassium-(18-crown-6)-(2-oxoperhydroazepinomethyl)tetrafluorosilicate ( 2 ) was synthesized by reaction of the trifluoride ( 1b ) with KF in the presence of 18-crown-6. Using 19 F, 29 Si NMR and X-ray diffraction techniques it was established that the silicon atom is pentacoordinate in the trifluorides ( 1a , b ) and hexacoordinate in the adduct 2 . Thus the internal coordination of the O → Si bond present in the trifluoride ( 1b ) is retained in the adduct 2 . The stereochemical non-rigidity of the trifluorides ( 1a , b ) and the N -(trifluorosilylmethyl)- N -methylacetamide ( 1c ) was investigated using dynamic 19 F NMR spectroscopy. The activation barriers for permutational isomerization are in the range 9.5–10 kcal mol −1 . Lower values of Δ G # for permutation of trifluorides ( 1a – c ) compared to the monofluorides with the coordination core OSiC 3 F together with small negative values for the activation entropy implies a non-dissociative mechanism. Quantum-chemical analysis suggests a mechanism involving a turnstile rotation.