Proportion of 1,3-phenyl migration in trifluoroethanolysis, methanolysis, and hydrolysis of (Me3Si)2C(SiMe2Ph)(SiEt2I)

Abstract

Solvolysis of the iodide (Me3Si)2C(SiMe2Ph)(SiEt2I), 2, in CF3CH2OH–CCl4 has been shown to give the rearranged and unrearranged products, (Me3Si)2C(SiEt2Ph)(SiMe2OCH2CF3) and (Me2Si)2C(SiMe2Ph)(SiEt2OCH2CF3), respectively, in ca. 85:15 ratio. Reaction of 2 with MeOH–CCl4 gives the rearranged and unrearranged methoxides in ca. 75:25 ratio in the presence of Ag2SO4(which promotes the formation of a Ph-bridged cation) and ca. 65:35 in its absence. In contrast, reaction with water–dioxane gives the rearranged and unrearranged hydroxides in only ca. 20 : 80 ratio, but the ratio becomes ca. 60:40 if Ag2SO4 is present. The results provide confirmation of the view reached previously, on the basis of the effects of the substituents Y on the rates of solvolyses of the compounds (Me3Si)2C(SiMe2C6H4Y)(SiMe2I), that the parent compound (Y = H) undergoes trifluoroethanolysis exclusively by an SN1 process (involving rate-determining formation of a phenyl-bridged cation), hydrolysis very predominantly by an SN2 process but with a small SN1 contribution, and methanolysis by a mixture of SN1 and SN2 processes with the former slightly predominating.