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 S_N1 process (involving rate-determining formation of a phenyl-bridged cation), hydrolysis very predominantly by an S_N2 process but with a small S_N1 contribution, and methanolysis by a mixture of S_N1 and S_N2 processes with the former slightly predominating.