COMPARISONS OF THE REACTIVITIES OF THE TRI-t-BUTYL- AND TRIS(TRIMETHYLSILYL)METHYL-SILICON COMPOUNDS

Article abstract of DOI:10.1016/0022-328X(84)85161-X

Comparisons of the reactions of t-Bu3SiX (X usually I, but in some cases OSO2CF3 or Cl) and the corresponding TsiMe2X species (Tsi = (Me3Si)3C) have led to the following conclusions: (a) Under conditions in which TsiSiMe2I is thought to react via a silicocationic intermediate (mainly, solvolysis in CF3CO2H or reactions with silver salts), this iodide is much more reactive than t-Bu3SiI. (b) The reactivity difference between the two iodides is markedly smaller in reactions with alkali metal salts, i.e.S_N2 processes, the TsiSiMe2I commonly being ca. 3-8 times the more reactive. (c) In methanolysis and hydrolysis under conditions in which an S_N2-intermediate mechanism may operate, the difference in reactivity between TsiSiMe2X and t-Bu3SiX compounds (X = I or OSO2CF3) vary considerably with the medium, with the former usually, though not always, the more reactive, but again the difference are much smaller than those in the reactions mentioned under (a) in which the ease of breaking of the Si-X bond is the greatly dominant factor. (d) The differences between the reactivities of iodides and the corresponding chlorides in these highly crowded systems are smaller in reactions in which participation by the nucleophile is important than in those in which the ease of ionization of the Si-X bond is dominant; in reaction with NaN3, KOCN or KSCN in MeCN, t-Bu3SiCl is more reactive than t-Bu3SiI.