Organosilicon compounds. XLVII. The substituent effects and leaving group abilities of mono-, bis- and tris-(trimethylsilyl)silyl groups in electrophilic aromatic substitution

Article abstract of DOI:10.1016/S0022-328X(00)92798-0

The rates of cleavage at 50° by a mixture of ethanol (5 vol) and aqueous perchloric acid (2 vol) of the aryl-SnMe₃ bonds of p-[(Me₃Si)_xMe_(3-x)Si]C₆H₄SnMe₃ compounds relative to that of phenyltrimethylstannane have been found to be 0.93 (x = 0), 1.31 (x = 1), 1.67 (x = 2) and 1.76 (x = 3). The increase in rate with the increasing magnitude of x can be attributed to inductive and hyperconjugative electron release from the SiSi bonds. The rates of cleavage at 50° by a mixture of methanol (5 vol) and aqueous perchloric acid (2 vol) of the aryl-Si bonds of the compounds [(Me₃Si)_xMe_(3-x)Si]Ph are 1.0 (x = 0), 2.1 (x = 1), 0.35 (x = 2), and 0.056 (x = 3). The reactivity sequence as x is increased is attributed to opposition between a rate enhancement associated with the increasing electron release and a rate retardation associated with increasing steric hindrance, especially hindrance to solvation of the transition state.