Base cleavage of R–SiMen(OMe)3 –n bonds (R =m-ClC6H4CH2, PhCC, or Cl2CH) and alkoxy exchange in RSiMen(OMe)3 –n(R =m-ClC6H4CH2)

Abstract

The rates of cleavage of R–SiMe_n(OMe)_{3 –n} bonds (n= 0–3) in NaOMe–MeOH have been measured for R =(i)m-ClC₆H₄CH₂, (ii) PhCC, and (iii) Cl₂CH. The relative reactivities as n is varied in the sequence 3, 2, 1, 0 within each series are: (i) 1, 7.2, 2.7, 0.13; (ii) 1, 27, 24, 5.5; (iii) 1, 38, 93, 29. These reactivity variations are discussed in terms of opposition between the rate-enhancing polar effects of the OMe groups and an unusual type of steric effect which arises on introduction of OMe in place of Me. The rates of replacement of one OMe group of m-ClC₆H₄CH₂Me_n(OMe)_{3 –n} by an OEt group in EtOH containing a base have also been measured; in this case the rates rise progressively with the value of n, the relative reactivities for n= 2,1, and 0 being 1,4.4, and 27, respectively.