114048-53-2Relevant academic research and scientific papers
Silicon-Oxygen and Acyl-Oxygen Bond Cleavage in Reactions of Sterically Hindered Organosilicon Carboxylates
Ayoko, G. Adefikayo,Eaborn, Colin
, p. 1357 - 1362 (2007/10/02)
Because of steric hindrance to attack at the functional silicon centre in VsiSiMe2OCOR with R = CF3 (1a) or Me (1b), nucleophiles in MeOH can preferentially attack at the carbonyl group to give VsiSiMe2OH, rather than at Si as would be usual for less hindered silicon carboxylates.With CsF or KSCN in MeOH the products are exclusively VsiSiMe2F and VsiSiMe2NCS, respectively, whereas KOCN gives exclusively VsiMe2OH, and NaN3 gives very predominantly VsiSiMe2OH along with a little VsiSiMe2N3.The overall effectiveness of the salts is KOCN > CsF, NaN3 > KSCN; the sequence of the ease of attack of the nucleophiles at Si is F- > SCN- (>N3-?), and that for attack at carbon is OCN- > N3- > F- > SCN-.The sequence of ability of various nucleophiles to catalyse cleavage of the SiO-COR bond of (1a) in MeOH is RNH2 (R=H2N, Me, Et, HOCH2CH2, or H2NCH2CH2), OCN-, HO2-, > MeO- > N3- > Me2NH > Me3N > 4-Me2NC5H4N >> C5H5N > PhNH2, and the sequence for reactions of the less reactive (1b) is HO2- > H2NNH2 > MeO- > H2NCH2CH2NH2 > MeNH2 > HOCH2CH2NH2 > EtNH2.Except for the unexpected effectiveness of OCN-, the sequences are reasonably consistent with those established, for example, for reactions of aryl acetates in water (and also with Ritchie's nucleophilic parameters N+); it is suggested that, as in the latter reactions, the cleavage of the acyl-oxygen bond is rate-determining.Reactions of (1a) with salts MX, namely NaN3, CsF, KSCN, and KOCN in MeCN, give exclusively the corresponding species VsiSiMe2X.In the representative reactions examined the reactivities of (1a) and (1b) were very similar to those of the corresponding compounds (Me3Si)3CSiMe2OCOR.
