91158-48-4Relevant academic research and scientific papers
Organometallic chemistry. 21. Silyl trifluoromethanesulfonate (triflate)-boron trichloride (tribromide) complexes
Olah, George A.,Laali, Khosrow,Farooq, Omar
, p. 1337 - 1340 (1984)
Trimethyl- and triethylsilyl triflate fonn with BCl3 and BBr3 strongly polarized donor-acceptor complexes. The deshielding of the 29Si NMR shifts [Δδ29Si (BCl3) 28.81 and 32.26, respectively] and shielding of 11B NMR shifts characteristic for tetracoordinated boron are consistent with the development of partial positive charge at silicon involving O-coordination of boron halide with the triflates. Data also show that no ionization to silicenium ions takes place. Similarly, dimethylisopropyl- and tri-n-butylsilyl triflate gave donor-acceptor complexes on reaction with BCl3 [Δδ29Si 30.51 and 25.18, respectively]. In general BCl3 was found to interact more strongly than BBr3. The reaction of a number of other alkylarylsilyl triflates or dialkylsilyl ditriflates with BX3 was also investigated. The deshielding of 29Si NMR shifts diminished when the steric bulkiness of the alkyl ligands on silicon was increased, such as in the case of (i-Pr)3SiOTf or Me2(t-Bu)SiOTf. Ligand exchange of the triflates with BX3 is a competing process in the reactions, the rate of which increases significantly by increasing the temperature or reaction time. The reaction of tris(alkylthio)silyl triflate with BCl3 at low temperature led only to ligand exchange. The reaction of Me3SiOR (R = Me, Et, Ph) with BBr3 (-30°C) or with BCl3 (-75°C) gave Me3SiBr, Me3SiCl, and the corresponding ROSiX2 indicative of initial complexation followed by rapid Si-O cleavage. The initial complexation, however, could not be observed by NMR. The reaction of AlCl3 and AlBr3 with silyl triflates resulted only in ligand exchange. Attempts to utilize the R3SiOTf-BX3 systems as electrophilic trialkylsilylating agents for aromatics were unsuccessful.
