135189-84-3Relevant academic research and scientific papers
Production of α-siloxycarbenium ions by protonation of photochemically generated α-siloxycarbenes. Formation mechanism and reactivities with nucleophiles
Kirmse, Wolfgang,Guth, Michael,Steenken, Steen
, p. 10838 - 10849 (1996)
The acyltrimethylsilanes 4-RC6H4C(O)SiMe3 (R = H, Me, MeO) and β-naphthylC(O)SiMe3, upon photolysis in acetonitrile with 20 ns pulses of 248 nm light from an KrF* excimer laser, give rise to the corresponding α-siloxycarbenes ArC:OSiMe3, whose absorption spectra (λ(max) between 270 and 310 nm), lifetimes (between 130 and 260 ns), and reactivities with proton donors (ROH, mainly alcohols) are reported. With highly acidic ROH, such as 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP), the reaction is of simple second order, rate constants being in the 109 M-1 s-1 range and virtually independent of the nature of the aromatic moiety of the carbene. Isotopic substitution of H in ROH by D has no effect on the rate constant for reaction with carbene. For less acidic alcohols such as, e.g., methanol, the reactivity of the carbenes increases with increasing [ROH]. This behavior is interpreted in terms of reversible adduct formation between carbene and alcohol followed by reaction with further alcohol molecule(s) to give product. On the basis of experiments in the acidic and only weakly nucleophilic solvents 2,2,2-trifluorethanol (TFE) and HFIP, protonation of the carbenes leads to the corresponding carbenium ions, whose absorption spectra (λ(max) between 305 and 355 nm), lifetimes (100 ns-5 μs in TFE), and reactivities with nucleophiles (halides, alcohols, and ethers) are reported. In the solvent HFIP, the reactivities of the carbenium ions with the alcohols and ethers increase with their concentration, in a way analogous to that observed in the reaction of the carbenes with the alcohols. This is explained as resulting from reversible formation of a cation-nucleophile complex followed by reaction of the complex with a second nucleophile molecule which acts as a base. In solvents more basic than HFIP, it is presumably the solvent which serves this function.
Binding interaction of the trimethylsilyl cation with oxygen and nitrogen bases in the gas phase. Acetopheones, benzaldehydes, pyridines, anilines, and N,N-dimethylanilines
Mustanir,Shimada,Ohta,Mishima
, p. 1845 - 1856 (2007/10/03)
The gas-phase basicities toward the trimethylsilyl cation, GB(Me3Si+), were determined for a series of acetophenones, benzaldehydes, pyridines, anilines, and N,N-dimethylanilines by measuring the equilibrium constants of trimethylsilyl cation transfer reactions. GB(Me3Si+) increases in the order aniline +) increases as benzaldehyde 3Si+) of the respective bases are, however, linearly correlated with the corresponding proton basicities with a slope of 0.8 to 1.0, showing family-dependent linear relationships. Furthermore, an analysis of the substituent effects on the GB(Me3Si+) of acetophenone and benzaldehyde showed that the ρ values are close to those for the proton basicities, though the resonance demand of Me3Si+ adduct ions is slightly reduced compared with that for the protonated ones. DFT calculations at the B3LYP/6-31+G(d) level of theory reproduced such a trend in substituent effects as well as the family-dependent linear correlations between the H+ and Me3Si+ basicities. Both the experimental and theoretical results lead to the conclusion that the binding interactions of Me3Si+ with O and N atoms of organic bases have a pronounced covalent character to a similar degree as that of a proton.
