Triphenylsilyl perchlorate

FIGURE 5. ORTEP drawing of the experimental structure of triphenylsilyl perchlorate (6). Hydrogen atoms are omitted for clarity. Bond lengths in A. Reprinted with permission from Reference 70. Copyright (1987) American Chemical Society... 

Triphenylpyrilium perchlorate, 3833 Triphenylsilyl perchlorate, 3744 Triphenyltin hydroperoxide, 3752 Triphosgene, see Trichloromethyl carbonate, 1039b Triphosphorus pentanitride, 4770 Tripotassium hexafluoroferrate(3-), 4353 Tripropylaluminium, 3209 Tripropylantimony, 3215... 

In light of the great affinity of silylenium ions for electron-rich species, one could be also skeptical about the possibility of the existence of the tricoordinate Si+ species in solvents like acetonitrile (AN) and sulfolane. These solvents are known to have nucleophilic coordination ability. Gut-mann s donicity number (84), 14.1 and 14.8 for AN and sulfolane, respectively, is comparable to that for acetone, 17.0. Coordination of acetonitrile to silicon has been considered in some systems (85,86). The small equivalent conductance of triphenylsilyl perchlorate in CH2C12 may be explained by the domination of the covalent form (18). Consequently, the absence of the coordination of acetonitrile and sulfolane with the tricoordinate Si+ observed in CH2C12 (with 1 or 6 equiv of acetonitrile) may simply indicate that C104 coordinates to Si+ under these conditions more readily than acetonitrile and sulfolane [Eq. (15)]. The reverse situation in acetonitrile... 

The dependence of NMR chemical shifts on the molar ratio of complex components may be used for studies of the stoichiometry of the complex (252,256,258,263) (Fig. 1). The resonance of some nuclei of the electron donors changes considerably on complexation with silanes. Particularly large changes are observed for the 15N resonance ( 100 ppm upfield) since the paramagnetic component of the 15N-NMR chemical shift is eliminated on quarternization of nitrogen. Mixing of equimolar amounts of pyridine and triphenylsilyl perchlorate was demonstrated to lead to a shift of the 15N-NMR signal from 314.0 to 216.8 ppm, which was taken as evidence for the formation of a 1 1 ionic complex (18). 

The alleged preparation of triphenylsilicenium (sityl) ions in different solvents, e.g. in sulpholane or dichloromethane , was reported by Lambert and coworkers in the mid-1980s. Based on conductance measurements and Cl/ Cl NMR spectra of the sityl perchlorate solutions, the authors concluded that the species which they observed were free siUcenium ions °. Unfortunately, Lambert and his coworkers did not report the Si NMR spectra of the sUyl compounds. Lambert s claims were challenged by Olah and coworkers and by Eaborn based on experimental data on related compounds. In particular, the reported silicon chemical shift of 3.0 ppm ° was that of a normal covalently bound, i.e. non-dissociated, triphenylsilyl perchlorate. In the case of MesSi-OClOs (529si = 43.4-47.0 ppm) and (i-PrS)3Si-0CI03 = 18 ppm) i,... 

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