Trivalent silyl ions

J. B. Lambert, W. J. Schulz, Jr., "Trivalent silyl ions", in "The chemistry of organic silicon compounds" (Eds. S, Patai and Z. Rappoport), John Wiley Sons, 1989, p. 1007. 

Lambert JB, Schulz WJ (1989) Trivalent silyl ions. In Patai S, Rappoport Z (eds) The chemistry of organic silicon compounds. Wiley, Chichester... 

Over the last decade, the synthesis and characterization of trivalent silyl cations (silylium ions), including silatropy-lium ion 1 (Figure 1), have remained as a major challenge in organosilicon chemistry, and, therefore, was the subject of intensive studies. The earlier suggestion that silatropylium ion 1 is more stable than silabenzyl cation 2 and may... 

ZSM5 type zeolites were used as catalysts for the one-step synthesis of phenol hy benzene partial oxidation with nitrous oxide. Isomorphous substitution of Al ions by other trivalent metal ions revealed a high catalytic performance of the H-Ga-ZSM5 in a wide temperature range. Systematic variation of the partial pressures of the reactants led to satisfactory preliminary kinetic models. Deactivation could be reduced by postsynthetic catalyst silylation which is believed to block the strongest acid sites responsible for coke formation. 

Vinyl cations [1], Oie dicoordinated unsaturated analogs of trivalent carbenium ions, were first detected by Grob and coworkers in the early 1960s in solvolysis reactions of a-aryl vinyl halides [2]. The direct NMR detection of vinyl cations in superacidic media was achieved in 1992 at temperatures below -100 °C [3]. We recently reported a convenient synthesis of unusually stable vinyl cations at room temperature [4,5]. One reason for the unusual high thermodynamic stabilization of these vinyl cations is the presence of two 3-silyl substituents. [4]. We report here details of the X-ray structure of the vinyl cation 1 and discuss the structural and spectroscopic consequences of P-SiC hyperconjugation [6]. 

It has been predicted that both cations are unstable toward a facile isomerization to a more stable complex HE /CgHg, 38. For the silyl species this was confirmed by fourier transform ion cyclotron resonance (FT-ICR) experiments, which demonstrated that indeed HSi" /C6H6 is formed and not the isomeric trivalent 7-si-lanorbornadienylium. Similarly, it was shown by our group that the 2,3-benzo-annelated 7-silanorbornadienylium 39 undergoes, at ambient temperature in nonpolar solvents, a fast isomerization to the complex PhSi /tetraphenylnaphthalene (TPN), 40, which decomposes yielding TPN as the only detectable product. ... 

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