Silyl cations stabilized by nitrogen donor groups

Silyl Cations Stabilized by Nitrogen Donor Groups 1. Dimethylaminoimidato-Coordinated Siliconium Complexes 

The equilibrium reaction between neutral hexacoordinate chelates and pentacoordinate siliconium halide salts is discussed in Section III.A.4 (Eq. 17). This reaction can be driven completely to the ionic side by replacement of the chloro ligand by better leaving groups triflate and bromide (Eq. (18), listed again with compound labels see Section III.A.4.iv). The products of this counterion-exchange reaction are stable siliconium salts 90(OTf)-92(OTf), 90(Br)-92(Br), which no 

Stable siliconium-ion salts can also be prepared without exchange of ions, in the case of the bulky -butyl ligand, directly from the TMS-hydrazide and t-BuSiCl3 (Eq. 35).66 The t-butylsiliconium chlorides 93(0) are the only known stable chloride salts of this kind. The chloride can still be exchanged with other anions, as shown in Eq. (18), to produce 93a,c,j bromide, iodide, and triflate.83 

Even the ionization-resistant hexacoordinate complexes with two electron-withdrawing monodentate ligands form stable ionic siliconium salts when treated with A1Q3, as shown in Eq. (36).66 

For several of the siliconium salts crystal structure analyses were obtained, confirming the pentacoordination and the ionic nature of the compounds (well separated cations and anions). The crystal structures for 90a(OTf), 90c(OTf), 91a(OTf), 91a(AlCl4), and 93a(OTf) are depicted in Figs. 47-51, respectively. Further structural support is found in the 29Si NMR chemical shifts (Table XXVI). A remarkable observation in Table XXVI is the nearly equal 29Si chemical shifts of siliconium salts sharing the same silicon complex, but with different anions [e.g. 91a(OTf), 91a(Br), and 91a(AlCl4)] the equal shifts are the evidence that the siliconium cations are essentially independent of 

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See also in sourсe #XX -- [ , , , , , , , , , , , ]

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