Synthesis stannylium ions

Investigations in the field of germylium and stannylium ions met with little success in the 1990s. Lambert et al. reported the synthesis of the protonated digermyl and distannyl ethers (R3E)20H TPFPB (R = Me, Et E = Ge, Sn), which possess significant amounts of germylium and stannylium ions character. ... 

The straightforward access to stable radicals opened the avenue for the synthesis of the corresponding cations by one-electron oxidations. Thus, the stable radicals (t-Bu2MeSi)3E (E = Si, Ge, Sn) can be oxidized by trityl cation in benzene, and for germanium and tin the free germylium, 22, and stannylium ion, 23, could be... 

The next landmark was the synthesis of the germylium, 22, and the stannylium ion, 23, by one-electron oxidations from the corresponding stable radicals with trityl TPFPB by Sekiguchi and co-workers. As in the case of the allyl cleavage to generate the mesityl-substituted cations, the reaction, in this case the oxidation, occurs at the periphery of the molecule and gives the possibility for efficient steric protection of the incipient cation. Both trivalent cations were obtained as their TPFBP salts and the crystal structure show well separated anions and cations. 

Lambert and coworkers reported the first crystallographic evidence for a free stannylium ion in 2003. Their breakthrough was the synthesis of the highly crowded starting material allyltris(2,4,6-triisopropylphenyl)stannane. The X-ray structure revealed a tricoordinate species of the type 1 without interaction between tin and either the solvent benzene or the anion TPFPB. No atom from the anion was closer than 4 A, and no solvent was present. The sum of the three C—Sn—C angles was 359.9(2)°, experimentally planar. The angle of twist of the aryl rings with respect to the plane was 61.1°, somewhat... 

---