Allyltridurylsilane has been prepared and converted to the tridurylsilylium
cation by treatment with electrophiles. Allyltridurylstannane has been pre
pared and converted to the tridurylstannylium cation under similar conditio
ns. The Si-29 chemical shift of the silylium cation indicates that it is fr
ee and tricoordinate, whereas the Sn-119 chemical shift of the stannylium c
ation indicates that it maintains loose fourth coordination with the solven
t or the anion.