Allyltridurylsilane has been prepared and converted to the tridurylsilylium cation by treatment with electrophiles. Allyltridurylstannane has been prepared and converted to the tridurylstannylium cation under similar conditions. The (29)Si chemical shift of the silylium cation indicates that it is free and tricoordinate, whereas the (119)Sn chemical shift of the stannylium cation indicates that it maintains loose fourth coordination with the solvent or the anion.