Abstract The first hypervalent compounds containing both a pentacoordinated silicon atom and a pentacoordinated phosphorus atom were synthesized by the cooperative three-component reaction of a phosphoranide, a silane, and THF accompanying the ring opening of THF, or by the nucleophilic addition of phosphoranylalkoxides to a silane. Hydrolysis of the phosphoranyloxysilicate and phosphoranylalkoxysilicates gave the hydroxysilicate and the corresponding phosphoranes.