Siloxides are chemical compounds with the formula R₃SiOM, where R is usually an organic group and M is usually a metal cation. Also called silanolates, they are derived by deprotonation of silanols. They also arise by the degradation of siloxanes by base:^[1]

R₃SiOSiR₃ + 2 NaOH → 2 R₃SiONa + H₂O

Cleavage of cyclic siloxanes affords siloxides:

(Me₂SiO)₃ + MeLi → Me₃SiOSiMe₂OSiMe₂OLi

These anions function as ligands for metal ions, forming complexes similar to metal alkoxides. Sodium trimethylsiloxide is useful for generating metal complexes by salt metathesis reactions. A very bulky siloxide is tert-butyl₃SiO⁻, sometimes called silox.

Siloxides are weaker net donors than alkoxides because p_π-d donation has to compete with backbonding from the oxygen atom into the low-lying Si-C σ^* orbitals.^[1]