Silicon can form bonds to other tetracoordinated silicon atoms and these bonds form the framework of many organosilicon compounds and crystalline silicon. Silicon can also form a pentacoordinated anionic structure-a so-called 'silicate'. No compounds containing a direct bond between two silicate moieties-'disilicates' where two silicate structures are combined in one species-have been reported because of the electronic repulsion between the anionic halves and difficulty preventing the release of anions. Here we report the synthesis of thermally stable and isolable disilicates by the reductive coupling reaction of a silane bearing two electron-withdrawing bidentate ligands. Two pentacoordinated silicons, positively charged despite the formal negative charge, constitute a single σ-bond and bind eight negatively charged atoms. They can be reversibly protonated, cleaving two Si-O bonds, to afford a tetracoordinated disilane. Their unique electronic properties could be promising for the construction of functional materials with silicon wire made up of silicate chains.

A silylsilicate, which is an intermediate in double protonation of a disilicate bearing two sets of a C,O-bidentate ligand at two pentacoordinated silicon atoms to give a disilane, was synthesized and isolated. The X-ray crystallographic analysis of both the silylsilicate and the disilane revealed intramolecular O···Si coordination, giving the silicon atoms pentacoordinated states. In the silylsilicate, the Si1–O2 and Si2–O3 bonds are almost in parallel. Deprotonation of the silylsilicate, which was also prepared by monodeprotonation of the disilane, gave the disilicate. The oxidation potential and UV/vis absorption maximum are both intermediate between those of the disilicate and the disilane, reflecting the changes in the charges.

The SiSi bond of a pentacoordinated disilicate was readily cleaved by treatment with 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone in the presence of sodium carbonate under mild conditions. The bond cleavage did not proceed under the same conditions after conversion of the disilicate into the corresponding monoanionic silylsilicate and neutral disilane by protonation. The difference in the charges of the SiSi bond compounds affects the reactivity toward an oxidant, resulting in the SiSi bond cleavage, considering that all of these compounds have a bond between pentacoordinated silicon atoms.

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