Diolate

Diolate is a term used in coordination chemistry to describe a dianionic ligand formed by deprotonation of a vicinal diol. In its dianionic form, both oxygen atoms bear negative charges and can bind to a metal center. The diolate ligand can act as a bidentate chelate or as a bridge between two metal centers, depending on the geometry and the metal involved.

Preparation and occurrence: diolate ligands are typically generated in situ by deprotonating a vicinal diol in the presence of a metal precursor, often using strong bases such as alkoxides, hydrides, or organolithium reagents. They are observed with a range of metals, including alkali, alkaline earth, and transition metals, in inorganic and organometallic complexes.

Typical examples and chemistry: the diolate derived from ethylene glycol serves as a representative case, coordinating through both oxygens to form stable metal complexes. More complex diolates can arise from diols with rigid backbones, which promote well-defined chelate rings. The binding mode and stability of diolates depend on factors such as the metal center, solvent, counterions, and substituents on the diol.

Properties and context: as dianions, diolate ligands are strong donors and can significantly influence the electronic structure, oxidation state, and reactivity of attached metal centers. They are studied within broader areas of coordination chemistry and organometallic catalysis, where thematically related ligands such as enediolates and catecholate derivatives are also encountered.

See also: enediolate, catecholate, glycolate derivatives.