catecholate

Catecholate is the conjugate base form of catechol, also known as 1,2-dihydroxybenzene. In chemistry, catecholate most often refers to the dianion produced by deprotonating both hydroxyl groups, giving the catecholate(2−) ligand. The monodeprotonated form, catecholate(−), can also occur when only one hydroxyl is deprotonated. The neutral molecule is catechol.

In coordination chemistry, catecholates are classic bidentate ligands, binding through the two deprotonated oxygens to metals to form five-membered chelate rings. They are common in iron, copper, nickel, and vanadium complexes and can stabilize unusually high oxidation states. Catecholate ligands are often redox-active and can interconvert with o-quinone species, impacting the electronic structure of the metal center.

Biological and ecological relevance: catecholates appear in natural siderophores such as enterobactin that bind Fe(III) with high affinity. They also occur as motifs in plant polyphenols and in enzymes such as catechol oxidases, which oxidize catechols to o-quinones, triggering polymerization to melanin-like pigments.

Chemically, catecholate chemistry overlaps with that of catechol and quinone interconversion and with the broader catecholamine family, though distinct in structure and function. The term is used mainly in inorganic and bioinorganic chemistry to describe the dianionic catechol-derived ligands.