Methylenate

Methylenate is a chemical term that appears in a range of contexts but lacks a single, universally accepted definition. In many sources, methylenate refers to a fragment or ligand containing a methylene unit (-CH2-) that links two other substituents, effectively a methylene bridge. The exact charge and connectivity of the methylenate fragment can vary: it may be neutral, or it may be part of a dianion derived from reduced formaldehyde derivatives such as methanediolate, depending on the conditions and the stoichiometry of the compound. Consequently, the term is not standard across chemical subdisciplines.

In inorganic and organometallic chemistry, methylenate fragments frequently arise as bridging ligands between metal centers or as part of larger anionic ligands. They can influence electronic properties and geometry around metal centers, often participating in 2-electron donation or acting as masked methylene equivalents in catalytic cycles. Because the term overlaps with more established descriptors such as methylene, methylenyl, and methylidene, authors typically define it explicitly when it appears in a report.

See also: Methylene, Methylidene, Methanediolate.