Transferrand

Transferrand is a neologism that appears in a limited number of discussions in organometallic chemistry and catalysis. It refers to a hypothetical species, or ensemble of species, proposed to mediate the transfer of a ligand, fragment, or oxidation state between two metal centers during a catalytic cycle. Because it is not a formally defined class of compounds, the precise meaning of transferrand varies by context; it may describe a discrete intermediate, a bridged arrangement of metals, or a transient transition state that enables exchange without isolation of a single molecule.

In practice, authors use the term to discuss the step in which a fragment moves from a donor metal to an acceptor metal, a process akin to transmetallation or ligand shuttling. The transferrand concept is often invoked in multi-metal catalysis, cross-coupling, or catalytic cycles involving metal–ligand transfer. Some writers treat transferrand as a useful heuristic for visualizing exchange steps; others argue for more precise descriptors, such as “transmetallation intermediate” or “ligand transfer transition state.”

Limitations: the term is not standardized and is not widely used in formal nomenclature; readers should consult the original source to understand its intended meaning. The word should not be confused with transferrin, the iron-transport protein, or with transferable ligands in general.

See also: Transmetallation, Transmetalation, Ligand transfer, Bridging ligand, Catalysis.