ligandless

Ligandless refers to a chemical system or reaction where no external ligand is intentionally added. Ligands are molecules or ions that bind to a central atom, typically a metal, to form a coordination complex. In many catalytic processes, ligands are crucial for stabilizing the metal center, influencing its electronic properties, and dictating its reactivity and selectivity. Therefore, a ligandless system implies that the metal is either unsupported or supported in a way that it does not involve the typical coordination of spectator ligands.

This term is often used in the context of heterogeneous catalysis, where a metal catalyst might be in the form of nanoparticles or clusters on a support material. In such cases, the metal itself, or the interaction with the support, might be considered the primary environment for the reactive species, rather than deliberately added soluble ligands. It can also refer to certain homogeneous catalytic reactions where the active catalytic species is generated without the addition of external ligands, or where the substrate itself acts as a transient ligand. The absence of added ligands can simplify reaction mixtures, reduce costs associated with ligand synthesis and purification, and sometimes lead to unique catalytic behavior. However, ligandless systems can also present challenges in controlling the stability and aggregation of the metal species, which can affect their activity and longevity.