Spectator ligand

[1] Spectator ligands tend to be of polydentate, such that the M-spectator ensemble is inert kinetically.

Although they do not participate in reactions of the metal, spectator ligands influence the reactivity of the metal center to which they are bound.

A few examples include trispyrazolylborates (Tp), cyclopentadienyl ligands (Cp), and many chelating diphosphines such as 1,2-bis(diphenylphosphino)ethane ligands (dppe).

Varying the substituents on the spectator ligands greatly influences the solubility, stability, electronic, and steric properties of the metal complex.

In the area of platinum-based antineoplastic agents, spectator (and nonspectator) ligands greatly affect efficacy.

Idealized structure of a Tp ligand bound to a metal center ML n . Tp − is a spectator ligand in this complex.
Ball-and-stick model of [PdCl 2 (dppe)]. Dppe is a spectator ligand in this complex.