In
coordination chemistry, a spectator ligand is a
ligand
In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...
that does not participate in chemical reactions of the complex. Instead, spectator ligands (vs "actor ligands") occupy coordination sites.
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. These ligands are sometimes referred to as ancillary ligands.
Several different classes of ligand exist that can be considered spectator ligands. A few examples include
trispyrazolylborates (Tp),
cyclopentadienyl ligands (Cp), and many chelating diphosphines such as
1,2-bis(diphenylphosphino)ethane
1,2-Bis(diphenylphosphino)ethane (dppe) is an organophosphorus compound with the formula (PhPCH) (Ph = phenyl). It is a commonly used bidentate ligand in coordination chemistry. It is a white solid that is soluble in organic solvents.
Preparat ...
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.
[Timothy C. Johnstone, Kogularamanan Suntharalingam, Stephen J. Lippard "The Next Generation of Platinum Drugs: Targeted Pt(II) Agents, Nanoparticle Delivery, and Pt(IV) Prodrugs" Chem. Rev., 2016, volume 116, pp 3436–3486. ]
References
{{reflist
Coordination chemistry
Organometallic chemistry