In coordination chemistry, a spectator ligand is a ligand that does not participate in chemical reactions of the complex. Instead, spectator ligands (vs "actor ligands") occupy coordination sites.[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. These ligands are sometimes referred to as ancillary ligands.[2]
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 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.[3]
Idealized structure of a Tp ligand bound to a metal center MLn. Tp− is a spectator ligand in this complex.Ball-and-stick model of [PdCl2(dppe)]. Dppe is a spectator ligand in this complex.
^"Spectator Ligand (Ion)". Encyclopedia of Inorganic and Bioinorganic Chemistry. 2011. doi:10.1002/9781119951438.eibd0729. ISBN 9781119951438.
^ Michael D. Fryzuk, T. S. Haddad, David J. Berg and Steven J. Rettig "Phosphine complexes of the early metals and the lanthanoids" Pure & Appl. Chem., Vol. 63, No. 6, pp. 845-850, 1991
^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. doi:10.1021/acs.chemrev.5b00597
chemistry, a spectatorligand is a ligand that does not participate in chemical reactions of the complex. Instead, spectatorligands (vs "actor ligands") occupy...
In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The...
the cyclooctadiene ("cod") ligands in bis(cyclooctadiene)nickel(0) are labile. In some cases, dienes are spectatorligands, remaining coordinated throughout...
Mixed ligand complexes are common for amino acids. Well known examples include [Co(en)2(glycinate)]2+, where en (ethylenediamine) is a spectatorligand. In...
metal such as cobalt, copper, zinc, palladium or platinum, and Ln are spectatorligands. March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms...
containing an imido ligand. Imido ligands can be terminal or bridging ligands. The parent imido ligand has the formula NH, but most imido ligands have alkyl or...
are deployed as ancillary ligands in organometallic chemistry. Such carbenes are usually very strong σ-donor spectatorligands, similar to phosphines. A...
NHCs are often compared with trialkylphosphine ligands. Like phosphines, NHCs serve as spectatorligands that influence catalysis through a combination...
ISSN 0001-4842. PMID 12379135. Helmstedt, Ulrike; Clot, Eric (2012-09-03). "Hydride ligands make the difference: density functional study of the mechanism of the Murai...
chemistry, alpha elimination refers to reactions of this type (other spectatorligands omitted): X-M-CH2R → M=CHR + HX Well studied case are found in organotantalum...
diphenylacetylene: Et3SiH + PhC≡CPh → Et3Si(Ph)C=CH(Ph) Using chiral phosphines as spectatorligands, catalysts have been developed for catalytic asymmetric hydrosilation...
reductive elimination from Cu(III) intermediates (Ln = one or more spectatorligands): ROCuAr(X)Ln → RO−Ar + CuLn The Ullmann ether synthesis is named...
When bound in the η6 manner, arenes often function as unreactive spectatorligands, as illustrated by several homogeneous catalysts used for transfer...
isocyanides are spectatorligands, but their reduced and oxidized complexes can prove reactive by virtue of the unsaturated nature of the ligand Cationic complexes...
phosphorus analogs of transition metal carbene complexes where L is a spectatorligand. The first terminal phosphinidene complex was reported by Marinetti...
reagents in organic synthesis. Although the Cp ligands are generally safely considered spectatorligands, they are not completely inert. For example, attempts...
carbenes in general, and Arduengo carbenes in particular, are popular ligands in organometallic chemistry. In 1957, Ronald Breslow proposed that a relatively...
complexes, which raised researchers' interests in germylenes' acting as spectatorligands in certain catalytic cycles. However, subsequent regeneration of Ge(II)...
gasotransmitter along with nitric oxide and carbon monoxide. SH− is a soft anionic ligand that forms complexes with most metal ions. Examples include [Au(SH)2]− and...
describes the stoichiometry of some chemical reactions in which one element or ligand is replaced by atom or group. It can be represented generically as: A +...
known. However, it has been shown to directly modulate a broad range of ligand-gated ion channels, and this likely plays a major role in many of its effects...
doi:10.1021/ic00009a015. Grimes, R. N. (1999). "Small Carborane Ligands as Spectators and as Players". Journal of Organometallic Chemistry. 581 (1–2):...
{\displaystyle {\ce {Ph-O- + Me2-SO4 -> Ph-O-Me + Me-SO4-}}} (with Na+ as a spectator ion) More complex alkylation of a alcohols and phenols involve ethoxylation...
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