chelating agent

(noun)

Any compound that reacts with a metal ion to produce a chelate.

Related Terms

Examples of chelating agent in the following topics:

  • Chelating Agents

    • Usually these ligands are organic compounds and are called chelants, chelators, chelating agents, or sequestering agents; the resulting complexes are called chelate compounds.
    • Chelation therapy is the use of chelating agents to detoxify poisonous metal agents, such as mercury, arsenic, and lead, by converting them to a chemically inert form that can be excreted without further interaction with the body.
    • Such chelating agents include the porphyrin rings in hemoglobin and chlorophyll.
    • Enterobactin, produced by E. coli, is the strongest chelating agent known.
    • Ethylenediamine serves as a chelating agent by binding via its two nitrogen atoms.

  • Coordination Number, Ligands, and Geometries

    • Ligands that bind via more than one atom are often termed polydentate or chelating.
    • Chelating ligands are commonly formed by linking donor groups via organic linkers.
    • A classic example of a polydentate ligand is the hexadentate chelating agent EDTA, which is able to bond through six sites, completely surrounding some metals.

  • Reactions of Coordination Compounds

    • In chemistry, a coordination or metal complex consists of an atom or ion (usually metallic) and a surrounding array of bound molecules or anions known as ligands or complexing agents.
    • These complexes are called chelate complexes, the formation of which is called chelation, complexation, and coordination.

  • Models for Addition to Acyclic Substrates

    • The silyl ether derivative in example 9 is a case of steric hindrance to chelation.
    • The chelation model leads to a similar prediction.
    • A further test of this rationalization is provided by removing the chelating metal species.
    • The absence of a chelating metal combined with the bulk of the hydride donor results in a >95 %de, despite the replacement of chlorine by the much stronger chelating ligands (CH3)2N- and CH3CO2-.
    • An interesting example in which steric effects and chelation are eliminated is shown at the bottom of the preceding diagram.

  • Enantioselective Aldol Reactions

    • Although the enolborinate by itself might be expected to exist in a chelated form, with two B–O bonds, the aldol reaction requires a reorganization of this chelation in order to activate the aldehyde carbonyl group for nucleophilic addition.
    • As shown by the formula in brackets, the free oxazolidinone ring has rotated 180º from its chelated position in order to minimize dipole repulsion.
    • If the auxiliary remains chelated to the enolate during the aldol reaction the stereochemical outcome is changed.
    • In the upper equation a chelated Z-titanium enolate is initially formed and then reacted with an aldehyde.
    • The change in selectivity relative to the siloxy substituent is due to its chelation effect in the lithium enolate and non-chelated polar effect in the boron enolate.

  • Sulfur Compounds

    • Thiosulfate salts(S2O32−), sometimes referred as "hyposulfites," are used in photographic fixing (HYPO) and as reducing agents.
    • Thiols or mercaptans (as they are mercury capturers as chelators) are the sulfur analogs of alcohols; treatment of thiols with base gives thiolate ions.

  • Allyl and Crotyl Addition to Aldehydes and Ketones

    • In this reaction addition is catalyzed by BF3-etherate, which functions as a fluoride ion transfer agent.
    • Because the allyl addition proceeds by a cyclic transition state incorporating a tetra-coordinate boron atom, the chelation model is not an option, and a non-chelation transition state accommodating the polarity of the substituent provides the best explanation.

  • 1:2-Diastereoselection in Reactions with Chiral Aldehydes

    • Since both BF3 and ZnCl2 produce strong anti-diastereoselectivity, the transition state does not seem to be chelated.
    • Reaction 6 introduces the influence of an achiral β-siloxy function, capable of chelating with the carbonyl oxygen.
    • The 4,5-diastereoselectivity remains exclusively syn, but the 5,6-selectivity is changed to anti (60% de) as a consequence of chelation (magenta shaded box).

  • Overview of Reducing Agents

    • Note that Lithium Aluminum Hydride (LiAlH4) is the strongest reducing agent listed, and it reduces all the substrates.

  • Phosphorus Compounds as Reducing Agents