Transition Metal Imido Complex on:
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In coordination chemistry
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ''ligands'' or complexing ...
and organometallic chemistry, transition metal imido complexes is a coordination compound containing an imido 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 ele ...
. Imido ligands can be terminal or bridging ligand
In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually ...
s. The parent imido ligand has the formula NH, but most imido ligands have alkyl or aryl groups in place of H. The imido ligand is generally viewed as a dianion, akin to oxide.
Structural classes
Complexes with terminal imido ligands
In some terminal imido complexes, the M=N−C angle is 180° but often the angle is decidedly bent. Complexes of the type M=NH are assumed to be intermediates innitrogen fixation
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. At ...
by synthetic catalysts.Nugent, W. A.; Mayer, J. M., "Metal-Ligand Multiple Bonds," J. Wiley: New York, 1988.
220px, Typical Schrock-style olefin metathesis catalyst features imides as spectator ligands.">spectator_ligand.html" ;"title="olefin metathesis catalyst features imides as spectator ligand">olefin metathesis catalyst features imides as spectator ligands.
Complexes with bridging imido ligands
Imido ligands are observed as doubly and, less often, triply bridging ligands.Synthesis
From metal oxo complexes
Commonly metal-imido complexes are generated from metal oxo complexes. They arise by condensation of amines and metal oxides and metal halides: :LnMO + H2NR → LnMNR + H2O This approach is illustrated by the conversion of MoO2Cl2 to the diimido derivative MoCl2(NAr)2(dimethoxyethane
Dimethoxyethane, also known as glyme, monoglyme, dimethyl glycol, ethylene glycol dimethyl ether, dimethyl cellosolve, and DME, is a colorless, aprotic, and liquid ether that is used as a solvent, especially in batteries. Dimethoxyethane is misc ...
), precursors to the Schrock carbenes of the type Mo(OR)2(NAr)(CH-t-Bu).
:LnMCl2 + 3 H2NR → LnMNR + 2 RNH3Cl
Aryl isocyanate
In organic chemistry, isocyanate is the functional group with the formula . Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyan ...
s react with metal oxides concomitant with decarboxylation:
:LnMO + O=C=NR → LnMNR + CO2
Alternative routes
Some are generated from the reaction of low-valence metal complexes with azides: :LnM + N3R → LnMNR + N2 A few imido complexes have been generated by the alkylation of metal nitride complexes: :LnMN− + RX → LnMNR + X−Utility
Metal imido complexes are mainly of academic interest. They are however assumed to be intermediates in ammoxidation catalysis, in theSharpless oxyamination The Sharpless oxyamination (often known as Sharpless aminohydroxylation) is the chemical reaction that converts an alkene to a vicinal amino alcohol. The reaction is related to the Sharpless dihydroxylation, which converts alkenes to vicinal dio ...
, and in nitrogen fixation
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. At ...
.
References