Metal amides

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Metal amides (systematic name metal azanides) are a class of

coordination compounds composed of a metal center with amide ligands of the form NR2−. Amido complexes of the parent amido ligand NH2− are rare compared to complexes with diorganylamido ligand, such as dimethylamido. Amide ligands
have two electron pairs available for bonding.

Geometry and structure

In principle, the M-NX2 group could be pyramidal or planar. The pyramidal geometry is not observed.

In many complexes, the amido is a bridging ligand. Some examples have both bridging and terminal amido ligands. Bulky amide ligands have a lesser tendency to bridge. Amide ligands may participate in metal-ligand π-bonding giving a complex with the metal center being co-planar with the nitrogen and substituents. Metal bis(trimethylsilyl)amides form a significant subcategory of metal amide compounds. These compounds tend to be discrete and soluble in organic solvents.

Alkali metal amides

Main articles: lithium amide, sodium amide, and potassium amide

Lithium amides are the most important amides. They are prepared from

n-butyllithium
and the appropriate amine

R2NH + BuLi → R2NLi + BuH

The lithium amides are more common and more soluble than the other alkali metal analogs. Potassium amides are prepared by transmetallation of lithium amides with

Schlosser base) or by reaction of the amine with potassium, potassium hydride, n-butylpotassium, or benzylpotassium.[2]

The alkali metal amides, MNH2 (M = Li, Na, K) are commercially available. Sodium amide (also known as sodamide) is synthesized from

ferric nitrate catalyst.[3][4]
The sodium compound is white, but the presence of metallic iron turns the commercial material gray.

2 Na + 2 NH3 → 2 NaNH2 + H2

n-butyllithium and diisopropylamine
.

Main group amido complexes

Amido derivatives of main group elements are well developed.[5]

Transition metal complexes

Early transition metal amides may be prepared by treating anhydrous metal chloride with alkali amide reagents. In some cases, two equivalents of a secondary amine can be used, one equivalent serving as a base:[6]

MCln + n LiNR2 → M(NR2)n + n LiCl
MCln + 2n HNR2 → M(NR2)n + n HNR2·HCl

Transition metal amide complexes have been prepared by these methods:[6]

  • treating a
    halide complex
    with an alkali amide
  • deprotonation of a coordinated amine
  • oxidative addition of an amine
Structure of the nitride-amido complex NMo(N(t-Bu)(C6H3Me2)3.[7]

Amido-ammine complexes

Highly cationic metal ammine complexes such as [Pt(NH3)6]4+ spontaneously convert to the amido derivative:

[Pt(NH3)6]4+ ↔ [Pt(NH3)5(NH2)]3+ + H+

Transition metal amides are intermediates in the base-induced substitution of

Sn1CB mechanism for the displacement of chloride from chloropentamminecobalt chloride by hydroxide proceeds via an amido intermediate:[8]

[Co(NH3)5Cl]2+ + OH− → [Co(NH3)4(NH2)]2+ + H2O + Cl−
[Co(NH3)4NH2]2+ + H2O → [Co(NH3)5OH]2+

See also

References

  1. doi:10.1002/zaac.19835040909
    .
  2. ISBN 978-0-470-74037-8.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  3. ^ Bergstrom, F. W. (1955). "Sodium Amide". Organic Syntheses; Collected Volumes, vol. 3, p. 778.
  4. ISBN 978-0-470-13233-3. {{cite book}}: |journal= ignored (help
    )
  5. doi:10.1016/S0277-5387(00)80578-1
    .
  6. ^
    ISBN 978-1-891389-53-5
    .
  7. PMID 18576632
    .
  8. ISBN 0-13-035471-6
    .
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