Metal amides

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.

{{main|lithium amide|sodium amide|potassium amide}}

Lithium amides are the most important amides. They are prepared from n-butyllithium and the appropriate amine

:{{chem2|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 potassium t-butoxide (see also Schlosser base) or by reaction of the amine with potassium, potassium hydride, n-butylpotassium, or benzylpotassium.{{cite book | chapter = 2. Alkali Metal Amides | title = Metal Amide Chemistry | author = Michael Lappert, Andrey Protchenko, Philip Power, Alexandra Seeber | publisher = John Wiley & Sons | year = 2009 | isbn = 978-0-470-74037-8}}

The alkali metal amides, MNH₂ (M = Li, Na, K) are commercially available. Sodium amide (also known as sodamide) is synthesized from sodium metal and ammonia with ferric nitrate catalyst.{{OrgSynth | author = Bergstrom, F. W. | year = 1955 | prep = cv3p0778 | title = Sodium Amide | collvol = 3 | collvolpages = 778}}{{cite book | doi = 10.1002/9780470132333.ch38 | journal = Inorg. Synth. | year = 1946 | last1 = Greenlee | first1 = K. W. | last2 = Henne | first2 = A. L. | last3 = Fernelius | first3 = W. Conard | title = Inorganic Syntheses | chapter = Sodium Amide | volume = 2 | pages = 128–135 | isbn = 978-0-470-13233-3}} The sodium compound is white, but the presence of metallic iron turns the commercial material gray.

:2 Na + 2 NH₃ → 2 NaNH₂ + H₂

Lithium diisopropylamide is a popular non-nucleophilic base used in organic synthesis. Unlike many other bases, the steric bulk prevents this base from acting as a nucleophile. It is commercially available, usually as a solution in hexane. It may be readily prepared from n-butyllithium and diisopropylamine.

Amido derivatives of main group elements are well developed.{{Cite journal | doi = 10.1016/S0277-5387(00)80578-1 | title = Structural and spectroscopic characterization of the compounds [Al(NMe2)3]2, [Ga(NMe2)3]2, [(Me2N)2Al{μ-N(H)1-Ad}]2 (1-Ad = 1-adamantanyl) and [{Me(μ-NPh2)Al}2NPh(μ-C6H4)] | year = 1990 | last1 = Waggoner | first1 = K.M. | last2 = Olmstead | first2 = M.M. | last3 = Power | first3 = P.P. | journal = Polyhedron | volume = 9 | issue = 2–3 | pages = 257–263}}

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:{{cite book | chapter = 4. Covalent (X-Type) Ligands Bound Through Metal-Heteroatom Bonds | title = Organotransition Metal Chemistry: From Bonding to Catalysis | author= John F. Hartwig | publisher = University Science Books | year = 2009 | isbn = 978-1-891389-53-5}}

:MCl_n + n LiNR₂ → M(NR₂)_n + n LiCl

:MCl_n + 2n HNR₂ → M(NR₂)_n + n HNR₂·HCl

Transition metal amide complexes have been prepared by these methods:

• treating a halide complex with an alkali amide
• deprotonation of a coordinated amine
• oxidative addition of an amine

File:COGZAA.png

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 transition metal ammine complexes. Thus, the Sn1CB mechanism for the displacement of chloride from chloropentamminecobalt chloride by hydroxide proceeds via an amido intermediate:G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher, {{ISBN|0-13-035471-6}}.

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

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

• Inorganic imide

Category:Coordination chemistry