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

coordination compound A coordination complex is a chemical compound consisting 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 ' ...

s 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

ligand 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 bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s have two electron pairs available for bonding. File:Tris(dimethylamino)aluminium dimer.png, Tris(dimethylamino)aluminium dimer File:Ti(NMe2)4.png, Tetrakis(dimethylamino)titanium File:Ta(NMe2)5.png,

Pentakis(dimethylamido)tantalum Pentakis(dimethylamido)tantalum is an organometallic compound of tantalum. It is a colorless solid that is soluble in organic solvents. It hydrolyzes readily to release dimethylamine. Synthesis and structure Ta(NMe2)5 is prepared by treating TaC ...

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 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 r ...

. 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 Metal bis(trimethylsilyl)amides (often abbreviated as metal silylamides) are coordination complexes composed of a cationic metal M with anionic bis(trimethylsilyl)amide ligands (the Valence (chemistry)#monovalent, monovalent anion, or monovalent ...

form a significant subcategory of metal amide compounds. These compounds tend to be discrete and soluble in organic solvents.

Alkali metal amides

Lithium amides are the most important amides. They are prepared from n-butyllithium and the appropriate amine : 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 Potassium ''tert''-butoxide (or potassium ''t''-butoxide) is a chemical compound with the formula CH3)3COKsub>''n'' (abbr. KOtBu). This colourless solid is a strong base (pKa of conjugate acid is 17 in H2O), which is useful in organic syn ...

(see also Schlosser base) or by reaction of the amine with

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

potassium hydride Potassium hydride, KH, is the inorganic compound of potassium and hydrogen. It is an alkali metal hydride. It is a white solid, although commercial samples appear gray. It is a powerful superbase that is useful in organic synthesis. It is sold com ...

, n-butylpotassium, or

benzylpotassium Benzylpotassium is an organopotassium compound with the formula C6H5CH2K, an orange powder. Like organo-alkali metal reagents in general, benzyl potassium is highly reactive, so much so that it reacts with most solvents. It is highly air sensitive ...

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

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

metal and

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

with

ferric nitrate Iron(III) nitrate, or ferric nitrate, is the name used for a series of inorganic compounds with the formula Fe(NO3)3.(H2O)n. Most common is the nonahydrate Fe(NO3)3.(H2O)9. The hydrates are all pale colored, water-soluble paramagnetic salts. Hy ...

catalyst. 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 Lithium diisopropylamide (commonly abbreviated LDA) is a chemical compound with the molecular formula . It is used as a strong base and has been widely utilized due to its good solubility in non-polar organic solvents and non-nucleophilic nature ...

is a popular

non-nucleophilic base As the name suggests, a non-nucleophilic base is a sterically hindered organic base that is a poor nucleophile. Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions. Typic ...

used in

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

. Unlike many other bases, the

steric bulk Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivi ...

prevents this base from acting as a

nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

. It is commercially available, usually as a solution in hexane. It may be readily prepared from n-butyllithium and

diisopropylamine Diisopropylamine is a secondary amine with the chemical formula (Me2CH)2NH (Me = methyl). Diisopropylamine is a colorless liquid with an ammonia-like odor. Its lithium derivative, lithium diisopropylamide, known as LDA is a widely used reagent. ...

Main group amido complexes

Amido derivatives of main group elements are well developed.

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: :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 Metal halides are compounds between metals and halogens. Some, such as sodium chloride are ionic, while others are covalently bonded. A few metal halides are discrete molecules, such as uranium hexafluoride, but most adopt polymeric structures, su ...

with an alkali amide * deprotonation of a coordinated amine *

oxidative addition Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre. Oxidat ...

of an amine COGZAA

Amido-ammine complexes

Highly cationic metal ammine complexes such as t(NH3)6+ spontaneously convert to the amido derivative: : t(NH₃)₆sup>4+ ↔ t(NH₃)₅(NH₂)sup>3+ + H⁺ Transition metal amides are intermediates in the base-induced substitution of

transition metal ammine complex In coordination chemistry, metal ammine complexes are metal complexes containing at least one ammonia () ligand. "Ammine" is spelled this way for historical reasons; in contrast, alkyl or aryl bearing ligands are spelt with a single "m". Almost al ...

es. Thus, the Sn1CB mechanism for the displacement of chloride from

chloropentamminecobalt chloride Chloropentamminecobalt chloride is the dichloride salt of the coordination complex

o(NH3)5Cl O, or o, is the fifteenth letter and the fourth vowel letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''o'' (pronounced ), p ...

+. It is a red-violet, diamagnetic, water-soluble salt. The compound has been of academic and historical interest. Synthesis and reactions The sa ...

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. : o(NH₃)₅Clsup>2+ + OH⁻ → o(NH₃)₄(NH₂)sup>2+ + H₂O + Cl⁻ : o(NH₃)₄NH₂sup>2+ + H₂O → o(NH₃)₅OHsup>2+

References