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.
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.
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.[3][4] The sodium compound is white, but the presence of metallic iron turns the commercial material gray.
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]
^Ouzounis, K.; Riffel, H.; Hess, H.; Kohler, U.; Weidlein, J. (1983). "Dimethylaminoalane, H3−nAl[N(CH3)2]n, n = 1, 2, 3 Kristallstrukturen und Molekülspektren". Zeitschrift für anorganische und allgemeine Chemie. 504 (9): 67–76. doi:10.1002/zaac.19835040909.
^Michael Lappert, Andrey Protchenko, Philip Power, Alexandra Seeber (2009). "2. Alkali Metal Amides". Metal Amide Chemistry. John Wiley & Sons. ISBN978-0-470-74037-8.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Waggoner, K.M.; Olmstead, M.M.; Power, P.P. (1990). "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)]". Polyhedron. 9 (2–3): 257–263. doi:10.1016/S0277-5387(00)80578-1.
^ abJohn F. Hartwig (2009). "4. Covalent (X-Type) Ligands Bound Through Metal-Heteroatom Bonds". Organotransition Metal Chemistry: From Bonding to Catalysis. University Science Books. ISBN978-1-891389-53-5.
^Curley, J. J.; Cook, T. R.; Reece, S. Y.; Müller, P.; Cummins, C. C. (2008). "Shining Light on Dinitrogen Cleavage: Structural Features, Redox Chemistry, and Photochemistry of the Key Intermediate Bridging Dinitrogen Complex". Journal of the American Chemical Society. 130 (29): 9394–9405. doi:10.1021/ja8002638. PMID18576632.
^G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher, ISBN0-13-035471-6.
![Tris(dimethylamino)aluminium dimer[1]](http://en.wikipedia.org/wiki/File:Tris%28dimethylamino%29aluminium_dimer.png)
