Metal amides

'''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.

<gallery widths="200px" heights="120px"> File:Tris(dimethylamino)aluminium dimer.png|Tris(dimethylamino)aluminium dimer<ref>{{cite journal | doi = 10.1002/zaac.19835040909 | title = Dimethylaminoalane, H3−nAl[N(CH3)2]n, n = 1, 2, 3 Kristallstrukturen und Molekülspektren | year = 1983 | last1 = Ouzounis | first1 = K. | last2 = Riffel | first2 = H. | last3 = Hess | first3 = H. | last4 = Kohler | first4 = U. | last5 = Weidlein | first5 = J. | journal = Zeitschrift für anorganische und allgemeine Chemie | volume = 504 | issue = 9 | pages = 67–76}}</ref> File:Ti(NMe2)4.png|Tetrakis(dimethylamino)titanium File:Ta(NMe2)5.png|Pentakis(dimethylamido)tantalum </gallery>

==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|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.<ref>{{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}}</ref>

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.<ref>{{OrgSynth | author = Bergstrom, F. W. | year = 1955 | prep = cv3p0778 | title = Sodium Amide | collvol = 3 | collvolpages = 778}}</ref><ref>{{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}}</ref> 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.

==Main group amido complexes== Amido derivatives of main group elements are well developed.<ref>{{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}}</ref>

==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:<ref name = hartwig>{{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}}</ref> :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:<ref name = hartwig/> * treating a halide complex with an alkali amide * deprotonation of a coordinated amine * oxidative addition of an amine

thumb|Structure of the nitride-amido complex NMo(N(t-Bu)(C6H3Me2)3.<ref>{{cite journal|author1=Curley, J. J. |author2=Cook, T. R. |author3=Reece, S. Y. |author4=Müller, P. |author5=Cummins, C. C. |title=Shining Light on Dinitrogen Cleavage: Structural Features, Redox Chemistry, and Photochemistry of the Key Intermediate Bridging Dinitrogen Complex|journal=Journal of the American Chemical Society |year=2008|volume=130|issue=29 |pages=9394–9405|doi=10.1021/ja8002638|pmid=18576632 }}</ref>

===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 transition metal ammine complexes. Thus, the Sn1CB mechanism for the displacement of chloride from chloropentamminecobalt chloride by hydroxide proceeds via an amido intermediate:<ref>G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher, {{ISBN|0-13-035471-6}}.</ref> :[Co(NH3)5Cl]2+ + OH− → [Co(NH3)4(NH2)]2+ + H2O + Cl− :[Co(NH3)4NH2]2+ + H2O → [Co(NH3)5OH]2+ ==See also== *Inorganic imide

==References== <references/>

Category:Metal amides Category:Coordination chemistry