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Metal amides

April 13, 2024

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 edit

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 edit

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 potassium t-butoxide (see also 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 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.

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 edit

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

Transition metal complexes edit

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]

 
Structure of the nitride-amido complex NMo(N(t-Bu)(C6H3Me2)3.[7]

Amido-ammine complexes edit

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:[8]

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

See also edit

References edit

  1. ^ 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.
  2. ^ Michael Lappert, Andrey Protchenko, Philip Power, Alexandra Seeber (2009). "2. Alkali Metal Amides". Metal Amide Chemistry. John Wiley & Sons. 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. ^ Greenlee, K. W.; Henne, A. L.; Fernelius, W. Conard (1946). "Sodium Amide". Inorganic Syntheses. Vol. 2. pp. 128–135. doi:10.1002/9780470132333.ch38. ISBN 978-0-470-13233-3. {{cite book}}: |journal= ignored (help)
  5. ^ 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.
  6. ^ a b John F. Hartwig (2009). "4. Covalent (X-Type) Ligands Bound Through Metal-Heteroatom Bonds". Organotransition Metal Chemistry: From Bonding to Catalysis. University Science Books. ISBN 978-1-891389-53-5.
  7. ^ 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. PMID 18576632.
  8. ^ G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.

April 13, 2024
metal, amides, systematic, name, metal, azanides, class, coordination, compounds, composed, metal, center, with, amide, ligands, form, amido, complexes, parent, amido, ligand, rare, compared, complexes, with, diorganylamido, ligand, such, dimethylamido, amide,. 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 Tris dimethylamino aluminium dimer 1 Tetrakis dimethylamino titanium Pentakis dimethylamido tantalumContents 1 Geometry and structure 2 Alkali metal amides 3 Main group amido complexes 4 Transition metal complexes 4 1 Amido ammine complexes 5 See also 6 ReferencesGeometry and structure editIn 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 p 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 editMain 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 BuHThe 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 2 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 2 Na 2 NH3 2 NaNH2 H2Lithium 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 editAmido derivatives of main group elements are well developed 5 Transition metal complexes editEarly 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 HClTransition 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 nbsp Structure of the nitride amido complex NMo N t Bu C6H3Me2 3 7 Amido ammine complexes edit Highly cationic metal ammine complexes such as Pt NH3 6 4 spontaneously convert to the amido derivative Pt NH3 6 4 lt gt 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 8 Co NH3 5Cl 2 OH Co NH3 4 NH2 2 H2O Cl Co NH3 4NH2 2 H2O Co NH3 5OH 2 See also editInorganic imideReferences edit Ouzounis K Riffel H Hess H Kohler U Weidlein J 1983 Dimethylaminoalane H3 nAl N CH3 2 n n 1 2 3 Kristallstrukturen und Molekulspektren Zeitschrift fur 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 amp Sons ISBN 978 0 470 74037 8 a href Template Cite book html title Template Cite book cite book a CS1 maint multiple names authors list link Bergstrom F W 1955 Sodium Amide Organic Syntheses Collected Volumes vol 3 p 778 Greenlee K W Henne A L Fernelius W Conard 1946 Sodium Amide Inorganic Syntheses Vol 2 pp 128 135 doi 10 1002 9780470132333 ch38 ISBN 978 0 470 13233 3 a href Template Cite book html title Template Cite book cite book a journal ignored help 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 m N H 1 Ad 2 1 Ad 1 adamantanyl and Me m NPh2 Al 2NPh m C6H4 Polyhedron 9 2 3 257 263 doi 10 1016 S0277 5387 00 80578 1 a b John F Hartwig 2009 4 Covalent X Type Ligands Bound Through Metal Heteroatom Bonds Organotransition Metal Chemistry From Bonding to Catalysis University Science Books ISBN 978 1 891389 53 5 Curley J J Cook T R Reece S Y Muller 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 PMID 18576632 G L Miessler and D A Tarr Inorganic Chemistry 3rd Ed Pearson Prentice Hall publisher ISBN 0 13 035471 6 Retrieved from https en wikipedia org w index php title Metal amides amp oldid 1176616881, wikipedia, wiki, book, books, library,

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