page_title: Metal bis(trimethylsilyl)amides
section_title: d-Block complexes
hierarchical_section_title: Metal bis(trimethylsilyl)amides / d-Block complexes
caption_attribution_description: English: Zinc bis(trimethylsilyl)amide, a en:metal bis(trimethylsilyl)amide. The compound is frozen; it melts at 12 &amp;deg:C.
context_page_description: Metal bis(trimethylsilyl)amides are coordination complexes composed of a cationic metal with anionic bis(trimethylsilyl)amide ligands and are part of a broader category of metal amides.
  Due to the bulky hydrocarbon backbone metal bis(trimethylsilyl)amide complexes have low lattice energies and are lipophilic. For this reason, they are soluble in a range of nonpolar organic solvents, in contrast to simple metal halides, which only dissolve in reactive solvents. These steric bulky complexes are molecular, consisting of mono-, di-, and tetramers. Having a built-in base, these compounds conveniently react with even weakly protic reagents. The class of ligands and pioneering studies on their coordination compounds were described by Bürger and Wannagat.
  The ligands are often denoted hmds in reference to the hexamethyldisilazide from which they are prepared.
context_section_description: In line with the general method, bis(trimethylsilyl)amides of transition metals are prepared by a reaction between the metal halides (typically chlorides) and sodium bis(trimethylsilyl)amide, some variation does exist however, for instance the synthesis of blue Ti(N(SiMe₃)₂)₃ using the soluble precursor TiCl₃(Et₃N)₃. The melting and boiling points of the complexes decrease across the series, with Group 12 metals being sufficiently volatile to allow purification by distillation.
  Iron complexes are notable for having been isolated in both the ferrous (II) and ferric (III) oxidation states. Fe[N(SiMe₃)₂]₃ can be prepared by treating iron trichloride with lithium bis(trimethylsilyl)amide and is paramagnetic as the high spin iron(III) contains 5 unpaired electrons.
  FeCl₃ + 3LiN(SiMe₃)₂ → Fe[N(SiMe₃)₂]₃ + 3LiCl
  Similarly, the two coordinate Fe[N(SiMe₃)₂]₂ complex is prepared by treating iron dichloride with lithium bis(trimethylsilyl)amide:
  FeCl₂ + 2LiN(SiMe₃)₂ → Fe[N(SiMe₃)₂]₂ + 2LiCl
  The dark green Fe[N(SiMe₃)₂]₂ complex exists in two forms depending on its physical state. At room temperature the compound is a monomeric liquid with two-coordinate Fe centers possessing S₄ symmetry, in the solid state it forms a dimer with trigonal planar iron centers and bridging amido groups. The low coordination number of the iron complex is largely due to the steric effects of the bulky bis(trimethylsilyl)amide, however the complex will bind THF to give the adduct, {(THF)Fe[N(SiMe₃)₂]₂}. Similar behavior can be seen in Mn(hmds)₂ and Co(hmds)₂, which are monomeric in the gas phase and dimeric in the crystalline phase. Group 11 complexes are especially prone to oligomerization, forming tetramers in the solid phase. The Lewis acid properties of the group 12 complexes have been reported  and the improved E and C numbers for the Zn and Cd complexes are listed in the  ECW model.
caption: Frozen zinc bis(trimethylsilyl)amide. This compound melts at 12.5 °C.
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