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Silylation of TREN using tert-butyldimethylsilyl chloride and subsequent tri-lithiation; Lithium triamidoamine [Li3(NN'3)(THF)3].

SyntheticPage 2
DOI: 10.1039/SP2
Submitted Jun 01, 2001, published Jun 01, 2001
Peter Scott (peter.scott@warwick.ac.uk)


			Reaction Scheme: Silylation of <span id="csm1276125113703" class="csm-chemical-name csm-not-validated" title="TREN">TREN</span> using <span id="ent634117249582057695_2059609696" class="csm-chemical-name csm-ambiguous" title="tert-butyldimethylsilyl chloride">tert-butyldimethylsilyl chloride</span> and subsequent tri-lithiation

Chemicals Used

Lithium butyl (2.50 M in hexanes, Aldrich)
tris(2-aminoethyl)amine (TREN) (Aldrich, distilled)
THF (distilled from K)
tert-butylchlorodimethylsilane (TBSCl, sublimed)
pentane (distilled from Na/K)

Procedure

Lithium butyl (98.5 cm3, 2.50 M in hexanes, 3 equivalents) was added dropwise at -50oC to a solution of distilled tris(2-aminoethyl)amine (TREN) (12 g, 0.082 mol) in dry tetrahydrofuran (200 cm3). The mixture was stirred for 30 min. during which time it was allowed to warm to 0oC. The solution was then cooled to -50oC and a solution of sublimed tert-butylchlorodimethylsilane (37.1 g, 0.246 mol, 3 equivalents) in tetrahydrofuran (40 cm3) was added over a period of 5 min. The mixture was stirred for 30 min. with slow warming to 0oC. After evaporation of volatiles under reduced pressure at ambient temperature, a liquid nitrogen cooled probe was inserted into the flask in order to facilitate removal of the last traces of solvent in vacuo. The oily residue was extracted into pentane (3 x 50 cm3) and filtered. If required, this solution may be evaporated to give virtually pure H3(NN'3). Lithium butyl (98 cm3, 2.5 M in hexanes) was added dropwise to the combined extracts at -80oC. The mixture was allowed to warm slowly to -30oC and was stirred for a further 15 minutes. The solution was then cooled to -50oC and tetrahydrofuran (18 cm3, 3 equivalents) was added. The white microcrystalline solid which precipitated was isolated by cannula filtration and dried in vacuo (46 g, 78%).

Author's Comments

Using pure TBSCl is important. The material from Aldrich is frequently a liquid. The Fluka material is a solid and usually good enough as supplied. If you need to sublime/distil it be careful not to pump the stuff away into a cold trap. It is a pretty volatile solid. We do the sublimation in a closed systen, making sure the chamber is frequently re-evacuated. The amount of THF present in the sample is frequently less than 3 equivalents. The exact figure is determined by NMR. The solid is stable for months at room temperature in the absence of air.

Data

1H NMR (293 K d8-toluene) 3.52 (m, 12H, THF), 3.15 (t, 6H, CH2), 2.35 (t, 6H, CH2), 1.37 (m, 12H, THF), 1.01 (s, 27H, But), 0.05 (s, 18H, SiMe2).

Lead Reference

P. Roussel, N. W. Alcock, and P. Scott, Inorganic Chemistry, 1998, 37, 3435

Other References

Cummins, C. C.; Lee, J.; Schrock, R. R.; Davis, W. M. Angew. Chem., Int. Ed. Eng., 1992, 31, 1501. Duan, Z.; Verkade, J. G. Inorg. Chem., 1995, 34, 1576.

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Keywords: amines lithiation silylation

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