PMDTA

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PMDTA
Skeletal formula of PMDTA
Ball and stick model of PMDTA
Spacefill model of PMDTA
Identifiers
3D model (JSmol)
1741396
ChEBI
ChemSpider
ECHA InfoCard 100.019.275
EC Number 221-201-1
27747
RTECS number IE2100000
UN number 2734
Properties
C9H23N3
Molar mass 173.30 g·mol−1
Appearance Colorless liquid
Odor Fishy, ammoniacal
Density 830 mg mL−1
Melting point −20 °C (−4 °F; 253 K)
Boiling point 198 °C (388 °F; 471 K)
Vapor pressure 31 Pa (at 20 °C)
1.442
Hazards
Safety data sheet sigmaaldrich.com
GHS pictograms The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
H302, H311, H314
P280, P305+351+338, P310
Flash point 53 °C (127 °F; 326 K)
155 °C (311 °F; 428 K)
Explosive limits 1.1–5.6%
Lethal dose or concentration (LD, LC):
  • 232 mg kg−1 (dermal, rabbit)
  • 1.351 g kg−1 (oral, rat)
Related compounds
Related amines
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

PMDTA (N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) is an organic compound with the formula [(CH3)2NCH2CH2]2NCH3. PMDTA is a basic, bulky, and flexible, tridentate ligand that is a used in organolithium chemistry, it is a colorless liquid, although impure samples appear yellowish.

Synthesis[edit]

PMDTA is prepared from diethylenetriamine by the Eschweiler-Clarke reaction, involving the use of formaldehyde and formic acid.[1]

[H2N(CH2)2]2NH + 5 CH2O + 5 HCO2H → [Me2NCH2CH2]2NMe + 5 CO2 + 5 H2O

Comparison with diethylenetriamine[edit]

Unlike diethylenetriamine, all three amines in PMDTA are tertiary. Both PMDTA and diethylenetriamine are tridentate ligands that form two five-membered chelate rings, the σ-donating properties of the amino groups of diethylenetriamine are greater than that of PMDTA in copper(II) complexes.[2] Both ligands can coordinate metal complexes in arrangements where the three nitrogen centers are co-planar or mutually cis.

Organolithium compounds and PMDTA[edit]

PMDTA is used to modify the reactivity of organolithium compounds, which deaggregate in the presence of Lewis bases to enhance their reactivity.[3] Commonly, the ditertiary amine TMEDA is used in these applications; it binds to the lithium center as a bidentate ligand. PMDTA behaves analogously, but since it is tridentate, it binds more strongly to lithium; in contrast to TMEDA, PMDTA forms monomeric complexes with organolithium compounds. Both amines affect the regiochemistry of metalation.[3][4]

In the PMDTA/n-BuLi adducts, the Li-C bonds are highly polarized, thus increasing the basicity of the butyl group.[5]

The effect of PMDTA on lithium anilide is illustrative of PMDTA's complexing power, the complex, [{PhN(H)Li}3·2PMDTA], is trinuclear, featuring approximately colinear Li+ centers that are three-, four-, and five-coordinate. The central three-coordinate lithium atom is not bonded to PMDTA. One of the terminal Li centers is pseudo-tetrahedral in an N4 coordination sphere. The other terminal lithium atom is five-coordinate and binds to two anilino N centers and the PMDTA.[6]

Transition metal and aluminium complexes[edit]

PMDTA often forms five-coordinate complexes due to steric bulk of the methyl groups. PMDTA stabilize unusual cations, the first cationic derivative of alane, [H2Al(PMDTA)]+[AlH4] was prepared by treating H3AlNMe3 with PMDTA.[5]

References[edit]

  1. ^ Marxer, A.; Miescher, K. (1951). "Über die stufenweise Quaternisierung von aliphatischen Polyaminen. Neue Verbindungen mit ganglienblockierender Wirkung". Helvetica Chimica Acta. 34 (3): 924–931. doi:10.1002/hlca.19510340327. 
  2. ^ Angelici, R. J.; Allison, J. W. (1971). "Stability Constants for Amino Acid Coordination by Substituted Diethylenetriamine Complexes of Copper(II) and the Kinetics of Amino Acid Ester Hydrolysis". Inorganic Chemistry. 10 (10): 2238–2243. doi:10.1021/ic50104a030. 
  3. ^ a b Strohmann, C.; Gessner, V. H. (2007). "From the Alkyllitium Aggregate (nBuLi)2·PMDTA2 to Lithiated PMDTA". Angewandte Chemie International Edition. 46 (24): 4566–4569. doi:10.1002/anie.200605105. 
  4. ^ Fraenkel, G. (2002). "PMDTA". Encyclopedia of Reagents for Organic Synthesis. Weinheim: Wiley-VCH. pp. 806–813. doi:10.1002/047084289X.rp028. ISBN 0-471-93623-5. 
  5. ^ a b Elschenbroich, C. (2006). Organometallics. Weinheim: Wiley-VCH. pp. 45–46. ISBN 978-3-527-29390-2. 
  6. ^ Barr, D.; Clegg, W.; Cowton, L.; Horsburgh, L.; Mackenzie, F. M.; Mulvey, R. (1995). "Lithium Anilide Complexed by pmdeta: Expectations of a simple monomer, but in Reality an Odd Trinuclear Composition Combining Three-, Four-, and Five-coordinate Lithium". Journal of the Chemical Society, Chemical Communications. 1995 (8): 891–892. doi:10.1039/C39950000891.