[3030-47-5]  · C9H23N3  · N,N,N,N,N-Pentamethyldiethylenetriamine  · (MW 173.35)

(ligand for lithium which enhances the reactivity of organolithium compounds)

Alternate Names: PMDTA; PMDETA.

Physical Data: mp -20 °C; bp 198 °C; d 0.830 g cm-3; nD 1.4420.

Solubility: sl sol H2O; sol ethanol, acetone, ethers, alkanes.

Form Supplied in: liquid; widely available. Drying: distilled from CaH2 at 10 mmHg, then stored under N2 or argon in the absence of moisture and oxygen.

Handling, Storage, and Precautions: use in a fume hood.

N,N,N,N,N-Pentamethyldiethylenetriamine forms monomeric complexes with several organolithium compounds1a-e in which lithium is tridentately coordinated to PMDTA as determined by 13C NMR (1a1 and 1b2) and X-ray crystallography (1c,3 1d,4 and 1e5) and the interesting chloride-bridged monocation in salt (2).6

Allylamine (3) undergoes, in diethyl ether, metalation at the vinyl carbon (to form 4), whereas in the presence of PMDTA, metalation takes place at the allylic carbon (to form 5). The dilithium species react with electrophiles (eq 1) in the expected fashion.7

The metalation of o- and p-fluoroanisole also shows dramatic changes in regiochemistry (eqs 2 and 3). With PMDTA, complete metalation ortho to fluoro was observed; in its absence, metalation occurred ortho to the methoxy group.7

Metalation of PMDTA by s-BuLi in cyclohexane at 25 °C yields a mixture of the two lithiomethyl compounds (8) and (9) in ratio of 98:2, as indicated by NMR and the products of reactions (10 and 11) with electrophiles (eq 4).8 Products (10) and (11) were not separated.

In hydrocarbon and benzene solution, the 1-lithiomethyl derivative of PMDTA, (8) has been shown, from NMR studies, to form two monomeric species in which lithium is tridentately coordinated.9 NMR lineshape analysis reveals DH&DDagger; for interconversion of the two monomers (A &ibond; B) to be 10.3 ± 1 kcal mol-1 with DS&DDagger; = -27 ± 1 cal K-1 mol-1.9

A variety of substituted 5-hexen-yllithiums (e.g. 12) are formed from the corresponding iodides (13) by halogen lithium exchange using t-Butyllithium.10 These compounds cyclize to the cyclopentylmethyllithiums (14) on warming to 20 °C in the presence of different lithium ligands such as THF, N,N,N,N-Tetramethylethylenediamine, and PMDTA (eq 5).10 The reaction is totally regiospecific and more stereospecific than the analogous radical-mediated cyclization which forms the same products.

Product distribution from electrogenerated (magnesium anode) nickel(0)-catalyzed Carbon Dioxide incorporation into a,o-diynes (16) is influenced by the nature of the ligands L used (eq 6).11 With L = PMDTA at 65 °C the ratio of (17):(18) is 80:20, whereas using TMEDA the ratio is 50:15; with bipy a 5:95 (17):(18) ratio was obtained.

Related Reagents.

N,N-Dimethylpropyleneurea; Hexamethylphosphoric Triamide; N,N,N,N-Tetramethylethylenediamine.

1. Fraenkel, G.; Chow, A.; Winchester, W. R. JACS 1990, 112, 6190.
2. Bauer, W.; Winchester, W. R.; Schleyer, P. v. R. OM 1987, 6, 2371.
3. Lappert, M. F.; Engelhardt, L. M.; Raston, C. L.; White, A. H. CC 1982, 1323.
4. Schumann, U.; Weiss, E.; Dietrich, H.; Mahdi, W. JOM 1987, 322, 299.
5. Schumann, U.; Kopf, J.; Weiss, E. AG(E) 1985, 24, 215.
6. Buttrus, N. H.; Eaborn, C.; Hitchcock, P. B.; Smith, J. D.; Stamper, J. G.; Sullivan, A. C. CC 1986, 969.
7. Barluenga, J.; Gonzalez, R.; Fananas, J. F. TL 1992, 33, 7573.
8. Schakel, M.; Aarnts, M.-P.; Klumpp, G. W. RTC 1990, 109, 305.
9. Klumpp, G. W.; Luitjes, H.; Schakel, M.; de Kanter, F. J. J.; Schimtz, R. F.; van Eikema Hommes, N. J. R. AG(E) 1992, 31, 633.
10. Bailey, W. F.; Khanolkar, A. D.; Gavaskar, K.; Ovaska, T. V.; Rossi, K.; Thiel, Y.; Wiberg, K. B. JACS 1991, 113, 5720.
11. Dérien, S.; Dûnach, E.; Périchou, J. JOM 1990, 385, C43.

Gideon Fraenkel

The Ohio State University, Columbus, OH, USA

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