X-ray crystal structures and some solution structures of lithium amides with intramolecular complexation of lithium by tertiary amide groups

Citation
Glj. Van Vliet et al., X-ray crystal structures and some solution structures of lithium amides with intramolecular complexation of lithium by tertiary amide groups, CHEM-EUR J, 5(3), 1999, pp. 1091-1094
Citations number
30
Categorie Soggetti
Chemistry
Journal title
CHEMISTRY-A EUROPEAN JOURNAL
ISSN journal
09476539 → ACNP
Volume
5
Issue
3
Year of publication
1999
Pages
1091 - 1094
Database
ISI
SICI code
0947-6539(199903)5:3<1091:XCSASS>2.0.ZU;2-8
Abstract
Lithium bis(N,N-dimethyl-2-aminoethyl)amide (la) and lithium N-methyl-N-(3, 6-diaza-3,6-dimethyl)heptylamide (2) are dimers in toluene, THF and in the crystalline state where they exhibit diamond-shaped Li2N2 cores. Tetracoord ination of lithium is achieved by intramolecular binding of the amine nitro gen atoms. The dimers are broken down by hexamethylphosphoramide (HMPA), in the case of la via 1a.HMPA, into solvent-separated ion pairs RR'N- [Li(HMP A)(4)](+) (R, R'= Me2NCH2CH2, Me2NCH2CH2; Me2NCH2CH2(Me)NCH2CH2, Me). For l ithium N-methyl-N-(N',N'-dimethyl-2-aminoethyl)am (3a), seven Li-6 NMR sign als are observed in toluene. In THF, 3a . 2 THF prevails, addition of HMPA leads to solvent-separated ion pairs through several intermediate species.