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

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.