Aggregation Behavior of Lithionaphthalenes in Solution: Experimental and Theoretical Study

The aggregation of a series of mono-
and dilithionaphthalenes in
THF solutions in the presence of tetramethylethylenediamine (TMEDA)
and pentamethyldiethylenetriamine (PMDTA) was studied by NMR spectroscopy
and quantum chemical calculations. The stability of dimeric species
in diluted solutions as well as reasons of their disaggregation in
some cases has been discussed. For the lithioderivatives of 1,8-bis­(dimethylamino)­naphthalene
(DMAN) the possibility of NMe2 group coordination to the
lithium atom in ortho-position of naphthalene core
under steric pressure of substituents was demonstrated by quantum
chemical calculations. For the first time, dilithionaphthalenes were
studied by 1H, 13C, and 7Li NMR spectroscopy.
It was shown that while β-dilithionaphthalenes form oligomeric
aggregates in solutions, α-dilithionaphthalenes exist as solely
monomeric species with each lithium atom coordinated to both peri-positions.