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 H-1, C-13, and Li-7 NMR spectroscopy. It was shown that while beta-dilithionaphthalenes form oligomeric aggregates in solutions, alpha-dilithionaphthalenes exist as solely monomeric species with both peri-positions.