Dilithium naphthalene (2) and its TMEDA complex 3 have been prepared, and their 'Hand I3C-NMR spectra were analyzed in terms of chemical shifts and coupling constants. From its Q value, 2 is characterized as delocalized [4n] B system and the 'H-as well as the 6Li-NMR shifts classify the ion as strongly paratropic. For the quarternary C-atoms, a down-field shift of 30.4 ppm is observed. The conclusions drawn from the NMR parameters are compared with the results of MNDO calculations for naphthalene and biphenylene and their ions.
Introduction.
-Recently, we reported on the complete NMR analysis of dilithium biphenylene (l), obtained by Li reduction of the hydrocarbon in THF at -78" [l]. A similar study for the well-known dilithium naphthalene (2), which can be stabilized as N,N,N',N'-tetramethylethylenediamine (TMEDA) complex (3) [3], seemed rewarding for several reasons. Firstly, an X-ray analysis of 3 is available, and an NMR investigation of this species should allow an interesting comparison between the structure of the organic ligand in the solid state and in solution. Secondly, strong shielding was reported for the 'H resonances of 2 [4], which indicates the presence of molecular paramagnetism in the ion. The transformation of a 1 0 ~ electron system into a 12~-electron system, thus, constitutes an intriguing test for our Q-value method [5] and allows at the same time a comparison with the 12n-tl47c transformation realized in the case of 1. Finally, the results for 2 were needed as important reference data for a new species obtained by Li reduction of benzo[b]biphenylene . 1 2 3
Results. -Treatment of naphthalene with Li sand in (DJTHF at -78" under Ar, using mechanical vibration of the reaction vessel (a 5-mm NMR tube) and 10% biphenylene as reduction catalyst yielded a dark bluelblack suspension which was stored at -30". The reduction progress was monitored by 'H-NMR spectroscopy. After 4 weeks, the 400-MHz 'H-NMR spectrum, which originally showed only broadened resonances, displayed several sharp signals, among them two 'triplets' at 3.09 and 1.27 ppm, typical for the A A ' X Y spin system expected for 2 (Fig. l a ) . The corresponding I3C-NMR spectrum yielded resonances at 163.65, 112.93, and 82.70 ppm, respectively, which were character-') This aspect remains unnoticed in a pure x-electron treatment as used in [19]; thus, in the PPPmodel the partial positive charge at C(9), C(10) is compensated by an increase of negative charges at the b-C-atoms.