Synthesis and Characterization of Ion Pairs between Alkaline Metal Ions and Anionic Anti-Aromatic and Aromatic Hydrocarbons with π-Conjugated Central Seven- and Eight-Membered Rings.

The synthesis, isolation and full characterization of ion pairs between alkaline metal ions (Li, Na, K) and mono-anions and dianions obtained from -dibenzo[,]cycloheptenyl (CH = trop) is reported. According to Nuclear Magnetic Resonance (NMR) spectroscopy, single crystal X-ray analysis and Density Functional Theory (DFT) calculations, the trop and trop anions show anti-aromatic properties which are dependent on the counter cation M and solvent molecules serving as co-ligands. For comparison, the disodium and dipotassium salt of the dianion of dibenzo[]cyclooctatetraene (CH = dbcot) were prepared, which show classical aromatic character. A d-Rh(I) complex of trop was prepared and the structure shows a distortion of the CH ligand into a conjugated 10π -benzo pentadienide unit-to which the Rh(I) center is coordinated-and an aromatic 6π electron benzo group which is non-coordinated. Electron transfer reactions between neutral and anionic trop and dbcot species show that the anti-aromatic compounds obtained from trop are significantly stronger reductants.