Interplay of Charge and Aromaticity Upon Chemical Reduction of p‑Quinquephenyl with Alkali Metals

Chemical reduction study of a paraphenylene comprising five para-connected aromatic rings, namely, p-quinquephenyl (C30H22, 1), with alkali metals in THF revealed a facile formation of the doubly reduced anion, 12–, which was crystallized with different alkali metal counterions. Several products were characterized using single-crystal X-ray diffraction and spectroscopic methods. The use of different alkali metals allowed tuning of metal binding in the resulting crystalline products. The consequences of electron addition and metal complexation on the core of p-quinquephenyl were investigated with the help of computational methods. Most notably, reduction results in a shift from locally aromatic to quinoidal character of 12–, which is mitigated by complexation to the alkali metal cations.