Fig. 2: ¹H NMR spectra of the dianion (top) and tetraanion (bottom) with Li⁺ counter ions.

THF-d₈; temperatures were −70 °C for 1²⁻ and 25 °C for 1⁴⁻; 500 MHz. The spectra were fully assigned using ¹H-¹H COSY and nuclear Overhauser effect spectroscopy techniques (Supplementary Figs. 32, 33, 38, 39 and 44–46).