CORANNULENE REDUCTION - SPECTROSCOPIC DETECTION OF ALL ANIONIC OXIDATION-STATES

The reduction of corannulene (1) has been followed by parallel detecti on of optical absorption, electron paramagnetic resonance (EPR), and n uclear magnetic resonance (NMR) spectroscopies. The major findings are the existence of a diamagnetic dianion that can be observed in NMR an d negligable counterion influences in the mono- and dianion. The diama gnetic state of the dianion is also supported by vanishing EPR intensi ty and semiempirical calculations and exhibits one indistinguishable p roton NMR resonance at -5.6 ppm for potassium and lithium as counterio ns; respectively. The NMR signal is strongly temperature dependent and can only be obtained at low temperature (T < 230 K) where the line wi dth decreases with temperature. Further reduction to the trianion and tetraanion succeeds with Li as the reducing metal, but not with K even at ambient temperatures. The EPR spectra of the trianion show a prono unced temperature dependence with at least two Li cations being strong ly coupled.