Reduction of Corannulene with Lithium

The reduction of 2 with Li is accompanied by a series of three color changes, [6, 7, 9], representing four anions, which can be observed by EPR for the paramagnetic mono- and trianions, and by NMR for the diamagnetic di- and tetraanions. The detection and characterization of all four reduction stages with Li metal allows the delineation of a full reduction path for 2. 

The corannulene monoanion 2 which is green in THF solution, has an EPR spectrum that contains 11-line hyperfine patterns [111] (uh = 0.157 mT [111]/ 0.156 mT [112], g = 2.0027 [lll]/2.0029 [112]) for the ten equivalent protons. At low temperatures the spectrum becomes more complicated. The radical anion 2  

The tetraanion 34 has been characterized as a sandwich compound, in which four Li cations glue together two tetraanion decks of 2, and four external Li cations that are attached the exterior. The Li NMR spectra show the formation of a dimer. The Li NMR spectrum of 34 recorded at a low temperature (210 K) [6] features two signals of equal intensity (bu —4.5 and —11.7 ppm). These chemical shifts represent two different types of Li cations, one sandwiched between the two 

The addition of LiBr to the solution causes an averaging of its signals with that of the broad (SSIP) Li signal, but the sharp Li signal (CIP) remains unchanged, indicating that it is tightly bound [6], 

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