Lithium metal reduction corannulenes

The first evidence for the self-assembly of corannulene tetraanions into a supramolecu-lar dimer, 44, was provided by studies on derivatives of 4371. Owing to their lower symmetry, dimers of monosubstituted corannulene tetraanions are expected to exhibit supramolec-ular stereochemistry, and thus exist in meso and/or as dl dimeric forms (Figure 14a, and b respectively). Reduction of tert-butylcorannulene (45) with excess lithium metal in THF-d i leads to two sets of alkyl groups in almost equal abundance, thus pointing to the presence of tightly bound dimers. Compelling evidence for dimerization comes from the successful detection of a mixed dimer between 434 and 454. In addition, diffusion... 

In the meantime, it was found that addition of corannulene, which serves as an efficient electron shuttle between the lithium metal and the solid fullerenes, facilitates the reduction of the fullerenes to their hexaanions (Figure 19). This finding was very crucial for the continuing study of charged fullerenes40b. 

Corannulene (1) displays interesting electrochemical properties. The reduction states of 1 lie between those of the neutral hydrocarbon and the tetraanion (1 740 ). Reduction of 1 at —78 C with excess lithium metal in [Dg]-THF over a period of several days led to a series of three color changes, first to green, then to purple, and finally to brownish-red [76]. Quenching this solution with water gave tetrahydrocorannulene as the major product accompanied by small amounts of dihydrocorannulene and 1. More recently, the structure of [Na(DME)3] [l ] was analyzed by X-ray crystallography, and its bowl depth (0.85 A) was found to be slightly shallower than the parent 1 [77]. 

The reduction of several annelated corannulene derivatives has been performed using lithium and potassium metals.7 It has been found that annelation affects the annulenic character of corannulene by changing its charge distribution the dianions of derivatives that are annelated with six-membered rings have less annulenic character and are less paratropic than corannulene dianion. 

---