Reduction of Bowl-Shaped Hydrocarbons:  Dianions and Tetraanions of Annelated Corannulenes

Abstract

[structure: see text] The reduction of several annelated corannulene derivatives was undertaken using lithium and potassium metals. It was 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. This effect is even more pronounced in corannulenes that are peri-annelated with five-membered rings. The alkali metal used in the reduction process has a great influence on the outcome, especially on the degree of reduction. Most derivatives get reduced to tetraanions only with potassium, and not with lithium, the exception being systems that can stabilize the tetraanion with lithium by special means, such as aggregation or dimerization. One such system is cyclopenta[bc]corannulene (acecorannulylene), which gives a coordinative dimer that consists of two cyclopentacorannulene tetraanions, bound together in a convex-convex fashion by lithium cations. The points of contact in this dimer are two rehybridized carbons from each cyclopentacorannulene unit, which are bridged together by two lithium cations.

Carbanions and Electrophilic Aliphatic Substitution

“…The highly enantioselective direct conjugate addition of ketones to nitroalkenes has been promoted by a chiral primary amine-thiourea catalyst (7). 31 The observed anti diastereoselectivity has suggested participation of a (Z)-enamine intermediate, given de the complementary diastereoselectivity obtained in analogous reactions involving (E)enamines generated from secondary amine catalysts.…”

“…66 By measuring the rates of loss of chlorobenzene in the varied media and also by certain 7 Li NMR studies, a gradual, controlled increase in the basicity of n-BuLi in cyclohexane with increasing increments of THF or TMEDA has been observed.…”

“…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. A systematic density functional theory level investigation of differently substituted pyridinium methylides has been carried out to determine the role of C ylidic lone-pairassociated hyperconjugative and negative hyperconjugative interactions in deciding conformational preferences.…”

Gas phase adiabatic electron affinities of cyclopenta-fused polycyclic aromatic hydrocarbons

“…1), unequivocally shows that 6-8 possess markedly more positive AEAs (Table 2). Hence, 6-8 are inherently better electron acceptors then 9 (see also [30]). Interestingly, the AEAs of 3 and 5-8 (Table 2), which are surface sub-structures of C 60 and C 70 , correspond to Ca.…”

Quadruple Anionic Buckybowls by Solid-State Chemistry of Corannulene and Cesium

“…26 In particular, it has been suggested that alkali- 1 complexes of the type X 4 C 20 H 10 (X ≠ Li) will not form sandwich structures with four alkali ions located between two bowl molecules, as was the case for Li 4 - 1 . 27 Until recently, 28 compounds containing anions of 1 were exclusively characterized in solution, and there only the tetraanionic Li- 1 aggregate has been identified. 29 Such tetraanionic Li- 1 motif has also been used to create supramolecular architectures with bicorannulenyl.…”