Buckybowls corannulene

The crystal structure of the first buckybowl, corannulene 1, was reported in 1971 [24]. It shows the noncolumnar crystal packing structure where the CH-Jt interaction rather than the Jt—Jt stacking interaction is the main factor... 

Sygula, A., 8c Rabideau, P. W. (1999). Non-pyrolytic syntheses of buckybowls Corannulene, cyclopentacorannulene, and a semibuckmin-sterfullerene. Journal of the American Chemical Society, 121, 7800-7803. 

Keywords Buckybowl Carbon nanotube Corannulene Sumanene... 

The chemistry of corannulene-based [4—12] and sumanene-based buckybowls [4, 12-15] has been described in several review articles. In 2006 we published a review article focusing on the solution-phase synthesis of buckybowls, and the structures and physical properties of compounds thus prepared [7]. Since then, this research field has expanded dramatically and many important results have appeared we update the contents herein, and introduce some important compotmds, which are not famished by solution-phase synthesis. Due to page limitations, some... 

The curvature and rigidity of a buckybowl can be characterized by the bowl depth, POAV (jt-orbital axis vector) pyramidalization angle [58-60], and bowl-to-bowl inversion barrier (AG i v). The experimental data of the first two are available by single-crystal X-ray crystallography of the desired bowl molecule. Because the barriers of many corannulene derivatives lie in the region of 7-20 kcal/mol, the can be conveniently analyzed by variable temperature NMR study of a suitably derivatized molecule. 

Stabilization of neutral radicals is another interesting property of bowl-shaped corannulene. The buckybowl neutral radicals 39 [52] and 40 [79] are stable as solids in air or as solutions in degassed toluene for long periods. Experimental results suggest spin delocalization of the radical species onto the corannulene moiety in 40 is more significant than 39. 

On the basis of crystallographic analysis, the corannulene cores in dibenzo[u,g]-corannulene (88) and A-octyldibenzo[ Z,m]-l,2-corannulimide (91) are shallow with a bowl depth of 0.83 and 0.65 A, respectively [120, 123]. The cyclopenta-annulated buckybowl 90 is much deeper, and its bowl depth was determined as 1.03 A. The maximum POAV pyramidalization angle of 90 was found to be 10.7°, which is very close to that of acecorannulene (69) [119]. However, the bowl inversion barrier for 90 was experimentally estimated as 23.5-23.6 kcal/mol, which is much smaller than that of acecorannulene (69, 27.6 kcal/mol). 

Scheme 46 presents an unexpected formation of buckybowl 149 from corannulene derivative 148, which was prepared by a protocol similar to Method C in Scheme 5 [25]. Under FVP conditions, 148 underwent cyclization to give hydrocarbon 149 through the formation of three C-C bonds. The key step in the cyclization should be 1,2-shift of the hydrogen atom of the rim radical, generated by the rupture of C—Br bond one at a time, for the formation of five-membered rings.

In 2011, Wu [43] applied intramolecular C-H arylation to the synthesis of highly curved buckybowls, which contain corannulene and sumanene fragments. Several polycyclic aromatic hydrocarbons (PAHs) to prepare less strained bowls have aheady been synthesized using palladium-catalyzed intramolecular arylation reactions [45]. 

Not only a planar x-conjugated molecule but also nonplanar x-conjugated molecules, highly curved buckybowls containing a corannulene fragment, were also synthesized via the rhodium-catalyzed [2+2+2] cycloaddition followed by dehydrochlorination (Scheme 21.15) [18]. 

SCHEME 21.15 Synthesis of highly curved buckybowls containing corannulene fragment. 

In contrast to the planar aromatic systems, examples of heterobuckybowls possessing heterocycles in the bowl-shaped skeleton are still very limited. Only heterobuckybowls possessing heteroatoms in the sumanene skeleton shown in Figure 3.4 have been reported to date. Since the discovery of C50. most synthetic organic chemists first focused on the construction of the strained all-carbon bowl structure itself as the partial structure of fuUerene. After the achievements of pristine buckybowls such as corannulene, or sumanene, the heterobuckybowls became one of the targets. The introduction of heteroatoms in the bowl-shaped skeleton is expected to yield significant electronic effects on the properties of the all-carbon buckybowls, such as electron-deficient or -rich nature, which is as same as in the planar arenes. However, the heteroatoms cause notable unique... 

Dinadayalane, T. G., Deepa, S., Sastry, G. N. (2003). Is peri hydrogen repulsion responsible for flattening buckybowls The effect of ring annelation to the rim of corannulene. Tetrahedron Letters, 44, 4527-4529. 

Barth and Lawton s production of [5]circulene or corannulene 114 (Fig. 1.9) in 1966 [90] was a significant achievement due to the fuDerene-based, nonplanar structure of 114. The 17-step synthesis began with acenaphthene and relied on alkylation, condensation, and Pdaromatization reactions to afford the macrocycle. The following decade would see continued efforts to isolate [7]circulene IIS (Fig. 1.9) but another decade would pass before 115 was successfiilly produced [Id], Sygula and Rabideau discuss more recent work on buckybowls and fiillerene fragments in Chapter 12, whereas fullerene reactivity is outlined by Kitagawa, Mur-ata, and Komatsu in Chapter 9. 

Bowl-to Bou/I Inversion in Buckybowls 551 Table 12.1. Barriers for ring inversion in substituted corannulenes. 

Only very recently some crystal structure determinations of buckybowl metal complexes became available. Petrukhina and Scott reported successful preparation of molecular solids by gas-phase co-deposition of 1 with Rh2(02CCF3)4 which were characterized by X-ray [61]. The resulting solids consisted of ID and 2D networks of Rh2(02CCF3)4 and corannulene units with the [Rh2] fragments // -coordinated... 

A quite different approach to the complexation of corannulene derivatives with transition metals was applied by Chin [65]. His group hydrogenated 1 to its octahy-dro derivative 67 which was subsequently deprotonated by BuLi to the respective fluorene-type anion 68. This species was then used for the formation of two complexes with (CpZrCh) and [Re(CO)3]+. In both cases X-ray structure determination showed // coordination of the metal to the central ring on the exo (convex) side of the very shallow bowl of 68. However, these complexes relate more to the fluorene anion chemistry than to buckybowls. 

Densely substituted fluoranthenes and indenocorannulenes were synthesized by RhCl(PPh3)3-catalyzed [2-t-2-1-2] cycloaddition of peri-dialkynyl naphthalenes and corannulenes with alkynes and norbornadiene (Scheme 4.29) [36], A highly curved buckybowl containing a corannulene fragment could also be synthesized via RhCl(PPh3)3-catalyzed [2 - - 2 - - 2] cycloaddition (Scheme 4.30) [37],... 

The preparation, stabilization, and characterization of buckybowl anions, ranging from archetypal corannulene to large hemifullerenes, have been reviewed. The synthetic potential and configurational stability of configurationally labile chiral carbanions next to electron-withdrawing groups has been summarized. ... 

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