Sumanene Explained

Sumanene is a polycyclic aromatic hydrocarbon and of scientific interest because the molecule can be considered a fragment of buckminsterfullerene. Suman means "sunflower" in both Hindi and Sanskrit.^[1] The core of the arene is a benzene ring and the periphery consists of alternating benzene rings (3) and cyclopentadiene rings (3). Unlike fullerene, sumanene has benzyl positions which are available for organic reactions.

Organic synthesis

The structure of Sumanene can be inferred from oxidation of 1,5,9-trimethyltriphenylene but the first practical synthesis starts from norbornadiene.^[2] Norbornadiene is converted into a stannane by action of n-butyllithium, dibromoethane and tributyltinchloride. An Ullmann reaction of this stannane with CuTC affords the benzene core. The methylene bridges (--) created in this conversion then migrate in a tandem ring-opening metathesis and ring-closing metathesis by the Grubbs' catalyst. The final structure is obtained by oxidation by DDQ.

Properties

Sumanene is a bowl-shaped molecule with a bowl depth of 118 picometers.^[3] The 6 hub carbon atoms are pyramidalized by 9° and the molecule displays considerable bond alternation (138.1 to 143.1 pm). Sumanene also experiences bowl-to-bowl inversion with an inversion barrier of 19.6 kcal/mol (82 kJ/mol) at 140 °C which is much higher than that found for its corannulene cousin.Like any benzylic proton, the sumanene protons can be abstracted by a strong base such as t-butyl lithium to form the sumanene mono carbanion. This strong nucleophile can react with an electrophile such as trimethylsilyl chloride to the trimethylsilyl derivative.

The trianion has also been reported.^[4] Electron transport properties have been investigated ^{[5] [6]} as well as carbon NMR^[7]

Derivatives

Sumanene derivatives ^[8] such as naphtosumanene ^[9] and trisialsumanene ^{[10] [11]} have been described. Chiral sumanenes are of some interest with respect to inherent chirality,^[12] examples are chiral trimethylsumanene ^[13] and a chiral sumanene cyclopentadienyl iron complex ^[14]

Notes and References

1. Towards the design of tricyclopenta [def, jkl, pqr] triphenylene (sumanene): a bowl-shaped hydrocarbon featuring a structural motif present in C₆₀ (buckminsterfullerene) Goverdhan Mehta, Shailesh R. Shah and K. Ravikumar Journal of the Chemical Society, Chemical Communications, 1993, (12), 1006 - 1008
2. A Synthesis of Sumanene, a Fullerene Fragment Hidehiro Sakurai, Taro Daiko, and Toshikazu Hirao Science, Vol 301, Issue 5641, 1878, 26 September 2003
3. Structural Elucidation of Sumanene and Generation of Its Benzylic Anions Hidehiro Sakurai, Taro Daiko, Hiroyuki Sakane, Toru Amaya, and Toshikazu Hirao J. Am. Chem. Soc., 127 (33), 11580 -11581, 2005
4. Hidehiro Sakurai, Taro Daiko, Hiroyuki Sakane, Toru Amaya, and Toshikazu Hira; J. Am. Chem. Soc., 2005, 127 (33), pp 11580–11581
5. Anisotropic Electron Transport Properties in Sumanene Crystal Toru Amaya, Shu Seki, Toshiyuki Moriuchi, Kana Nakamoto, Takuto Nakata, Hiroyuki Sakane, Akinori Saeki, Seiichi Tagawa and Toshikazu Hirao J. Am. Chem. Soc., 2009, 131 (2), pp 408–409
6. The electrochemical inspection of the redox activity of sumanene and its concave CpFe complex Piero Zanello, Serena Fedi, Fabrizia Fabrizi de Biani, Gianluca Giorgi, Toru Amaya, Hiroyuki Sakane and Toshikazu HiraoDalton Trans., 2009, 9192-9197
7. Solid-state 13C NMR investigations of 4,7-dihydro-1H-tricyclopenta[def,jkl,pqr]triphenylene (sumanene) and indeno[1,2,3-cd]fluoranthene: Buckminsterfullerene moieties Merrill D. Halling, Anita M. Orendt, Mark Strohmeier, Mark S. Solum, Vikki M. Tsefrikas, Toshikazu Hirao, Lawrence T. Scott, Ronald J. Pugmire and David M. Grant Phys. Chem. Chem. Phys., 2010, 12, 7934-7941
8. Bowl-to-bowl inversion of sumanene derivatives Toru Amaya, Hiroyuki Sakane, Toshiko Muneishi and Toshikazu Hirao Chem. Commun., 2008, 765-767
9. Synthesis of Highly Strained π-Bowls from Sumanene Toru Amaya, Takuto Nakata and Toshikazu Hirao, Japan J. Am. Chem. Soc., 2009, 131 (31), pp 10810–10811
10. Communication Development of a Sila-Friedel−Crafts Reaction and Its Application to the Synthesis of Dibenzosilole Derivatives Shunsuke Furukawa, Junji Kobayashi and Takayuki Kawashima J. Am. Chem. Soc., 2009, 131 (40), pp 14192–14193
11. Synthesis, structures and optical properties of trisilasumanene and its related compounds Tomoharu Tanikawa, Masaichi Saito, Jing Dong Guo and Shigeru Nagase Org. Biomol. Chem., 2011, 9, 1731-1735
12. Inherently chiral concave molecules—from synthesis to applications Agnieszka Szumna Chem. Soc. Rev., 2010, 39, 4274-4285
13. Asymmetric Synthesis of a Chiral Buckybowl, Trimethylsumanene Shuhei Higashibayashi and Hidehiro Sakurai J. Am. Chem. Soc., 2008, 130 (27), pp 8592–8593
14. Sakane, H., Amaya, T., Moriuchi, T. and Hirao, T. (2009), A Chiral Concave-Bound Cyclopentadienyl Iron Complex of Sumanene. Angewandte Chemie International Edition, 48: 1640–1643.