Extremely Close π–π Stacking

 

Extremely Close π–π Stacking

 

Date: 19^thJune, 2025 (Thursday)

Time: 5 - 6 pm (HKT)

 

Venue: Lecture Theatre P3, Chong Yuet Ming Physics Building

 

Nagoya University

 

Norcorrole is a ring-contracted antiaromatic porphyrin, which lacks two meso-carbons from porphyrin. We have synthesized stable norcorrole Ni(II) complexes and investigated their reactivities, optical properties, and electrochemical properties, which are markedly different from aromatic porphyrins.[1] We previously reported that norcorrole dimer 1 exhibited a closely stacked orientation.[2] The remarkable proximity of the two norcorrole units is rationalized by the emergence of the stacked-ring aromaticity between two antiaromatic systems.[3]

 

Recently, we have prepared norcorrole cyclophane 2.[4] Interestingly, cyclophane 2 exhibited crystal polymorphism leading to three different solid-state structures, in which the orientation of the two norcorrole units is different. Importantly, the stacked-ring aromaticity of 2 is dependent on the twist angle between two norcorrole units. Furthermore, the introduction of electron-withdrawing C6F5 substituents to norcorrole resulted in even a shorter stacking distance of less than 3.0 Å in 3.[5] We have elucidated that the extremely close stacking originates from intermolecular double-bonding interactions between two antiaromatic molecules.

 

[1] T. Ito, Y. Hayashi, S. Shimizu, J.-Y. Shin, N. Kobayashi, H. Shinokubo, Angew. Chem. Int. Ed. 2012, 51, 8542.

[2] (a) R. Nozawa, H. Tanaka, W.-Y. Cha, Y. Hong, I. Hisaki, S. Shimizu, J.-Y. Shin, T. Kowalczyk, S. Irle, D. Kim, H. Shinokubo, Nat. Commun. 2016, 7, 13620. (b) Nozawa, R.; Kim, J.; Oh, J.; Lamping, A.; Wang, Y.; Shimizu, S.; Hisaki, I.; Kowalczyk, T.; Fliegl, H.; Kim, D.; Shinokubo, H. Nat. Commun. 2019, 10, 3576.

[3] (a) C. Corminboeuf, P. v. R. Schleyer, P. Warner, Org. Lett. 2007, 9, 3263. (b) D. E. Bean, P. W. Fowler, Org. Lett. 2008, 10, 5573.

[4] Kawashima, H.; Ukai, S.; Nozawa, R.; Fukui, N.; Fitzsimmons, G.; Kowalczyk, T.; Fliegl, H.; Shinokubo, H. J. Am. Chem. Soc. 2021, 143, 10676.

[5] Kino, S.; Ukai, S.; Fukui, N.; Haruki, R.; Kumai, R.; Wang, Q.; Horike, S.; Phung, Q. M.; Sundholm, D.; Shinokubo, H. J. Am. Chem. Soc. 2024, 146, 9311.