Self-Assembled, Helically Stacked Anionic Aggregates of 2,5,8,11-Tetra-tert-butylcycloocta[1,2,3,4-def;5,6,7,8-d'e'f']bisbiphenylene, Stabilized by Electrostatic Interactions

J. Am. Chem. Soc., 124 (17), 4685 -4692, 2002. 10.1021/ja012140u S0002-7863(01)02140-0
Web Release Date: April 5, 2002

Self-Assembled, Helically Stacked Anionic Aggregates of 2,5,8,11-Tetra-tert-butylcycloocta[1,2,3,4-def;5,6,7,8-d'e'f']bisbiphenylene, Stabilized by Electrostatic Interactions

Roy Shenhar, Hua Wang, Roy E. Hoffman, Limor Frish, Liat Avram, Itamar Willner, Andrzej Rajca, and Mordecai Rabinovitz*

Contribution from the Department of Organic Chemistry, Safra Campus, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel, Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, and School of Chemistry, The Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel

Received September 4, 2001

Abstract:

Tetraanions of alkyl-substituted derivatives of cycloocta[1,2,3,4-def;5,6,7,8-d'e'f']bisbiphenylene (BPD) and their counter lithium cations self-assemble to form helically stacked assemblies, including a dimer, a trimer, and a tetramer. NMR self-diffusion measurements and unprecedented magnetic shielding effects for the sandwiched lithium cations support their aggregated nature. The D₂-tetramer assembly is fully characterized by NMR spectroscopy, providing unequivocal evidence for a helix of four tetraanionic BPD layers with an estimated relative twist angle of about 45 and interlayer spacing of ca. 4 Å. The barrier for racemization through the in-plane inter-deck rotation is G₂₀₀ = 9.5 ± 0.2 kcal mol^-¹ in the dimer compared to >15 kcal mol^-¹ in the tetramer.

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