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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

Citation:

R Shenhar, Wang, H , Hoffman, RE , Frish, L , Avram, L. , Willner, I. , Rajca, A , and Rabinovitz, M . 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”. Journal Of The American Chemical Society, 124, Pp. 4685-4692. doi:10.1021/ja012140u.

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 45degrees and interlayer spacing of ca. 4 Angstrom. The barrier for racemization through the in-plane inter-deck rotation is DG200(double dagger) = 9.5 +/- 0.2 kcal mol-1 in the dimer compared to >15 kcal mol-1 in the tetramer.