title: 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.
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 D(2)-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 degrees and interlayer spacing of ca. 4 A. The barrier for racemization through the in-plane inter-deck rotation is DeltaG(200)= 9.5 +/- 0.2 kcal mol(-1) in the dimer compared to >15 kcal mol(-1) in the tetramer.
authors.affiliation: Department of Organic Chemistry, Safra Campus, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel.
authors.forename: Roy
authors.initials: R
authors.lastname: Shenhar
authors.forename: Hua
authors.initials: H
authors.lastname: Wang
authors.forename: Roy E
authors.initials: RE
authors.lastname: Hoffman
authors.forename: Limor
authors.initials: L
authors.lastname: Frish
authors.forename: Liat
authors.initials: L
authors.lastname: Avram
authors.forename: Itamar
authors.initials: I
authors.lastname: Willner
authors.forename: Andrzej
authors.initials: A
authors.lastname: Rajca
authors.forename: Mordecai
authors.initials: M
authors.lastname: Rabinovitz