title: To flip or not to flip? Assessing the inversion barrier of the tetraphenylene framework with enantiopure 2,15-dideuteriotetraphenylene and 2,7-dimethyltetraphenylene.
abstract: Two chiral tetraphenylenes, 2,15-dideuteriotetraphenylene (7) and 2,7-dimethyltetraphenylene (15) were synthesized and resolved to address the tetraphenylene inversion barrier problem. Neutron diffraction investigation of enantiopure 7 showed that the molecule retained its chirality integrity during its synthesis from enantiopure precursors and therefore rules out the possibility of the tetraphenylene framework possessing a low-energy barrier to inversion. Thermal study on 15 and tetraphenylene 1 further revealed that their inversion barriers were not overcome up to 600 degrees C, at which temperature these compounds underwent skeletal contraction into triphenylene with activation energies of 62.8 and 58.2 kcal/mol, respectively. This result is supported by computational studies which yielded an inversion barrier of 135 kcal/mol for tetraphenylene as a consequence of the peri-hydrogen repulsions at its planar conformation.
authors.affiliation: Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis, Shanghai Institute of Organic Chemistry, The Chinese Academy of Sciences, 354 Feng Lin Road, Shanghai 200032, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Huang
authors.forename: Timothy
authors.initials: T
authors.lastname: Stewart
authors.forename: Matthias
authors.initials: M
authors.lastname: Gutmann
authors.forename: Takashi
authors.initials: T
authors.lastname: Ohhara
authors.forename: Nobuo
authors.initials: N
authors.lastname: Niimura
authors.forename: Yu-Xue
authors.initials: YX
authors.lastname: Li
authors.forename: Jian-Feng
authors.initials: JF
authors.lastname: Wen
authors.forename: Robert
authors.initials: R
authors.lastname: Bau
authors.forename: Henry N C
authors.initials: HN
authors.lastname: Wong
mesh_terms: D003198:Computer Simulation; D008956:Models, Chemical; D015394:Molecular Structure; D033363:Neutron Diffraction; D013237:Stereoisomerism; D013730:Terphenyl Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013997:Time Factors
chemical_list: C535001:2,15-dideuteriotetraphenylene; C535002:2,7-dimethyltetraphenylene; D013730:Terphenyl Compounds