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From Hexaoxy‐[6]Pericyclynes to Carbo ‐Cyclohexadienes, Carbo ‐Benzenes, and Dihydro‐ Carbo ‐Benzenes: Synthesis, Structure, and Chromophoric and Redox Properties
Author(s) -
Leroyer Léo,
Lepetit Christine,
Rives Arnaud,
Maraval Valérie,
SaffonMerceron Nathalie,
Kandaskalov Dmytro,
Kieffer David,
Chauvin Remi
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102993
Subject(s) - aromaticity , benzene , chemistry , crystallinity , chemical shift , crystallography , aryl , proton nmr , nmr spectra database , double bond , crystal structure , spectral line , molecule , stereochemistry , organic chemistry , alkyl , physics , astronomy
When targeting the quadrupolar p ‐dianisyltetraphenyl‐ carbo ‐benzene by reductive treatment of a hexaoxy‐[6]pericyclyne precursor 3 with SnCl 2 /HCl, a strict control of the conditions allowed for the isolation of three C 18 ‐macrocyclic products: the targeted aromatic carbo ‐benzene 1 , a sub‐reduced non‐aromatic carbo ‐cyclohexadiene 4 A , and an over‐reduced aromatic dihydro‐ carbo ‐benzene 5 A . Each of them was fully characterized by its absorption and NMR spectra, which were interpreted by comparison with calculated spectra from static structures optimized at the DFT level. According to the nucleus‐independent chemical shift (NICS) value (NICS≈−13 ppm), the macrocyclic aromaticity of 5 A is indicated to be equivalent to that of 1 . This is confirmed by the strong NMR spectroscopic deshielding of the ortho ‐C H protons of the aryl substituents, but also by the strong shielding of the internal proton of the endocyclic trans ‐CHCH double bond that results from the hydrogenation of one of the CC bonds of 3 . Both the aromatics 1 and 5 A exhibit a high crystallinity, revealed by SEM and TEM images, which allowed for a structural determination by using an X‐ray microsource. A good agreement with calculated molecular structures was found, and columnar assemblies of the C 18 macrocycles were evidenced in the crystal packing. The non‐aromatic carbo ‐cyclohexadiene 4 A is shown to be an intermediate in the formation of 1 from 3 . It exhibits a remarkable dichromism in solution, which is related to the occurrence of two intense bands in the visible region of its UV/Vis spectrum. These properties could be attributed to the dibutatrienylacetylene (DBA) unit that occurs in the three chromophores, but which is not involved in a macrocyclic π‐delocalization in 4 A only. A versatile redox behavior of the carbo ‐chromophores is evidenced by cyclic voltammetry and was analyzed by calculation of the ionization potential, electron affinity, and frontier molecular orbitals.