Shape‐Switchable Azo‐Macrocycles

• Published in: European Journal of Organic Chemistry Vol. 2009; no. 15; pp. 2562 - 2575
• Main Authors: Müri, Marcel, Schuermann, Klaus C., De Cola, Luisa, Mayor, Marcel
• Format: Book Review Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 01.05.2009; Wiley; Wiley-VCH
• Subjects: Azo compounds; Chemistry; Chemistry, Organic; Cross‐coupling; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Isomerization; Kinetics and mechanisms; Macrocycles; Noncondensed benzenic compounds; Organic chemistry; Physical Sciences; Preparations and properties; Reactivity and mechanisms; Science & Technology; Cross-coupling; SELF-ASSEMBLED MONOLAYERS; COUPLING REACTIONS; PHOTOISOMERIZATION; Isomerization; INDUCED MOLECULAR-MOVEMENTS; CIS-TRANS ISOMERIZATION; FIELD; AZOBENZENE; Azo compounds; Macrocycles; DERIVATIVES; Nitro compound; Stabilization; NMR spectrometry; Thermal reaction; Macrocycle; Hydrogen 1; Chemical reduction; Azo compound; Functionalization; Cross reaction; Osmometry; Chemical synthesis; Dimerization; Anti stereoisomer; Terphenyl derivatives; Photoisomerization; Cis stereoisomer; Suzuki coupling; Irradiation; Benzenic compound; Kinetics; Mass spectrometry; Ultraviolet visible spectrometry
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.200801282

The synthesis of four shape‐switchable macrocycles comprising different peripheral substituents is described. The macrocycles 1–4 consist of m‐terphenyl semicircles interlinked by two azo joints. These macrocycles were assembled from nitro‐functionalized m‐terphenyl moieties through reductive dimerization. The semicircles were assembled through Suzuki cross‐coupling reactions. The molecular weights of the macrocycles were determined by vapour pressure osmometry, because mass spectrometry failed in the cases of 2 and 3. The E → Z photoisomerization reactions were analysed by UV/Vis spectroscopy complemented by 1H NMR studies. A very slow thermal back‐reaction indicated considerable stabilization of the Z isomer. The reduced efficiency of the thermal back‐reaction probably arises from the reduced degree of freedom due to the mechanical interlinking of the two azo groups. The photostationary state consisted of all‐Z (85 %) and all‐E isomers (15 %). The E → Z transformation induced by irradiation displayed simple exponential kinetics, which indicates pairwise switching of the two azo groups in a macrocycle, at least on the timescale under investigation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) The synthesis of four differently substituted azo‐macrocycles is reported. Their optically and/or thermally triggered isomerization reactions were investigated by UV/Vis spectroscopy and displayed very slow thermal back‐reactions due to the mechanical interlinking of the two azo groups within each compound.