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Non‐Oxido‐Vanadium(IV) Metalloradical Complexes with Bidentate 1,2‐Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution
Author(s) -
Schlüter Dirk,
Kleemiss Florian,
Fugel Malte,
Lork Enno,
Sugimoto Kunihisa,
Grabowsky Simon,
Harmer Jeffrey R.,
Vogt Matthias
Publication year - 2020
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.201904103
Subject(s) - chemistry , electron paramagnetic resonance , vanadium , ligand (biochemistry) , atropisomer , photochromism , crystallography , denticity , chirality (physics) , molecular switch , redox , stereochemistry , antiparallel (mathematics) , photochemistry , crystal structure , molecule , inorganic chemistry , nuclear magnetic resonance , biochemistry , physics , receptor , nambu–jona lasinio model , chiral symmetry breaking , quantum mechanics , organic chemistry , quark , magnetic field
Abstract Derivatives of 1,2‐dithienylethene (DTE) have superb photochromic properties due to an efficient reversible photocyclization reaction of their hexatriene structure and, thus, have application potential in materials for optoelectronics and (multi‐responsive) molecular switches. Transition‐metal complexes bearing switchable DTE motifs commonly incorporate their coordination site rather distant from the hexatriene system. In this work the redox active ligand 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethane‐1,2‐dione is described, which reacts with [V(TMEDA) 2 Cl 2 ] to give a rare non‐oxido vanadium(IV) species 3( M,M/P,P ) . This blue complex has two bidentate en‐diolato ligands which chelate the V IV center and give rise to two five‐membered metallacycles with the adjacent hexatriene DTE backbone bearing axial chirality. Upon irradiation with UVA light or prolonged heating in solution, the blue compound 3 (M,M/P,P ) converts into the purple atropisomer 4( para,M/para,P ) . Both complexes were isolated and structurally characterized by single‐crystal X‐ray diffraction analysis (using lab source and synchrotron radiation). The antiparallel configuration ( M or P helicity) present in both 3( M,M/P,P ) and 4( para,M/para,P ) is a prerequisite for (reversible) 6π cyclization reactions. A CW EPR spectroscopic study reveals the metalloradical character for 3( M,M/P,P ) and 4( para,M/para,P ) and indicates dynamic reversible cyclization of the DTE backbone in complex 3( M,M/P,P ) at ambient temperature in solution.