Non‐Oxido‐Vanadium(IV) Metalloradical Complexes with Bidentate 1,2‐Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution

Abstract

Derivatives of 1,2-dithienylethene (DTE)h ave 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 motifsc ommonly incorporate their coordination site ratherd istantf rom the hexatriene system.I nt his work the redoxa ctive ligand 1,2-bis(2,5-dimethylthiophen-3-yl)ethane-1,2-dione is described,w hich reacts with [V(TMEDA) 2 Cl 2 ]t og ive ar are nonoxido vanadium(IV) species 3(M,M/P,P).T his blue complex has two bidentate en-diolato ligandsw hich chelate the V IV center and give rise to two five-membered metallacycles with the adjacent hexatriene DTE backboneb earing axial chirality.U pon irradiation with UVAl ight or prolonged heating in solution, the blue compound 3(M,M/P,P) converts into the purple atropisomer 4(para,M/para,P).B othc omplexes 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 aprerequisite for (reversible)6 p cyclization reactions. AC WE PR spectroscopic study reveals the metalloradical character for 3(M,M/P,P) and 4(para,M/para,P) and indicatesd ynamic reversible cyclization of the DTE backbonei nc omplex 3(M,M/ P, P ) at ambient temperature in solution.

A photo-switchable molecular capsule: sequential photoinduced processes

“…Uncoordinated diarylethene based ligands such as (DAE) in their ring-open form exist as a mixture of three rapidly interconverting isomers in solution, namely, a pair of enantiomers R a , R a, and S a ,S a that adopt the antiparallel conformation (O A ) and the meso R a , S a isomer that adopts the parallel (O P ) conformation. 29 Only (O A ) can undergo light-driven conrotatory electrocyclization to yield a racemic mix of R, R, and S, S ring closed forms with extended conjugation (Figure 2). Molecular capsule (1) is constructed by bridging two trilacunary Please do not adjust margins Please do not adjust margins {PMo 9 } polyanions with three molecules of (O A ).…”

Hexacoordinated MIV (M=Ti, Zr, Hf) Tetrachlorido Complexes with Chelating Dithienylethane Based 1,2 Diketone Ligand – π‐Conjugation as Decisive Factor for Axial Chirality Mode

“…Hence the rotation about the two C−C axes (C1−C7; C8−C9) is hampered. We have identified this structural feature as decisive for the nature and number of the chiral axes with respect to the closely related complexes with a five‐membered metallacycle carrying the en‐diolato ligand (1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethene‐1,2‐diolate, Scheme 1, B , a ), [18] which encompass thiophene rings that are not coplanar to their neighboring five‐membered metallacycle. While the latter results in two C−C chiral axes leading to chiral helicity (Scheme 2, E ), the former gives rise to only one chiral axis (C7−C8) thus bringing forth axial chirality as, for instance, observed for classical biaryl compounds (Scheme 2, F ).…”

“…We have recently reported on the novel DTE‐based complexes encompassing a five‐membered metallacycle including an chelating en‐diolato motif, which coordinates a vanadium(IV) metal center in direct proximity of the hexa‐trien system (Scheme 1, B ). The obtained compounds showed interesting interconversion of distinct atropisomers upon irradiation with UV light and evidence was observed for dynamic reversible C−C bond formation within the ligand backbone, indicating a fast cyclization/ring‐opening in solution [18] . The synthesis involved the in‐situ reduction of the pre‐ligand 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethane‐1,2‐dione ( 1 , DTEthane ) to the corresponding en‐diolato motif (1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethene‐1,2‐diolate) by an excess of the V(II) precursor.…”

“… A Generalization of the rotameric structures in dithienylethene photochromic switches (DTE); B in‐situ reduction of 1,2‐diketone (1) by V(II) to form a [VO 2 C 2 ] en‐diolato metallacycle; [18] C and D Synthesis of complex 2 – 4 .…”

“…The typical alkene motif, as part of a (metalla) cyclic system [18–20] with the two thiophene groups in mutual cis ‐arrangement, gives rise to two C−C rotational axes and therefore different rotameric configurations can occur. The rotamers can be described according to the alignment of the thiophenes and the observed helicity: That is, two helical structures with antiparallel alignment of the thiophene units in M‐ and P‐helicity, respectively, can arise, as well as a conformer in parallel alignment (see Scheme 1, A ) [21] .…”