Thiophene-benzoquinones: synthesis, crystal structures and preliminary coordination chemistry of derived anilate ligands

Abstract

2,5-Bis(thiophene) and 2,5-bis(ethylenedioxy-thiophene) (EDOT) derivatives of 3,6-diethoxy-1,4-benzoquinone (para isomers) were prepared by Stille coupling between the 2,5-dibromo-3,6-diethoxy-1,4-benzoquinone precursors and (n-Bu)3Sn-R (R = 2-thiophenyl or 3,4-ethylenedioxy-2-thiophenyl) reagents. In a parallel series of experiments 2,6-bis(thiophene) and 2,6-EDOT-3,5-diethoxy-1,4-benzoquinone (meta isomers) were synthesized by the same strategy. The four compounds were structurally characterized. The thiophene derivatives show essentially planar conformation thanks to the conjugation and establishment of S···O 1,5-nonbonded interactions, while in the EDOT derivatives the thiophene moieties are twisted with respect to the benzoquinone ring because of the steric hindrance. TD-DFT calculations were performed on both para and meta thiophene isomers in order to explain the differences observed in the UV-Vis absorption spectra. The 2,5-derivatives are valuable precursors for thiophene containing anilate (An) ligands, as the first examples of electron rich substituent based anilates. The Cu(II) complex [Cu(Th2An)(tbbpy)]·2H2O (Th2An = thiophene-anilate; tbbpy = 4,4'-bis(tert-butyl)-2,2'-bipyridine) was isolated and structurally characterized. The metal center lies within a square planar coordination geometry, while the ligands engage in a set of intermolecular contacts.

Recent Advances on Anilato-Based Molecular Materials with Magnetic and/or Conducting Properties

“…The paramagnetic anionic complexes worked well as magnetic components of multifunctional molecular materials based on BEDT-TTF organic donors (24)(25)(26)(27) which has furnished the pathway for combining electrical conductivity with magnetic properties, in analogy with the relevant class of [M(ox) 3 ] 3− (ox = oxalate) tris-chelated complexes which have produced the first family of molecular paramagnetic superconductors. The introduction of chirality in the BEDT-TTF organic donor has been successful and a complete series of radical-cation salts have been obtained by combining the TM-BEDT-TTF organic donor in its (S,S,S,S) and (R,R,R,R) enantiopure forms, or their racemic mixture (rac), with 2D heterobimetallic anionic layers formed "in situ" by self-assembling of the tris(chloranilato)ferrate(III) metal complexes in the presence of potassium cations in the usual honey-comb packing pattern (28)(29)(30). Another advantage of anilato-ligands compared to the oxalato ones is their bigger size leading to hexagonal cavities that are twice larger than those of the oxalato-based layers, where a large library of cationic complexes can be inserted.…”

Switching-on luminescence in anilate-based molecular materials

“…The special interest devoted to this class of ligands is related to (i) the ability to coordinate metal ions in various coordination modes, 10 (ii) the ability to further coordinate a second metal ion due to the presence of two peripheral coordinating C-O groups, 10,[14][15][16][17] (iii) non-innocent redox properties and an easy reduction process to a radical-anion form. 10,19,20 Moreover, anilate ligands can be easily functionalized by introducing suitable substituents on the 3 and 6 positions which are capable of (i) modulating the magnetic exchange interactions between coordinated metal ions, 14,21 (ii) giving rise to various supramolecular interactions which affect the dimensionality and the physical properties of the final system, [11][12][13]22 and (iii) promoting intramolecular charge-transfer (CT) towards the electron-poor benzoquinone moiety, 23 without affecting the coordinating properties.…”

Combined Experimental/Theoretical Study on the Luminescent Properties of Homoleptic/Heteroleptic Erbium(III) Anilate-Based 2D Coordination Polymers

“…14,15 On the other hand, CPs based on 3,5-disubstituted-2,6-dihydroxy-1,4-benzoquinone, commonly called anilates, have been widely studied over the past decade. [16][17][18][19] Anilates are excellent building blocks for constructing layered mono/multifunctional materials showing magnetic, [20][21][22][23][24][25] conducting, [26][27][28][29] and luminescent properties. [30][31][32] Among them, the first example of heterosubstituted anilate, the chlorocyananilate ligand (3-chloro-6-cyano-2,5-dihydroxybenzoquinone-ClCNAn 2-), is an interesting antenna linker for constructing Ln-CPs, due to the absence of IR quenchers in its molecular structure.…”