Metal-Promoted Intermolecular Electron Transfer in Tetrathiafulvalene–Thiacalix[4]arene Conjugates and Tetrachlorobenzoquinone

Abstract

In this work, two series of tetrathiafulvalene (TTF) and thiacalix[4]arene (TCA) conjugates (TTF-TCA) were designed by CuAAC click reactions. The results obtained from NMR and (1)H NMR NOE indicated that their conformations of thiacalix[4]arene framework may prefer to 1,3-alternate. The cyclic voltammograms of four TTF-TCA compounds containing electroactive TTF units were provided. Meanwhile, their intermolecular electron-transfer (ET) behaviors with tetrachlorobenzoquinone (Q) mediated by different metal ions, Sc(3+), Pb(2+), Ag(+), Cd(2+), and Zn(2+), in CH3CN-CH2Cl2 (V/V = 1:1) solution were studied and analyzed via UV-vis spectroscopy. It was determined that intermolecular ET between each TTF-TCA and Q ensemble was not observed without introduction of the metal ions mentioned above. The added specified metal ions most likely induced the intermolecular ET between TTF-TCA and Q ensemble, and the effects of Sc(3+) functions were the most imperative. The intermolecular ET also proved to be reliant on the structure of TTF-TCA, where TTF-TCA 7a and 7b were more effective than TTF-TCA 6a and 6b. The difference may be credited to TTF-TCA 7a or 7b possessing two independent TTF pendants and providing a more synergic coordination among the TTF radical cation and Q radical anion with a metal ion.

Redox‐Responsive Macrocyclic Hosts Based on Calix[4]arene and Calix[4]resorcinarene Scaffolds

“…Several low rim TTF‐calixarene conjugates were prepared using the click reaction between TTF‐azide and calixarene‐propyne derivatives [116,117] . These receptors were used to study intermolecular electron transfer (ET) to quinone acceptors promoted by the simultaneous complexation of the metal ions.…”

“…These receptors were used to study intermolecular electron transfer (ET) to quinone acceptors promoted by the simultaneous complexation of the metal ions. In particular, one example of thiacalix[4]arene receptor 12 it was shown that ET between TTF and Q was possible only upon complexation of metal ions (such as Sc 3+ , Pb 2+ , Ag + , Cd 2+ , and Zn 2+ ) between two “legs” on the lower rim of thiacalixarene [117] . Intramolecular ET was investigated using calixarene derivatives with electron donors (TTF) and acceptors (quinone) attached side‐by‐side to the calixarene scaffold [118,119] .…”

“…In particular, one example of thiacalix [4]arene receptor 12 it was shown that ET between TTF and Q was possible only upon complexation of metal ions (such as Sc 3 + , Pb 2 + , Ag + , Cd 2 + , and Zn 2 + ) between two "legs" on the lower rim of thiacalixarene. [117] Intramolecular ET was investigated using calixarene derivatives with electron donors (TTF) and acceptors (quinone) attached side-by-side to the calixarene scaffold. [118,119] Receptor 13, with adjacent TTF, quinone, and crown ether-type loop on the lower rim of calix [4]arene, was designed and synthesized to study intramolecular electron transfer promoted by the metal ions coordinated to the crown ether domain of the molecule.…”

Scandium Ion-Promoted Electron-Transfer Disproportionation of 2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-Oxide (PTIO•) in Acetonitrile and Its Regeneration Induced by Water

“…Redox-inactive metal ions have attracted much attention because they are known to affect the redox behavior of redox active compounds acting as a Lewis acid [1][2][3][4][5][6][7][8][9]. Among such metal ions, scandium ion (Sc 3+ ) shows the strongest Lewis acidity because of the small ionic radius with trivalent positive charge, leading to a significant positive shift of the reduction potentials of compounds [10][11][12][13][14][15][16][17][18][19][20][21][22][23], including metal-oxygen complexes [19][20][21] and radical species [22,23]. Of special interest is the fact that Sc 3+ enables the electrontransfer reactions, which would otherwise never take place in the absence of Sc 3+ , to occur thermodynamically as well as kinetically [10][11][12][13][14][15]20,21].…”

“…Among such metal ions, scandium ion (Sc 3+ ) shows the strongest Lewis acidity because of the small ionic radius with trivalent positive charge, leading to a significant positive shift of the reduction potentials of compounds [10][11][12][13][14][15][16][17][18][19][20][21][22][23], including metal-oxygen complexes [19][20][21] and radical species [22,23]. Of special interest is the fact that Sc 3+ enables the electrontransfer reactions, which would otherwise never take place in the absence of Sc 3+ , to occur thermodynamically as well as kinetically [10][11][12][13][14][15]20,21]. We have reported that an electrontransfer disproportionation of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH • ) occurs upon the addition of scandium triflate, Sc(OTf)3 (OTf = OSO2CF3), to an acetonitrile (MeCN) solution of DPPH • to produce one-electron-oxidized and -reduced species of DPPH • , DPPH + , and DPPH − , respectively [23].…”