A Mechanistic Study of Halogen Addition and Photoelimination from π-Conjugated Tellurophenes

Abstract

The ability to drive reactivity using visible light is of importance for many disciplines of chemistry and has significant implications for sustainable chemistry. Identifying photochemically active compounds and understanding photochemical mechanisms is important for the development of useful materials for synthesis and catalysis. Here we report a series of photoactive diphenyltellurophene compounds bearing electron-withdrawing and electron-donating substituents synthesized by alkyne coupling/ring closing or palladium-catalyzed ipso-arylation chemistry. The redox chemistry of these compounds was studied with respect to oxidative addition and photoelimination of bromine, which is of importance for energy storage reactions involving X2. The oxidative addition reaction mechanism was studied using density functional theory, the results of which support a three-step mechanism involving the formation of an initial η(1) association complex, a monobrominated intermediate, and finally the dibrominated product. All of the tellurophene derivatives undergo photoreduction using 430, 447, or 617 nm light depending on the absorption properties of the compound. Compounds bearing electron-withdrawing substituents have the highest photochemical quantum efficiencies in the presence of an alkene trap, with efficiencies of up to 42.4% for a pentafluorophenyl-functionalized tellurophene. The photoelimination reaction was studied in detail through bromine trapping experiments and laser flash photolysis, and a mechanism is proposed. The photoreaction, which occurs by release of bromine radicals, is competitive with intersystem crossing to the triplet state of the brominated species, as evidenced by the formation of singlet oxygen. These findings should be useful for the design of new photochemically active compounds supported by main-group elements.

Marriage of heavy main group elements with π-conjugated materials for optoelectronic applications

“…The groups of Seferos and Scaiano combined efforts to explore the reactivity of the substituted 2,5-diaryltellurophenes 212-220 (Scheme 26) in detail. 170 These diaryltellurophenes contained a wide range of electron-donating and accepting units, with some aryl-tellurophene linkages prepared via an ipso-arylative cross coupling initially employed by Grubbs and coworkers to prepare polytellurophenes. 171,172 Compounds (212-220) were found to undergo oxidative addition of Br 2 to yield the dibromotellurophenes 221-229.…”

Anion recognition by a bidentate chalcogen bond donor

“…The concentration dependence of the decrease in absorbance at 338 nm was fitted to a 1:1 binding isotherm, giving an association constant K a of 310 AE 20 M À1 (Table 1). 16 The calculated molecular electrostatic potential of 1d in the chloride-bound conformation shows regions of electron-deficiency at tellurium and at the centroid of the perfluoroaryl group (Fig. Binding of Bu 4 N + Br À and Bu 4 N + BzO À by 1d was also observed in THF, but other anions resulted in decomposition (I À ) or showed no evidence of binding (NO 3 À , toluenesulfonate (TsO À )).…”

“…2). 16 Anion affinities were assessed by monitoring changes in optical absorbance spectra upon addition of tetrabutylammonium chloride (Bu 4 N + Cl À ) in tetrahydrofuran (THF) at 298 K. The bis(4-cyanophenyl)-and bis(4-(trifluoromethyl)phenyl)-substituted congeners 1a and 1b, as well as unsymmetrically substituted 1c, did not interact with chloride to a measurable extent under these conditions. The compounds were prepared either by reaction of the conjugated diyne with sodium telluride 14 or by palladium ipso-arylation of 2,5-bis[(diphenyl)hydroxymethyl]tellurophene, 15 as described previously.…”

Synthesis of Diphenylchalcogenophene Diboronic Acid Bis(pinacol) Esters and Halogen Photoelimination from Tellurium by Triplet–Triplet Annihilation

“…Triplet states of Te‐containing compounds are accessible owing to the heavy‐atom effect imparted by Te. Laser flash photolysis studies on substituted diphenyltellurophenes showed that intersystem crossing is competitive with halogen photoelimination from the photoactive singlet excited state . Here, we report a high‐yielding synthesis of new boronic‐ester‐capped diphenylthiophene, diphenylselenophene, and diphenyltellurophene.…”