Laser-flash photolysis of naphthyl diselenides; reactivities of naphthylseleno radicals

Abstract

Transient absorption spectra of 1-naphthylseleno and 2-naphthyl-и(1-NaphSe ), seleno radicals, which are generated by laser-flash photolysis of the correspond-и (2-NaphSe ) ing diselenides, were observed. The reactions of and with 2-methyl-и и 1-NaphSe , 2-NaphSe 1,3-butadiene and ␣-methylstyrene were investigated by following the decay rates of these seleno radicals. By both steady-state and laser-flash photolysis, it is proved that these seleno radicals add to alkenes in a reversible manner. The reaction rate constants for such reversible addition reactions were determined by conducting the reaction in the presence of O 2 , which traps selectively the carbon-centered radicals formed by the addition reaction of the seleno radicals to the alkenes. The reactivity of is higher than that of both of и и 2-NaphSe 1-NaphSe , which are less reactive than These reactivities were interpreted with the properties of и PhSe . SOMO calculated by MO method.

A Novel Antioxidant Mechanism of Ebselen Involving Ebselen Diselenide, a Substrate of Mammalian Thioredoxin and Thioredoxin Reductase

“…The ebselen diselenide has two strong and broad absorption bands (from 250 to 300 nm and from 300 to 420 nm) overlapping each other. The band from 250 to 300 nm can be ascribed to the phenyl moieties, and a tailed broad band from 300 to 420 nm is caused by the Se-Se moiety (36). The extinction coefficient of (EbSe) 2 at 340 nm (⑀ 340 ) was calculated to be 21,000 M Ϫ1 cm Ϫ1 using several known concentrations of (EbSe) 2 .…”

Selenium–Selenium Bond Cleavage of Diaryl Diselenide Radical Anions During Pulse Radiolysis

“…<PhSe . ,15 thus suggesting that the electronic interaction between the aromatic group and Se atom decreases in the order of α NpSe . > β NpSe .…”

“…The excited state of a NpSeSe a Np generated during the 355 nm laser flash photolysis in tetrahydrofuran underwent SeÀSe bond scission to provide the corresponding a-naphthylselenyl radical ( a NpSeC) with absorption bands at 420, 635, and 690 nm. [15] In pulse radiolysis of a substrate in benzene (Bz), ionization of Bz gave excited species of the substrate by charge recombination of the substrate ionization species. [16] The absorption peaks at 420, 620, and 690 nm are similar to those of a NpSeC generated during the pulse radiolysis of a NpSeSe a Np in Bz (Figure 1c, dotted line).…”

“…This is consistent with the k values for the mesolysis, that is, PhSeSePhC À > b NpSeSe b NpC À > a NpSeSe a NpC À . Alam et al reported that the unpaired electron density of the singly occu-pied molecular orbital (SOMO) at the Se atom in ArSeC increases in the order of a NpSeC < b NpSeC < PhSeC, [15] thus suggesting that the electronic interaction between the aromatic group and Se atom decreases in the order of a NpSeC > b NpSeC > PhSeC. However, no electronic interaction is involved between methyl substituents, and the spin density is sufficiently localized on the SeÀSe bond of MeSeSeMeC À .…”

Visible‐Light Promoted Stereoselective Arylselanyl Functionalization of Alkynes

“…The yields, reaction times and stereoselectivity were highly dependent on the alkyne substituents and ( ii ) the use of visible light (Xenon, >300 nm) on similar transformations, e.g., reduction of dienes with benzenethiol and diphenyl diselenide to internal alkenes, also on three‐component coupling between diphenyl diselenide, alkenes and ethyl propiolate . They propose the formation of α‐seleno radical specie, which was already observed by trapping with isoprene in the absence of oxygen …”