Photoinduced reactions of 1-(dimethylethyl)-2,2-dimethylpropyl and cyclohexyl radicals in low-temperature solids

Koizumi, Hideaki; Takada, Tomoya; Ichikawa, Tsuneki; Lund, Anders

doi:10.1016/s0009-2614(01)00428-6

Cited by 4 publications

(3 citation statements)

References 14 publications

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“…As described, photoirradiation to all three catalysts with O 2 (1 Torr) at 77 K does not show ESR signals assigned to oxygen radicals (O 2 •- , O 3 •- ), ,, meaning that oxygen radicals are not involved in the photocatalytic reactions occurring on T d 4+ * and T d 5+ * species. As shown in Figure A, ii, photoirradiation to Cr−SiO 2 with CHA (1 Torr) at 77 K does not show any signals of radical species derived from CHA, but leads to an appearance of a new T d 5+ * signal ( g ⊥ = 1.978; g ∥ = 1.967). The O T , formed by photoinduced electron transfer, has an electrophilic character and, hence, acts as a positive hole .…”

Section: Resultsmentioning

confidence: 90%

Visible Light-Induced Partial Oxidation of Olefins on Cr-Containing Silica with Molecular Oxygen

2006

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Photocatalytic oxidation of olefins on Cr-containing silica with molecular oxygen by visible light irradiation (lambda > 400 nm) has been investigated. Cr-SiO(2) catalyst prepared by a conventional sol-gel method, containing highly dispersed chromate species, catalyzes efficient olefin oxidation with very high selectivity for partially oxidized products (>90%), whereas semiconductor TiO(2) promotes complete decomposition (CO(2) production). The Cr-SiO(2) catalyst shows much higher activity than Cr/SiO(2) prepared by an impregnation method or Cr proportional variant MCM-41 prepared by a templating method. ESR analysis reveals that photoirradiation of the chromate species with a tetrahedral coordination (T(d)(6+)) on Cr/SiO(2) and Cr proportional variant MCM-41 catalysts leads to the formation of excited state T(d)(5+) species (T(d)(5+*)), while irradiation to T(d)(6+) on Cr-SiO(2) produces T(d)(4+*) species. This can be explained by a homogeneous T(d)(6+) arrangement with Si species on the Cr-SiO(2) catalyst. On the strongly reduced T(d)(4+*), olefins are strongly attracted by an electron and/or proton donation, resulting in high oxidation activity. The Cr-SiO(2) catalyst is applicable to partial oxidation of various aliphatic and aromatic olefins with very high selectivity, and does not promote undesirable dimerization. The obtained findings suggest a potential use of Cr-SiO(2) as an efficient and recyclable heterogeneous photocatalyst for partial oxidation of olefins.

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Section: Resultsmentioning

confidence: 90%

Visible Light-Induced Partial Oxidation of Olefins on Cr-Containing Silica with Molecular Oxygen

2006

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“…15 Photoirradiation to Cr-SiO 2 with cyclohexane (1 Torr) without O 2 at 77 K (see Fig. S2{) leads to an appearance of a new signal (g H 5 1.979, g || 5 1.968), which is not attributable to a cyclohexanyl radical 18 *. Cyclohexanone may form via reaction of this complex with O 2 (Scheme 1).…”

Section: +mentioning

confidence: 97%

Visible light-induced selective oxidation of cyclohexane to cyclohexanone on Cr–Si binary oxide with molecular oxygen

2005

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“…Radical clocks have played an important role in disentangling the mechanistic subtleties of classical organic chemistry, − organometallic chemistry, − photochemistry, − and bioorganic and bioinorganic chemistries. − These molecular tools, which make it possible to monitor, at a microscopic level, which elementary steps occur in an overall transformation, have been far less used to gain insight into the events occurring at the solid−liquid interface involved in electrochemically induced reactions . Hoffmann recently discussed the relative overlook of this tool to study reactions at the solid−liquid interface .…”

Section: Introductionmentioning

confidence: 99%

Radical Clocks, Solvated Electrons, and Magnesium. Heterogeneous versus Homogeneous Electron Transfer. Selectivity at Interfaces

Hazimeh¹,

Kanoufi²,

Combellas³

et al. 2008

J. Phys. Chem. C

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Ammonia solutions of solvated electrons may be prepared by electrolyzing the solvent in the presence of Mg(BF4)2 and Mg++ provided by a magnesium anode. The reactions of these solutions (−40 °C) with the two radical clocks 1-bromo-2-(3-butenyl)benzene 1 and 1-(allyloxy)-2-bromobenzene 7 (0.007−0.008 M) are examined. Both probes yield very high percentages of cyclized products (>97%) when the concentration of solvated electrons is low (0.028 M). These percentages diminish when the metallic character of the solution is increased (0.183 M concentration in solvated electrons). These results strongly contrast with those obtained for the reactions of these radical probes with magnesium turnings or potassium lumps in THF. Under these conditions, the percentages of cyclized products are lower than 4%. We propose that the main cause of this contrasting behavior is the higher reducing efficiency of the heterogeneous electron transfer with respect to the homogeneous electron transfer. This holds even if the reducing agent in the bulk is one of the strongest known reducing agents (solvated electron). The causes for the striking difference between heterogeneous and homogeneous electron transfer are discussed in terms of selectivity within a double-layer perspective. These differences allow the rationalization of an apparent discordance. The behavior of MgX2 (X = halogen) under pulse radiolysis conditions (Mostafavi's group) shows that MgX2 are so weakly oxidizing that in most solvents they do not react with the solvated electron. Nevertheless, the reduction of MgX2 by alkali metals (Rieke's method) is the basis for the preparation of very active slurries of magnesium. This principle has been widely extended for the preparation of various metallic nanoparticles. The difference between homogeneous and heterogeneous electron transfer to MgX2 lies at the heart of the problem as explained in the framework of molecular electrochemistry at the cathode surface. Kinetic treatment of the selectivity at the metal−liquid interface is contrasted with selectivity obtained in homogeneous solution.

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Photoinduced reactions of 1-(dimethylethyl)-2,2-dimethylpropyl and cyclohexyl radicals in low-temperature solids

Cited by 4 publications

References 14 publications

Visible Light-Induced Partial Oxidation of Olefins on Cr-Containing Silica with Molecular Oxygen

Visible Light-Induced Partial Oxidation of Olefins on Cr-Containing Silica with Molecular Oxygen

Visible light-induced selective oxidation of cyclohexane to cyclohexanone on Cr–Si binary oxide with molecular oxygen

Radical Clocks, Solvated Electrons, and Magnesium. Heterogeneous versus Homogeneous Electron Transfer. Selectivity at Interfaces

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