The photooxidation of various olefins in homogeneous solution under an oxygen atmosphere, using visible light, a dye sensitizer, and an oxygen-transfer catalyst has been investigated. The oxygen transfer from molecular oxygen to olefin involves the following steps: i) photoinduced singlet-oxygen formation, ii) alkylhydroperoxide formation through ene-reaction, iii) intermediacy of a reactive molybdenum-peroxide, and iv) olefin epoxidation of the remaining substrate or of a second olefin. Among the various sensitizers and catalysts tested, electron deficient free base porphyrin 5,10,15,20-tetrakis(2’,6’-dichlorophenyl)-b-octabromoporphyrin and molybdenum hexacarbonyl showed the best performances in terms of robustness and activity. Under proper conditions, a complete olefin conversion may be obtained, adopting molar ratios of sensitizer/catalyst/substrate=1/50/2000, with the formation of the corresponding epoxide up to 38% yield, which corresponds to 77% of the theoretical maximum. Quite interestingly, olefins reluctant to undergo ene-reaction may be epoxidized in the presence of a second sacrificial olefin yielding the corresponding epoxides with up to 80% total selectivity.

Photoinitiated Olefin Epoxidation with Molecular Oxygen, Sensitized by Free Base Porphyrins and Promoted by Hexacarbonylmolybdenum in Homogeneous Solution

CAMPESTRINI, SANDRO;TONELLATO, UMBERTO
2002

Abstract

The photooxidation of various olefins in homogeneous solution under an oxygen atmosphere, using visible light, a dye sensitizer, and an oxygen-transfer catalyst has been investigated. The oxygen transfer from molecular oxygen to olefin involves the following steps: i) photoinduced singlet-oxygen formation, ii) alkylhydroperoxide formation through ene-reaction, iii) intermediacy of a reactive molybdenum-peroxide, and iv) olefin epoxidation of the remaining substrate or of a second olefin. Among the various sensitizers and catalysts tested, electron deficient free base porphyrin 5,10,15,20-tetrakis(2’,6’-dichlorophenyl)-b-octabromoporphyrin and molybdenum hexacarbonyl showed the best performances in terms of robustness and activity. Under proper conditions, a complete olefin conversion may be obtained, adopting molar ratios of sensitizer/catalyst/substrate=1/50/2000, with the formation of the corresponding epoxide up to 38% yield, which corresponds to 77% of the theoretical maximum. Quite interestingly, olefins reluctant to undergo ene-reaction may be epoxidized in the presence of a second sacrificial olefin yielding the corresponding epoxides with up to 80% total selectivity.
2002
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2459596
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