| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1987: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1986: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
The reaction pathway for photochemical epoxidation of olefins along with activation of molecular oxygen as catalyzed by niobium and molybdenum porphyrins was presumed to consist of the following steps: photoreduction of metalloporphyrins, coordination of molecular oxygen to the reduced complex to from oxygenated metalloporphyrins, transfer of an exygen atom from the oxygenated complex to a substrate, and regeneration of the oxygenated complex. Effects of solvents, coexisting species, and structure of a catalyst, the porphyrin complex, on the epoxidation reaction were studied.
1. Effects of coexisting ligands. Photoreduction of niobium and molybdenum porphyrin in benzene under anaerobic irradiation conditions was accelerated on addition of alcohols or phenols to the reaction system. Alcohols and phenols coordinated to the reduced complex afforded oxoalkoxo- or oxophenoxo-metalloporphyrins. Alkoxo complexes reacted readily with molecular oxygen to afford oxygenated complexes, while phenol
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ligands disturbed oxygenation becuase of the strong coordination tendency of phenols. The oxygenated complex reacted readily with alcohols or phenols to form inactive alkoxo complexex or radikal complexes containing phenol ligands. Solvents or coexisting molecules having an oxygen donor atom disturbed the epoxidation reaction, despite of acceleration of the first step of the reaction.
2. Steric effect of porphyrin ligands. Introduction of picket-fence substituent groups into the porphyrin ligand reduced the catalytic activity for bulky substrates such as norbornene and cyclododecene. For smaller substrates, both catalytic activity and substrate selectivity were enhanced by introduction of the fence to the porphyrin ligand. The enhancement of catalytic activity was presumed to be originated from protection of oxygenated species from bimolecular deactivation. The enhancement of substrate selectivity was attributed to an increase in steric interaction between a substrate and the porphyrin ligand.
3. Active intermediate in the photochemical epoxidation. The epoxidation reaction proceeded via retention of configuration for cis- and trans-1,2-disubstituted olefins, indicating strongly that the reaction proceeded via formation of an ion-pair intermediate. Less
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