Photocatalyzed oxidation of cyclohexene and cyclooctene with (nBu(4)N)(4)W10O32 and (nBu(4)N)(4)W10O32/Fe-III[meso-tetrakis(2,6-dichlorophenyl)-porphyrin] in homogeneous and heterogeneous systems

Photoexcitation of (nBu(4)N)(4)W10O32 is a suitable mean of oxidizing cyclo hexene and cyclooctene with O-2 at room temperature and pressure. This proc ess can be carried out in homogeneous solution as well as using the decatun gstate in a dispersed form after its heterogenisation on silica. Cyclohexen e and cyclooctene are mainly oxidized to the corresponding hydroperoxides a s a consequence of primary photoprocesses which lead to the formation of al lylic radicals. The presence of the Fe-III[meso-tetrakis (2,6-dichloropheny l)porphyrin] chloride as cocatalyst strongly affects the photocatalytic pro perties of (nBu(4)N)(4)W10O32, playing a key role in the allylic-hydroperox ide dependent oxidation of the cycloalkenes. In the photooxidation of cyclo hexene, the porphyrin increases the photocatalytic efficiency of the decatu ngstate in terms of total turnover number and catalyses the decomposition o f cyclohexenyl hydroperoxide with the selective formation of cyclohex-2-en- 1-ol. On the other hand, its presence during the photoinduced oxidation of cyclooctene favours the formation of cyclooctene epoxide by addition of ROO . and RO . radicals to the double bond. In the case of cyclooctene, the he terogenisation of the decatungstate on the solid support also affects the c hemoselectivity of the photocatalytic process in the absence of the iron po rphyrin complex.