Redox properties of photoexcited (nBu4N)3PW12O40/FeIIIporphyrins composite systems
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- 作者：Maldotti ; Andrea ; Molinari ; Alessandra ; Argazzi ; Roberto ; Amadelli ; Rossano ; Battioni ; Pierrette ; et. al.
- 关键词：Polyoxotungstates ; Photocatalysis ; Iron porphyrins ; Oxygen activation ; Laser flash photolysis ; Biomimetic oxidation
- 刊名：Journal of Molecular Catalysis A: Chemical
- 出版年：1996
- 出版时间：December 23, 1996
- 年：1996
- 卷：114
- 期：1-3
- 页码：141-150
- 全文大小：553 K
文摘
The photochemical and photocatalytic properties of (nBu4N)3PW12O40 (PW12O3−40) was investigated in the presence of several FeIII-meso-tetrarylporphyrins. The photochemical excitation of the polyoxotungstate in the presence of 2-propanol or cyclohexane leads to its reduction and simultaneous oxidation of the organic substrate. The reduced polyoxotungstate is able, in turn, to transfer one electron to the FeIII porphyrin to give the ferrous complex. In the presence of anaerobic cyclohexane, σ-alkyl-FeIII complexes are obtained as a consequence of the reaction between cyclohexyl radicals and the iron porphyrin in its reduced form. Subsequent oxidative migration of the σ-bound cyclohexyl group from the iron to one of the pyrrole nitrogens leads to the formation of N-substituted porphyrin. The results obtained by laser flash photolysis experiments indicate that the electron transfer from the photoreduced polyoxotungstate to the FeIIIporphyrin complexes is faster than to O2. Therefore, the photoexcited polyoxotungstate can operate as a source of electrons for the reduction of the FeIIIporphyrin to the ferrous form, thus creating the site at which O2 is reductively activated. Continuous irradiation of the composite systems under aerobic conditions leads to the oxidation of cyclohexane to cyclohexanol and cyclohexanone. In comparison with the FeIIIporphyrins alone, the composite photocatalysts present higher yields of the oxidation products. In comparison with PW12O3−40 alone, they produce higher amounts of the hydroxylated product.