Covalently immobilized porphyrins on silica modified structures as photooxidation catalysts

Heterogeneous photooxidation catalysts were prepared by the covalent linkage of a porphyrin to aminoalkylated silica particles by chlorosulphonation activation of the porphyrin nucleus. These catalysts were tested in [4+2] cycloaddition and ene reactions promoted by singlet oxygen. Photooxidation of substrates originates high yields of products but with longer reaction times compared to the free porphyrin catalysts. Quenching of singlet oxygen by the silica structure can be the plausible explanation. In the case of the ene reaction with citronellol the supported catalysts originate a distribution of the regioisomeric products which is opposite to that of the homogeneous catalyst.

Covalent immobilization of a porphyrin on silica modified structures was achieved through a selective chlorosulphonation reaction. The resulting heterogeneous catalysts are active in singlet oxygen oxidation of α-terpinene and citronellol.Figure optionsDownload high-quality image (53 K)Download as PowerPoint slide