Synthesis of Iron Phthalocyanine Grafted onto SBA-15 through Single Siloxane Bond and its Application in Liquid-Phase Hydroxylation of Phenol

Abstract

For a long time, iron phthalocyanines are well known as efficient oxidation catalysts. However, the use of ungrafted tert-butyl-substituted iron phthalocyanine (tBuPcFe) complexes is severely limited by the necessity of their isolation from the reaction mixtures after catalytic reactions. This drawback can be avoided by applying their immobilization upon the surface of inorganic supports such as silica gel, MCM-41 or SBA-15. Immobilization of tBuPcFe can be performed through simple adsorption, [1] coordinative bonding with an anchoring group[2,3] and covalent bonding with surface silanol groups of the support.[4] Both free and heterogenized tBuPcFe complexes have been shown to be active in oxidation of cyclohexane,[5] phenol,[2] 2,3,6-trimethylphenol[4] and 2-methyl-1-naphthol.[6] The covalent attaching of Pc complex is also possible by siloxane bond if Pc has an (alkoxy)3Si-containing substituent. In this case siloxane bond is formed between a silicon atom of Pc and oxygen atom of support surface. Iron(III) phthalocyanine complexes symmetrically substituted by (EtO)3Si functional groups were described previously,[7] but monomeric derivatives seem to be more suitable for controlled immobilization that affords a stable heterogeneous catalyst with spatially separated active iron species.