Anchored ironporphyrins - the role of talc-aminofunctionalyzed phyllosilicates in the catalysis of oxidation of alkanes and alkenes

FcTFPPCl [5,10,15,20-tetrakis(pentafluorophenyl)porphyrin iron(III) chloride] has been covalently supported on two series of previously aminated phyllosilicates, Talx (natural) and Silx (synthesized through sol/gel process), where x (=1-3) represents the length of the organic chain (arms) binding the ironporphyrin to the support. These systems have been characterized (UV-Vis, IR and EPR) and used as catalysts for the oxidation of alkanes and alkenes by iodosylbenzene and hydrogen peroxide. All systems proved to be efficient catalysts for cyclohexane hydroxylation and alkene epoxidation with both oxidants. FeTalx are better catalysts than FeSilx for all the investigated substrates. The intermediate arms of FeTal2 have been the most adequate since they are not short enough to maintain the ironporphyrin near the polar support or long enough to favor axial bis-coordination of the free amino group to the iron center. Protection of the excess NH2 groups through acetylation was essential to prevent such bis-coordination and improve product yields. Surprisingly, FeTalx systems have proved better catalysts for such hydrocarbon oxidations with hydrogen peroxide than the homogeneous iron porphyrin. (C) 2004 Elsevier B.V. All rights reserved.