CHARACTERIZATION AND CATALYTIC ACTIVITY OF 2,6-DICHLOROPHENYL SUBSTITUTED IRON(III) PORPHYRIN SUPPORTED ON SILICA-GEL AND IMIDAZOLE PROPYL GEL

In this work we have made use of the study of the interaction between Fe(TDCPP)(+) and the axial ligands OH- and imidazole in order to help characterize the heterogenized catalysts Fe(TDCPP)SG and Fe(TDCPP)IPG through UV-VIS and EPR spectroscopies and thus, better understand thei r different catalytic activity in the oxidation of cyclohexane by PhIO . We have found out that in Fe(TDCPP)SG (containing 1.2 X 10(-6) mol F e(TDCPP)(+)/g of support), the FeP bis-coordinates to silica gel throu gh Fe-O coordination and it is high-spin (FeP)-P-III species. In Fe(TD CPP)IPG 1 (containing 1.1 X 10(-6) mol Fe(TDCPP)(+) and 2.2 X 10(-4) m ol imidazole/g of support), the FeP is bis-ligated to imidazole propyl gel through Fe-imidazole coordination and using NO as a paramagnetic probe, we present evidence that Fe(TDCPP)(+) is present as a mixture o f low-spin (FeP)-P-III and (FeP)-P-II species. This catalyst led to a relative low yield of cyclohexanol (25%) because the bis-coordination of the (FeP)-P-III to the support partially blocks the reaction betwee n Fe(TDCPP)(+) and PhIO, thus leading to the formation of only a small amount of the active species Fe-IV(OP+, while the (FeP)-P-II species do not react with the oxygen donor. Increasing the amount of Fe(TDCPP) (+) and decreasing the amount of imidazole in the support led to the o btention of high-spin (FeP)-P-III EPR signals in the spectra of Fe(TDC PP)IPG 5 (containing 4.4 X 10(-6) mol Fe(TDCPP)(+) and 2.2 X 10(-5) mo l imidazole/g of IPG), together with low-spin (FeP)-P-III species. Thi s latter catalyst led to better cyclohexanol yields (67%) than Fe(TDCP P)IPG 1. Fe(TDCPP)IPG 5 was further used in a study of the optimizatio n of its catalytic activity and in recycling experiments in the optimi zed conditions. Recycling oxidation reactions of Fe(TDCPP)IPG 5 led to a total turnover number of 201 and total cyclohexanol yield of 201%, which could not be attained with Fe(TDCPP)Cl in homogeneous solution ( turnover = 96) due to the difficulty in recovering and reusing it.