FACTORS WHICH AFFECT THE CATALYTIC ACTIVITY OF IRON(III) MESO TETRAKIS(2,6-DICHLOROPHENYL)PORPHYRIN CHLORIDE IN HOMOGENEOUS SYSTEM

An optimization study of the reaction conditions of Fe(TDCPP)Cl when i t is used as catalyst in the hydroxylation of cyclohexane by iodosylbe nzene (PhIO) has been carried out, It was found that Fe(TDCPP)Cl follo ws the classical PhIO mechanism described for Fe(TPP)Cl, which involve s the monomeric active species Fe-IV(O)P-+. (I). In the optimized cond ition ([Fe(TDCPP) = 3.0 X 10(-4) mol l(-1) in 1,2-dichloroethane (DCE) ; ultrasound stirring at 0 degrees C; PhIO/FeP molar ratio = 100), thi s FeP led to a yield of cyclohexanol (C-ol) of 96% and a turnover numb er of 96, Therefore, Fe(TDCPP)Cl may be considered a good biomimetic m odel and a very stable, resistant and selective catalyst, which yields C-ol as the sole product. DCE showed to be a better solvent than dich loromethane (DCM), 1 DCE:1 MeOH mixture or acetonitrile (ACN). Since t he Fe-IV(O)P-+. is capable of abstracting hydrogen atom from DCM, MeOH or ACN, the solvent competes with the substrate. Presence of O-2 lowe rs the yield of C-ol, as it can further oxidize this alcohol to carbox ylic acid in the presence of radicals, Presence of H2O also causes a d ecrease in the yield, since it converts the active species I into Fe-I V(OH)P, which cannot oxidize cyclohexane. Addition of excess imidazole or OH- to the system results in a decrease in the yield of C-ol, due to the formation of the hexacoordinated complexes Fe(TDCPP)Im(2)(+) (l ow-spin, beta(2) = 2.5 X 10(8) mol(-2) l(2)) and Fe(TDCPP)(OH)(2)(-) ( high-spin, beta(2) = 6.3 X 10(7) mol(-2) l(2)), The formation of both Fe(TDCPP)Im(2)(+) and Fe(TDCPP)(OH)(2)(-) complexes were confirmed by EPR studies. The catalytic activities of Fe(TDCPP)C and Fe(TFPP)Cl wer e compared, The unusually high yields of C-ol with Fe(TFPP)Cl obtained when ultrasound, DCM and O-2 atmosphere were used, suggest that a par allel mechanism involving the mu-oxo dimer form, O-2 and radicals may also be occurring with this FeP, besides the PhIO mechanism.