Characterization and catalytic activity of iron(III) mono(4-N-methyl pyridyl)-tris(halophenyl) porphyrins in homogeneous and heterogeneous systems

The synthesis, characterization and catalytic activity of the cationic iron porphyrins Fe[M(4-N-MePy)TDCPP]Cl-2 and Fe[M(4-N-MePy)TFPP]Cl-2 in the epo xidation of (Z)-cyclooctene by PhIO in homogeneous solution and supported o n silica gel (SG), imidazole propyl gel (IPG) or SG modified with 2-(4-sulf onatophenyl)ethyl groups (SiSO3) have been accomplished. When supported on IPG, both cationic FeP bind to the support via Fe-imidazole coordination. F e[M(4-N-MePy)TDCPP]IPG contains a mixture of low-spin bis-coordinated (FeP) -P-III and high-spin mono-coordinated (FeP)-P-III species, whereas Fe[M(4-N -MePy)TFPP]IPG only contains high-spin mono-coordinated (FeP)-P-III. These FePIPG catalysts also contain (FeP)-P-II species, whose presence was confir med by EPR spectroscopy using NO as a paramagnetic probe. Both cationic FeP s coordinate to SG through Fe-O ligation and they are present as high-spin (FeP)-P-III species. The cationic FePs supported on SiSO3- are also high-sp in (FeP)-P-III species and they bind to the support via electrostatic inter action between the 4-N-methylpyridyl groups and the SO3- groups present on the matrix. In homogeneous solution, both Fe[M(4-N-MePy)TDCPP]Cl-2 and Fe[M (4-N-MePy)TFPP]Cl-2 have similar catalytic activity to Fe(TDCPP)Cl and Fe(T FPP)Cl, leading to cis-epoxycyclooctane yields of 92%. When supported on in organic matrices,both FePs lead to epoxide yields comparable to their homog eneous analogues and their anchoring enables catalyst recovery and re-use. Recycling of Fe[M(4-N-MePy)TDCPP]SiSO3- shows that this FeP maintains its a ctivity in a second reaction. (C) 1999 Elsevier Science B.V. All rights res erved.