Spectroscopic properties of p/p and o/o type iron(III)-metal-free porphyrin dimers and their catalysis as Cytochrome P450 model

Two series of p/p and o/o type iron(III)-metal-free porphyrin dimers were s ynthesized and characterized. The dimers consist of a ferric porphyrin and a free-base porphyrin, covalently linked with an alkoxy chain -O(CH2)(n)O- (n = 2-10) at the para and ortho position of two phenyl rings. The ferric p aramagnetic effect and ring current effect on these dimers were discussed b y H-1 NMR study; vibration modes sensitive to the conformations of the dime rs were investigated from IR spectra; the electron density and spin state o f ferric ion were examined using XPS and EPR spectroscopy. The catalytic ac tivities of p/p and o/o type dimers on the hydroxylation of cyclohexane wer e studied under mild conditions. As a chemical mimic model of Cyto. P450, t hese porphyrins exhibit higher catalytic activities than the corresponding monomer FeTPPCl. With increase of the carbon numbers of alkoxy chain, the c atalytic activity order of p/p dimers is C-2 < C-3 < C-4 < C-5 < C-6 > C-8 > C-10, the corresponding order of o/o dimers is C-2 > C-4 > C-6 > C-8 > C- 10. Catalytic results of dimers are shown to strongly depend on their speci al conformation equilibrium, which affect the steric hindrance and electron transfer between two porphyrin rings. Copyright (C) 2001 John Wiley & Sons , Ltd.