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 synthesized 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 paramagnetic effect and ring current effect on these dimers were discussed by H-1 NMR study; vibration modes sensitive to the conformations of the dimers were investigated from IR spectra; the electron density and spin state of ferric ion were examined using XPS and EPR spectroscopy. The catalytic activities of p/p and o/o type dimers on the hydroxylation of cyclohexane were studied under mild conditions. As a chemical mimic model of Cyto. P450, these porphyrins exhibit higher catalytic activities than the corresponding monomer FeTPPCl. With increase of the carbon numbers of alkoxy chain, the catalytic 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 special conformation equilibrium, which affect the steric hindrance and electron transfer between two porphyrin rings. Copyright (C) 2001 John Wiley & Sons, Ltd.