A siloxyl bis-pocket thiolate-tailed Fe(III) porphyrin complex

We report the synthesis and characterization of a bis-pocket iron(III) porphyrin complex that has a covalently attached siloxy thiolate group as the axial ligand. As a new cytochrome P450 model compound, this siloxyl bis-pocket thiolate-tailed iron(III) porphyrin is easily synthesized and is surprisingly stable under air due to the extreme steric protection of the siloxy pockets on both faces of the porphyrin. A single-crystal XRD structure has been determined; the Fe-S bond distance is 2.237 (7) angstrom with Fe-N bond distances of 2.100 (8) and the Fe is 0.5 angstrom out of the mean porphyrin plane. The Fe-S bond distance in the siloxy thiolate-tailed iron(III) porphyrin is very similar to that in cytochrome P450 and this structure represents a very rare crystallographically-characterized five-coordinate high spin alkylthiolate-tailed ferric porphyrin. EPR spectrum of this compound showed g values and an E/D ratio very similar to those of cytochrome P450 (CYP450) enzyme, demonstrating the importance of using a very basic thiolate group as the axial ligand in P450 model studies. UV-vis studies of its reduced form with carbon monoxide shows a hyper spectrum, which is characteristic of carbonyl complexes of Fe(II) porphyrin thiolates.