"Radical clock investigation with a metalloporphyrin enzyme model"

A significant tool for better understanding the complex nature of the cofactor of heme thiolate proteins such as Cytochromes P450 is the investigation of model compounds. In this context a new family of iron porphyrins has been synthesized by replacing the native thiolate ligand for a SO3- group coordinating the heme iron. The porphyrin mimics designed and synthesized during the course of this thesis were successfully used as catalytic oxidants in radical clock experiments. trans-2-Phenyl-methylcyclopropane was oxidized using PhIO and the porphyrin model. Analysis of the product distribution revealed a ratio of 9:1 of the non-rearranged cyclopropyl methanol over 1,1-allyl phenyl methanol. Given the rate of rearrangement k = 1.8·1011 sec -1 of the phenyl cyclopropyl methyl radical in solution, the life time of the intermediate radical cluster IC- H can be calculated as 625 fsec. This time is analogous to the lifetimes observed in enzymatic hydroxylations. It was proposed that this intermediate is not a free radical but instead a cluster containing a CH2 group carrying spin density joined to the spin system of the …H…O-Fe(III) porphyrin radical cation. The two routes to the final oxidized products, originating from this intermediate I - H, are C divergent, the unrearranged alcohol is formed via a concerted route whereas the rearranged product is produced from either a high-spin or low spin pathway. The hydroxylation proceeds by concerted non-synchronous ‘O’-insertion into the C-H bond of the methyl group.