Synthesis, Characterization And Reactivity Of Model Complexes For The Active Site Of Acetylacetone Dioxygenase

Acetylacetone dioxygenase (β-diketone dioxygenase, Dkel) has recently received considerable attention in bioinorganic chemistry. Dkel activates dioxygen to catalyze the oxidative cleavage of carbon-carbon bonds ofβ-diketones to the corresponding carboxylic acids and a-diketones. In order to get insights into the role of the carboxylate group of Glu98, electronic substituent effects of the substrates and steric effects of the ligands on the structure, reactivity and the catalytic mechanism of Dkel, we synthesized a series of iron complexes as the structural and functional models for the active site of Dkel. The results are as follows:(1) Two new binary model Fe(II)-complexes [FenIIL(OAc)] and a new ternary model Fe(II)-complex [FeIILlS3H](LlH:2-[bis(6-methyl-pyridin-2-ylmethyl)amino]-acetic acid, L2H:2-[bis(6-pivaloylamino-pyridin-2-ylmethyl)amino]-acetic acid, S3H:1,3-diphenyl-propane-1,3-dione) have been synthesized. X-ray crystallographic studies of [L1FeIII(μ-O)(μ-OAc)2FeIIILl] and[Fe(S3H)3]revealed distorted octahedral environment.(2) The reactivities of S3R with dioxygen catalyzed by the binary model complexes have been investigated. Our conclusions are as follows:①Benzoic acid, subsitituted benzoic aicds, and a-diketone derivatives as the final oxidative cleavege products are similar to the natural Dkel-enzyme products.②Methylene-bridged bis-1,3-diketone products are also obtained using DMF as the carbon source and molecular dioxygen as the oxidant, indicating the binary model complexes also have the C-C bond formation catalytic reactivity.③Electronic effects of the model substrates:with the same ligands, the catalytic reactivities of different substrates are in the order of S3NO2>S3Br> S3H> S3Me>S3OMe, indicating the reaction is nucleophilic reaction.④Steric effects of the model ligands:with the same substrates, the reactivities of the model complexes are in the order of L1(-CH3)> L2(-NHCOBut), indicating the steric hindrance group of the pyridine ring of the ligands plays a major role.