Iron(II) Complexes with Bio‐Inspired N,N,O Ligands as Oxidation Catalysts: Olefin Epoxidation and cis‐Dihydroxylation

The Rieske dioxygenases are a group of non‐heme iron enzymes, which catalyze the stereospecific cis‐dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3‐bis(1‐methylimidazol‐2‐yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3‐bis(1‐methylimidazol‐2‐yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1were determined and two different coordination modes of the ligand were observed. In [FeII(PrL1)2](BPh4)2(3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [FeII(PrL1)2(MeOH)2](OTf)2(4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cisarrangement with respect to each other. Complex 4is a close structural mimic of the crystallographically characterized non‐heme iron(II) enzyme apocarotenoid‐15–15′‐oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non‐heme iron complexes [FeII(PrL1)2](OTf)2(2) and [FeII(PrL1)2](BPh4)2(3) were tested in olefin oxidation reactions with H2O2as the terminal oxidant. Whereas 2was an active catalyst and both epoxide and cis‐dihydroxylation products were observed, 3showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction.