title: Iron(II) complexes with bio-inspired N,N,O ligands as oxidation catalysts: olefin epoxidation and cis-dihydroxylation.
abstract: 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 PrL1 were determined and two different coordination modes of the ligand were observed. In [Fe(II)(PrL1)(2)](BPh(4))(2) (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [Fe(II)(PrL1)(2)(MeOH)(2)](OTf)(2) (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is 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 [Fe(II)(PrL1)(2)](OTf)(2) (2) and [Fe(II)(PrL1)(2)](BPh(4))(2) (3) were tested in olefin oxidation reactions with H(2)O(2) as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis-dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction.
authors.affiliation: Chemical Biology & Organic Chemistry, Department of Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Pieter C A
authors.initials: PC
authors.lastname: Bruijnincx
authors.forename: Inge L C
authors.initials: IL
authors.lastname: Buurmans
authors.forename: Silvia
authors.initials: S
authors.lastname: Gosiewska
authors.forename: Marcel A H
authors.initials: MA
authors.lastname: Moelands
authors.forename: Martin
authors.initials: M
authors.lastname: Lutz
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Spek
authors.forename: Gerard
authors.initials: G
authors.lastname: van Koten
authors.forename: Robertus J M
authors.initials: RJ
authors.lastname: Klein Gebbink
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006900:Hydroxylation; D007259:Infrared Rays; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D011422:Propionates / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D000475:Alkenes; D005296:Ferrous Compounds; D008024:Ligands; D011422:Propionates