title: Ligand topology effects on olefin oxidations by bio-inspired [FeII(N2Py2)] catalysts.
abstract: Linear tetradentate N2Py2 ligands can coordinate to an octahedral FeII center in three possible topologies (cis-alpha, cis-beta, and trans). While for the N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane (bpmen) complex, only the cis-alpha topology has been observed, for N,N'-bis(2-pyridylmethyl)-1,2-diaminocyclohexane (bpmcn) both cis-alpha and cis-beta isomers have been reported. To date, no facile interconversion between cis-alpha and cis-beta topologies has been observed for ironII complexes even at high temperatures. However, this work provides evidence for facile interconversion in solution of cis-alpha, cis-beta, and trans topologies for [Fe(bpmpn)X2] (bpmpn=N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane; X=triflate, CH3CN) complexes. As reported previously, the catalytic behavior of cis-alpha and cis-beta isomers of [Fe(bpmcn)(OTf)2] with respect to olefin oxidation depends dramatically on the geometry adopted by the iron complex. To establish a general pattern of the catalysis/topology dependence, this work presents an extended comparison of the catalytic behavior for oxidation of olefins of a family of [Fe(N2py2)] complexes that present different topologies. 18O labeling experiments provide evidence for a complex mechanistic landscape in which several pathways should be considered. Complexes with a trans topology catalyze only non-water-assisted epoxidation. In contrast, complexes with a cis-alpha topology, such as [Fe(bpmen)X2] and [Fe(alpha-bpmcn)(OTf)2], can catalyze both epoxidation and cis-dihydroxylation through a water-assisted mechanism. Surprisingly, [Fe(bpmpn)X2] and [Fe(beta-bpmcn)(OTf)2] catalyze epoxidation via a water-assisted pathway and cis-dihydroxylation via a non-water-assisted mechanism, a result that requires two independent and distinct oxidants.
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, USA.
authors.forename: Rubén
authors.initials: R
authors.lastname: Mas-Ballesté
authors.forename: Miquel
authors.initials: M
authors.lastname: Costas
authors.forename: Tieme
authors.initials: T
authors.lastname: van den Berg
authors.forename: Lawrence
authors.initials: L
authors.lastname: Que
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D005296:Ferrous Compounds; D006861:Hydrogen Peroxide; D008024:Ligands; D017672:Nitrogen Compounds; D010084:Oxidation-Reduction
chemical_list: D000475:Alkenes; D005296:Ferrous Compounds; D008024:Ligands; D017672:Nitrogen Compounds; D006861:Hydrogen Peroxide