Ligand Topology Variations and the Importance of Ligand Field Strength in Non-Heme Iron Catalyzed Oxidations of Alkanes

England, Jason, Britovsek, G.J.P., Rabadia, N. and White, A.J.P. (2007) Ligand Topology Variations and the Importance of Ligand Field Strength in Non-Heme Iron Catalyzed Oxidations of Alkanes. Inorganic Chemistry, 46 (9). pp. 3752-3767. ISSN 0020-1669

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A series of iron(II)−bis(triflate) complexes [Fe(L)(OTf)2] containing linear tetradentate bis(quinolyl)-diamine and bis(quinolylmethyl)-diamine ligands with a range of ligand backbones has been prepared. The coordination geometries of these complexes have been investigated in the solid state by X-ray crystallography and in solution by 1H and 19F NMR spectroscopy. Because of the labile nature of high-spin iron(II) complexes in solution, dynamic equilibria of complexes with different coordination geometries (cis-α, cis-β, and trans) are observed with certain ligand systems. In these cases, the geometry observed in the solid-state does not necessarily represent the only or even the major geometry present in solution. The ligand field strength in the various complexes has been investigated by variable-temperature (VT) magnetic moment measurements and by UV−vis spectroscopy. The strongest ligand field is observed with the most rigid ligand that generates [Fe(L)(OTf)2] complexes with a cis-α coordination geometry, and the corresponding [Fe(L)(CH3CN)2]2+ complex displays spin crossover behavior. The catalytic properties of the complexes for the oxidation of cyclohexane have been investigated using hydrogen peroxide as the oxidant. An increased flexibility in the ligand results in a weaker ligand field, which increases the lability of the complexes. The activity and selectivity of the catalysts appear to be related to the strength of the ligand field and the stability of the catalyst.

Keywords:Catalysis, alkane hydroxylation, alkane oxidation, non-heme iron complexes, hydrogen peroxide, spin crossover, X-ray structure
Subjects:F Physical Sciences > F120 Inorganic Chemistry
F Physical Sciences > F110 Applied Chemistry
Divisions:College of Science > School of Chemistry
ID Code:51935
Deposited On:19 Oct 2022 11:13

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