Engineering the Oxidative Potency of Non-Heme Iron(IV) Oxo Complexes in Water for C-H Oxidation by a cis Donor and Variation of the Second Coordination Sphere

Summary, in English

A series of iron(IV) oxo complexes, which differ in the donor (CH2py or CH2COO-) cis to the oxo group, three with hemilabile pendant donor/second coordination sphere base/acid arms (pyH/py or ROH), have been prepared in water at pH 2 and 7. The νFe=O values of 832 ± 2 cm-1 indicate similar FeIV=O bond strengths; however, different reactivities toward C-H substrates in water are observed. HAT occurs at rates that differ by 1 order of magnitude with nonclassical KIEs (kH/kD = 30-66) consistent with hydrogen atom tunneling. Higher KIEs correlate with faster reaction rates as well as a greater thermodynamic stability of the iron(III) resting states. A doubling in rate from pH 7 to pH 2 for substrate C-H oxidation by the most potent complex, that with a cis-carboxylate donor, [FeIVO(Htpena)]2+, is observed. Supramolecular assistance by the first and second coordination spheres in activating the substrate is proposed. The lifetime of this complex in the absence of a C-H substrate is the shortest (at pH 2, 3 h vs up to 1.3 days for the most stable complex), implying that slow water oxidation is a competing background reaction. The iron(IV)=O complex bearing an alcohol moiety in the second coordination sphere displays significantly shorter lifetimes due to a competing selective intramolecular oxidation of the ligand.

• Author: Christina Wegeberg; Mathias L. Skavenborg; Andrea Liberato; James N. McPherson; Wesley R. Browne; Erik D. Hedegård; Christine J. McKenzie
• Department/s: Computational Chemistry
• Publishing year: 2021
• Language: English
• Pages: 1975-1984
• Publication/Series: Inorganic Chemistry
• Volume: 60
• Issue: 3
• Links: http://dx.doi.org/10.1021/acs.inorgchem.0c03441
• Document type: Journal article
• Publisher: The American Chemical Society (ACS)
• Topic: Inorganic Chemistry
• Status: Published
• ISBN/ISSN/Other: ISSN: 0020-1669