A bis-Phenolate Carbene-Supported bis-μ-Oxo Iron(IV/IV) Complex with a [FeIV(μ-O)2FeIV] Diamond Core Derived from Dioxygen Activation

Gravogl L, Kass D, Pyschny O, Heinemann FW, Haumann M, Katz S, Hildebrandt P, Dau H, Swain A, García-Serres R, Ray K, Munz D, Meyer K (2024)

Publication Type: Journal article

Publication year: 2024

Journal

DOI: 10.1021/jacs.4c07582

Abstract

The diiron(II) complex, [(OCO)Fe(MeCN)]2 (1, MeCN = acetonitrile), supported by the bis-phenolate carbene pincer ligand, 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)benzimidazolin-2-ylidene (OCO), was synthesized and characterized by single-crystal X-ray diffraction, ¹H nuclear magnetic resonance, infrared (IR) vibrational, ultraviolet/visible/near-infrared (UV/vis/NIR) electronic absorption, ⁵⁷Fe Mossbauer, X-band electron paramagnetic resonance (EPR) and SQUID magnetization measurements. Complex 1 activates dioxygen to yield the diferric, μ-oxo-bridged complex [(OCO)Fe(py)(μ-O)Fe(O(C═O)O)(py)] (2) that was isolated and fully characterized. In 2, one of the iron-carbene bonds was oxidized to give a urea motif, resulting in an O(CNHC═O)O binding site, while the other Fe(OCO) unit remained unchanged. When the reaction is performed at −80 °C, an intensively colored, purple intermediate is observed (INT, λmax = 570 nm; ϵ = 5600 mol L^-1 cm^-1). INT acts as a sluggish oxidant, reacting only with easily oxidizable substrates, such as PPh3 or 2-phenylpropionic aldehyde (2-PPA). The identity of INT can be best described as a dinuclear complex containing a closed diamond core motif [(OCO)Fe^IV(μ-O)2Fe^IV(OCO)]. This proposal is based on extensive spectroscopic [UV/vis/NIR electronic absorption, ⁵⁷Fe Mossbauer, X-band EPR, resonance Raman (rRaman), X-ray absorption, and nuclear resonance vibrational (NRVS)] and computational studies. The conversion of the diiron(II) complex 1 to the oxo diiron(IV) intermediate INT is reminiscent of the O2 activation process in soluble methane monooxygenases (sMMO). Most importantly, the low reactivity of INT supports the consensus that the [Fe^IV(μ-O)2Fe^IV] diamond core in sMMO is kinetically inert and needs to open up to terminal Fe^IV═O cores to react with the strong C-H bonds of methane.

Authors with CRIS profile

Involved external institutions

Humboldt-Universität zu Berlin Germany (DE) Freie Universität Berlin Germany (DE) Technische Universität Berlin Germany (DE) Universität des Saarlandes (UdS) Germany (DE) University of Grenoble Alpes (UGA) / Université de Grenoble France (FR)

How to cite

APA:

Gravogl, L., Kass, D., Pyschny, O., Heinemann, F.W., Haumann, M., Katz, S.,... Meyer, K. (2024). A bis-Phenolate Carbene-Supported bis-μ-Oxo Iron(IV/IV) Complex with a [FeIV(μ-O)2FeIV] Diamond Core Derived from Dioxygen Activation. Journal of the American Chemical Society. https://doi.org/10.1021/jacs.4c07582

MLA:

Gravogl, Lisa, et al. "A bis-Phenolate Carbene-Supported bis-μ-Oxo Iron(IV/IV) Complex with a [FeIV(μ-O)2FeIV] Diamond Core Derived from Dioxygen Activation." Journal of the American Chemical Society (2024).

BibTeX: Download