Effects of Noncovalent Interactions on High-Spin Fe(IV)–Oxido Complexes

Abstract

High-valent nonheme Fe IV −oxido species are key intermediates in biological oxidation, and their properties are proposed to be influenced by the unique microenvironments present in protein active sites. Microenvironments are regulated by noncovalent interactions, such as hydrogen bonds (H-bonds) and electrostatic interactions; however, there is little quantitative information about how these interactions affect crucial properties of high valent metal−oxido complexes. To address this knowledge gap, we introduced a series of Fe IV −oxido complexes that have the same S = 2 spin ground state as those found in nature and then systematically probed the effects of noncovalent interactions on their electronic, structural, and vibrational properties. The key design feature that provides access to these complexes is the new tripodal ligand [poat] 3− , which contains phosphinic amido groups. An important structural aspect of [Fe IV poat(O)] − is the inclusion of an auxiliary site capable of binding a Lewis acid (LA II ); we used this unique feature to further modulate the electrostatic environment around the Fe−oxido unit. Experimentally, studies confirmed that H-bonds and LA II s can interact directly with the oxido ligand in Fe IV −oxido complexes, which weakens the FeO bond and has an impact on the electronic structure. We found that relatively large vibrational changes in the Fe−oxido unit correlate with small structural changes that could be difficult to measure, especially within a protein active site. Our work demonstrates the important role of noncovalent interactions on the properties of metal complexes, and that these interactions need to be considered when developing effective oxidants.

Closed Shell Iron(IV) Oxo Complex with an Fe–O Triple Bond: Computational Design, Synthesis, and Reactivity

“…We calculated theoretical IR spectra (B3LYP‐D3/6–311+G**) for all spin states of 1 + . In our experience, B3LYP‐D3/6–311+G** provides the best predictions for ligand vibrations, [50, 51] while it significantly blue‐shifts Fe‐O stretching bands by 50–100 cm −1 in iron(IV)‐oxo complexes [38, 52] . Majority of the bands in these spectra correspond to the C−H bending modes and the skeletal stretching modes and show a good agreement with the measured IR spectra (Figure 4 b).…”

“…shifts Fe-O stretching bands by 50-100 cm À1 in iron(IV)-oxo complexes. [38,52] Majority of the bands in these spectra correspond to the C À Hb ending modes and the skeletal stretching modes and show ag ood agreement with the measured IR spectra (Figure 4b). As can be seen, the main difference among the calculated IR spectra for the different spin states of 1 + is the position of the n(Fe-O) band (1023, 939, and 866 cm À1 for 1 1 + , 3 1 + ,a nd 5 1 + ,r espectively).…”

The Hydricity and Reactivity Relationship in [ FeFe ]-hydrogenases

“…Metal-ligand complexes have fundamental roles in reduction-oxidation reactions, where covalent and non-covalent interactions strongly in uence the metal-ligand reactivity. 1 One class of metal-ligand complexes, the transition metal hydrides, functions as intermediates in a broad number of chemical transformations. 2,3 For example, in small molecule activation reactions, hydricity of a catalytic metal site strongly in uences the control of turnover rates and end-product speci cities.…”

Iron(IV) Complexes with Tetraazaadamantane-based Ligands: Synthesis, Structure, Application in Dioxygen Activation and Labeling of Biomolecules

“…[5][6][7][8][9][10] Although this goal remains elusive at the moment, much research has been done in the field of high-valent, and in particular, Fe(IV) complexes. 11,12 In recent years, numerous high-valent iron complexes including heme-and non-heme Fe(IV) and Fe(IV)-oxo/nitride complexes, which mimic the structure and activity of natural oxidases have been generated and characterized. [13][14][15][16][17][18][19] However, these species are generally unstable under ambient conditions in aqueous solution, thus complicating their study and application.…”