Probing Hydrogen Bonding Interactions to Iron‐Oxido/Hydroxido Units by <sup>57</sup>Fe Nuclear Resonance Vibrational Spectroscopy

Weitz, Andrew C.; Hill, Ethan A.; Oswald, Victoria F.; Bominaar, Emile L.; Borovik, A. S.; Hendrich, Michael P.; Guo, Yisong

doi:10.1002/anie.201810227

Cited by 13 publications

(13 citation statements)

References 46 publications

(29 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The energy of this vibration is 49 cm –1 lower than that found for [Fe IV poat(O)] − (Figure ). We further used Badger’s rule, an empirical formula that relates bond length to vibrational frequency (eq ), to evaluate how the Fe IV –O oxido bond lengths vary within [Fe IV poat(O)] − and [Fe IV H 3 buea(O)] − . , We have already determined the values of C Fe–O (56.69) and d Fe–O (1.038) using a training set composed of related Fe–oxido and Fe–hydroxido complexes with tripodal ligands that include [H 3 buea] 3– . From this analysis, we found Fe IV –O oxido bond lengths of 1.70 Å for [Fe IV H 3 buea(O)] − and 1.67 Å for [Fe IV poat(O)] − .…”

Section: Results and Discussionmentioning

confidence: 99%

“…74,75 We have already determined the values of C Fe−O (56.69) and d Fe−O (1.038) using a training set composed of related Fe−oxido and Fe−hydroxido complexes with tripodal ligands that include [H 3 buea] 3− . 75 From this analysis, we found Fe IV −O oxido bond lengths of 1.70 Å for [Fe IV H 3 buea- S1). An Fe IV −O oxido bond length of 1. doublets (Figure 5).…”

Section: ■ Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2020

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Results and Discussionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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

et al. 2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…No Fe–X vibrational features >600 cm –1 were observed for this species, and the features observed between 447 and 475 cm –1 were proposed to be Fe–O vibrations, weakened because of protonation of the oxido ligand and H-bonding with the bulk aqueous solvent. However, these features are comparable or weaker in energy than those of a series of Fe III –OH complexes that we have developed (477–594 cm –1 ), which does not support the assignment for an Fe IV –OH species . Additionally, electrochemical experiments on [(TAML)Fe III –OH 2 ] − revealed a Nernstian one-electron redox event, which suggests that oxidation does not result in geometric rearrangement or ligand modification, posing the possibility that an Fe IV –OH 2 species could be produced.…”

Section: Reactivitymentioning

confidence: 99%

“…However, these features are comparable or weaker in energy than those of a series of Fe III −OH complexes that we have developed (477−594 cm −1 ), which does not support the assignment for an Fe IV −OH species. 138 Additionally, electrochemical experiments on [(TAML)Fe III − OH 2 ] − revealed a Nernstian one-electron redox event, which suggests that oxidation does not result in geometric rearrangement or ligand modification, posing the possibility that an Fe IV −OH 2 species could be produced.…”

Section: Reboundmentioning

confidence: 99%

C–H Bond Cleavage by Bioinspired Nonheme Metal Complexes

et al. 2021

Self Cite

View full text Add to dashboard Cite

The functionalization of C−H bonds is one of the most challenging transformations in synthetic chemistry. In biology, these processes are well-known and are achieved with a variety of metalloenzymes, many of which contain a single metal center within their active sites. The most well studied are those with Fe centers, and the emerging experimental data show that high-valent iron oxido species are the intermediates responsible for cleaving the C−H bond. This Forum Article describes the state of this field with an emphasis on nonheme Fe enzymes and current experimental results that provide insights into the properties that make these species capable of C−H bond cleavage. These parameters are also briefly considered in regard to manganese oxido complexes and Cu-containing metalloenzymes. Synthetic iron oxido complexes are discussed to highlight their utility as spectroscopic and mechanistic probes and reagents for C−H bond functionalization. Avenues for future research are also examined.

show abstract

“…The k 1 and k 2 values, obtained from the intercept and the slope of Figure , represent the ET rate constants from [Fe II (bpy) 3 ] 2+ to [Fe IV (O)(N4Py)] 2+ –(Sc 3+ ) and [Fe IV (O)(N4Py)] 2+ –(Sc 3+ ) 2 , respectively. Other than the metal ions acting through charge-stabilization, there also have been reports on the effect of Brønsted acids to promote proton-coupled electron transfer (PCET). − Banse and co-workers examined the role of external electrons and protons on the generation and stability of iron(IV)-oxo species using BPh 4 – and HClO 4 as the source of electrons and protons . Iron(II) complexes with TMC ligand or structural analogues, TMC-py (1-(2′-pyridylmethyl)-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) were found to be inactive toward oxidation at room temperature in an oxygenated CH 3 CN solution.…”

Section: Biomimetic Studies On Second-coordination Sphere and Seconda...mentioning

confidence: 99%

Inspiration from Nature: Influence of Engineered Ligand Scaffolds and Auxiliary Factors on the Reactivity of Biomimetic Oxidants

et al. 2021

View full text Add to dashboard Cite

Enzymes are highly efficient catalysts in Nature that often react with high stereo-, chemo-, and regioselectivity. Usually, enzymes achieve this selectivity through substrate binding and positioning in the active site. The second-coordination sphere effects (also called noncovalent interactions) position the substrate and oxidant in close vicinity, and their effects include electrostatic interactions, hydrogen-bonding interactions, salt-bridges, and also long-range charge-effects from bound cations and anions. Each of these environmental perturbations can affect the kinetics and selectivity of reactions differently. Over the past couple of years, a variety of biomimetic model complexes have been developed and designed that have a similar first-coordination sphere to mononuclear iron-containing enzymes. However, sometimes the reactivity patterns of the biomimetic models in solution are different from the analogous enzymatic systems, and often the selectivity of the reaction is lost. To understand the functional differences between enzymes and biomimetic models, large catalytic clusters have been developed that incorporate second-coordination sphere effects that influence spectroscopic features as well as reactivity patterns. In this Review, we summarize and highlight recent advances in biomimetic chemistry on the creation and design of iron catalysts and the insights that have been obtained when elaborate ligand features are added, which influence the substrate approach to the catalytic center. We start with a highlight of the axial and distal ligand effects of metal centers and how these can be perturbed by hydrogen bonding as well as steric restraints. The syntheses of the active oxidants through the addition of a proton-donating or -accepting groups to the structure have also been discussed in detail in this article. As shown in this work, second-coordination sphere effects can be useful not only to trap and characterize short-lived intermediates but also to enable high selectivity and specificity of a chemical reaction in analogy to enzymatic systems. These biomimetic models appear highly useful for biotechnological and engineering applications with reasonable turnover numbers and consequently have great potential for the future of stereo-and chemoselective synthetic catalytic reactions.

show abstract

Probing Hydrogen Bonding Interactions to Iron‐Oxido/Hydroxido Units by ⁵⁷Fe Nuclear Resonance Vibrational Spectroscopy

Cited by 13 publications

References 46 publications

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

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

C–H Bond Cleavage by Bioinspired Nonheme Metal Complexes

Inspiration from Nature: Influence of Engineered Ligand Scaffolds and Auxiliary Factors on the Reactivity of Biomimetic Oxidants

Contact Info

Product

Resources

About

Probing Hydrogen Bonding Interactions to Iron‐Oxido/Hydroxido Units by 57Fe Nuclear Resonance Vibrational Spectroscopy

Cited by 13 publications

References 46 publications

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

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

C–H Bond Cleavage by Bioinspired Nonheme Metal Complexes

Inspiration from Nature: Influence of Engineered Ligand Scaffolds and Auxiliary Factors on the Reactivity of Biomimetic Oxidants

Contact Info

Product

Resources

About

Probing Hydrogen Bonding Interactions to Iron‐Oxido/Hydroxido Units by ⁵⁷Fe Nuclear Resonance Vibrational Spectroscopy