1
|
Querci L, Piccioli M, Ciofi-Baffoni S, Banci L. Structural aspects of iron‑sulfur protein biogenesis: An NMR view. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2024; 1871:119786. [PMID: 38901495 DOI: 10.1016/j.bbamcr.2024.119786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2024] [Revised: 05/15/2024] [Accepted: 06/10/2024] [Indexed: 06/22/2024]
Abstract
Over the last decade, structural aspects involving iron‑sulfur (Fe/S) protein biogenesis have played an increasingly important role in understanding the high mechanistic complexity of mitochondrial and cytosolic machineries maturing Fe/S proteins. In this respect, solution NMR has had a significant impact because of its ability to monitor transient protein-protein interactions, which are abundant in the networks of pathways leading to Fe/S cluster biosynthesis and transfer, as well as thanks to the developments of paramagnetic NMR in both terms of new methodologies and accurate data interpretation. Here, we review the use of solution NMR in characterizing the structural aspects of human Fe/S proteins and their interactions in the framework of Fe/S protein biogenesis. We will first present a summary of the recent advances that have been achieved by paramagnetic NMR and then we will focus our attention on the role of solution NMR in the field of human Fe/S protein biogenesis.
Collapse
Affiliation(s)
- Leonardo Querci
- Magnetic Resonance Center CERM, University of Florence, Via Luigi Sacconi 6, Sesto Fiorentino, 50019 Florence, Italy; Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, 50019 Florence, Italy
| | - Mario Piccioli
- Magnetic Resonance Center CERM, University of Florence, Via Luigi Sacconi 6, Sesto Fiorentino, 50019 Florence, Italy; Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, 50019 Florence, Italy
| | - Simone Ciofi-Baffoni
- Magnetic Resonance Center CERM, University of Florence, Via Luigi Sacconi 6, Sesto Fiorentino, 50019 Florence, Italy; Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, 50019 Florence, Italy.
| | - Lucia Banci
- Magnetic Resonance Center CERM, University of Florence, Via Luigi Sacconi 6, Sesto Fiorentino, 50019 Florence, Italy; Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, 50019 Florence, Italy; Consorzio Interuniversitario Risonanze Magnetiche di Metalloproteine (CIRMMP), Via Luigi Sacconi 6, Sesto Fiorentino, 50019 Florence, Italy.
| |
Collapse
|
2
|
Querci L, Grifagni D, Trindade IB, Silva JM, Louro RO, Cantini F, Piccioli M. Paramagnetic NMR to study iron sulfur proteins: 13C detected experiments illuminate the vicinity of the metal center. JOURNAL OF BIOMOLECULAR NMR 2023; 77:247-259. [PMID: 37853207 PMCID: PMC10687126 DOI: 10.1007/s10858-023-00425-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 09/25/2023] [Indexed: 10/20/2023]
Abstract
The robustness of NMR coherence transfer in proximity of a paramagnetic center depends on the relaxation properties of the nuclei involved. In the case of Iron-Sulfur Proteins, different pulse schemes or different parameter sets often provide complementary results. Tailored versions of HCACO and CACO experiments significantly increase the number of observed Cα/C' connectivities in highly paramagnetic systems, by recovering many resonances that were lost due to paramagnetic relaxation. Optimized 13C direct detected experiments can significantly extend the available assignments, improving the overall knowledge of these systems. The different relaxation properties of Cα and C' nuclei are exploited in CACO vs COCA experiments and the complementarity of the two experiments is used to obtain structural information. The two [Fe2S2]+ clusters containing NEET protein CISD3 and the one [Fe4S4]2+ cluster containing HiPIP protein PioC have been taken as model systems. We show that tailored experiments contribute to decrease the blind sphere around the cluster, to extend resonance assignment of cluster bound cysteine residues and to retrieve details on the topology of the iron-bound ligand residues.
Collapse
Affiliation(s)
- Leonardo Querci
- Magnetic Resonance Center and Department of Chemistry, University of Florence, Via L. Sacconi 6, 50019, Sesto Fiorentino, Italy
| | - Deborah Grifagni
- Magnetic Resonance Center and Department of Chemistry, University of Florence, Via L. Sacconi 6, 50019, Sesto Fiorentino, Italy
| | - Inês B Trindade
- Instituto de Tecnologia Química e Biológica António Xavier (ITQB-NOVA), Universidade Nova de Lisboa, Av. da República (EAN), 2780-157, Oeiras, Portugal
- Division of Biology and Biological Engineering, California Institute of Technology, CA 91125, Pasadena, USA
| | - José Malanho Silva
- Magnetic Resonance Center and Department of Chemistry, University of Florence, Via L. Sacconi 6, 50019, Sesto Fiorentino, Italy
| | - Ricardo O Louro
- Instituto de Tecnologia Química e Biológica António Xavier (ITQB-NOVA), Universidade Nova de Lisboa, Av. da República (EAN), 2780-157, Oeiras, Portugal
| | - Francesca Cantini
- Magnetic Resonance Center and Department of Chemistry, University of Florence, Via L. Sacconi 6, 50019, Sesto Fiorentino, Italy
| | - Mario Piccioli
- Magnetic Resonance Center and Department of Chemistry, University of Florence, Via L. Sacconi 6, 50019, Sesto Fiorentino, Italy.
| |
Collapse
|
3
|
Üngör Ö, Sanchez S, Ozvat TM, Zadrozny JM. Asymmetry-enhanced 59Co NMR thermometry in Co(iii) complexes. Inorg Chem Front 2023; 10:7064-7072. [PMID: 38021440 PMCID: PMC10660387 DOI: 10.1039/d3qi01641b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Accepted: 10/20/2023] [Indexed: 12/01/2023]
Abstract
Design strategies for molecular thermometers by magnetic resonance are essential for enabling new noninvasive means of temperature mapping for disease diagnoses and treatments. Herein we demonstrate a new design strategy for thermometry based on chemical control of the vibrational partition function. To do so, we performed variable-temperature 59Co NMR investigations of four air-stable Co(iii) complexes: Co(accp)3 (1), Co(bzac)3 (2), Co(tBu2-acac)3 (3), and Co(acac)3 (4) (accp = 2-acetylcyclopentanonate; bzac = benzoylacetonate; tBu2-acac = 2,2,6,6-tetramethyl-3,5-heptanedionate and acac = acetylacetonate). We discovered 59Co chemical shift temperature sensitivity (Δδ/ΔT) values of 3.50(2), 3.39(3), 1.63(3), and 2.83(1) ppm °C-1 for 1-4, respectively, at 100 mM concentration. The values observed for 1 and 2 are new records for sensitivity for low-spin Co(iii) complexes. We propose that the observed heightened sensitivities for 1 and 2 are intimately tied to the asymmetry of the accp and bzac ligands versus the acac and tBu2-acac ligands, which enables a larger number of low-energy Raman-active vibrational modes to contribute to the observed Δδ/ΔT values.
Collapse
Affiliation(s)
- Ökten Üngör
- Department of Chemistry, Colorado State University Fort Collins Colorado 80523 USA
| | - Stephanie Sanchez
- Department of Chemistry, Colorado State University Fort Collins Colorado 80523 USA
| | - Tyler M Ozvat
- Department of Chemistry, Colorado State University Fort Collins Colorado 80523 USA
| | - Joseph M Zadrozny
- Department of Chemistry, Colorado State University Fort Collins Colorado 80523 USA
| |
Collapse
|
4
|
Iwanov C, Hopp MP, Lorenz D, Ballmann J, Enders M. Dioxygen Activation and Reduction by a Soluble Iron Phthalocyanine. Chemistry 2023:e202302761. [PMID: 37831012 DOI: 10.1002/chem.202302761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 10/11/2023] [Accepted: 10/13/2023] [Indexed: 10/14/2023]
Abstract
Iron ions in a square-planar coordination can bind molecules at the vacant axial positions and are able to transform them in stoichiometric and catalytic reactions. Nature takes advantage of these properties by incorporating iron into porphyrin systems, which play a key role not only in the binding and transport of oxygen, but also in catalytic oxidation and reduction reactions involving cytochrome P450. Although these systems have been studied extensively, there are still unresolved questions regarding the interplay between the iron ions and the surrounding ligands. Phthalocyanines (Pc) create a similar environment for metal atoms and FePc is known for a long time. However, without axial ligands FePc aggregates leading to solids of low solubility. In this work we used a known six-coordinate iron phthalocyanine derivative with bulky substituents and removed the stabilizing axial ligands. The resulting paramagnetic, four-coordinate compound does not aggregate and dissolves well so that NMR spectroscopy can be employed for studying the molecular structure and the reactivity. Solvent molecules bind weakly to the iron centers and oxygen is reduced in the presence of H-atom donors. The stoichiometric and catalytic reactivity with oxygen was studied in more detail.
Collapse
Affiliation(s)
- Christian Iwanov
- Institute of Inorganic Chemistry, Heidelberg University, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany
| | - Moritz Philipp Hopp
- Institute of Inorganic Chemistry, Heidelberg University, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany
| | - Domenik Lorenz
- Institute of Inorganic Chemistry, Heidelberg University, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany
| | - Joachim Ballmann
- Institute of Inorganic Chemistry, Heidelberg University, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany
| | - Markus Enders
- Institute of Inorganic Chemistry, Heidelberg University, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany
| |
Collapse
|
5
|
Mysegaes F, Spiteller P, Bernarding J, Plaumann M. 19 F VT NMR: Novel Tm 3+ and Ce 3+ Complexes Provide New Insight into Temperature Measurement Using Molecular Sensors. Chemphyschem 2023; 24:e202300057. [PMID: 37384817 DOI: 10.1002/cphc.202300057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2023] [Revised: 06/23/2023] [Accepted: 06/26/2023] [Indexed: 07/01/2023]
Abstract
In the past few decades, magnetic resonance spectroscopy (MRS) and MR imaging (MRI) have developed into a powerful non-invasive tool for medical diagnostic and therapy. Especially 19 F MR shows promising potential because of the properties of the fluorine atom and the negligible background signals in the MR spectra. The detection of temperature in a living organism is quite difficult, and usually external thermometers or fibers are used. Temperature determination via MRS needs temperature-sensitive contrast agents. This article reports first results of solvent and structural influences on the temperature sensitivity of 19 F NMR signals of chosen molecules. By using this chemical shift sensitivity, a local temperature can be determined with a high precision. Based on this preliminary study, we synthesized five metal complexes and compared the results of all variable temperature measurements. It is shown that the highest 19 F MR signal temperature dependence is detectable for a fluorine nucleus in a Tm3+ -complex.
Collapse
Affiliation(s)
- Felix Mysegaes
- University Bremen, Instrumental Analytics, Leobener Str. 7, 28359, Bremen, Germany
- Otto-von-Guericke University Magdeburg, Medical Faculty, Institute of Biometry and Medical Informatics, Leipziger Str. 44, 39120, Magdeburg, Germany
| | - Peter Spiteller
- University Bremen, Instrumental Analytics, Leobener Str. 7, 28359, Bremen, Germany
| | - Johannes Bernarding
- Otto-von-Guericke University Magdeburg, Medical Faculty, Institute of Biometry and Medical Informatics, Leipziger Str. 44, 39120, Magdeburg, Germany
| | - Markus Plaumann
- Otto-von-Guericke University Magdeburg, Medical Faculty, Institute of Biometry and Medical Informatics, Leipziger Str. 44, 39120, Magdeburg, Germany
| |
Collapse
|
6
|
Campanella AJ, Üngör Ö, Zadrozny JM. Quantum Mimicry With Inorganic Chemistry. COMMENT INORG CHEM 2023; 44:11-53. [PMID: 38515928 PMCID: PMC10954259 DOI: 10.1080/02603594.2023.2173588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Quantum objects, such as atoms, spins, and subatomic particles, have important properties due to their unique physical properties that could be useful for many different applications, ranging from quantum information processing to magnetic resonance imaging. Molecular species also exhibit quantum properties, and these properties are fundamentally tunable by synthetic design, unlike ions isolated in a quadrupolar trap, for example. In this comment, we collect multiple, distinct, scientific efforts into an emergent field that is devoted to designing molecules that mimic the quantum properties of objects like trapped atoms or defects in solids. Mimicry is endemic in inorganic chemistry and featured heavily in the research interests of groups across the world. We describe a new field of using inorganic chemistry to design molecules that mimic the quantum properties (e.g. the lifetime of spin superpositions, or the resonant frequencies thereof) of other quantum objects, "quantum mimicry." In this comment, we describe the philosophical design strategies and recent exciting results from application of these strategies.
Collapse
Affiliation(s)
- Anthony J. Campanella
- Department of Chemistry, Colorado State University, Fort Collins, CO, USA, Address: 200 W. Lake St, Campus Delivery 1872, Fort Collins, CO 80523, USA
| | - Ökten Üngör
- Department of Chemistry, Colorado State University, Fort Collins, CO, USA, Address: 200 W. Lake St, Campus Delivery 1872, Fort Collins, CO 80523, USA
| | - Joseph M. Zadrozny
- Department of Chemistry, Colorado State University, Fort Collins, CO, USA, Address: 200 W. Lake St, Campus Delivery 1872, Fort Collins, CO 80523, USA
| |
Collapse
|
7
|
Jaworski A, Hedin N. Electron correlation and vibrational effects in predictions of paramagnetic NMR shifts. Phys Chem Chem Phys 2022; 24:15230-15244. [PMID: 35703010 DOI: 10.1039/d2cp01206e] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electronic structure calculations are fundamentally important for the interpretation of nuclear magnetic resonance (NMR) spectra from paramagnetic systems that include organometallic and inorganic compounds, catalysts, or metal-binding sites in proteins. Prediction of induced paramagnetic NMR shifts requires knowledge of electron paramagnetic resonance (EPR) parameters: the electronic g tensor, zero-field splitting D tensor, and hyperfine A tensor. The isotropic part of A, called the hyperfine coupling constant (HFCC), is one of the most troublesome properties for quantum chemistry calculations. Yet, even relatively small errors in calculations of HFCC tend to propagate into large errors in the predicted NMR shifts. The poor quality of A tensors that are currently calculated using density functional theory (DFT) constitutes a bottleneck in improving the reliability of interpretation of the NMR spectra from paramagnetic systems. In this work, electron correlation effects in calculations of HFCCs with a hierarchy of ab initio methods were assessed, and the applicability of different levels of DFT approximations and the coupled cluster singles and doubles (CCSD) method was tested. These assessments were performed for the set of selected test systems comprising an organic radical, and complexes with transition metal and rare-earth ions, for which experimental data are available. Severe deficiencies of DFT were revealed but the CCSD method was able to deliver good agreement with experimental data for all systems considered, however, at substantial computational costs. We proposed a more computationally tractable alternative, where the A was computed with the coupled cluster theory exploiting locality of electron correlation. This alternative is based on the domain-based local pair natural orbital coupled cluster singles and doubles (DLPNO-CCSD) method. In this way the robustness and reliability of the coupled cluster theory were incorporated into the modern formalism for the prediction of induced paramagnetic NMR shifts, and became applicable to systems of chemical interest. This approach was verified for the bis(cyclopentadienyl)vanadium(II) complex (Cp2V; vanadocene), and the metal-binding site of the Zn2+ → Co2+ substituted superoxide dismutase (SOD) metalloprotein. Excellent agreement with experimental NMR shifts was achieved, which represented a substantial improvement over previous theoretical attempts. The effects of vibrational corrections to orbital shielding and hyperfine tensor were evaluated and discussed within the second-order vibrational perturbation theory (VPT2) framework.
Collapse
Affiliation(s)
- Aleksander Jaworski
- Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden.
| | - Niklas Hedin
- Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden.
| |
Collapse
|
8
|
Üngör Ö, Ozvat TM, Ni Z, Zadrozny JM. Record Chemical-Shift Temperature Sensitivity in a Series of Trinuclear Cobalt Complexes. J Am Chem Soc 2022; 144:9132-9137. [PMID: 35549174 DOI: 10.1021/jacs.2c03115] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Designing spins that exhibit long-lived coherence and strong temperature sensitivity is central to designing effective molecular thermometers and a fundamental challenge in the chemistry/quantum-information space. Herein, we provide a new pathway to both properties in the same molecule by designing a nuclear spin, which possesses a robust spin coherence, to mimic the strong temperature sensitivity of an electronic spin. This design strategy is demonstrated in the group of trinuclear Co(III) spin-crossover compounds [(CpCo(OP(OR)2)3)2Co](SbCl6) where Cp = cyclopentadienyl and R = Me (1), Et (2), i-Pr (3), and t-Bu (4). Nuclear magnetic resonance analyses of the 59Co nuclear spins reveal 59Co chemical-shift temperature sensitivity (Δδ/ΔT) values that span from 101(1) ppm/°C in 1 to 149(1) ppm/°C in 2 and 150(2) ppm/°C in 4, where the latter two are record temperature sensitivities for any nuclear spin. Additionally, complexes 2 and 4 have T2* values of 74 and 78 μs in solution at ambient temperatures surpassing those from electron-spin-based complexes, which typically display long coherence times only at extremely low temperatures. Our results suggest that spin-crossover phenomena can enable electron-spin-like temperature sensitivities in nuclear spins while retaining robust coherence times at room temperature.
Collapse
Affiliation(s)
- Ökten Üngör
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Tyler M Ozvat
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Zhen Ni
- Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, Texas 77843, United States
| | - Joseph M Zadrozny
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
| |
Collapse
|
9
|
Swartjes A, White PB, Bruekers JPJ, Elemans JAAW, Nolte RJM. Paramagnetic relaxation enhancement NMR as a tool to probe guest binding and exchange in metallohosts. Nat Commun 2022; 13:1846. [PMID: 35388004 PMCID: PMC8986849 DOI: 10.1038/s41467-022-29406-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 02/21/2022] [Indexed: 11/11/2022] Open
Abstract
Paramagnetic metallohost systems can bind guest molecules and find application as biomimetic catalysts. Due to the presence of the paramagnetic metal center, rigorous characterization of these systems by NMR spectroscopy can be very difficult. We report here that metallohost-guest systems can be studied by using the paramagnetic relaxation enhancement (PRE) effect. Manganese(III) porphyrin cage compounds are shown through their PRE to thread and bind viologen guests, including a polymeric one. The binding constants and dethreading activation parameters are lower than those of the metal-free porphyrin cage compounds, which is proposed to be a result of charge repulsion of the trivalent metal center and dicationic viologen guest. The threading rate of the manganese(III) porphyrin cage onto the polymer is more than 10 times faster than that of the non-metallated one, which is ascribed to initial binding of the cage to the polymer chain prior to threading, and to an entron effect. Paramagnetic metallohost systems are difficult to characterize. Here the authors report that the paramagnetic relaxation enhancement effect can be used to prove by nuclear magnetic resonance experiments that Mn(III) porphyrin cage compounds can bind and thread low molecular weight and polymeric guests.
Collapse
Affiliation(s)
- Anne Swartjes
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands
| | - Paul B White
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands.
| | - Jeroen P J Bruekers
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands
| | - Johannes A A W Elemans
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands.
| | - Roeland J M Nolte
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands.
| |
Collapse
|
10
|
Ott JC, Bürgy D, Guan H, Gade LH. 3d Metal Complexes in T-shaped Geometry as a Gateway to Metalloradical Reactivity. Acc Chem Res 2022; 55:857-868. [PMID: 35164502 DOI: 10.1021/acs.accounts.1c00737] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
ConspectusLow-valent, low-coordinate 3d metal complexes represent a class of extraordinarily reactive compounds that can act as reagents and catalysts for challenging bond-activation reactions. The pursuit of these electron-deficient metal complexes in low oxidation states demands ancillary ligands capable of providing not only energetic stabilization but also sufficiently high steric bulk at the metal center. From this perspective, pincer ligands are particularly advantageous, as their prearranged, meridional coordination mode scaffolds the active center while the substituents of the peripheral donor atoms provide effective steric shielding for the coordination sphere. In a T-shaped geometry, the transition metal complexes possess a precisely defined vacant coordination site, which, combined with the often observed high-spin electron configuration, exhibits unusually high selectivity of these compounds with respect to one-electron redox chemistry. In light of the intractable reaction pathways typically observed with related electronically unsaturated 3d transition metal complexes, the pincer coordination mode enables the isolation of low-valent compounds with more controlled and unique reactivity. We have thus investigated a series of T-shaped metal(I) complexes using three different types of pincer ligands, which may be regarded as "metalloradicals" due to their selectively exposed unpaired electrons.These compounds display remarkably high thermal stability and represent rarely observed "naked" monovalent metal species featuring both monomeric and dimeric structures. Extensive reactivity studies using various organic substrates highlight a strong tendency of these paramagnetic compounds to undergo one-electron oxidation, leading to the isolation of a plethora of metal(II) species with reduced organic ligands as unusual structural elements. The exploration of C2 symmetric T-shaped Ni(I) complexes as asymmetric catalysts also shows success in enantioselective hydrodehalogenation of geminal dihalogenides. In addition, this specific class of low-valent, low-coordinate complexes can be further diversified by introducing redox-active pincer ligands or building homobimetallic systems with two T-shaped units.This Account focuses on the discussion of selected examples of iron, cobalt, and nickel pincer complexes bearing a [P,N,P] or [N,N,N] donor set; however, their electronic structure and radical-type reactivity can be broadly extended to other pincer systems. The availability of various types of pincer ligands should allow fine-tuning of the reactivity of the T-shaped complexes. Given the unprecedented reactivity observed with these compounds, we expect the studies of T-shaped 3d metal complexes to be a fertile field for advancing base metal catalysis.
Collapse
Affiliation(s)
- Jonas C. Ott
- Anorganisch-Chemisches Institut, Universität Heidelberg, 69120 Heidelberg, Germany
| | - David Bürgy
- Anorganisch-Chemisches Institut, Universität Heidelberg, 69120 Heidelberg, Germany
| | - Hairong Guan
- Department of Chemistry, University of Cincinnati, P.O. Box 210172, Cincinnati, Ohio 45221-0172, United States
| | - Lutz H. Gade
- Anorganisch-Chemisches Institut, Universität Heidelberg, 69120 Heidelberg, Germany
| |
Collapse
|
11
|
Ott JC, Suturina EA, Kuprov I, Nehrkorn J, Schnegg A, Enders M, Gade LH. Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts. Angew Chem Int Ed Engl 2021; 60:22856-22864. [PMID: 34351041 PMCID: PMC8518043 DOI: 10.1002/anie.202107944] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Indexed: 12/27/2022]
Abstract
We report an experimental observation of 31 P NMR resonances shifted by over 10 000 ppm (meaning percent range, and a new record for solutions), and similar 1 H chemical shifts, in an intermediate-spin square planar ferrous complex [tBu (PNP)Fe-H], where PNP is a carbazole-based pincer ligand. Using a combination of electronic structure theory, nuclear magnetic resonance, magnetometry, and terahertz electron paramagnetic resonance, the influence of magnetic anisotropy and zero-field splitting on the paramagnetic shift and relaxation enhancement is investigated. Detailed spin dynamics simulations indicate that, even with relatively slow electron spin relaxation (T1 ≈10-11 s), it remains possible to observe NMR signals of directly metal-bonded atoms because pronounced rhombicity in the electron zero-field splitting reduces nuclear paramagnetic relaxation enhancement.
Collapse
Affiliation(s)
- Jonas C. Ott
- Anorganisch-Chemisches InstitutUniversität HeidelbergIm Neuenheimer Feld 27669120HeidelbergGermany
| | | | - Ilya Kuprov
- School of ChemistryUniversity of SouthamptonSouthamptonSO17 1BJUK
| | - Joscha Nehrkorn
- EPR Research GroupMPI for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim RuhrGermany
| | - Alexander Schnegg
- EPR Research GroupMPI for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim RuhrGermany
| | - Markus Enders
- Anorganisch-Chemisches InstitutUniversität HeidelbergIm Neuenheimer Feld 27669120HeidelbergGermany
| | - Lutz H. Gade
- Anorganisch-Chemisches InstitutUniversität HeidelbergIm Neuenheimer Feld 27669120HeidelbergGermany
| |
Collapse
|