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Konsewicz K, Laczkó G, Pápai I, Zhivonitko VV. Activation of H 2 using ansa-aminoboranes: solvent effects, dynamics, and spin hyperpolarization. Phys Chem Chem Phys 2024; 26:3197-3207. [PMID: 38193236 DOI: 10.1039/d3cp05816f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2024]
Abstract
Spin hyperpolarization generated upon activation of parahydrogen, the spin-0 isomer of H2, by ansa-aminoboranes (AABs) constitutes a rare but interesting example of applied metal-free catalysis in parahydrogen-induced polarization (PHIP). AAB molecular moieties made of light elements would be useful in important areas of NMR, such as chemosensing and the production of hyperpolarized substances, or generally in NMR sensitivity enhancement. At the same time, little is known about the detailed mechanistic aspects of underlying chemical processes. Herein, we present a joint experimental-computational study of the kinetic and thermodynamic aspects of H2 activation by AABs, for the first time providing molecular-level details and results of PHIP experiments with AABs in various solvents. Specifically, a large number of kinetic and thermodynamic parameters are measured experimentally for H2 activation by 2-aminophenylboranes of variable steric bulkiness of the boryl site. A clear correlation between the experimental and DFT-predicted thermochemical parameters is observed. PHIP effects in toluene, dichloromethane, and acetonitrile are characterized and rationalized based on the use of the kinetic and nuclear spin relaxation parameters. Altogether, the obtained results provide valuable information for the further rational design of efficient AAB catalysts for metal-free PHIP based on frustrated Lewis pair (FLP) chemistry.
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Affiliation(s)
- Karolina Konsewicz
- NMR Research Unit, Faculty of Science, University of Oulu, P.O. Box 3000, Oulu, 90014, Finland.
| | - Gergely Laczkó
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar Tudósok Körútja 2, H-1117 Budapest, Hungary
- Hevesy György PhD School of Chemistry, Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
| | - Imre Pápai
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar Tudósok Körútja 2, H-1117 Budapest, Hungary
| | - Vladimir V Zhivonitko
- NMR Research Unit, Faculty of Science, University of Oulu, P.O. Box 3000, Oulu, 90014, Finland.
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2
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Zander E, Bresien J, Zhivonitko VV, Fessler J, Villinger A, Michalik D, Schulz A. Rational Design of Persistent Phosphorus-Centered Singlet Tetraradicals and Their Use in Small-Molecule Activation. J Am Chem Soc 2023. [PMID: 37315222 PMCID: PMC10368346 DOI: 10.1021/jacs.3c03928] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Biradicals are important intermediates in the process of bond formation and breaking. While main-group-element-centered biradicals have been thoroughly studied, much less is known about tetraradicals, as their very low stability has hampered their isolation and use in small-molecule activation. Herein, we describe the search for persistent phosphorus-centered tetraradicals. Starting from an s-hydrindacenyl skeleton, we investigated the introduction of four phosphorus-based radical sites linked by an N-R unit and bridged by a benzene moiety. By varying the size of the substituent R, we finally succeeded in isolating a persistent P-centered singlet tetraradical, 2,6-diaza-1,3,5,7-tetraphospha-s-hydrindacene-1,3,5,7-tetrayl (1), in good yields. Furthermore, it was demonstrated that tetraradical 1 can be utilized for the activation of small molecules such as molecular hydrogen or alkynes. In addition to the synthesis of P-centered tetraradicals, the comparison with other known tetraradicals as well as biradicals is described on the basis of quantum mechanical calculations with respect to its multireference character, coupling of radical electrons, and aromaticity. The strong coupling of radical electrons enables selective discrimination between the first and the second activations of small molecules, which is shown by the example of H2 addition. The mechanism of hydrogen addition is investigated with parahydrogen-induced hyperpolarization NMR studies and DFT calculations.
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Affiliation(s)
- Edgar Zander
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
| | - Jonas Bresien
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
| | | | - Johannes Fessler
- Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
| | - Alexander Villinger
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
| | - Dirk Michalik
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
- Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
| | - Axel Schulz
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
- Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
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Rosenboom J, Chojetzki L, Suhrbier T, Rabeah J, Villinger A, Wustrack R, Bresien J, Schulz A. Radical Reactivity of the Biradical [⋅P(μ-NTer) 2 P⋅] and Isolation of a Persistent Phosphorus-Cantered Monoradical [⋅P(μ-NTer) 2 P-Et]. Chemistry 2022; 28:e202200624. [PMID: 35445770 PMCID: PMC9322606 DOI: 10.1002/chem.202200624] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Indexed: 11/06/2022]
Abstract
The activation of C-Br bonds in various bromoalkanes by the biradical [⋅P(μ-NTer)2 P⋅] (1) (Ter=2,6-bis-(2,4,6-trimethylphenyl)-phenyl) is reported, yielding trans-addition products of the type [Br-P(μ-NTer)2 P-R] (2), so-called 1,3-substituted cyclo-1,3-diphospha-2,4-diazanes. This addition reaction, which represents a new easy approach to asymmetrically substituted cyclo-1,3-diphospha-2,4-diazanes, was investigated mechanistically by different spectroscopic methods (NMR, EPR, IR, Raman); the results suggested a stepwise radical reaction mechanism, as evidenced by the in-situ detection of the phosphorus-centered monoradical [⋅P(μ-NTer)2 P-R].< To provide further evidence for the radical mechanism, [⋅P(μ-NTer)2 P-Et] (3Et⋅) was synthesized directly by reduction of the bromoethane addition product [Br-P(μ-NTer)2 P-Et] (2 a) with magnesium, resulting in the formation of the persistent phosphorus-centered monoradical [⋅P(μ-NTer)2 P-Et], which could be isolated and fully characterized, including single-crystal X-ray diffraction. Comparison of the EPR spectrum of the radical intermediate in the addition reaction with that of the synthesized new [⋅P(μ-NTer)2 P-Et] radical clearly proves the existence of radicals over the course of the reaction of biradical [⋅P(μ-NTer)2 P⋅] (1) with bromoethane. Extensive DFT and coupled cluster calculations corroborate the experimental data for a radical mechanism in the reaction of biradical [⋅P(μ-NTer)2 P⋅] with EtBr. In the field of hetero-cyclobutane-1,3-diyls, the demonstration of a stepwise radical reaction represents a new aspect and closes the gap between P-centered biradicals and P-centered monoradicals in terms of radical reactivity.
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Affiliation(s)
- Jan Rosenboom
- Institut für Chemie, UniversitätAlbert-Einstein-Straße 3a18059RostockGermany
| | - Lukas Chojetzki
- Institut für Chemie, UniversitätAlbert-Einstein-Straße 3a18059RostockGermany
| | - Tim Suhrbier
- Institut für Chemie, UniversitätAlbert-Einstein-Straße 3a18059RostockGermany
| | - Jabor Rabeah
- Leibniz-Institut für Katalyse e.V.Albert-Einstein-Straße 29a18059RostockGermany
| | - Alexander Villinger
- Institut für Chemie, UniversitätAlbert-Einstein-Straße 3a18059RostockGermany
| | - Ronald Wustrack
- Institut für Chemie, UniversitätAlbert-Einstein-Straße 3a18059RostockGermany
| | - Jonas Bresien
- Institut für Chemie, UniversitätAlbert-Einstein-Straße 3a18059RostockGermany
| | - Axel Schulz
- Institut für Chemie, UniversitätAlbert-Einstein-Straße 3a18059RostockGermany
- Leibniz-Institut für Katalyse e.V.Albert-Einstein-Straße 29a18059RostockGermany
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Tickner BJ, Zhivonitko VV. Advancing homogeneous catalysis for parahydrogen-derived hyperpolarisation and its NMR applications. Chem Sci 2022; 13:4670-4696. [PMID: 35655870 PMCID: PMC9067625 DOI: 10.1039/d2sc00737a] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2022] [Accepted: 03/21/2022] [Indexed: 12/18/2022] Open
Abstract
Parahydrogen-induced polarisation (PHIP) is a nuclear spin hyperpolarisation technique employed to enhance NMR signals for a wide range of molecules. This is achieved by exploiting the chemical reactions of parahydrogen (para-H2), the spin-0 isomer of H2. These reactions break the molecular symmetry of para-H2 in a way that can produce dramatically enhanced NMR signals for reaction products, and are usually catalysed by a transition metal complex. In this review, we discuss recent advances in novel homogeneous catalysts that can produce hyperpolarised products upon reaction with para-H2. We also discuss hyperpolarisation attained in reversible reactions (termed signal amplification by reversible exchange, SABRE) and focus on catalyst developments in recent years that have allowed hyperpolarisation of a wider range of target molecules. In particular, recent examples of novel ruthenium catalysts for trans and geminal hydrogenation, metal-free catalysts, iridium sulfoxide-containing SABRE systems, and cobalt complexes for PHIP and SABRE are reviewed. Advances in this catalysis have expanded the types of molecules amenable to hyperpolarisation using PHIP and SABRE, and their applications in NMR reaction monitoring, mechanistic elucidation, biomedical imaging, and many other areas, are increasing.
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Affiliation(s)
- Ben J Tickner
- NMR Research Unit, Faculty of Science, University of Oulu P.O. Box 3000 Oulu 90014 Finland
- Department of Chemical and Biological Physics, Faculty of Chemistry, Weizmann Institute of Science Rehovot 7610001 Israel
| | - Vladimir V Zhivonitko
- NMR Research Unit, Faculty of Science, University of Oulu P.O. Box 3000 Oulu 90014 Finland
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Zakharov DO, Chernichenko K, Sorochkina K, Yang S, Telkki V, Repo T, Zhivonitko VV. Parahydrogen-Induced Polarization in Hydrogenation Reactions Mediated by a Metal-Free Catalyst. Chemistry 2022; 28:e202103501. [PMID: 34928532 PMCID: PMC9303582 DOI: 10.1002/chem.202103501] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2021] [Indexed: 11/28/2022]
Abstract
We report nuclear spin hyperpolarization of various alkenes achieved in alkyne hydrogenations with parahydrogen over a metal-free hydroborane catalyst (HCAT). Being an intramolecular frustrated Lewis pair aminoborane, HCAT utilizes a non-pairwise mechanism of H2 transfer to alkynes that normally prevents parahydrogen-induced polarization (PHIP) from being observed. Nevertheless, the specific spin dynamics in catalytic intermediates leads to the hyperpolarization of predominantly one hydrogen in alkene. PHIP enabled the detection of important HCAT-alkyne-H2 intermediates through substantial 1 H, 11 B and 15 N signal enhancement and allowed advanced characterization of the catalytic process.
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Affiliation(s)
| | - Konstantin Chernichenko
- Department of ChemistryUniversity of HelsinkiA. I. Virtasen aukio 100014HelsinkiFinland
- Present address: Discovery, Product Development & Supply (DPDS)Janssen Pharmaceutical Companies of Johnson & JohnsonTurnhoutseweg 302340BeerseBelgium
| | - Kristina Sorochkina
- NMR Research UnitUniversity of OuluP.O. Box 300090014OuluFinland
- Department of ChemistryUniversity of HelsinkiA. I. Virtasen aukio 100014HelsinkiFinland
| | - Shengjun Yang
- NMR Research UnitUniversity of OuluP.O. Box 300090014OuluFinland
| | | | - Timo Repo
- Department of ChemistryUniversity of HelsinkiA. I. Virtasen aukio 100014HelsinkiFinland
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Beer H, Linke A, Bresien J, Mlostoń G, Celeda M, Villinger A, Schulz A. Synthesis of Bicyclic P,S-Heterocycles via the Addition of Thioketones to a Phosphorus-Centered Open-Shell Singlet Biradical. Inorg Chem 2022; 61:2031-2038. [PMID: 35041414 DOI: 10.1021/acs.inorgchem.1c03207] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Formal addition reactions between the open-shell singlet biradical [P(μ-NTer)]2 (1Ter) and xanthione, thioxanthione, as well as ferrocenyl naphthyl thioketone were studied in detail. Reactions were performed at room temperature and led to the formation of strained [2.1.1]-cage P,S-heterocycles (3). All addition products were isolated and fully characterized by spectroscopic methods. Furthermore, reversible cleavage of the xanthenthione-biradical addition product into the parent compounds (biradical and thioketone) could be demonstrated by 31P{1H} NMR spectroscopy. The thermodynamic stability of all cyclization products with respect to the elimination of thioketone was studied by quantum-chemical computations including solvent effects. Regarding the dissociation of addition products 3 into the fragment molecules 1Ter and ketone/thioketone, calculations prove that a significantly larger distortion energy in ketones compared with thioketones causes lower thermodynamic stability of the ketone adducts.
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Affiliation(s)
- Henrik Beer
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, D-18059 Rostock, Germany
| | - Alexander Linke
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, D-18059 Rostock, Germany.,Leibniz-Institut für Katalyse eV, Universität Rostock, Albert-Einstein-Straße 29a, D-18059 Rostock, Germany
| | - Jonas Bresien
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, D-18059 Rostock, Germany
| | - Grzegorz Mlostoń
- Department of Organic and Applied Chemistry, University of Łódź, Tamka 12, PL-91-403 Łódź Poland
| | - Małgorzata Celeda
- Department of Organic and Applied Chemistry, University of Łódź, Tamka 12, PL-91-403 Łódź Poland
| | - Alexander Villinger
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, D-18059 Rostock, Germany.,Leibniz-Institut für Katalyse eV, Universität Rostock, Albert-Einstein-Straße 29a, D-18059 Rostock, Germany
| | - Axel Schulz
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, D-18059 Rostock, Germany.,Leibniz-Institut für Katalyse eV, Universität Rostock, Albert-Einstein-Straße 29a, D-18059 Rostock, Germany
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7
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Zakharov DO, Chernichenko K, Sorochkina K, Repo T, Zhivonitko VV. Parahydrogen-induced polarization study of imine hydrogenations mediated by a metal-free catalyst. Dalton Trans 2022; 51:13606-13611. [DOI: 10.1039/d2dt02178a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Parahydrogen-induced polarization is a nuclear spin hyperpolarization technique that can provide strongly enhanced NMR signals of catalytic hydrogenation reaction products and intermediates. Among other matters, this can be employed to...
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8
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Zhivonitko VV, Beer H, Zakharov DO, Bresien J, Schulz A. Hyperpolarization Effects in Parahydrogen Activation with Pnictogen Biradicaloids: Metal-free PHIP and SABRE. Chemphyschem 2021; 22:813-817. [PMID: 33725397 PMCID: PMC8251785 DOI: 10.1002/cphc.202100141] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Revised: 03/11/2021] [Indexed: 01/30/2023]
Abstract
Biradicaloids attract attention as a novel class of reagents that can activate small molecules such as H2, ethylene and CO2. Herein, we study activation of parahydrogen (nuclear spin‐0 isomer of H2) by a number of 4‐ and 5‐membered pnictogen biradicaloids based on hetero‐cyclobutanediyl [X(μ‐NTer)2Z] and hetero‐cyclopentanediyl [X(μ‐NTer)2ZC(NDmp)] moieties (X,Z=P,As; Ter=2,6‐Mes2−C6H3, Dmp=2,6‐Me2−C6H3). The concerted mechanism of this reaction allowed observing strong nuclear spin hyperpolarization effects in 1H and 31P NMR experiments. Signal enhancements from two to four orders of magnitude were detected at 9.4 T depending on the structure. It is demonstrated that 4‐membered biradicaloids activate H2 reversibly, leading to SABRE (signal amplification by reversible exchange) hyperpolarization of biradicaloids themselves and their H2 adducts. In contrast, the 5‐membered counterparts demonstrate rather irreversible parahydrogen activation resulting in hyperpolarized H2 adducts only. Kinetic measurements provided parameters to support experimental observations.
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Affiliation(s)
| | - Henrik Beer
- Institute of Chemistry, University of Rostock, Albert-Einstein-Strasse 3a, 18059, Rostock, Germany
| | - Danila O Zakharov
- NMR Research Unit, University of Oulu, P.O. Box 3000, 90014, Oulu, Finland
| | - Jonas Bresien
- Institute of Chemistry, University of Rostock, Albert-Einstein-Strasse 3a, 18059, Rostock, Germany
| | - Axel Schulz
- Institute of Chemistry, University of Rostock, Albert-Einstein-Strasse 3a, 18059, Rostock, Germany.,Leibniz-Institut für Katalyse e.V., Universität Rostock, Albert-Einstein-Strasse 29a, 18059, Rostock, Germany
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