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Krämer K, Schmitz M, Kelm H, van Wüllen C, Krüger HJ. Unexpected Reduction of a Coordinated Diazapyridinophane Ligand Bound to Chromium(III) Ion Leading to Delocalization of the Unpaired Electron across Two Isolated Pyridine Units. Chemistry 2024; 30:e202301099. [PMID: 37903737 DOI: 10.1002/chem.202301099] [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: 04/06/2023] [Revised: 10/06/2023] [Accepted: 10/27/2023] [Indexed: 11/01/2023]
Abstract
In the tetraazamacrocyclic ligand N,N'-dimethyl-2,11-diaza-[3.3](2,6)pyridinophane (L-N4 Me2 ), the two pyridine units are separated from each other by sp3 -hybridized triatomic bridges. Such electronically isolated pyridine moieties are considerably less prone to reductions than di- or triimines. A detailed structural, magnetic, and spectroscopic investigation of the complexes [Cr(L-N4 Me2 )(OAc)2 ] and [Cr(L-N4 Me2 )(OAc)2 ](PF6 ), in combination with theoretical calculations, reveals that the reduced complex must be described as a chromium(III) ion coordinated to the anionic radical ligand (L-N4 Me2 )⋅- rather than a low-spin chromium(II) ion bound to closed-shell ligands. Thus, it is, to the best of our knowledge, only the second example of a stable and structurally characterized metal complex containing a reduced isolated pyridine unit. The stability is attributed to the delocalization of the unpaired electron across the two pyridine units, mediated by their interaction to the metal ion.
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Affiliation(s)
- Kristin Krämer
- RPTU Kaiserslautern-Landau, Department of Chemistry, Erwin-Schrödinger Straße 54, 67663, Kaiserslautern, Germany
| | - Markus Schmitz
- RPTU Kaiserslautern-Landau, Department of Chemistry, Erwin-Schrödinger Straße 54, 67663, Kaiserslautern, Germany
| | - Harald Kelm
- RPTU Kaiserslautern-Landau, Department of Chemistry, Erwin-Schrödinger Straße 54, 67663, Kaiserslautern, Germany
| | - Christoph van Wüllen
- RPTU Kaiserslautern-Landau, Department of Chemistry and Forschungszentrum OPTIMAS, Erwin-Schrödinger Straße 54, 67663, Kaiserslautern, Germany
| | - Hans-Jörg Krüger
- RPTU Kaiserslautern-Landau, Department of Chemistry, Erwin-Schrödinger Straße 54, 67663, Kaiserslautern, Germany
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Naher M, Su C, Harmer JR, Williams CM, Bernhardt PV. Electrocatalytic Atom Transfer Radical Addition with Turbocharged Organocopper(II) Complexes. Inorg Chem 2023; 62:15575-15583. [PMID: 37712595 DOI: 10.1021/acs.inorgchem.3c02106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/16/2023]
Abstract
The utility and scope of Cu-catalyzed halogen atom transfer chemistry have been exploited in the fields of atom transfer radical polymerization and atom transfer radical addition, where the metal plays a key role in radical formation and minimizing unwanted side reactions. We have shown that electrochemistry can be employed to modulate the reactivity of the Cu catalyst between its active (CuI) and dormant (CuII) states in a variety of ligand systems. In this work, a macrocyclic pyridinophane ligand (L1) was utilized, which can break the C-Br bond of BrCH2CN to release •CH2CN radicals when in complex with CuI. Moreover, the [CuI(L1)]+ complex can capture the •CH2CN radical to form a new species [CuII(L1)(CH2CN)]+ in situ that, on reduction, exhibits halogen atom transfer reactivity 3 orders of magnitude greater than its parent complex [CuI(L1)]+. This unprecedented rate acceleration has been identified by electrochemistry, successfully reproduced by simulation, and exploited in a Cu-catalyzed bulk electrosynthesis where [CuII(L1)(CH2CN)]+ participates as a radical donor in the atom transfer radical addition of BrCH2CN to a selection of styrenes. The formation of these turbocharged catalysts in situ during electrosynthesis offers a new approach to the Cu-catalyzed organic reaction methodology.
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Affiliation(s)
- Masnun Naher
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia
| | - Chuyi Su
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia
| | - Jeffrey R Harmer
- Centre for Advanced Imaging, University of Queensland, Brisbane 4072, Australia
| | - Craig M Williams
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia
| | - Paul V Bernhardt
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia
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Brzeska S, Brzeski J, Niedziałkowski P, Zarzeczańska D. Macrocyclic chemosensors with anthraquinone signaling unit built into ionophore. Experimental and computational studies (part I) - synthesis and effect of proton binding on spectrophotometric and electrochemical properties. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023; 292:122405. [PMID: 36716604 DOI: 10.1016/j.saa.2023.122405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 01/19/2023] [Accepted: 01/22/2023] [Indexed: 06/18/2023]
Abstract
Two macrocyclic chemosensors with anthraquinone signaling unit incorporated into ionophore system (via positions 1 and 8) have been synthesized and subsequently their physicochemical properties became the subject of our extensive research. First ligand, labeled in the paper as AQ-Ncrown is characterized by a cyclic structure of a crown ether, while second one AQ-Ncrypt includes an additional ethoxy bridge, which ensures the bicyclic character of a cryptand. The studied macrocycles possess both oxygen and nitrogen heteroatoms in the ionophore cavity. Dualistic (chromophore and electrophore) signaling nature of described compounds, makes them potentially attractive molecular recognition systems. The aim of our research was to synthesize and analyze the spectroscopic, acid-base and redox properties of aforesaid macrocycles. Furthermore, we have combined experimental approach together with theoretical investigations. The equilibrium structures of AQ-Ncrown and AQ-Ncrypt were determined with the use of DFT calculations. The sensitivity of studied macrocycles towards interactions with protons was scrutinized. The complete pH-spectrophotometric characteristic of studied ligands together with their protolytic forms and corresponding pKa values were determined. The influence of medium (aprotic and protic solvent) on spectral effects was described. Furthermore, the molecular electrostatic potential maps for ligands and differential electron densities for their mono and dianions were calculated. The redox reactions was investigated at different pHs by cyclic voltammetry. Electrochemical results have presented intriguing phenomenon: the specific stabilization of the reduced form of the protonated molecules. The calculations have revealed that this is a consequence of barrierless intramolecular proton transfer (from the macrocycle cavity onto the anthraquinone moiety) that might occur during the reduction process in acidic medium.
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Affiliation(s)
- Sandra Brzeska
- Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308 Gdańsk, Poland
| | - Jakub Brzeski
- Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308 Gdańsk, Poland; Department of Chemistry, University of Pittsburgh, Pittsburgh, 15260 Pennsylvania, United States
| | - Paweł Niedziałkowski
- Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308 Gdańsk, Poland
| | - Dorota Zarzeczańska
- Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308 Gdańsk, Poland.
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Mekhail MA, Smith KJ, Freire DM, Pota K, Nguyen N, Burnett ME, Green KN. Increased Efficiency of a Functional SOD Mimic Achieved with Pyridine Modification on a Pyclen-Based Copper(II) Complex. Inorg Chem 2023; 62:5415-5425. [PMID: 36995929 PMCID: PMC10820499 DOI: 10.1021/acs.inorgchem.2c04327] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/31/2023]
Abstract
A series of Cu(II) complexes with the formula [CuRPyN3]2+ varying in substitution on the pyridine ring were investigated as superoxide dismutase (SOD) mimics to identify the most efficient reaction rates produced by a synthetic, water-soluble copper-based SOD mimic reported to date. The resulting Cu(II) complexes were characterized by X-ray diffraction analysis, UV-visible spectroscopy, cyclic voltammetry, and metal-binding (log β) affinities. Unique to this approach, the modifications to the pyridine ring of the PyN3 parent system tune the redox potential while exhibiting high binding stabilities without changing the coordination environment of the metal complex within the PyN3 family of ligands. We were able to adjust in parallel the binding stability and the SOD activity without compromising on either through simple modification of the pyridine ring on the ligand system. This goldilocks effect of high metal stabilities and high SOD activity reveals the potential of this system to be explored in therapeutics. These results serve as a guide for factors that can be modified in metal complexes using pyridine substitutions for PyN3, which can be incorporated into a range of applications moving forward.
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Affiliation(s)
- Magy A Mekhail
- Department of Chemistry and Biochemistry, Texas Christian University, Fort Worth, Texas 76129, United States
| | - Katherine J Smith
- Department of Chemistry and Biochemistry, Texas Christian University, Fort Worth, Texas 76129, United States
| | - David M Freire
- Department of Chemistry and Biochemistry, Texas Christian University, Fort Worth, Texas 76129, United States
| | - Kristof Pota
- Department of Chemistry and Biochemistry, Texas Christian University, Fort Worth, Texas 76129, United States
| | - Nam Nguyen
- Department of Chemistry and Biochemistry, Texas Christian University, Fort Worth, Texas 76129, United States
| | - Marianne E Burnett
- Department of Chemistry and Biochemistry, Texas Christian University, Fort Worth, Texas 76129, United States
| | - Kayla N Green
- Department of Chemistry and Biochemistry, Texas Christian University, Fort Worth, Texas 76129, United States
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Panza N, di Biase A, Caselli A. Structural and spectroscopical characterization of µ-oxo bridged Iron(III) bromide complexes of Pyclen ligands. Inorganica Chim Acta 2022. [DOI: 10.1016/j.ica.2022.121091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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