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Albrecht M. The Monomer-Dimer Equilibrium of Triscatechol Titanium(IV)-Based Hierarchical Helicates as a Tool for the Development of Molecular Balances and Molecular Switches. Acc Chem Res 2023; 56:3271-3281. [PMID: 37955356 DOI: 10.1021/acs.accounts.3c00525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2023]
Abstract
ConspectusHierarchical helicates are formed by noncovalent connection of two or more monomeric metal complex units, e.g., by bridging metal cations. A unique kind of hierarchical helicate is obtained from 3-carbonyl substituted catechol ligands with titanium(IV) ions in the presence of lithium cations. This kind of supramolecular complex shows in solution a "monomer-dimer" equilibrium. There are different possibilities (solvent, countercation, substituents at carbonyl unit, etc.) to shift this equilibrium to either the monomer or the dimer side. Thus, the lithium-bridged catecholate-based hierarchical helicates resemble a molecular switch. In this Account, different aspects are discussed of how this unique behavior of the dimeric titanium catecholates can be used for application.Thorough investigation of the energetics of the monomer-dimer equilibrium leads to a deeper understanding of the thermodynamic and kinetic effects of the dimerization (or dissociation) process. In this context, even weak interaction of substituents in the periphery of the complexes can be observed. Hereby on the one hand, solvent effects have an important influence and can be easily evaluated. The thorough understanding of the behavior of the monomer-dimer equilibrium allows one to develop some novel applications. In this respect, the use of the hierarchical helicate-based switch as a platform for reaction control and catalysis is described. Decent enantioselectivities up to ee = 58% can be found in Diels-Alder reactions in the periphery of the dimers, while switching to the monomer as a reaction platform still allows the cycloaddition reaction but turns the selectivity off. Additionally, it is described that catalytically important units can be introduced and hydrogenation reactions as well as Michael-type reactions are catalyzed at the helicates.Covalent connection of two catechol ester units leads to classical helicates. Depending on the alkaline metal cation, those can be switched from a compressed to an expanded form or vice versa. Hereby the monomer-dimer equilibrium is transformed into a structural switch. The switching process can be initiated by removal or addition of lithium cations (e.g., by addition of [2.1.1]cryptand). Alternative switching possibilities are based in the case of glycol bridged helicates on cation translocation isomerism and with thioester derivatives it occurs spontaneously in DMSO. Introduction of chiral tethers results in a three state switch allowing expansion/compression as well as switching of the helicity.
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Affiliation(s)
- Markus Albrecht
- Institut für Organische Chemie, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany
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Joseph J, Mobian P, Chaumont A, Wytko JA, Weiss J. Going Up the Ladder: Stacking Four 4,4'-Bipyridine Moieties within a Ti(IV)-Based Tetranuclear Architecture. Inorg Chem 2022; 61:16448-16457. [PMID: 36201371 DOI: 10.1021/acs.inorgchem.2c02566] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Biphenol-based ligands have proven their ability to bind titanium(IV) centers and generate sophisticated self-assembled structures in which auxiliary nitrogen ligands often complete the coordination sphere of the metal and improve stability. Here, a central 4,4'-bipyridine, which acts as both a spacer and a source of monodentate nitrogen to complete the coordination sphere of the Ti(IV) complex, was incorporated within two bis-2,2'-biphenol strands, 3H4 and 4H4. Both proligands possess structural features that are well adapted to form self-assembled structures built from titanium-oxygen-nitrogen units; however, their different degrees of torsional freedom strongly influenced the nuclearity of the complexes formed. The presence of a phenyl spacer between the bipyridine and the biphenol moieties of 3H4 provided enough flexibility for the ligand to wrap around one titanium(IV) center to form a mononuclear complex Ti(3)(DMF)2 in the presence of dimethylformamide (DMF). Assembly of the more rigid ligand 4H4 with Ti(OiPr)4 afforded a tetranuclear complex Ti4(4)2(4H)2(OEt)2 containing four stacked 4,4'-bipyridine units as shown by the X-ray structure of the complex. Density functional theory studies suggested that the assembly of this tetrametallic complex involves a dimetallic intermediate with TiO6 nodes that is converted to the thermodynamically stable tetranuclear complex with two TiO6 nodes and two TiO5N units with enhanced covalent character.
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Affiliation(s)
- Jean Joseph
- Institut de Chimie de Strasbourg, UMR 7177 CNRS-Université de Strasbourg, 4 rue Blaise Pascal, 67008Strasbourg, France
| | - Pierre Mobian
- Chimie de la matière complexe, UMR 7140 CNRS-Université de Strasbourg, 4 rue Blaise Pascal, 67008Strasbourg, France
| | - Alain Chaumont
- Chimie de la matière complexe, UMR 7140 CNRS-Université de Strasbourg, 4 rue Blaise Pascal, 67008Strasbourg, France
| | - Jennifer A Wytko
- Institut de Chimie de Strasbourg, UMR 7177 CNRS-Université de Strasbourg, 4 rue Blaise Pascal, 67008Strasbourg, France
| | - Jean Weiss
- Institut de Chimie de Strasbourg, UMR 7177 CNRS-Université de Strasbourg, 4 rue Blaise Pascal, 67008Strasbourg, France
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Gonzálvez MA, Bernhardt PV, Font-Bardia M, Gallen A, Jover J, Ferrer M, Martínez M. Molecular Approach to Alkali-Metal Encapsulation by a Prussian Blue Analogue Fe II/Co III Cube in Aqueous Solution: A Kineticomechanistic Exchange Study. Inorg Chem 2021; 60:18407-18422. [PMID: 34766767 PMCID: PMC8715505 DOI: 10.1021/acs.inorgchem.1c03001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The preparation of a series of alkali-metal inclusion complexes of the molecular cube [{CoIII(Me3-tacn)}4{FeII(CN)6}4]4- (Me3-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), a mixed-valent Prussian Blue analogue bearing bridging cyanido ligands, has been achieved by following a redox-triggered self-assembly process. The molecular cubes are extremely robust and soluble in aqueous media ranging from 5 M [H+] to 2 M [OH-]. All the complexes have been characterized by the standard mass spectometry, UV-vis, inductively coupled plasma, multinuclear NMR spectroscopy, and electrochemistry. Furthermore, X-ray diffraction analysis of the sodium and lithium salts has also been achieved, and the inclusion of moieties of the form {M-OH2}+ (M = Li, Na) is confirmed. These inclusion complexes in aqueous solution are rather inert to cation exchange and are characterized by a significant decrease in acidity of the confined water molecule due to hydrogen bonding inside the cubic cage. Exchange of the encapsulated cationic {M-OH2}+ or M+ units by other alkali metals has also been studied from a kineticomechanistic perspective at different concentrations, temperatures, ionic strengths, and pressures. In all cases, the thermal and pressure activation parameters obtained agree with a process that is dominated by differences in hydration of the cations entering and exiting the cage, although the size of the portal enabling the exchange also plays a determinant role, thus not allowing the large Cs+ cation to enter. All the exchange substitutions studied follow a thermodynamic sequence that relates with the size and polarizing capability of the different alkali cations; even so, the process can be reversed, allowing the entry of {Li-OH2}+ units upon adsorption of the cube on an anion exchange resin and subsequent washing with a Li+ solution.
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Affiliation(s)
- Miguel A Gonzálvez
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072, Australia.,Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
| | - Paul V Bernhardt
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072, Australia
| | - Mercè Font-Bardia
- Unitat de Difracció de Raigs, X. Centre Científic i Tecnològic,Departament de Cristal·lografia, and Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona, 08028 Barcelona, Spain
| | - Albert Gallen
- Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
| | - Jesús Jover
- Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.,Institut de Química Teòrica i Computacional, Universitat de Barcelona, 08028 Barcelona, Spain
| | - Montserrat Ferrer
- Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.,Institute of Nanoscience and Nanotechnology, Universitat de Barcelona, 08028 Barcelona, Spain
| | - Manuel Martínez
- Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.,Institute of Nanoscience and Nanotechnology, Universitat de Barcelona, 08028 Barcelona, Spain
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