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20 pages, 2807 KiB

Open AccessArticle

Synthesis, Structural, and Cytotoxic Properties of New Water-Soluble Copper(II) Complexes Based on 2,9-Dimethyl-1,10-Phenanthroline and Their One Derivative Containing 1,3,5-Triaza-7-Phosphaadamantane-7-Oxide

by Ewelina I. Śliwa, Urszula Śliwińska-Hill, Barbara Bażanów, Miłosz Siczek, Julia Kłak and Piotr Smoleński

Molecules 2020, 25(3), 741; https://doi.org/10.3390/molecules25030741 - 08 Feb 2020

Cited by 12 | Viewed by 4178

Abstract

A series of water-soluble copper(II) complexes based on 2,9-dimethyl-1,10-phenanthroline (dmphen) and mixed-ligands, containing PTA=O (1,3,5-triaza-7-phosphaadamantane-7-oxide) have been synthesized and fully characterized. Two types of complexes have been obtained, monocationic [Cu(NO₃)(O-PTA=O)(dmphen)][PF₆] (1), [Cu(Cl)(dmphen)₂][PF₆] ( [...] Read more.

A series of water-soluble copper(II) complexes based on 2,9-dimethyl-1,10-phenanthroline (dmphen) and mixed-ligands, containing PTA=O (1,3,5-triaza-7-phosphaadamantane-7-oxide) have been synthesized and fully characterized. Two types of complexes have been obtained, monocationic [Cu(NO₃)(O-PTA=O)(dmphen)][PF₆] (1), [Cu(Cl)(dmphen)₂][PF₆] (2), and neutral [Cu(NO₃)₂(dmphen)] (3). The solid-state structures of all complexes have been determined by single-crystal X-ray diffraction. Magnetic studies for the complex 1–3 indicated a very weak antiferromagnetic interaction between copper(II) ions in crystal lattice. Complexes were successfully evaluated for their cytotoxic activities on the normal human dermal fibroblast (NHDF) cell line and the antitumor activity using the human lung carcinoma (A549), epithelioid cervix carcinoma (HeLa), colon (LoVo), and breast adenocarcinoma (MCF-7) cell lines. Complexes 1 and 3 revealed lower toxicity to NHDF than A549 and HeLa cells, meanwhile compound 2 appeared to be more toxic to NHDF cell line in comparison to all cancer lines. Additionally, interactions between the complexes and human apo-transferrin (apo-Tf) using fluorescence and circular dichroism (CD) spectroscopy were also investigated. All compounds interacted with apo-transferrin, causing same changes of the protein conformation. Electrostatic interactions dominate in the 1/2 – apo- Tf systems and hydrophobic and ionic interactions in the case of 3. Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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16 pages, 5980 KiB

Open AccessFeature PaperArticle

Coordination Chemistry of Ru(II) Complexes of an Asymmetric Bipyridine Analogue: Synergistic Effects of Supporting Ligand and Coordination Geometry on Reactivities

by Komi Akatsuka, Ryosuke Abe, Tsugiko Takase and Dai Oyama

Molecules 2020, 25(1), 27; https://doi.org/10.3390/molecules25010027 - 19 Dec 2019

Cited by 7 | Viewed by 4942

Abstract

The reactivities of transition metal coordination compounds are often controlled by the environment around the coordination sphere. For ruthenium(II) complexes, differences in polypyridyl supporting ligands affect some types of reactivity despite identical coordination geometries. To evaluate the synergistic effects of (i) the supporting [...] Read more.

The reactivities of transition metal coordination compounds are often controlled by the environment around the coordination sphere. For ruthenium(II) complexes, differences in polypyridyl supporting ligands affect some types of reactivity despite identical coordination geometries. To evaluate the synergistic effects of (i) the supporting ligands, and (ii) the coordination geometry, a series of dicarbonyl–ruthenium(II) complexes that contain both asymmetric and symmetric bidentate polypyridyl ligands were synthesized. Molecular structures of the complexes were determined by X-ray crystallography to distinguish their steric configuration. Structural, computational, and electrochemical analysis revealed some differences between the isomers. Photo- and thermal reactions indicated that the reactivities of the complexes were significantly affected by both their structures and the ligands involved. Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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16 pages, 8096 KiB

Open AccessArticle

Chiral Chalcogen Bond Donors Based on the 4,4′-Bipyridine Scaffold

by Robin Weiss, Emmanuel Aubert, Paola Peluso, Sergio Cossu, Patrick Pale and Victor Mamane

Molecules 2019, 24(24), 4484; https://doi.org/10.3390/molecules24244484 - 06 Dec 2019

Cited by 25 | Viewed by 5032

Abstract

Organocatalysis through chalcogen bonding (ChB) is in its infancy, as its proof-of-principle was only reported in 2016. Herein, we report the design and synthesis of new chiral ChB donors, as well as the catalytic activity evaluation of the 5,5′-dibromo-2,2′-dichloro-3-((perfluorophenyl)selanyl)-4,4′-bipyridine as organocatalyst. The latter [...] Read more.

Organocatalysis through chalcogen bonding (ChB) is in its infancy, as its proof-of-principle was only reported in 2016. Herein, we report the design and synthesis of new chiral ChB donors, as well as the catalytic activity evaluation of the 5,5′-dibromo-2,2′-dichloro-3-((perfluorophenyl)selanyl)-4,4′-bipyridine as organocatalyst. The latter is based on the use of two electron-withdrawing groups, a pentafluorophenyl ring and a tetrahalo-4,4′-bipyridine skeleton, as substituents at the selenium center. Atropisomery of the tetrahalo-4,4′-bipyridine motif provides a chiral environment to these new ChB donors. Their synthesis was achieved through either selective lithium exchange and trapping or a site-selective copper-mediated reaction. Pure enantiomers of the 3-selanyl-4,4′-bipyridine were obtained by high performance liquid chromatography enantioseparation on specific chiral stationary phase, and their absolute configuration was assigned by comparison of the measured and calculated electronic circular dichroism spectra. The capability of the selenium compound to participate in σ-hole-based interactions in solution was studied by ¹⁹F NMR. Even if no asymmetric induction has been observed so far, the new selenium motif proved to be catalytically active in the reduction of 2-phenylquinoline by Hantzsch ester. Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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20 pages, 4133 KiB

Open AccessFeature PaperArticle

Towards Covalent Photosensitizer-Polyoxometalate Dyads-Bipyridyl-Functionalized Polyoxometalates and Their Transition Metal Complexes

by Andreas Winter, Patrick Endres, Erik Schröter, Michael Jäger, Helmar Görls, Christof Neumann, Andrey Turchanin and Ulrich S. Schubert

Molecules 2019, 24(24), 4446; https://doi.org/10.3390/molecules24244446 - 04 Dec 2019

Cited by 5 | Viewed by 3575

Abstract

A triol-functionalized 2,2′-bipyridine (bpy) derivative has been synthesized and used for the tris-alkoxylation of polyoxometalate (POM) precursors. The resultant POM-bpy conjugates of the Wells–Dawson- and Anderson-type feature a C–C bond as a linkage between the POM and bpy fragments. This structural motif is [...] Read more.

A triol-functionalized 2,2′-bipyridine (bpy) derivative has been synthesized and used for the tris-alkoxylation of polyoxometalate (POM) precursors. The resultant POM-bpy conjugates of the Wells–Dawson- and Anderson-type feature a C–C bond as a linkage between the POM and bpy fragments. This structural motif is expected to increase the hydrolytic stability of the compounds. This is of particular relevance with respect to the application of POM-bpy metal complexes, as photocatalysts, in the hydrogen-evolution reaction (HER) in an aqueous environment. Accordingly, Rh(III) and Ir(III) complexes of the POM-bpy ligands have been prepared and characterized. These catalyst-photosensitizer dyads have been analyzed with respect to their electrochemical and photophysical properties. Cyclic and square-wave voltammetry, as well as UV/vis absorption and emission spectroscopy, indicated a negligible electronic interaction of the POM and metal-complex subunits in the ground state. However, emission–quenching experiments suggested an efficient intramolecular electron-transfer process from the photo-excited metal centers to the POM units to account for the non-emissive nature of the dyads (thus, suggesting a strong interaction of the subunits in the excited state). In-depth photophysical investigations, as well as a functional characterization, i.e., the applicability in the HER reaction, are currently ongoing. Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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13 pages, 2728 KiB

Open AccessArticle

A Novel Ruthenium(II) Polypyridyl Complex Bearing 1,8-Naphthyridine as a High Selectivity and Sensitivity Fluorescent Chemosensor for Cu²⁺ and Fe³⁺ Ions

by Chixian He, Shiwen Yu, Shuye Ma, Zining Liu, Lifeng Yao, Feixiang Cheng and Pinhua Liu

Molecules 2019, 24(22), 4032; https://doi.org/10.3390/molecules24224032 - 07 Nov 2019

Cited by 7 | Viewed by 3143

Abstract

A novel ruthenium(II) polypyridyl complex bearing 1,8-naphthyridine was successfully designed and synthesized. This complex was fully characterized by EI-HRMS, NMR, and elemental analyses. The recognition properties of the complex for various metal ions were investigated. The results suggested that the complex displayed high [...] Read more.

A novel ruthenium(II) polypyridyl complex bearing 1,8-naphthyridine was successfully designed and synthesized. This complex was fully characterized by EI-HRMS, NMR, and elemental analyses. The recognition properties of the complex for various metal ions were investigated. The results suggested that the complex displayed high selectivity and sensitivity for Cu²⁺ and Fe³⁺ ions with good anti-interference in the CH₃CN/H₂O (1:1, v/v) solution. The fluorescent chemosensor showed obvious fluorescence quenching when the Cu²⁺ and Fe³⁺ ions were added. The detection limits of Cu²⁺ and Fe³⁺ were 39.9 nmol/L and 6.68 nmol/L, respectively. This study suggested that this Ru(II) polypyridyl complex can be used as a high selectivity and sensitivity fluorescent chemosensor for Cu²⁺ and Fe³⁺ ions. Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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16 pages, 4166 KiB

Open AccessFeature PaperArticle

Hinged and Wide: A New P^P Ligand for Emissive [Cu(P^P)(N^N)][PF₆] Complexes

by Sarah Keller, Matthias Bantle, Alessandro Prescimone, Edwin C. Constable and Catherine E. Housecroft

Molecules 2019, 24(21), 3934; https://doi.org/10.3390/molecules24213934 - 31 Oct 2019

Cited by 12 | Viewed by 3000

Abstract

Heteroleptic [Cu(BIPHEP)(N^N)][PF₆] complexes (BIPHEP = 1,1′-biphenyl-2,2′-diylbis(diphenylphosphane)), in which N^N is 2,2′-bipyridine (bpy), 6-methyl-2,2′-bipyridine (6-Mebpy), 6-ethyl-2,2′-bipyridine (6-Etbpy), or 5,5′-dimethyl-2,2′-bipyridine (5,5′-Me₂bpy), have been synthesized and characterized using multinuclear NMR spectroscopies and electrospray ionization mass spectrometry. The single crystal structures of [Cu(BIPHEP)(bpy)][PF [...] Read more.

Heteroleptic [Cu(BIPHEP)(N^N)][PF₆] complexes (BIPHEP = 1,1′-biphenyl-2,2′-diylbis(diphenylphosphane)), in which N^N is 2,2′-bipyridine (bpy), 6-methyl-2,2′-bipyridine (6-Mebpy), 6-ethyl-2,2′-bipyridine (6-Etbpy), or 5,5′-dimethyl-2,2′-bipyridine (5,5′-Me₂bpy), have been synthesized and characterized using multinuclear NMR spectroscopies and electrospray ionization mass spectrometry. The single crystal structures of [Cu(BIPHEP)(bpy)][PF₆]∙CH₂Cl₂, [Cu(BIPHEP)(5,5′-Me₂bpy)][PF₆]∙CH₂Cl₂, [Cu(BIPHEP)(6-Mebpy)][PF₆]∙Et₂O∙0.5H₂O and [Cu(BIPHEP)(6-Etbpy)][PF₆] confirm distorted tetrahedral {Cu(P^P)(N^N)} coordination environments. Each compound shows a quasi-reversible Cu⁺/Cu²⁺ process. In deaerated solution, the compounds are weak emitters. Powdered samples are yellow emitters (λ_em^max in the range 558–583 nm) and [Cu(BIPHEP)(5,5′-Me₂bpy)][PF₆] exhibits the highest photoluminescence quantum yield (PLQY = 14%). On cooling to 77 K (frozen 2-methyloxolane), the emission maxima are red-shifted and the excited state lifetimes increase from τ_1/2 < 8 μs, to τ_1/2 values of up to 53 μs, consistent with the compounds with N^N = 6-Mebpy, 6-Etbpy and 5,5′-Me₂bpy exhibiting thermally activated delayed fluorescence (TADF). Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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Review

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14 pages, 4049 KiB

Open AccessReview

Applications of Bolm’s Ligand in Enantioselective Synthesis

by Eva Bednářová, Štefan Malatinec and Martin Kotora

Molecules 2020, 25(4), 958; https://doi.org/10.3390/molecules25040958 - 20 Feb 2020

Cited by 4 | Viewed by 2940

Abstract

One pathway for the preparation of enantiomerically pure compounds from prochiral substrates is the use of metal complex catalysis with chiral ligands. Compared to the other frequently used chiral ligands, chiral 2,2’-bipyridines have been underexploited, despite the data indicating that such ligands have [...] Read more.

One pathway for the preparation of enantiomerically pure compounds from prochiral substrates is the use of metal complex catalysis with chiral ligands. Compared to the other frequently used chiral ligands, chiral 2,2’-bipyridines have been underexploited, despite the data indicating that such ligands have considerable potential in synthetic chemistry. One of those is the so-called Bolm’s ligand, a compound possessing chiral alcohol moieties in the side chains attached to the 2,2’-bipyridine scaffold. Various metal salts have been used in combination with Bolm’s ligand as potent catalysts able to bring about enantioselective alkylations, allylations, conjugate additions, desymmetrization of meso-epoxides, aldol reactions, etc. This review aims to summarize Bolm’s ligand applications in the area of enantioselective synthesis over the last three decades since its preparation. Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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30 pages, 9923 KiB

Open AccessReview

Mono- and Di-Quaternized 4,4′-Bipyridine Derivatives as Key Building Blocks for Medium- and Environment-Responsive Compounds and Materials

by Raffaello Papadakis

Molecules 2020, 25(1), 1; https://doi.org/10.3390/molecules25010001 - 18 Dec 2019

Cited by 20 | Viewed by 6157

Abstract

Mono- and di-quaternized 4,4′-bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4′-bipyridine-based derivatives are exploited: [...] Read more.

Mono- and di-quaternized 4,4′-bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4′-bipyridine-based derivatives are exploited: their redox activity and their electrochromic aptitude. Contemporary materials and compounds encompassing these skeletons as building blocks are often characterized as multifunctional, as their presence often gives rise to interesting phenomena, e.g., various types of chromism. This research trend is acknowledged, and, in this review article, recent examples of multifunctional chromic materials/compounds of this class are presented. Emphasis is placed on solvent-/medium- and environment-responsive 4,4′-bipyridine derivatives. Two important classes of 4,4′-bipyridine-based products with solvatochromic and/or environment-responsive character are reviewed: viologens (i.e., N,N′-disubstituted derivatives) and monoquats (i.e., monosubstituted 4,4′-bipyridine derivatives). The multifunctional nature of these derivatives is analyzed and structure–property relations are discussed in connection to the role of these derivatives in various novel applications. Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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38 pages, 7780 KiB

Open AccessReview

The Early Years of 2,2′-Bipyridine—A Ligand in Its Own Lifetime

by Edwin C. Constable and Catherine E. Housecroft

Molecules 2019, 24(21), 3951; https://doi.org/10.3390/molecules24213951 - 31 Oct 2019

Cited by 87 | Viewed by 17088

Abstract

The first fifty years of the chemistry of 2,2′-bipyridine are reviewed from its first discovery in 1888 to the outbreak of the second global conflict in 1939. The coordination chemistry and analytical applications are described and placed in the context of the increasingly [...] Read more.

The first fifty years of the chemistry of 2,2′-bipyridine are reviewed from its first discovery in 1888 to the outbreak of the second global conflict in 1939. The coordination chemistry and analytical applications are described and placed in the context of the increasingly sophisticated methods of characterization which became available to the chemist in this time period. Many of the “simple” complexes of 2,2′-bipyridine reported in the early literature have been subsequently shown to have more complex structures. Full article

(This article belongs to the Special Issue Bipyridines: Synthesis, Functionalization and Applications)

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