Cleavage Of Metal-ligand Bonds Research Articles

Construction of a bioactive copper-based metal organic framework-embedded dual-crosslinked alginate hydrogel for antimicrobial applications

Metal-organic frameworks (MOFs) containing bioactive metals have the potential to exhibit antimicrobial activity by releasing metal ions or ligands through the cleavage of metal-ligand bonds. Recently, copper-based MOFs (Cu-MOFs) with sustained release capability, porosity, and structural flexibility have shown promising antimicrobial properties. However, for clinical use, the controlled release of Cu2+ over an extended time period is crucial to prevent toxicity. In this study, we developed an alginate-based antimicrobial scaffold and encapsulated MOFs within a dual-crosslinked alginate polymer network. We synthesized Cu-MOFs containing glutarate (Glu) and 4,4′-azopyridine (AZPY) (Cu(AZPY)-MOF) and encapsulated them in an alginate-based hydrogel through a combination of visible light-induced photo and calcium ion-induced chemical crosslinking processes. We confirmed Cu(AZPY)-MOF synthesis using scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, and thermogravimetric analysis. This antimicrobial hydrogel demonstrated excellent antibacterial and antifungal properties against two bacterial strains (MRSA and S. mutans, with >99.9 % antibacterial rate) and one fungal strain (C. albicans, with >78.7 % antifungal rate) as well as negligible cytotoxicity towards mouse embryonic fibroblasts, making it a promising candidate for various tissue engineering applications in biomedical fields.

Immobilization of antibacterial copper metal-organic framework containing glutarate and 1,2-bis(4-pyridyl)ethylene ligands on polydimethylsiloxane and its low cytotoxicity

Metal-organic frameworks (MOFs) that include bioactive metals may exhibit activity against various microbes through metal–ligand bond cleavage to release metal ions or ligands into the media. However, controlled release over an extended time is required to avoid toxicity due to excess metal ions for successful clinical applications. Recently, copper-based MOFs (Cu-MOFs), which showed sustained release capability, porosity, and structural flexibility, exhibited antibacterial properties. Herein, toward the development of regenerative biomedical applications, we immobilized a robust Cu-MOF containing glutarate and 1,2-bis(4-pyridyl)ethylene ligands within biocompatible polydimethylsiloxane (PDMS) via simple hydrosilylation at 25 °C. The PDMS-immobilized Cu-MOF (PDMS@Cu-MOF) exhibited concentration-dependent antibacterial activities against five bacterial strains: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, and methicillin-resistant Staphylococcus aureus. Furthermore, PDMS@Cu-MOF maintained the physical and thermal properties of PDMS and showed low cytotoxicity toward mouse embryonic fibroblasts. Owing to its antibacterial properties and low cytotoxicity, PDMS@Cu-MOF exhibited potential for medicinal applications, such as implants, skin disease treatment, wound healing, and drug delivery.

Activation of a Metal-Halogen Bond by Halogen Bonding.

In recent years, the non‐covalent interaction of halogen bonding (XB) has found increasing application in organocatalysis. However, reports of the activation of metal‐ligand bonds by XB have so far been limited to a few reactions with elemental iodine or bromine. Herein, we present the activation of metal‐halogen bonds by two classes of inert halogen bond donors and the use of the resulting activated complexes in homogenous gold catalysis. The only recently explored class of iodolium derivatives were shown to be effective activators in two test reactions and their activity could be modulated by blocking of the Lewis acidic sites. Bis(benzimidazolium)‐based halogen bonding activators provided even more rapid conversion, while the non‐iodinated reference compound showed little activity. The role of halogen bonding in the activation of metal‐halogen bonds was further investigated by NMR experiments and DFT calculations, which support the mode of activation occurring via halogen bonding.

Ligand exchanges and selective catalytic hydrogenation in molecular single crystals

Chemical reactions inside single crystals are likely to be highly selective, but examples of single crystal to single crystal (SC-SC) transformations are uncommon, because crystallinity is difficult to retain following the rearrangement of atoms in the solid state. The most widely studied SC-SC transformations involve solvent exchange reactions in porous coordination polymers or metal-organic frameworks, which take advantage of the robust polymeric networks of the hosts. Examples of reactions occurring within molecular organic crystals generally involve photo-induced reactions, such as the coupling of alkenes or alkynes within the crystal. For nonporous molecular inorganic or organometallic crystals, single-crystal transformations involving the formation or cleavage of metal-ligand bonds are rare; known examples usually involve ligand loss from the single crystal and reversible religation, a process sometimes accompanied by decay of the single crystal to a microcrystalline powder. Here we report a series of SC-SC transformations that involve the interchange of multiple small gaseous ligands (N(2), CO, NH(3), C(2)H(4), H(2) and O(2)) at an iridium centre in molecular single crystals of a pincer Ir(I) complex. The single crystal remains intact during these ligand-exchange reactions, which occur within the crystal and do not require prior ligand extrusion. We reveal a selective catalytic transformation within a nonporous molecular crystal: pincer iridium single crystals ligated with nitrogen, ethylene or hydrogen show selective hydrogenation of ethylene relative to propylene (25:1) when surface sites are passified by CO.

η1‐Coordination of Phosphinine C5H5P and Arsenine C5H5As to Ruthenium(II) and Osmium(II)

AbstractReductive complexation of RuCl3 and OsCl3 in the presence of phosphinine C5H5P and arsenine C5H5As yields the species trans‐Cl2(η1‐C5H5E)4MII (M = Ru, E = P, As; M = Os, E = P). trans‐Cl2(η1‐C5H5As)4Ru constitutes the first arsenine complex of a late transition metal. Further reduction and isolation of the binary complexes (C5H5E)nM0 (n = 2, 4, 5) failed, presumably because of metal–ligand bond cleavage. According to X‐ray diffraction analysis, trans‐Cl2(η1‐C5H5P)4Ru (3) features two pairs of coplanar trans‐phosphinine ligands, which adopt eclipsed and staggered orientations, respectively, with regard to the Cl–Ru–Cl backbone. DFT calculations indicate a flat curvature of the potential governing conformational change and predict a structure for 3 that differs from that observed in the crystal. This illustrates the need to include intermolecular Ru–Cl···H hydrogen bonding as a structural director. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Structures and anion-binding properties of M4L6 tetrahedral cage complexes with large central cavities

Reaction of the bis-bidentate bridging ligand L(3), in which two bidentate chelating 3(2-pyridyl)pyrazole units are separated by a 3,3'-biphenyl spacer, with Co(II) salts affords tetranuclear cage complexes of composition [Co(4)(L(3))(6)]X(8)(X =[BF(4)](-), [ClO(4)](-), [PF(6)](-) or I(-)) in which four 6-coordinate Co(II) ions in an approximately tetrahedral array are connected by six bis-bidentate bridging ligands, one spanning each of the six edges of the Co(4) tetrahedron. In every case, X-ray crystallography reveals that the 'apical' Co(II) ion has a fac tris-chelate geometry, whereas the other three Co(II) ions have mer tris-chelate geometries, resulting in (non-crystallographic)C(3) symmetry for the cages; that this structure is retained in solution is confirmed by (1)H NMR spectroscopy of the paramagnetic cages. In every case one of the anions is located inside the central cavity of the cage, with the remaining seven outside. We found no clear evidence for an anion-based templating effect. The cage superstructure is sufficiently large to leave gaps in the centres of the faces through which the internal and external anions can exchange. Variable-temperature (19)F NMR spectroscopy was used to investigate the dynamic behaviour of the cages with X =[BF(4)](-) and [PF(6)](-) in MeCN solution: in both cases two separate signals, corresponding to external and internal anions, are clear at 233 K which have coalesced to a single signal at room temperature. Analysis of the linewidth of the minor signal (for the internal anion) at various temperatures below coalescence gave an activation energy for anion exchange of ca. 50 kJ mol(-1) in each case, a figure which suggests that anion exchange can occur via a conformational rearrangement of the cage superstructure in solution rather than opening of the cavity by cleavage of metal-ligand bonds.

Femtochemistry of organometallics: dynamics of metal-metal and metal-ligand bond cleavage in M 2(CO) 10

We report femtochemical studies of the organometallic dimetal decacarbonyl. By the use of mass spectrometry, we obtain the temporal dynamics in the channels for metal-metal and metal-ligand bond cleavage. The time scale observed for cleavage and for structural bridging indicates the nature of the repulsion along the two reaction coordinates and the interplay between the bond order and the femtosecond dynamics.

Metastable ion study of substituted cyclopentadienylmanganese cations in the gas phase

The behavior of some substituted cyclopentadienylmanganese ions has been studied by tandem mass spectrometry. This metastable ion study showed that only C 5H 5Mn + and (C 5H 4CN)Mn + ions retain their nido-cluster structure ( 1), which is characterized by a simple metal-ligand bond cleavage. Other substituted ions, RXC 5H 4Mn +, rearrange to a different extent, depending on the nature of the substituent. The first rearrangement step is R radical migration to the central metal atom, leading to RMnC 5H 4X +-type ions ( 2). These ions decompose by elimination of X (for X = CO) or with formation of RMn +, but further rearrangements can also occur. These are the reverse migration of R from the metal atom to the π-ligand (for R = H, Ph) and cyclopentadienyl ring expansion (for X = Ch 2). Collisional activation mass spectra contained an Mn + ion peak, which can indicate the existence of stable type 1 structures for most cyclopentadienylmanganese ions. Carboxyl and hydroxymethyl derivatives exist, presumably as ions of type 2. The neutralization-reionization mass spectra of RXC 5H 4Mn + ions are also discussed.

Dissociative chemistry of ionic transition metal cluster fragments

The ionic fragments formed by collision-induced dissociation of Mn2(CO) + ions (y=1–10) are reported. The ratio of product ions formed by metal-metal vs. metal-ligand bond cleavage are discussed in terms of the dependence of the metal-metal bond energy on the metal-to-ligand ratio. The collision-induced dissociation data indicate that the metal-metal bond energy of Mn2(CO) 5 + and Mn2(CO) 10 + is less than that for Mn2(CO) + (y=1–4 and 6–9). The product ions arising by metal-metal and metal-ligand bond cleavage reactions for collision-induced dissociation and photodissociation are compared. On the basis of this data and the known photochemistry/photophysics of Mn2(CO)10, it is proposed that the difference in collision-induced dissociation and photodissociation product ion branching ratios is attributable to spin-orbit transitions of the activated ions.

Intramolekulare Umwandlung von syn‐ und anti‐ Tricarbonyl(1‐ethoxy‐1,2‐dihydrocyclobutabenzol)chrom; Abfangreaktion des ortho‐Chinodimethan‐Intermediats

Ohne Metall‐Ligand‐Bindungsspaltung läuft die reversible Isomerisierung von syn‐1 zu anti‐1 ab, wie durch Abfangen des ortho‐Chinodimethan‐Intermediats in einer [4 + 2]‐Cycloaddition mit trans‐1,2‐Bis(trimethylsilyl)ethen als Dienophil sowie durch kinetische Untersuchungen belegt wurde. Die Ringöffnung ist bei 1 beträchtlich langsamer als bei nichtkomplexierten Analoga; dies ist auf Entropieeffekte zurückzuführen.magnified image

Intramolecular Interconversion of syn‐ and anti‐Tricarbonyl(1‐ethoxy‐1,2‐dihydrocyclobutabenzene)chromium. Trapping of the ortho‐Quinodimethane Intermediate

The reversible isomerization of syn-1 to anti-1 occurs without cleavage of metal-ligand bonds, as demonstrated through a [4 + 2] cycloaddition with trans-1,2-bis(trimethylsilyl)ethene as the dienophile, which led to the trapping of an ortho-quinodimethane intermediate. Further evidence comes from kinetic studies. Ring opening in 1 proceeds considerably more slowly than in the case of the non-complexed analogue, a finding that can be explained by entropy effects.

Mass spectrometry of ? complexes of transition metals. Communication 33. Carboranyl derivatives of benzenechromium tricarbonyl

1. The degree of fragmentation of carboranyl derivatives of benzenechromium tricarbonyl with cleavage of metal-ligand bonds depends linearly on the number of vibrational degrees of freedom of the π ligand. 2. Coordination of phenylcarboranes with a chromium tricarbonyl group inhibits the process of dehydrogenation of the carborane nucleus under electron impact.

Thermal decomposition of metal complexes: I. Complexes of iron(II) iodide with 1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline

The thermoanalytical behaviour of the tris complexes of 1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline with Fe(II) iodide is discussed. In conversion of the tris into the bis complexes, the reaction rate is controlled by the metal—ligand bond cleavage so that the “activation energy” can be regarded as an indirect measure of the bond strength.

Computation of kinetic parameters from differential enthalpimetric data

The thermal decompositions of sodium hydrogen carbonate, calcium oxalate monohydrate, and the compounds NiL4Cl2(L = pyridine, 3- and 4-methylpyridine) have been studied with a differential scanning calorimeter. Activation energies, orders of reactions, and pre-exponential factors have been calculated from the calorimetric data by a least-squares computer program. The results for the decompositions of sodium hydrogen carbonate and calcium oxalate monohydrate are compared with those obtained by other workers. The rate-determining step in the decompositions of the nickel complexes is shown to be metal–ligand bond cleavage.