Kinetics and mechanism of ligand substitution of aquopropylenediaminetetraacetato ruthenate(III) in water

Summary The reaction of pentadentate PDTA complex of ruthenium(III) with various sulphur containing ligands such as thiourea and 2-mercaptopyrimidine were studied as a function of pH (1.5–9.0), temperature (30–45°C) and substituting ligand concentration at 0.2 M ionic strength (NaClO₄) in water. The reaction of Ru(PDTA)(H₂O)^– with 2-mercaptopyrimidine proceeds with the formation of a red product (_max=511 nm) which undergoes pH-dependent conversion into a violet product (_max=511 nm). The activation parameters at pH 5 lie in the range 21.9 < H < 28.8 KJ mol^-1 and -120.4 < S < -96.7 J mol^-1deg^-1 and support the operation of an associatively activated ligand substitution. The experiments are discussed with reference to data for the corresponding ethylenediaminetetraacetate complex and the labilisation effect of such chelated ligands.     

Selective oxidation of cyclohexane by a Ru(III) analogue of the gif-system. RuIIIacetic acid-pyridine-KHSO5

Selective oxidation of cyclohexane to cyclohexanone was carried out in a RuCl₃-pyridine-acetic acid-KHSO₅ mixture. This system yields 2.8% of cyclohexanone (based on oxone concentration) under the conditions employed. Mechanistic postulate for the oxidation reaction involves the formation of a carbene intermediate (Ru=C) prior to the ketone formation.     

Photophysical Properties of 7‐(diethylamino)Coumarin‐3‐carboxylic Acid in the Nanocage of Cyclodextrins and in Different Solvents and Solvent Mixtures

The photophysical properties of 7‐(diethylamino) coumarin‐3‐carboxylic acid (7‐DCCA) were studied in cyclodextrins (α, β, γ,‐CDs), different neat solvents and solvent mixtures by using steady state absorption, emission and time‐resolved fluorescence spectroscopy. We have observed that with gradual increase in concentration of β‐CD the fluorescence quantum yield and lifetime decreased in a regular pattern whereas with gradual increase in concentration of γ‐CD the fluorescence quantum yield and lifetime gradually increased. With addition of urea, the fluorescence quantum yield and lifetime of 7‐DCCA in CDs increased. Binding constant calculation shows that 7‐DDCA forms 1:1 complex with β‐CD and with γ‐CD it forms 1:1 and 1:2 (guest:host) inclusion complex. We proposed that the dye molecule formed capping complex with β‐CD by means of hydrogen bonding and after addition of urea the hydrogen bonding network broke down and part of dye molecule entered inside the cavity of β‐CD. The photophysics of 7‐DCCA was studied in dioxane‐water mixture and ethylene glycol‐acetonitrile mixture to know the effect of polarity and viscosity of the media. The photophysics of 7‐DCCA was also studied in different neat solvents. It was found that the photophysics of 7‐DCCA depended on the structural feature of the solvents and solvent mixtures.     

An Effective Route to Angular Ester Substituted trans-Octahydrophenanthrene Ring System Related to Diterpenes

A synthesis of the keto-ester 10 has been accomplished from the aromatic ketone 5 through the intermediates 6,7,8 and 9.     

Ene-Reductase: A Multifaceted Biocatalyst in Organic Synthesis

Biocatalysis integrate microbiologists, enzymologists, and organic chemists to access the repertoire of pharmaceutical and agrochemicals with high chemoselectivity, regioselectivity, and enantioselectivity. The saturation of carbon-carbon double bonds by biocatalysts challenges the conventional chemical methodology as it bypasses the use of precious metals (in combination with chiral ligands and molecular hydrogen) or organocatalysts. In this line, Ene-reductases (ERs) from the Old Yellow Enzymes (OYEs) family are found to be a prominent asymmetric biocatalyst that is increasingly used in academia and industries towards unparalleled stereoselective trans-hydrogenations of activated C=C bonds. ERs gained prominence as they were used as individual catalysts, multi-enzyme cascades, and in conjugation with chemical reagents (chemoenzymatic approach). Besides, ERs’ participation in the photoelectrochemical and radical-mediated process helps to unlock many scopes outside traditional biocatalysis. These up-and-coming methodologies entice the enzymologists and chemists to explore, expand and harness the chemistries displayed by ERs for industrial settings. Herein, we reviewed the last five year's exploration of organic transformations using ERs.     

Triphenylpyridine-based star-shaped π-conjugated oligomers with triphenylamine core: synthesis and photophysical properties

Two novel star-shaped π-conjugated oligomers bearing a triphenylpyridine moiety as peripheral units and triphenylamine as a core have been synthesized via the threefold Heck/Sonogoshira coupling reaction protocol and their absorption and fluorescence properties have been examined. These oligomers showed excellent solubility in common organic solvents, emit light in blue and violet regions, and have high thermal stability.     

Pyridine-cored V-shaped π-conjugated oligomers: synthesis and optical properties

A new series of V-shaped pyridine-cored π-conjugated oligomers are synthesized utilizing two-fold Heck/Suzuki coupling reactions. Optical properties of these compounds (λ_max=390–449 nm, Φ_fl=79–5%, in solutions) are discussed. They are shown to be thermally stable and soluble in common organic solvents. Stilbenoid oligomers exhibited much higher fluorescence quantum yields than tri- and tetra-phenylethylene substituted oligomers in solutions.     

Towards using molecular ions as qubits: Femtosecond control of molecular fragmentation with multiple knobs

Non-resonant molecular fragmentation of n-propyl benzene with femtosecond laser pulses is dependent on the phase and polarization characteristics of the laser. We find that the effect of the chirp and polarization of the femtosecond pulse when applied simultaneously is mutually independent of each other, which makes chirp and polarization as useful ‘logic’ implementing knobs.     

22pi smaragdyrin molecular conjugates with aromatic phenylacetylenes and ferrocenes: Syntheses, electrochemical, and photonic properties

Syntheses, spectroscopic, electrochemical, and third-order nonlinear optical susceptibilities of a series of 22pi smaragdyrins and their corresponding Rh(I) derivatives bearing phenylacetylene substituents and ferrocene-containing substituents are reported. The synthetic strategy involved a [3 + 2] acid-catalyzed oxidative coupling reaction of the appropriate dipyrromethane and oxatripyrrane. The desired meso substituents, such as phenylacetylenylphenyl and the ferrocenes, were incorporated to the dipyrromethane unit prior to the oxidative coupling reaction. The optical absorption, emission characteristics, and the quantum yield of the smaragdyrin conjugates depends on the nature of the substituent, nature of linker group, and the spacer length. Theoretical studies at the DFT level suggest high delocalization of electrons confined to only four of the five available heterocyclic rings for the free bases. However, upon Rh(I) metalation, the pi-electron delocalization is extended to all the heterocyclic rings. The two-photon absorption cross section (TPA) values sigma(2) measured through the open aperture Z-scan method, increases linearly with enhanced pi-electron delocalization for the smaragdyrins containing phenylacetylene substituents. The meta branching of substituents decreases sigma(2) values. Introduction of Rh(I) to the smaragdyrin cavity enhances the sigma(2) values by about 3-10 orders of magnitude, attributed to the increased aromatic character upon Rh(I) insertion. The calculated molecular electrostatic potential (MESP) and harmonic oscillator model of aromaticity (HOMA) for the free bases and the Rh(I) derivatives justifies such a conclusion. A linear correlation observed for the second oxidation potential of Rh(I) derivatives and corresponding free bases also support the increased aromaticity upon Rh(I) insertion. The electrochemical data for ferrocene-containing smaragdyrins reveal easier ring oxidation by about 50-130 mV and harder ferrocene oxidation by 40-180 mV suggesting electron-donating nature of the ferrocene upon linking with the smaragdyrin system. The TPA cross section value of 88782 GM observed for 5g represents one of the highest values known for a metalloexpanded porphyrin derivative.