• Volume 123, Issue 5

September 2011,   pages  531-763

• Photoprocesses of coordination compounds and dyes in solution and nanoporous materials: Evolution from milliseconds to femtoseconds

The photoredox reactions of cobalt(III), nickel(II) complexes and organic dyes are reviewed with particular emphasis on using flash photolysis methods to identify the transients in the time scale from milliseconds to subpicoseconds. The excitation flash radiation initially was limited to flash lamps with a time resolution to study the decay of the excited states and the fast reactions of photo produced transients in milliseconds and microseconds. Some of the photolysis reactions investigated provide details in real time including the thermal reactions of molecular oxygen with cobalt(II) amine systems and the cobalt (III) alkyl complex formation on photolysis of cobalt(III) aminoacid complexes. Photoredox reactions of thiazine and safranine dyes are investigated using time resolved absorption and emission techniques in solution and on encapsulation in micro and mesoporous host materials. Picosecond and femtosecond diffuse reflectance fluorescence investigations in the porous solid host materials show intramolecular proton transfer reactions of the dyes and deprotonation of the dyes in the excited states. Photosensitization of nanoparticles of semiconductors, anatase TiO2 and ZnO by the excited states of dyes in meso and microporous silicate hosts is investigated using pico and femtosecond fluorescence and transient absorptions techniques and the results are reviewed.

• Ruthenium(II)- bipyridyl with extended 𝜋-system: Improved thermo-stable sensitizer for efficient and long-term durable dye sensitized solar cells

A new extended thermo-stable high molar extinction coefficient bipyridyl ruthenium(II) complex "cis-Ru(4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine)(Ln)(NCS)2 H101", where Ln = 4,4'-dicarboxylic acid-2,2'-bipyridine; was synthesized and characterized by 1H-NMR, FT-IR and ESI-MASS spectroscopes. The H101 sensitized solar cell constructed with an active area of 0.54 cm2 in combination with an ionic liquid electrolyte exhibited broader photocurrent action spectrum with solar-to-electric energy conversion efficiency (𝜂) of 5.89 (JSC = 12.14 mA/cm2, VOC = 690 V, fill factor = 0.699) under Air Mass (AM) 1.5 sunlight, while the reference cis-Ru(4,4'-dinonyl-2,2'-bipyridine)(Ln)(NCS)2', Z907 sensitized solar cell exhibited 𝜂-value of 5.17% (JSC = 11.93 mA/cm2, VOC = 650 V, fill factor = 0.666). TGA analysis of H101 showed extended thermal-stability and under continuous light exposure and aging at 55°C, the DSSC retained 85% of its initial 𝜂-value, while under comparable conditions Z907 sensitized solar cell retained 88%. As compared to 4,4'-dinonyl-2,2'-bipyridine in Z907, the new ancillary bipyridyl ligand 4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine’ in H101 shifts the absorption bands remarkably towards blue. The Density Functional Theory (DFT) and Time-Dependent DFT excited state calculations of the new sensitizer show that the first three HOMOs have t2g character with sizeable mixing from the NCS ligands with 𝜋-bonding orbitals of 4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine. The LUMO is a $\pi^\ast$-orbital localized on the 4,4-dicarboxylic acid-2,2'-bipyridine and higher un-occupied frontier orbitals have $\pi^\ast$-combinations with 4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine.

• Ruthenium(II) carbonyl complexes containing chalconates and triphenylphosphine/arsine

A series of new hexa-coordinated ruthenium(II) carbonyl complexes of the type [RuCl(CO)(EPh3)(B)(L$^{1−4}$)] (4-15) (E = P or As; B = PPh3, AsPh3 or Py; L = 2'-hydroxychalcone) were synthesized from the reaction of [RuHCl(CO)(EPh3)2(B)] (1-3) (E = P or As; B = PPh3, AsPh3 or Py) with equimolar chalcone in benzene under reflux. The new complexes have been characterized by analytical and spectroscopic (IR, electronic, 1H, 31P{1H}, and 13C NMR) methods. On the basis of data obtained, an octahedral structure has been assigned for all the complexes. The complexes exhibit catalytic activity for the oxidation of primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of 𝑁-methylmorpholine-𝑁-oxide (NMO) as co-oxidant and were also found to be efficient transfer hydrogenation catalysts. The antifungal properties of the ligands and their complexes have also been examined and compared with standard Bavistin.

• Ru4+ ion in CeO2 (Ce0.95Ru0.05O$_{2−\delta}$): A non-deactivating, non-platinum catalyst for water gas shift reaction

Hydrogen is a clean energy carrier and highest energy density fuel. Water gas shift (WGS) reaction is an important reaction to generate hydrogen from steam reforming of CO. A new WGS catalyst, Ce$_{1−x}$Ru$_x$O$_{2−\delta}$ ($0 ≤ x ≤ 0.1$) was prepared by hydrothermal method using melamine as a complexing agent. The Catalyst does not require any pre-treatment. Among the several compositions prepared and tested, Ce0.95Ru0.05O$_{2−\delta}$ (5% Ru4+ ion substituted in CeO2) showed very high WGS activity in terms of high conversion rate (20.5 𝜇mol.g-1.s-1 at 275°C) and low activation energy (12.1 kcal/mol). Over 99% conversion of CO to CO2 by H2O is observed with 100% H2 selectivity at ≥ 275°C. In presence of externally fed CO2 and H2 also, complete conversion of CO to CO2 was observed with 100% H2 selectivity in the temperature range of 305-385°C. Catalyst does not deactivate in long duration on/off WGS reaction cycle due to absence of surface carbon and carbonate formation and sintering of Ru. Due to highly acidic nature of Ru4+ ion, surface carbonate formation is also inhibited. Sintering of noble metal (Ru) is avoided in this catalyst because Ru remains in Ru4+ ionic state in the Ce$_{1−x}$Ru$_x$O$_{2−\delta}$ catalyst.

• Interesting reactivity of diketones with pyrrole under acidic condition

The acid catalysed condensation of diketones with pyrrole did not result in the formation of expected divergent bisdipyrromethane always; instead the product depends on the chain length of the diketones, in particular the distance between the two carbonyl functional groups.When the two carbonyl groups are linked via one or two methylene groups, unusual ring annulation occurs resulting in the formation of various bridged bipyrroles. However, on further increase in the length of the spacer, between the two carbonyl groups, synthesis of the expected bisdipyrromethanes could be achieved.

• Quinolizidines alkaloids: Petrosin and xestospongins from the sponge Oceanapia sp.

A bisquinolizidine alkaloid, petrosin (1) and a series of bis-1-oxaquinolizidine, xestospongins (2-9), were obtained from the ethyl acetate extract of the sponge Oceanapia sp. Petrosin was obtained along with xestospongin- C, D, E, F, G, H, I and J having di-hetroatom rings, from the ethyl acetate extract of the sponge. The compounds exhibited moderate to high activities against some microorganisms and clinical isolates. The structures of the alkaloids were elucidated by NMR and ESIMS spectroscopic data. The structure of petrosin was confirmed by an X-ray diffraction study.

• Simple and efficient Knoevenagel synthesis of (𝐸)-2-((1H-indol-3-yl) methylene)-3-oxoindolylnitrile catalysed by PPh3

Triphenylphosphine (TPP) is found to be an efficient catalyst for the Knoevenagel condensation of indole-3-carboxyaldehydes 1(a-e) and their 𝑁-substituted derivatives 4(a-e) with the active methylene compound, i.e., 3-cyanoacetylindole (2), affording novel substituted olefins 3(a-e) and 5(a-e) respectively. The latter products reacted with DMS in the presence of PEG-600 to afford the corresponding N, N1 dimethylated derivatives 6(a-e).

• ZnO nanoparticle as catalyst for efficient green one-pot synthesis of coumarins through Knoevenagel condensation

Green chemistry protocols with the reusability of the nano particle as catalyst in the synthesis of coumarins is described. The zinc oxide (ZnO) nanoparticles functions as highly effective catalyst for the reactions of various 𝑜-hydroxy benzaldehydes with 1,3-dicarbonyl compounds under microwave and thermal conditions to afford the corresponding coumarins in moderate to good yields. The catalyst is inexpensive, stable, can be easily recycled and reused for several cycles with consistent activity.

• Investigation of Prins reaction for the synthesis of 2, 4- disubstituted tetrahydropyran derivatives and 1, 3-dioxanes using polyaniline supported acid as reusable catalyst

The Prins cyclization of homoallyl alcohol with a variety of aldehydes were observed under reflux condition in dichloromethane using both polyaniline supported TsOH (PANI-TsOH) and FeCl3 (PANI- FeCl3) as reusable acid catalysts with the formation of 2,4-disubstituted tetrahydropyran ether as single product. In case of $4-$, $3-$ and $2-$ nitro benzaldehydes, the reaction generated acetal of the aldehyde and homoallylic alcohol as single product. Additionally, both catalysts were investigated for the synthesis of 1, 3-dioxane in dichloromethane under reflux and at ambient temperature.

• Synthesis of new series of N-3-[-{2-(substituted phenyl-4-oxo-5-(substituted benzylidene)-1,3-thiazolidine}-carbamyl]-propyl-2-aminothiazole and their biological importance

Synthesis of new series of N-3-[-{2-(substituted phenyl-4-oxo-5-(substituted benzylidene)-1,3-thiazolidine}-carbamyl]-propyl-2-aminothiazole, 5(a-s) have been developed. The cycloaddition reaction of thioglycolic acid with N-{3-(substituted benzylidine-carbamyl)-propyl}-2-aminothiazole, 3(a-s) in the presence of anhydrous ZnCl2 afforded new heterocyclic compounds N1-3-[-{2-(substituted phenyl-4-oxo-1,3-thiazolidine}-carbamyl]-propyl-2-aminothiazole 4(a-s). The latter product on treatment with several selected substituted aromatic aldehydes in the presence of C2H5ONa undergoes Knoevenagel reaction to yield 5(a-s). The structure of compounds 1, 2, 3(a-s), 4(a-s) and 5(a-s) were confirmed by IR, 1H NMR, 13C NMR, FAB mass and chemical analysis. All final compounds were screened for their antimicrobial activity against some selected bacteria and fungi and antituberculosis study against M. tuberculosis, gave acceptable activity.

• Synthesis of New dihydropyrimidinones catalysed by dicationic ionic liquid

A convenient multi step synthetic protocol for new dihydropyrimidinones bearing quinolynyl methoxy phenyl moiety has been developed from 2-chloro-3-formyl quinolines. The last step is one-pot Biginelli reaction of multicomponents, 4-((2-chloroquinolin-3-yl) methoxy) benzaldehydes, ethyl acetoacetate and urea mediated and catalysed by dicationic ionic liquid (3-methyl-1-[3-(methyl-1H-imidazolium-1-yl) propyl]-1H-imidazolium dibromide (C3 [min]2 2 [Br] )). Simple work-up procedures and moderate to good yields of the pyrimidinones and the intermediates are the merits of the route.

• An expeditious green synthesis of Schiff bases and azetidinones derivatised with 1,2,4-triazoles

An efficient green approach to the synthesis of Schiff bases (11-21) of 1-amino-2-aryl-3-oxo-1,2,4-triazoles (1-3) have been reported under Mg(ClO4)2 as catalyst followed by the reaction with chloroacetyl chloride in solvent-free conditions to yield the azetidinones (22-32) with excellent yields. The synthesized compounds were evaluated for the extent of penetration into biological membranes ($clogP$), drug-likeliness and finally drug score was calculated and also screened for antitubercular and antimicrobial activities.

• Facile solvent-free one-pot synthesis of pyranobenzopyrans and their derivatives

The condensation of hydroxyl coumarins in a facile one-pot procedure with active methylene esters to afford novel benzopyrans under solventless conditions is described. The products underwent further condensation and cyclization reactions to form novel heterocycles.

• An efficient ultrasound promoted catalyst-free protocol for the synthesis of chromeno[4,3-b]quinolin-6-ones

A convenient, catalyst-free protocol for the quantitative synthesis of fused chromeno[4,3-b]quinolin-6-ones has been developed by simple one-pot reaction of substituted anilines with 4-chloro-3-formylcoumarin using ultrasound irradiation. The protocol offers the advantages of mild reaction conditions, short reaction times and high yields.

• A new method for the chemoselective reduction of aldehydes and ketones using boron tri-isopropoxide, B(O$^i$Pr)3: Comparison with boron tri-ethoxide, B(OEt)3

A chemoselective Meerwein-Ponndorf-Verley reduction process of various aliphatic and allylic 𝛼,𝛽-unsaturated aldehydes and ketones is described. This chemoselective reduction is catalysed by boron triisopropoxide B(O$^i$Pr)3. Kinetics of reduction of aldehydes and ketones to corresponding alcohols were also examined and rate constant of each carbonyl compounds were measured. Rate constant and reduction yield of each carbonyl compounds in the presence of B(O$^i$Pr)3 were compared with those in the presence of B(OEt)3. The alcohols that are the reduction product were analysed by GC-MS. The rate constants and alcohol yields were found to be higher with B(OEt)3 than with B(O$^i$Pr)3. The mechanism proposed involves a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same boron centre of a boron alkoxide catalyst.

• Solvothermal synthesis and theoretical study of a polypyridium trimesylate adduct

The title compound (C9H3O6·C20H17N4)4·0.5H2O 1 was isolated from solvothermal synthesis of 4'-(4-pyridyl)-2,2':6',2'-terpyridine (pytpy) and trimesic acid (1,3,5-benzenetricarboxylic acid, H3BTC). It was characterized by element analysis, IR, TGA, XRD, X-ray single-crystal diffraction, and spectroscopy properties, together with quantum chemistry calculation of spectrum (UV-vis spectra) through the method b3lyp/6-31 t g (d,p) are also investigated. Single-crystal X-ray diffraction shows 1 possesses a 3-D supramolecular network with 1-D six-fold helical double chains built from protonated (H3pytpy)$^{3+}_n$ cations and deprotonated (BTC)$^{3−}_n$ anions. The maximum of the fluorescent emission bands of 1 is located at 427 nm ($\lambda_{\text{ex}}$ = 266 nm), with a shoulder at about 390 nm. The result of theoretic calculations confirms that 1 has small HOMO-LUMO energy gap (1.24 eV) and high chemical reactivity.

• Microwave-assisted efficient synthesis of 2-arylbenzo[b]furans and 2-ferrocenylbenzo[b]furans from readily prepared propargylic alcohols and 𝑜-iodophenols

A simple, efficient and expeditious method for synthesis of 2-arylbenzo[b]furans and 2-ferrocenylbenzo[b]furans from readily prepared propargylic alcohols, 𝑜-iodophenols and silica gel with the catalyst of PdCl2(PPh3)2 (2 mol%)/CuI (2mol%) and microwave-promoted Sonogashira coupling/cyclization reaction is developed. The methodology can produce good to excellent yields. In addition, this method can also be completed in one-pot with iodobenzene, 2-methyl-3-butyn-2-ol and 2-iodo-4-methylphenol as reactants.

• Rapid and highly efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalysed by in situ generated I2 using Oxone®/KI or cerium ammonium nitrate (CAN)/KI systems under mild conditions

Structurally diverse alcohols and phenols were trimethylsilylated in clean and efficient reactions with hexamethyldisilazane (HMDS) in the presence of a catalytic amount of I2 generated in situ from Oxone®/KI or CAN/KI systems. The reactions occur rapidly in good to high yields in wet CH2Cl2 at room temperature.

• Diversity in electrochemical oxidation of dihydroxybenzenes in the presence of 1-methylindole

Electrochemical oxidation of some catechol derivatives (1a-e) have been studied in water/acetonitrile solution containing 1-methylindole (3) as a nucleophile, using cyclic voltammetry and controlledpotential coulometry. An interesting diversity in the mechanisms has been observed in electrochemical oxidation of catechol derivatives (1a-e) in the presence of 3. In this work, we have proposed reaction schemes $ECEC$, $ECECE$ and $ECECECE$ for oxidation of 1a-e in the presence of 3.

• Relationship between global indices of reactivity, electrodonating and electroaccepting powers, and the hammet constant in isatoic anhydride derivatives

The possible correlation between Hammett’s constant ($\sigma_p$), a characteristic parameter of functional groups with electrodonating or electroaccepting properties, and two indices of global reactivity were calculated in the gas phase. Parameters associated to a set of 22 structural variants of isatoic anhydride ($2H-3$, 1-benzoxazin-2,4($1H$)-dione, ISA), replaced with diverse functional groups, were explored applying linear and quadratic statistical models for numerical analysis of the results.

• DFT study on structure, electronic properties, and reactivity of cis-isomers of [(NC5H4-S)2Fe(CO)2]

Three cis-isomers of [(NC5H4-S)2Fe(CO)2], models for the active site of [Fe] hydrogenase, have been examined by computational method at DFT B3LYP/6-311+G(d,p) level. The computed geometric parameters are remarkably close to experimental values. DFT global chemical reactivity descriptors (chemical hardness, total energy, electronic chemical potential, and electrophilicity) are calculated for the isomers and used to predict their relative stability and reactivity. The chemical reactivity indices are found to be related to the bond angle defined by the cis carbonyls and the iron center.

• Computational study on decomposition kinetics of CH3CFClO radical

The present study deals with the decomposition of haloalkoxy radical (CH3CFClO) formed from 1,1-dichloro-1-fluoroethane (HCFC-141b) in the atmosphere. The sudy is performed using ab-initio quantum mechanical methods. Out of the three plausible pathways of decomposition of the titled species, the one that involved the C-C bond scission and the other occurring via Cl-atom elimination have been considered for detailed study. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at MP2 level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2(MP2) level of theory. The path involving the Cl-elimination is found to be dominant and found to occur with a barrier height of 3.6 kcal mol-1 whereas the C-C bond scission path proceeds with a barrier of 10.0 kcal mol-1. The thermal rate constants for the above two decomposition pathways are evaluated using Canonical Transition State Theory (CTST) and these are found to be $2.9 \times 10^8 s^{−1}$ and $4.3 \times 10^5 s^{−1}$ for Cl-elimination and C-C bond scission respectively at 298 K and 1 atm. pressure. The existence of transition states on the corresponding potential energy surface is ascertained by the occurrence of only one imaginary frequency obtained during the frequency calculation. The Intrinsic Reaction Coordinate (IRC) calculation has also been performed to confirm the smooth connection of the TS to the reactant and the products.

• A density functional study on the adsorption of hydrogen molecule onto small copper clusters

An all-electron scalar relativistic calculation on the adsorption of hydrogen molecule onto small copper clusters has been performed by using density functional theory with the generalized gradient approximation (GGA) at PW91 level. Our results reveal that after adsorption of H2 molecule, the Cu-Cu interaction is strengthened and the H-H interaction is weakened, the reactivity enhancement of H2 molecule is obvious. The VIPs, HLGs and VEAs of Cu$_n$H2 clusters show an obvious odd-even oscillation. It is suggested that the H2 molecule is more favourable to be adsorbed by the even-numbered small copper clusters. Meanwhile, the odd-even alteration of magnetic moments is also observed and may be served as the material with tunable code capacity of 0’ and 1' by adsorbing hydrogen molecule onto odd or even-numbered small copper clusters. Some discrepancies of dissociative adsorption between our work and previous works are found and may be understood in terms of the electron pairing effect and the scalar relativistic effect.

• Theoretical study of the reactivity trends in the Cl-abstraction reactions of CHCl3 + CHX·−/CX$_2^{·−}$ (X = Cl, Br and I)

To better understand how and to what extent the halosubstituted carbene radical anions effect the chlorine abstraction of CHCl3, a detailed theoretical investigation has been performed at the UMP2/6-311++G (d, p)/RECP level of theory. The model system CHCl3+CHX·−/CX$^{·−}_2$ (X = Cl, Br, and I) has been chosen for the present study. According to the detailed discussions of geometries and energetics of the optimized stationary points, our theoretical findings suggest that the Cl-abstraction reactions by CHX·− are energetically favourable, indicating the less massive substitution X in CHX·− the easier abstraction reaction, as compared to those by CX$^{·−}_2$, which are energetically unfavourable and would be endothermic.

• # Journal of Chemical Sciences

Volume 132, 2019
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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019