Designing Cobalt(II) Complex for Chemoselective Synthesis of 2-Aryl-3-formyl indoles from Amino Alcohols and Alcohols†.

An air-stable, inexpensive, and isolable cobalt(II) complex (C1) of N-((1-methyl-1H-imidazol-2-yl)methyl)-2-(phenylselanyl)ethan amine (L1) was synthesized and characterized. The complex was used to catalyze a one-pot cascade reaction between 2-(2-aminophenyl)ethanols and benzyl alcohol derivatives. Interestingly, 2-aryl-3-formylindole derivatives were formed instead of N-alkylated or C-3 alkylated indoles. A broad substrate scope can be activated using this protocol with only 5.0 mol% catalyst loading to achieve up to 87% yield of 2-aryl-3-formylindole derivatives. The mechanistic studies suggested that the reaction proceeds through tandem imine formation followed by cyclization.

Catalysis with magnetically retrievable and recyclable nanoparticles layered with Pd(0) for C-C/C-O coupling in water.

Nanoparticles layered with palladium(0) were prepared from nano-sized magnetic Fe3O4 by coating it with silica and then reacting sequentially with phenylselenyl chloride under an N2 atmosphere and palladium(ii) chloride in water. The resulting Fe3O4@SiO2@SePh@Pd(0) NPs are magnetically retrievable and the first example of NPs in which the outermost layer of Pd(0) is mainly held by selenium. The weight percentage of Pd in the NPs was found to be 1.96 by ICP-AES. The NPs were authenticated via TEM, SEM-EDX, XPS, and powder XRD and found to be efficient as catalysts for the C-O and C-C (Suzuki-Miyaura) coupling reactions of ArBr/Cl in water. The oxidation state of Pd in the NPs having size distribution from ∼12 to 18 nm was inferred as zero by XPS. They can be recycled more than seven times. The main features of the proposed protocols are their mild reaction conditions, simplicity, and efficiency as the catalyst can be separated easily from the reaction mixture by an external magnet and reused for a new reaction cycle. The optimum loading (in mol% of Pd) was found to be 0.1-1.0 and 0.01-1.0 for O-arylation and Suzuki-Miyaura coupling, respectively. For ArCl, the required amount of NPs was more as compared to that needed for ArBr. The nature of catalysis is largely heterogeneous.

Graphene oxide supported cobalt phosphide nanorods designed from a molecular complex for efficient hydrogen evolution at low overpotential.

Thermolysis of molecular inorganic complex [CoCl2(PPh3)2] has resulted in uniform Co2P nanorods which on grafting on graphene oxide exhibit ultra high hydrogen evolution activity with a cathodic current density of 100 mA cm-2 at an overpotential of 154 mV and excellent stability for at least 70 h.

Solvent-tailored Pd3P0.95 nano catalyst for amide-nitrile inter-conversion, the hydration of nitriles and transfer hydrogenation of the C[double bond, length as m-dash]O bond.

For the first time, a one pot thermolysis of [Pd(PPh3)2Cl2] prepared by reacting Ph3P with PdCl2 in a 2 : 1 molar ratio in MeOH at 280 °C in a trioctylphosphine (TOP) and oleylamine(OA)-octadecane(ODE) mixture (1 : 1) was used to prepare quantum dots (QDs; size ∼2-3 nm) and nanoparticles (NPs; size ∼13-14 nm), respectively, of composition Pd3P0.95. TEM, SEM-EDX, powder-XRD and XPS (for QDs only) were used to authenticate the two nanophases. 31P{1H}NMR experiments performed to monitor the progress of thermolysis reactions revealed that the phosphorus present in the Pd3P0.95 QDs had come from TOP, whereas in Pd3P0.95 NPs, its source is triphenylphosphine. The nature of the solvent did not affect the chemical composition of the nano-phase but controlled its size. Probably, solvent dependent, unique, single source precursors (SSPs) of palladium were generated in situ, and controlled the size. The catalytic activity of both Pd3P0.95 QDs and NPs was explored. The QDs were found to be efficient as a catalyst for the amide-nitrile interconversion at room temperature (yield up to 92% in 4 h), hydration of nitriles and transfer hydrogenation (TH) of carbonyl compounds with yields up to 96% in 3-4 h. The yields and reaction rates of amide-nitrile inter-conversion and TH when catalyzed by Pd3P0.95 QDs were found to be higher compared to the ones observed with the Pd/C catalyst. The binding energy of Pd(3d) in the X-ray photoelectron spectrum (XPS) of Pd3P0.95 indicated an electron transfer from the metal to phosphorus, resulting in electron deficient palladium, which facilitates the coordination of a substrate to Pd and drives the reaction. The reusability of Pd3P0.95 QDs for the interconversion was found to be up to 4-times, while for the transfer hydrogenation of carbonyl compounds it was up to 6-times, but with a diminished yield. Pd3P0.95 NPs were found to be less active (yield up to 36% in optimized reaction conditions) in comparison to Pd3P0.95 QDs. The mercury poisoning test suggested that the catalysis predominantly proceeded heterogeneously on the surface of the QDs. The PXRD and XPS results did not suggest a significant variation in the phase of QDs after the third catalytic cycle. The bleeding of Pd during catalysis (determined by flame AAS) and the agglomeration of QDs as supported by the SEM-EDX and TEM results are probably responsible for the reduction in the catalytic activity of QDs after reusing three times.

Palladacycles of sulfated and selenated Schiff bases of ferrocene-carboxaldehyde as catalysts for O-arylation and Suzuki-Miyaura coupling.

Schiff base ligands (L1: sulfated and L2: selenated) having a ferrocene core synthesized by reacting ferrocene-carboxaldehyde with 2-(phenylthio/seleno)ethylamine on treatment with Na2PdCl4 in the presence of NaOAc give cyclopalladated complexes [Pd(L1/L2-H)Cl] (1/2). Complex 1 of a sulfated Schiff base L1, on reacting with one equivalent of triphenylphosphine gives complex [Pd(L1-H)PPh3Cl] (3), formed due to cleavage of a Pd-S bond. With 2 such a reaction does not occur, as a Pd-Se bond being stronger than that of its sulfur analogue does not get cleaved. L1, L2 and their complexes 1-3 were authenticated with HR-MS, 1H, 13C{1H} and 77Se{1H} NMR spectroscopy. The single crystal structures of 1-3 were determined with X-ray diffraction. Palladium in all three complexes has nearly a square planar geometry. The Pd-S, Pd-Se and Pd-P bond distances are 2.4249(12), 2.5058(14) and 2.2445(17) Šrespectively. The catalytic activity of complexes 1-3 was explored for O-arylation of phenol and Suzuki-Miyaura coupling (SMC) of phenylboronic acid with aryl bromides and chlorides. The optimum reaction time for SMC of ArBr is 3 h whereas for ArCl it is 6 h. The TON values of O-arylation catalyzed with complexes 1-3 are up to ∼170 (TOF, 28 h-1) and SMC ∼9300 (TOF, 3100 h-1) for the reaction time of the order of 3 and 6 h respectively. The catalytic process is somewhat more efficient with 2 (Pd bonded with a selenoether group), than 3, followed by 1.

Sonogashira (Cu and amine free) and Suzuki coupling in air catalyzed via nanoparticles formed in situ from Pd(ii) complexes of chalcogenated Schiff bases of 1-naphthaldehyde and their reduced forms.

The reaction of 1-naphthaldehyde with 2-(phenylthio/seleno)ethylamine afforded air- and moisture-insensitive Schiff bases: C10H7-1-CH[double bond, length as m-dash]N-CH2CH2EPh (L1: E = S; L2: E = Se). Then, on treatment with NaOAc and Li2PdCl4, palladacycles, [Pd(L1-H/L2-H)Cl] (1/2) were formed at room temperature, in which L1/L2 are ligated as an unsymmetric (C-, N, E) pincer. The reduction of >C[double bond, length as m-dash]N bonds of L1 and L2 with sodium borohydride gave C10H7-1-CH2NH-CH2CH2EPh (L3: E = S; L4: E = Se). The reactions of L3/L4 at room temperature, similar to those of L1/L2, resulted in the formation of complex [Pd(L3/L4)Cl2] (3/4), in which the ligand is coordinated in a bidentate (N, E) mode. The yield of all the complexes was >85%. Characterization by HR-MS, 1H, 13C{1H} and 77Se{1H} NMR spectra of L1-L4 and their complexes 1-4 were performed. The structures of L1 and 1-4 were established with single-crystal X-ray diffraction. In all the complexes, the geometry of palladium was distorted square planar. The Pd-S bond distances in 1 and 3 were 2.426(12) and 2.259(2) Å, respectively, whereas Pd-Se bond lengths (Å) were 2.523(11) (2) and 2.369(10) (4) Å. The catalytic activities of 1-4 were explored for copper- and amine-free Sonogashira and Suzuki-Miyaura coupling (SMC) of aryl halides under aerobic conditions. The amount of catalyst required for achieving good conversion was 0.01 and 0.05 mol% for SMC and Sonogashira coupling, respectively. The conversion of some substrates reached a maximum in 1 and 2 h for Sonogashira coupling and SMC, respectively. The palladacycles as catalysts gave good conversion efficiency. The generation of palladium-containing nanoparticles (NPs) during both coupling reactions was observed. These were isolated and HR-TEM studies were performed on them and revealed their size as ∼2-7 nm. The SEM-EDX analysis indicated the presence of organochalcogen ligands or their fragments in the samples. They independently catalyzed both reactions. Therefore, the role of 1-4 in catalysis undoubtedly exists. For Sonogashira coupling, the formation and role of such Pd-based NPs under aerobic conditions were observed for the first time. The complexes 1-4 showed the potential for reuse, as in the eighth cycle, conversion dropped by only 20%.

Complexes of (η5-Cp*)Ir(iii) with 1-benzyl-3-phenylthio/selenomethyl-1,3-dihydrobenzoimidazole-2-thione/selenone: catalyst for oxidation and 1,2-substituted benzimidazole synthesis.

The treatment of 1-benzyl-3-phenylthio/selenomethyl-1,3-dihydrobenzoimidazole-2-thione/selenone [L1-L4] with [(η5-Cp*)IrCl(µ-Cl)]2 at 25 °C followed by NH4PF6 results in [(η5-Cp*)Ir(L)Cl][PF6] (1-4 for L = L1 to L4), authenticated with high-resolution mass spectrometry (HR-MS) and multi-nuclei nuclear magnetic resonance (NMR) imaging (1H, 13C{1H} and 77Se{1H}). The structures of 1-4, established with single-crystal X-ray diffraction, reveal a "piano-stool" geometry around the Ir. The Ir-thio/selenoether (Ir-S/Ir-Se) bond distances (Å) are 2.347(18)-2.355(4)/2.4663(12)-2.4663(13) and Ir-thione/selenone (Ir-S/Ir-Se) distances are 2.4146(19)-2.417(2)/2.5141(16)-2.5159(12). The reaction of 1,2-phenylenediamine with benzylic alcohols and furfuryl alcohol under mild and ambient conditions, catalyzed efficiently with complexes 1-4, generates bisimine in situ. Cyclization and rearrangement via 1,3-hydride shift triggered by its electrophilic activation with Ir(iii) species finally results in 1,2-disubstituted benzimidazole. The yield of the heterocycles in this one-pot synthesis is excellent to good. The aldehydes generated in situ by aerial oxidation of alcohols in the presence of 1-4 as catalysts are precursors to the bisimine as the protocols of this heterocycle synthesis carried out in the absence of 1,2-phenylenediamine give them in excellent-to-good yield. The oxidation of alcohols by hydrogen transfer to acetone was catalyzed efficiently with complexes 1-4 and resulted in aldehyde/ketone in excellent-to-good yield. Each catalytic process is marginally more efficient with 1 than its counterparts.

Reusable Catalyst for Transfer Hydrogenation of Aldehydes and Ketones Designed by Anchoring Palladium as Nanoparticles on Graphene Oxide Functionalized with Selenated Amine.

The treatment of graphene oxide with ClCH2COOH, thionyl chloride, and 2-(phenylselenyl)ethylamine successively has resulted in functionalization of its surface with selenated ethylamine molecules which may act as chelating (Se, N) ligands. The graphene oxide grafted with (Se, N) donor sites (GO-Se) on treatment with Na2PdCl4 and NaOH gave GO-Se anchored with Pd(0) nanoparticles (NPs) (GO-Se-Pd). The X-ray diffraction (powder), FT-IR, XPS, Raman spectroscopy, thermogravimetric analysis (TGA), and electron microscopic techniques (SEM and HR-TEM) authenticated the formation of GO-Se-Pd. The distribution of Pd(0) NPs of size ∼1-3 nm on GO-Se was found nearly uniform. The transfer hydrogenation of carbonyl compounds (aldehydes/ketones) with 2-propanol was catalyzed with GO-Se-Pd. The catalyst equivalent to 0.25 mol % of Pd was sufficient to convert aldehydes and ketones to alcohols in good yield (nearly quantitative for some substrates) and found somewhat more efficient for aldehydes than ketones. The reusability of GO-Se-Pd studied for transfer hydrogenation of 4-anisaldehyde to the corresponding alcohol can be understood by ∼96% conversion even in the sixth catalytic run. Flame AAS analysis of GO-Se-Pd revealed negligible leaching of Pd even after the sixth catalytic reaction cycle. Hot filtration experiments suggested the heterogeneous nature of the catalyst.

Hypobaric hypoxia induces oxidative stress in rat brain.

High altitude exposure results in decreased partial pressure of oxygen and an increased formation of reactive oxygen and nitrogen species (RONS), which causes oxidative damage to lipids, proteins and DNA. Exposure to high altitude appears to decrease the activity and effectiveness of antioxidant enzyme system. The antioxidant system is very less in brain tissue and is very much susceptible to hypoxic stress. The aim of the present study was to investigate the time dependent and region specific changes in cortex, hippocampus and striatum on oxidative stress markers on chronic exposure to hypobaric hypoxia. The rats were exposed to simulated high altitude equivalent to 6100 m in animal decompression chamber for 3 and 7 days. Results indicate an increase in oxidative stress as seen by increase in free radical production, nitric oxide level, lipid peroxidation and lactate dehydrogenase levels. The magnitude of increase in oxidative stress was more in 7 days exposure group as compared to 3 days exposure group. The antioxidant defence system such as reduced glutathione (GSH), glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD) and reduced/oxidized glutathione (GSH/GSSG) levels were significantly decreased in all the three regions. The observation suggests that the hippocampus is more susceptible to hypoxia than the cortex and striatum. It may be concluded that hypoxia differentially affects the antioxidant status in the cortex, hippocampus and striatum.

Acridine based (S,N,S) pincer ligand: designing silver(I) complexes for the efficient activation of A³ (aldehyde, alkyne and amine) coupling.

Complexes [AgL(NO3)CH3CN](1) and [AgLNO3] (2) were formed on reacting AgNO3 with L in acetonitrile for 12 h (at room temperature) and 24 h (at 90 °C), respectively, where L is a (S,N,S) pincer ligand, 4,5-bis(phenylthiomethyl)acridine, synthesized by the reaction of in situ generated PhS(-) with 4,5-bis(bromomethyl)acridine under N2 atmosphere. (1)H and (13)C{(1)H} NMR and the mass spectra of L and its two Ag-complexes were characterized. The structures of complexes 1 and 2 were established with single crystal X-ray crystallography. The Ag-S bond distances of complexes 1 and 2 are 2.5682 (11)/2.5017 (11) Å and 2.4894 (15)/2.4834 (15) Å, respectively. The ligand L in complex 2 is coordinated with the metal in a pincer mode and the complex has a pseudo-pyramidal geometry of donor atoms around the Ag. In 1, the metal is encapsulated by a ten-membered chelate ring. The two Ag(I) complexes were explored for the coupling of aldehyde, alkyne and amine (A(3) reaction) and were found to be efficient as a 2.0 mol% loading of 1 and 0.5 mol% of 2 for good conversion. Complex 2 is a rare example of a catalyst that can efficiently activate A(3) coupling at a 0.5 mol% loading of Ag.

Palladium-phosphorus/sulfur nanoparticles (NPs) decorated on graphene oxide: synthesis using the same precursor for NPs and catalytic applications in Suzuki-Miyaura coupling.

PdP2 and Pd4S nanoparticles (NPs) (size: ∼2-6 and 9-15 nm respectively) have been prepared for the first time from a single source precursor complex [Pd(L)Cl2] (1) by its one pot thermolysis at 200 °C in TOP and OA/ODE (1 : 1) respectively. These NPs were stirred with graphene oxide (GO) at room temperature to prepare NP composites, GO-PdP2 and GO-Pd4S. The GO-PdP2 NPs have been synthesized for the first time. The thioether ligand L prepared by reaction of 1,3-dibromo-2-propanol with the in situ generated PhSNa reacts with [PdCl2(CH3CN)2] in CH3CN at 70 °C resulting in 1. The L and 1 have been characterized by (1)H and (13)C{(1)H} NMR and HR-MS. The single crystal structure of 1 determined by X-ray diffraction reveals nearly square planar geometry around the Pd metal centre. The catalytic activities of two palladium nano-phases having phosphorus and sulphur respectively as a co-constituent for Suzuki-Miyaura coupling have been found to be exceptionally different, as PdP2 nanoparticles (NPs) grafted on graphene oxide (GO-PdP2) are significantly more efficient than Pd4S NPs grafted on GO. Without grafting PdP2 and Pd4S both have low efficiency. This is the first report comparing the influence of P and S on the catalytic activity of Pd NPs. TEM, SEM-EDX and powder-XRD have been used to authenticate all NPs. The GO-PdP2 NPs have been found to be efficient catalysts for Suzuki-Miyaura coupling reactions (yield up to 96% in 30 min) at room temperature to 80 °C. Their recyclability has been found up to 6 cycles. In contrast, GO-Pd4S NPs are little active in comparison with GO-PdP2 NPs. The size of NPs and their distribution on GO appear to be key factors affecting the catalytic efficiency of the composite NPs. Leaching of Pd from GO-PdP2 NPs contributes significantly to the catalysis as evidenced by the three phase test, hot-filtration and recycling experiments. The catalysis is almost homogeneous.

Magnetite nanoparticles coated with ruthenium via SePh layer as a magnetically retrievable catalyst for the selective synthesis of primary amides in an aqueous medium.

The nanostructured magnetic oxide Fe3O4 has been coated with silica and then reacted with phenylselenyl chloride under a N2 atmosphere and RuCl3·xH2O successively in an aqueous medium to prepare Fe3O4@SiO2@SePh@Ru(OH)x nanoparticles (NPs) for the first time. These magnetically retrievable NPs have been authenticated using TEM, SEM-EDX and powder-XRD and found to be an efficient catalyst for one pot conversion (organic solvent not required) of aldehydes, nitriles and benzyl amine to primary amides in water. For aldehydes and nitriles, the yields of primary amides are up to 93%. These NPs can be recycled more than 7 times for the conversion of benzonitrile to the corresponding amide. Gram-scale transformation carried out by using Fe3O4@SiO2@SePh@Ru(OH)x NPs as a catalyst gives ∼86% yield.

Single source precursor routes for synthesis of PdTe nanorods and particles: solvent dependent control of shapes.

The PdTe NPs (hexagonal) and nanorods (first example) have been synthesized for the first time from single source precursors (SSPs), [Pd(L1)Cl2] (1) and [Pd(L2)Cl]BF4 (2) [L1, 4-bromo-1-[2-(4-methoxyphenyltellanyl)ethyl]-1H-pyrazole; L2, bis-[2-(4-bromopyrazol-1-yl)ethyl]telluride], by their thermolysis in an OA­ODE mixture (1:1) and TOP respectively. The composition of the PdTe phase does not change with SSP/solvent. Complex 2 gives small size nanostructures.

Graphene oxide grafted with Pd17Se15 nano-particles generated from a single source precursor as a recyclable and efficient catalyst for C-O coupling in O-arylation at room temperature.

The Pd17Se15 nanoparticles, synthesized for the first time from a single source precursor [Pd(L)Cl2] {L = 1,3-bis(phenylselenyl)propan-2-ol} and grafted onto graphene oxide, show high catalytic activity in C-O coupling between aryl/heteroaryl chlorides/bromides and phenol at room temperature (Pd loading 1 mol%; yield up to 94%).