Browsing by Author "Sarkar, Bibhas R."

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Anchored Pd Complex in MCM-41 and MCM-48: Novel Heterogeneous Catalysts for Hydrocarboxylation of Aryl Olefins and Alcohols
(ACS, 2002) Sarkar, Bibhas R.
We report here, for the first time, synthesis of anchored Pd complexes in mesoporous supports such as MCM-41 and MCM-48 as true heterogeneous catalysts for hydrocarboxylation of aryl olefins and alcohols to give excellent conversion (∼100%) and regioselectivity (∼99%) for 2-arylpropionic acids. The catalysts were characterized by powder-XRD, 31P CP-MAS NMR, FT-IR, TEM, XPS and ICP-AES. Recycle studies with these anchored Pd mesoporous catalysts were performed to confirm true heterogeneity.
Biphasic carbonylation of vinyl aromatic compounds using novel water-soluble Pd catalyst: activity, selectivity and mechanistic studies
(Elsiever, 2002-03) Sarkar, Bibhas R.
The biphasic carbonylation of vinyl aromatic compounds to the isomeric arylpropanoic acids has been studied in detail using a novel water-soluble palladium complex, [Pd(Pyca)(TPPTS)]+TsO−. The effect of various reaction and catalyst parameters such as promoters, solvents, P/Pd ratio, CO partial pressure, temperature and concentration of substrate on the catalytic activity and selectivity has been investigated using styrene as the model substrate. High catalytic activity and selectivity to the branched product (∼91%) was observed with [Pd(Pyca)(TPPTS)]+TsO− catalyst. 31P NMR experiments were carried out to study the mechanistic details and to understand the nature of catalytic species formed under the reaction conditions, based on which a plausible catalytic cycle has been proposed.
“Clickable” SBA-15 mesoporous materials: synthesis, characterization and their reaction with alkynes
(RSC, 2009) Sarkar, Bibhas R.
SBA-15 mesoporous silica has been functionalized with azidopropyl groups through both one-pot co-condensation and post-synthetic grafting. For both these methodologies, azidopropyltriethoxysilane was used to introduce the azidopropyl groups. The azidopropyl modified SBA-15 material synthesized by one-pot co-condensation had hexagonal crystallographic order, pore diameters up of 50 Å, and the content of azidopropyl groups was found to be 1.3 mmol g−1. The presence of the azidopropyl group was confirmed by multinuclear (13C, 29Si) solid state NMR and IR spectroscopy. Both these materials underwent very efficient Cu(I)-catalyzed azide alkyne “click” reaction (CuAAC) with a variety of alkynes. Nearly 85% of the azide present in the SBA-15 material was converted to the corresponding triazole when propargyl alcohol was used as the substrate. This methodology was also used to incorporate mannose into SBA-15. Incubation of this mannose labeled SBA-15 with fluorescein labeled Concanavalin-A led to the formation of a fluorescent silica-protein hybrid material. The ease of synthesis for the azide labeled SBA-15 material together with its ability to undergo very efficient chemoselective CuAAC in water would make it a very attractive platform for the development of covalently anchored catalysts, enzymes and sensors.
Continuous Hydroformylation with Phosphine-Functionalized Polydimethylsiloxane Rhodium Complexes as Nanofilterable Homogeneous Catalysts
(ACS, 2015) Sarkar, Bibhas R.
Commercially available polydimethylsiloxane (PDMS) was functionalized with phosphine and used to form a Rh complex catalyst. The PDMS-based Rh catalyst complex shows promise as an inexpensive, readily synthesized and nanofilterable homogeneous catalyst for performing continuous hydroformylation. Batch hydroformylation of several substrates including 1-octene, 1-decene, 1-dodecene and styrene showed good activity and selectivity. For 1-octene hydroformylation, the observed catalyst activity with the PDMS-based Rh complex is 2-fold greater compared to that with a conventional Rh-triphenylphosphine complex under similar conditions. Continuous 1-octene hydroformylation for up to 120 h was demonstrated in a membrane nanofiltration system, showing stable conversion (∼60%) and high chemoselectivity (>95%). The total turnover number (TON) after 120 h was approximately 12 000 and the permeate Rh concentration was <2 ppm.
Efficient Mizoroki–Heck coupling reactions using phosphine-modified Pd(II)–picolinate complex
(Taylor & Francis, 2018-03) Sarkar, Bibhas R.
Efficient Mizoroki–Heck couplings were obtained using a very easily synthesizable palladium(II) complex of hemilabile N–O ligand (picolinate), with high turnover frequencies up to >10,000 h−1, in just 15 min, with high selectivity of >99% to the desired products. Wide applicability of the simple-looking palladium complex catalyst was established with differently functionalized substrates. Catalyst screening studies revealed intricate details of dependence of catalyst performance on different reaction parameters and conditions and arriving at the optimized facile methodology.
Microwave-Assisted Efficient Suzuki-Miyaura Cross-Coupling Reactions in Water Catalyzed by Nano-Pd/gC3N4 Composite
(Wiley, 2017-10-02) Pande, Surojit; Sarkar, Bibhas R.
Easy to make and highly efficient catalyst system comprising of Pd-nanoparticles supported on graphitic carbon nitride reported for Suzuki-Miyaura cross coupling reactions in water medium under aerobic conditions using microwave irradiation. Catalyst showed high TOFs (∼ 12,000 h−1) within very short durations (∼ 5 min). High chemoselectivity to biaryls for a wide variety of substrates and good catalyst stability observed over at least six recycle runs.
A Novel Approach for Immobilisation of Platinum Group Metal Complex Catalysts
(Johnson Matthey, 2010) Sarkar, Bibhas R.
The technique known as ‘ossification’ has emerged as one of the most promising approaches for immobilisation of metal complexes, generating highly selective, stable and recyclable heterogeneous counterparts of homogeneous catalysts. ‘Ossification’ involves modifying the ligand(s) in a metal complex catalyst to achieve inherently insoluble forms of the metal complexes, without destroying the configuration responsible for their catalytic properties. The ossified catalysts have been demonstrated to show high catalytic activity and selectivity for a number of industrially important reaction classes such as palladium-catalysed carbonylation and Suzuki coupling and rhodium-catalysed hydroformylation. The characterisation of these catalysts has also shown that the key features of their homogeneous metal complex analogues are retained on immobilisation. The approach is very useful for the design and development of immobilised catalysts with specific features and functionality for various applications. It is also advantageous for catalyst–product separation. This article reviews the recent work on ossification involving platinum group metal complex catalysts in our research group.
Ossification: A new approach to immobilize metal complex catalysts—applications to carbonylation and Suzuki coupling reactions
(Elsiever, 2006-08-15) Sarkar, Bibhas R.
A simple approach for immobilization of transition metal complexes is reported here based on the transformation of the complex into its intrinsically insoluble counterpart, thus generating solid molecular catalysts. This approach that we call “ossification” is based on a principle, in which the water-soluble analogues of the metal complexes are precipitated out from aqueous solutions as insoluble ionic ensembles having catalytically active metal-centered coordination environments and robust framework. The approach has been illustrated for Pd complex catalyzed carbonylation and Suzuki coupling reactions. “Ossification” was found to be an economically and environmentally attractive alternative to other exotic immobilization methodologies.
Synthesis of Highly Ordered TiO2 Nanorods on a Titanium Substrate Using an Optimized Hydrothermal Method
(Springer, 2022-02) Sarkar, Bibhas R.; Hazra, Arnab
In this study, highly stable and well-oriented one-dimensional (1D) TiO2 nanorods were grown over a conductive titanium (Ti) substrate by optimizing various physical and chemical parameters involved in the hydrothermal method. Previous works have reported extensively on the synthesis of 1D TiO2 nanorods on fluorine-doped tin oxide-coated glass substrates using the hydrothermal method. However, glass substrates suffer from poor integration, compatibility, and stability issues when implemented in device applications. To overcome the challenges with glass substrates, in the current study, we propose an optimized hydrothermal route to synthesize highly ordered 1D TiO2 nanorods on a metal (Ti) substrate. The structural and morphological parameters of the nanostructures, including crystal phase, length, diameter, and density of nanorods, were studied with the help of field emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction spectroscopy, and photoluminescence spectroscopy. The morphology of the nanostructures was varied by changing the chemical composition of the mother solution and physical parameters of time and temperature of the reactions involved during hydrothermal synthesis. It was shown that by optimizing the reaction parameters, multi-crystalline three-dimensional TiO2 nanoflowers could be transformed to single-crystalline 1D TiO2 nanorods. One-dimensional TiO2 nanorods on the Ti substrate were then implemented in a metal–insulator–metal (MIM) type of device (Au/TiO2 nanorods/Ti) and used for ethanol sensing. At 100°C, the sensor showed the maximum response magnitude of 61% towards 300 ppm of ethanol.
Tethered Pd-complex on solid support: Catalyst for acid-free carbonylation reactions
(Elsiever, 2007-09) Sarkar, Bibhas R.
Palladium complex [Pd(pyca)(PPh3)(OTs)] has been immobilized on solid matrices having ordered framework and high surface area as zeolite NaY (surface area ∼ 700 m2 g−1), using phosphotungstic acid [H3PW12O40, xH2O] as the molecular tether to form highly stable catalyst materials. The materials were thoroughly characterized using numerous techniques such as 31P CP-MAS NMR, XPS, powder XRD, SEM, etc. to confirm the immobilization and determine the state of the complex after tethering. Carbonylation of substituted olefins and alcohols was performed using this tethered catalyst without the addition of any free acid (protic/aprotic) promoter, with highly promising results. Thus, we can achieve dual advantages of efficient immobilization and partially promoter-free carbonylation catalysts, which is a substantial advancement in carbonylation catalysis.
USPTO Patent Application Publication, Title: Single Solvent gas expanded hydroformylation process
(Patent Scope, 2014) Sarkar, Bibhas R.
Allyl alcohol, particularly from biobased sources such as glycerol, is hydroformylated to products including 4-hydroxybutyraldehyde and 4-hydroxy-2-methylpropionaldehyde by forming a homogeneous reaction mixture including allyl alcohol, a rhodium-based hydroformylation catalyst and a near critical liquefiable petroleum gas or mixture of such gases, reacting the near critical liquefiable petroleum gas (or gas mixture)-expanded allyl alcohol substrate with carbon monoxide and with hydrogen in the presence of the catalyst, and recovering substantially all of the petroleum gas or gases overhead by reducing the pressure and degassing the product mixture. Dense propane is especially useful as a single inert solvent/diluent, and substantially no other solvent/diluent is needed.