Arindam Modak

Triazine functionalized ordered mesoporous polymer: a novel solid support for Pd-mediated C–C cross-coupling reactions in water

A new functionalized mesoporous polymer (MPTAT-1) has been synthesized via organic–organic radical polymerization of 2,4,6-triallyloxy-1,3,5-triazine (TAT) in aqueous medium in the presence of an anionic surfactant (sodium dodecyl sulfate) as template. Powder XRD and TEM image analysis suggests the presence of ordered 2D-hexagonal arrangement of pores in the material. N2 sorption analysis reveals a moderately good surface area 135 m2 g−1 for this mesoporous polymer. The template free MPTAT-1 acts as an excellent support for immobilizing Pd(II) at its surface and the resulting material showed very good catalytic activity in several C–C cross-coupling reactions like Mizoroki–Heck, Sonogashira and Suzuki–Miyaura in an environmentally benign reaction medium, water. The catalyst exhibits very high catalytic activity for the coupling of various aryl halides including aryl chlorides with alkenes or alkynes and the sodium salt of (trihydroxy)phenylborate. Due to strong binding with the functional groups of the polymer, the anchored Pd(II) could not leach out from the surface of the mesoporous catalyst during the reaction and it has been reused several times without appreciable loss in catalytic activity.

Pd-grafted periodic mesoporous organosilica: an efficient heterogeneous catalyst for Hiyama and Sonogashira couplings, and cyanation reactions

The high surface area of 2D-hexagonal periodic mesoporous organosilica (PMO) containing a phloroglucinol-diimine moiety inside the pore wall has been utilized for grafting Pd(II) at the surface of the mesopores. This Pd-containing PMO material (Pd-LHMS-3) shows excellent catalytic activity in fluoride-free Hiyama cross-coupling reactions in water at alkaline pH conditions. Sonogashira cross-couplings between terminal alkynes and aryl halides take place in the presence of water and hexamine as base in the absence of any Cu co-catalyst. Cyanation of aryl halides is equally promoted with K4[Fe(CN)6] as the cyanide source (in the absence of poisonous KCN, NaCN or Zn(CN)2) over Pd-LHMS-3. Excellent yield of the products, reusability and the facile work-up could make this Pd-grafted PMO material a unique catalyst for the synthesis of substituted benzonitriles, unsymmetrical biphenyls and di-substituted alkynes under environmentally benign reaction conditions. Further good yield of products and no evidence of leached Pd from the catalyst surface during the reaction and its smooth recovery confirm the true heterogeneity in these catalytic reactions.

One-pot thioetherification of aryl halides with thiourea and benzyl bromide in water catalyzed by Cu-grafted furfural imine-functionalized mesoporous SBA-15

Surface functionalization of SBA-15 followed by its reaction with Cu(OAc)(2) has been carried out to develop a new Cu-grafted functionalized mesoporous material, which catalyzes one-pot three component coupling of different aryl halides with thiourea and benzyl bromide in aqueous medium to produce aryl thioethers in very good yields (80-88%).

A triazine functionalized porous organic polymer: excellent CO2 storage material and support for designing Pd nanocatalyst for C–C cross-coupling reactions

One-pot bottom-up synthesis involving extended aromatic electrophilic substitution on to a pyrrole has been employed for the design of a novel triazine-functionalized porphyrin-based porous organic polymer, TPOP-1. Hydrothermal treatment of 4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)tris(oxy)tribenzaldehyde and pyrrole in glacial acetic acid in the presence of FeCl3 leads to the formation of TPOP-1, which is a highly porous and robust material, and which exhibits a high surface area and bimodal pore sizes ranging from large micropores to mesopores. The presence of porphyrin and triazine functionality within the network structure enables formation of electron-donating basic N-sites at the surface of the porous organic framework and thus favors the adsorption of Lewis acidic CO2 molecules and decoration of the material by palladium nanoparticles at its surface to form Pd-TPOP-1. TPOP-1 showed good CO2 storage capacity (6.2 mmol g−1 or 27.3 wt% at 3 bar/273 K), suggesting its potential application in environmental clean-up. Moreover, this post Pd-functionalized material forms fine colloidal suspensions in organic solvent and exhibits high catalytic activity for Sonogashira cross-coupling of aryl halides with aryl alkynes under mild reaction conditions.

A new periodic mesoporous organosilica containing diimine-phloroglucinol, Pd(II)-grafting and its excellent catalytic activity and trans-selectivity in C–C coupling reactions

A new organosilane precursor has been designed via Vilsmeier–Haack formylation of phloroglucinol followed by its Schiff base condensation with 3-aminopropyl-triethoxysilane (APTES). A novel organic–inorganic hybrid periodic mesoporous organosilica (PMO) LHMS-3 containing the highly coordinating bis(propyliminomethyl)-phloroglucinol moiety inside the pore wall has been synthesized by using this precursor organosilane molecule. Phenolic-OH and imine-N donor sites present in this PMO material have been utilized to anchor Pd(II) species at the surface of the mesopores. Small angle neutron scattering, XRD, HR TEM, SEM, 13C and 29Si solid state MAS NMR, UV-vis and FT IR spectroscopic tools are utilized to characterize the 2D-hexagonal mesophase and the presence of the bis(propyliminomethyl)-phloroglucinol moiety inside the pore wall. This Pd-anchored material Pd-LHMS-3 showed excellent catalytic activity and trans-selectivity in Heck C–C bond formation reactions for the synthesis of a series of value-added aromatic and aliphatic olefins.

Triazine functionalized ordered mesoporous organosilica as a novel organocatalyst for the facile one-pot synthesis of 2-amino-4H-chromenes under solvent-free conditions

A highly ordered 2D-hexagonal mesoporous material functionalized with a triazine moiety has been synthesized via post-synthetic modification of mesoporous SBA-15 with thiols followed by a thiol–ene click reaction using 2,4,6-triallyloxy-1,3,5-triazine. A facile one-pot three-component condensation reaction of aromatic aldehyde, malononitrile and activated phenols for the synthesis of a diverse range of 2-amino-4H-chromenes has been efficiently catalyzed over this novel mesoporous metal-free heterogeneous organocatalyst under solvent-free reaction conditions. Further, this organocatalytic reaction is waste-free, easy to work-up and efficiently reused. The organic products have been isolated from the reaction mixture by using easily disposable solvents and can be easily purified by re-crystallization.

Facile C–S coupling reaction of aryl iodide and thiophenol catalyzed by Cu-grafted furfural functionalized mesoporous organosilica

A new functionalized mesoporous organosilica has been designed via Schiff-base condensation of furfural and 3-aminopropyltriethoxy-silane (APTES) followed by its hydrothermal co-condensation with tetraethylorthosilicate (TEOS) in the presence of a cationic surfactant CTAB. Subsequent reaction of this mesoporous organosilica with Cu(OAc)(2) in absolute ethanol leads to the formation of a new Cu(II)-grafted mesoporous organosilica catalyst 1. Powder XRD, HR TEM, FE SEM, N(2) sorption and FT IR spectroscopic tools are used to characterize the materials. This Cu-anchored mesoporous material acts as an efficient, reusable catalyst in the aryl-sulfur coupling reaction between aryl iodide and thiophenol for the synthesis of value added diarylsulfides.

A novel mesoporous silica-grafted organocatalyst for the Michael addition reaction, synthesized via the click method

An efficient and recyclable mesoporous silica-grafted bifunctional acid–base organocatalyst for the Michael addition of ketones to β-nitrostyrenes has been synthesized by click chemistry, affording the products with excellent diastereoselectivity. A remarkable enhancement in the reaction rates could be observed with respect to the corresponding monofunctional organocatalyst.

Highly Porous Organic Polymer containing Free ‐CO2H Groups: A Convenient Carbocatalyst for Indole CH Activation at Room Temperature

Functionalized porous organic materials are very demanding, owing to their huge potential applications in adsorption, supercapacitors, gas storage and catalysis. Since indole compounds represent privileged structural motifs in several valuable medicinal formulations, synthesis of indole derivatives through metal-free catalytic pathway is very challenging. “Carbocatalysis” is the process in which a metal-free carbonaceous material (bearing C, H, O) acts as catalyst and this has several advantages like ecologically viable, highly stable, noncorrosive and sustainable. Carbocatalysis has gained particular attention after the discovery of functionalized graphene oxides and thus it is highly desirable to design a highly porous carbocatalyst for indole C H activation at room temperature employing bottom-up chemistry approach. Being abundant in nature and inexpensive, carbon-based precursors are widely studied for material design and their utility. From the perspective of green synthesis, carbon-based catalysts have immense potential in the advancement of sustainable alternatives over existing MOFs, zeolite, metal oxides and metal-grafted heterogeneous catalysts. Microporosity and high probability of metal leaching from the active sites of those metal based catalysts to the solution retards their catalytic activity and the best alternative lies on the utilization of high surface area metal free carbocatalyst from the perspective of green catalytic reactions. However, little attention has been paid so far on carbon-based solid acid catalysts and their superiority over traditional homogeneous acid catalysts, which produces large chemical wastes. Synthesis of solid acid carbocatalysts reported in the literature involves incomplete carbonization of polycyclic hydrocarbons and carbohydrates, nanocasting using SBA-15 or mesoporous silica template and carbonization of zinc chloride impregnated wood powder followed by sulfonation. However, materials obtained under such circumstances possess low surface area, poor catalytic activity towards hydrophobic reactants, together with the need of high temperature and prolonged reaction time. These conditions are unsuitable for large scale production of organic fine chemicals. On the other hand, although the solid carbocatalyst generated on chemical activation of biomass waste with phosphoric acid is interesting but their catalytic activity is considerably low. Recent progress on graphene oxide, activated charcoal, carbon nanotube, polymeric carbon nitride based supports needs the presence of transition metals for successful catalytic reactions. For designing metal-free carbocatalysts these supports require high temperature together with complicated methodology for catalyst preparation. However, poor surface areas associated with such acidic carbon materials is a major drawback for carrying out the environmentally viable catalytic reactions. On the other hand, although inorganic zeolites possesses high BET surface area, but the dimension of pores (typically less than 1 nm) is a barrier for bulky organic species to penetrate inside the framework. Further, the leaching of active metal sites from the inorganic catalysts to the solution may hamper the purity of pharmacologically valuable products. Thus, porous acidic organic polymer would have inherent advantages over zeolites and other carbon materials in catalysis. Herein, we have designed a new highly porous cross-linked organic polymer COP-M through Friedel–Crafts alkylation reaction between 2,4,6-tris(bromomethyl)mesitylene and 4,4’-bis(bromomethyl)-1,1’-biphenyl over Lewis acid catalyst FeCl3. Alkaline KMnO4 oxidation of methyl functionalized COPM resulted COP-A bearing highly acidic -CO2H groups at the surface of the carbon framework via oxidation of benzylic C H groups to the corresponding -CO2H group (Scheme 1). COP-A showed unprecedented catalytic activity in indole C H activation at 298 K. Quantitative estimation of the number of acid sites of COP-A has been elucidated by performing acidimetric titration using phenolphthalein as indicator, which revels the presence of 4.4 mmol g 1 acid sites in the catalyst. This result suggests that the COP-A contains high heterogeneity and acidity due to the surface -CO2H groups. Other related carbon-based polymers like Davankov resin, vinyl chloride suspension polymers, or polymers obtained from dichloroxylene (DCX) and 4,4’-bis(chloromethyl)-1,10-biphenyl (BCMBP) etc. are devoid of any catalytically active groups. Extensive cross-linking facilitates the highly robust character of COP-M and COP-A, and their chemical stability and insolubility in common organic solvents, like DMF, DMSO, THF, CH3CN, pet ether, acetone etc. , and also to boiling water and hydrochloric acid. The very high thermal stability of COP-M and COP-A has been evidenced from their thermogravimetric analysis (Figure S1 and S2). As seen from Figure S1, COP-M exhibits weight loss of 20 % up to 500 8C and beyond this temperature range it exhibits a sharp [a] A. Modak, J. Mondal, Prof. A. Bhaumik Department of Materials Science Indian Association for the Cultivation of Science 2A & B, Raja S.C. Mullick Road Jadavpur, Kolkata 700 032 (India) Fax: (+ 91) 33-2473-2805 E-mail : msab@iacs.res.in Homepage: http ://www.iacs.res.in/matsc/msab/ Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201300009.

A luminescent nanoporous hybrid material based drug delivery system showing excellent theranostics potential for cancer

A novel hybrid nanoporous material (LNH-1) bearing a tris(propyliminomethyl)-phloroglucinol fluorescent moiety in the framework has been designed and administration of an LNH-1 based drug delivery system containing doxorubicin to cancer cells showed inhibition of proliferation, suggesting its future potential theranostics application in cancer.