Subratanath Koner

Immobilization of palladium in mesoporous silica matrix: preparation, characterization, and its catalytic efficacy in carbon-carbon coupling reactions.

Palladium(0) has been immobilized into the silica-based mesoporous material to develop catalyst Pd(0)-MCM-41, which is found to be highly active in carbon-carbon coupling reactions. [Pd(NH3)4]2+ ions have been incorporated into the mesoporous material during synthesis of MCM-41 and subsequently upon treatments with hydrazine hydrate Pd2+ ions present in mesoporous silica matrix were reduced to Pd(0) almost instantaneously. The catalyst has been characterized by small-angle X-ray diffraction, N2 sorption, and transmission electron microscopy (TEM). TEM and surface area measurements clearly demonstrate that the immobilization of Pd(0) into the mesoporous silica has a significant effect on pore structure of the catalyst. Nevertheless, after immobilization of palladium the meso-porosity of the material is retained, as evidenced in the nitrogen sorption measurement. The TEM micrograph shows that both MCM-41 and Pd(0)-MCM-41 have similar types of external surface morphology; however, Pd(0)-MCM-41 was less ordered. Pd(0)-MCM-41 showed high catalytic activity toward carbon-carbon bond formation reactions like Heck and Sonogashira coupling, as evidenced in high turn-over numbers. In contrast to many other Pd-based catalysts reported so far, Pd(0)-MCM-41 acts as a truly heterogeneous catalyst in C-C coupling reactions. Notably, the new heterogeneous catalyst is found to be efficient in the activation of arylchloride to give impressive conversion in cross coupling (15-45% for Heck and 30% for Sonogashira) reactions under mild conditions.

Anchoring of Palladium onto Surface of Porous Metal−Organic Framework through Post-Synthesis Modification and Studies on Suzuki and Stille Coupling Reactions under Heterogeneous Condition

An ecofriendly solid catalyst has been synthesized by anchoring palladium(II) into post synthetically modified metal organic framework IRMOF-3. The pore of IRMOF-3 was first modified with pyridine-2-aldehyde. The amine group of IRMOF-3 upon condensation with pyridine-2-aldehyde afforded a bidentate Schiff base moiety in the porous matrix. The Schiff base moieties were used to anchor palladium(II) ions. The prepared catalyst has been characterized by UV-vis, IR spectroscopy, X-ray powder diffraction, and nitrogen sorption measurements. Framework structure of the catalyst is not being destroyed in the multistep synthesis procedure as evidenced in X-ray powder diffraction studies. The catalyst has shown high activity toward the Suzuki and Stille cross-coupling reaction in 20% H2O/EtOH and EtOH medium, respectively, at 80 °C. The immobilized complex did not leach or decompose during the catalytic reactions, showing practical advantages over the homogeneous catalysis.

1D coordination polymer of copper(II) containing μ-1,1,3 azido ligand with alternating ferro–antiferromagnetic interactions

Abstract Single crystals of the copper(II) chain of formula [(μ-1,1,3-N 3 ) 2 {Cu 2 (ampy) 2 (N 3 ) 2 }] n (ampy=1-(2-aminoethyl)pyrrolidine) were prepared and characterized by X-ray diffraction methods. The copper(II) possesses the pseudo-octahedral environment with a terminal azido, one substituted alicyclic diamine and the remaining coordination occupied by N atoms of the unusual μ-1,1,3-N 3 bridging azido ligand. The magnetic behavior was investigated in the temperature range 2.0–300 K and show ferro-antiferromagnetic alternating chain. The fit of the experimental data with the expression derived for an alternating S =1/2 chains based on the exchange Hamiltonian H =−∑ N −1 i −1 [ J AF S → 2i · S → 2i +1 +J FM S → 2i · S → 2i −1 ] gave the best parameters J AF =−2.80, J FM =0.15 cm −1 , α =0.054, g =2.15 and R =1.2×10 −5 , which are consistent with a dominant antiferromagnetic coupling.

Controlled Construction of Metal–Organic Frameworks: Hydrothermal Synthesis, X‐ray Structure, and Heterogeneous Catalytic Study

The role of pH in the formation of metal-organic frameworks (MOFs) has been studied for a series of magnesium-based carboxylate framework systems. Our investigations have revealed the formation of five different zero-dimensional (0D) to three-dimensional (3D) ordered frameworks from the same reaction mixture, merely by varying the pH of the medium. The compounds were synthesized by the hydrothermal method and characterized by single-crystal X-ray diffraction. Increase of the pH of the medium led to abstraction of the imine hydrogen from the ligand and a concomitant increase in the OH(-) ion concentration in the solution, facilitating the construction of higher dimensional framework compounds. A stepwise increase in pH resulted in a stepwise increase in the dimensionality of the network, ultimately leading to the formation of a 3D porous solid. A gas adsorption study of the 3D framework compound confirmed its microporosity with a BET surface area of approximately 450 m(2)  g(-1). Notably, the 3D framework compound catalyzes aldol condensation reactions of various aromatic aldehydes with acetone under heterogeneous conditions.

Tridentate (NNO) Schiff-base copper(II) complex: synthesis, crystal structure, and magnetic study

A new azido adduct of a tridentate Schiff-base copper(II) complex has been synthesized and characterized structurally and magnetically. X-ray single crystal structure analysis reveals that the asymmetric unit of [Cu2(L)2(µ1,1-N3)2][Cu(L)(N3)] (1) [HL = 1-(N-ortho-hydroxyacetophenimine)-2,2-diethyl-aminoethane] has two independent moieties. One of these forms a dimer, containing end-on azido bridges, with its center of inversion related equivalents. The complex crystallizes in monoclinic space group P21/c with a = 10.112(2), b = 31.938(4), c = 9.718(2) Å and β = 95.00(2)°. Variable temperature magnetic susceptibility data show antiferromagnetic interactions between copper(II) centers.

Layered transition metal carboxylates: efficient reusable heterogeneous catalyst for epoxidation of olefins.

Layered metal carboxylates [M(malonato)(H(2)O)(2)](n) (M = Ni(II) and Mn(II)) that have a claylike structure have been synthesized hydrothermally and characterized. The interlayer separation in these layered carboxylates is comparable to that of the intercalation distance of the naturally occurring clay materials or layered double hydroxides (LDHs). In this study, we have demonstrated that, instead of intercalating the metal complex into layers of the clay or LDH, layered transition metal carboxylates, [M(malonato)(H(2)O)(2)](n), as such can be used as a recyclable heterogeneous catalyst in olefin epoxidation reaction. Metal carboxylates [M(malonato)(H(2)O)(2)](n) exhibit excellent catalytic performance in olefin epoxidation reaction.

Oxo-Vanadium(IV) Dihydrogen Phosphate: Preparation, Magnetic Study, and Heterogeneous Catalytic Epoxidation

A layered oxo-vanadium(IV) dihydrogen phosphate, {VO(H2PO 4)2} n has been synthesized hydrothermally and characterized by several physicochemical methods. Single-crystal X-ray analysis (crystal system, tetragonal; space group, P4/ ncc; unit cell dimensions, a = b = 8.9632(4), c = 7.9768(32) A) of {VO(H2PO4) 2} n reveals that the compound has an extended two-dimensional structure. The VO2+ moieties are connected through bridging H 2PO4 (-) ions, and this type of connection propagates parallel to the crystallographic ab plane which gives rise to a layered structure. The layers are staked parallel to the crystallographic c axis with a separation between the layers of ca. 4.0 A. Magnetic susceptibility of {VO(H2PO4)2} n has been measured in the temperature range 2-300 K on a SQUID magnetometer. The magnetic property of {VO(H2PO4)2} n is explicable in the light of a two-dimensional quantum Heisenberg antiferromagnet model. Magnetic pathways are available through the dihydrogen-phosphato bridges within the layer and provide for weak antiferromagnetic interactions. Notably {VO(H2PO4)2} n catalyzes the epoxidation reaction of alkenes with tert-BuOOH in acetonitrile medium under heterogeneous condition.

MCM-41-supported oxo-vanadium(IV) complex: a highly selective heterogeneous catalyst for the bromination of hydroxy aromatic compounds in water.

An ecofriendly solid catalyst has been synthesized by anchoring vanadium(IV) into organically modified MCM-41. First, the surface of Si-MCM-41 was modified with 3-aminopropyl-triethoxysilane (3-APTES), the amine group of which upon condensation with ortho-hydroxy-acetophenone affords a N(2)O(2)-type Schiff base moiety in the mesoporous matrix. The Schiff base moieties were used to anchor oxo-vanadium(IV) ions. The prepared catalyst has been characterized by UV-vis, IR spectroscopy, small-angle X-ray diffraction (SAX), nitrogen sorption, and transmission electron microscopy (TEM) studies. It is observed that the mesostructure has not been destroyed in the multistep synthesis procedure, as evidenced by SAX and TEM measurements. The catalyst has shown unprecedented high conversion as well as para selectivity toward the bromination of hydroxy aromatic compounds using aqueous 30% H(2)O(2)/KBr in water. The reaction proceeds according to the stoichiometric ratio, and the monobrominated product was obtained as the major product using a stoichiometric amount of the bromine source. The immobilized complex does not leach or decompose during the catalytic reactions, showing practical advantages over the free metal complex.

Aromatic N‐Arylations Catalyzed by Copper‐Anchored Porous Zinc‐Based Metal–Organic Framework under Heterogeneous Conditions

A highly porous Zn‐based metal–organic framework (MOF) IRMOF‐3 was covalently decorated with pyridine‐2‐aldehyde. The free amine group of IRMOF‐3 upon condensation with pyridine‐2‐aldehyde affords a bidentate Schiff‐base moiety in the porous matrix. The Schiff base moieties are availed to anchor copper(II) ions to display the catalyst’s utility towards catalytic reactions. The catalyst was characterized by UV/Vis and IR spectroscopy, powder XRD spectrometry, SEM energy‐dispersive X‐ray spectrometry, and nitrogen sorption measurements. The catalyst exhibits excellent activity in catalyzing the N‐arylation reaction of nitrogen‐containing heterocycles with aryl bromides in DMSO medium, under mild condition (90 °C) in the presence of Cs2CO3. The porous catalyst demonstrates size selectivity towards substrate as a result of the presence of active sites inside the pores of the MOF. The anchored complex seems to be not leached or decomposed during the catalytic reactions up to five successive catalytic cycles, demonstrating practical advantages over homogeneous catalysis.

Immobilization of Cr(salen) moiety in MCM-41 and studies on its catalytic properties

Abstract The [Cr III (salen)] + complex moiety is immobilized in MCM-41 matrix to obtain a new hybrid catalytic system; to test its activity, epoxidation of norbornene and hydroxylation reaction of 1-naphthol are carried out by using TBHP ( tert -butylhydroperoxide) as oxidant.