Susanta Hazra

Sulfonated Schiff base dinuclear and polymeric copper(II) complexes: crystal structures, magnetic properties and catalytic application in Henry reaction

The syntheses and X-ray diffraction structures of water soluble copper(II) compounds containing the Schiff base ligand 2-(2-pyridylmethyleneamino)benzenesulfonate (L−), viz. the dinuclear bis-μ1,1-azido [CuL(μ1,1-N3)]2 (1) and bis-μ1,3-thiocyanato [CuL(μ1,3-NCS)]2·2H2O (2) complexes and the μ1,5-dicyanamide coordination polymer [CuL(μ1,5-NCNCN)]n·nH2O (3), are reported. The one dimensional chain in 3 propagated through μ1,5-dicyanamide bridges is stabilized by a new type of sixteen membered metallacycle supported by copper and H-bonds. Variable-temperature (2–300 K) magnetic studies indicate that there is a weak ferromagnetic exchange coupling in 1, while 2 and 3 have weak antiferromagnetic exchange interactions. They catalyze the diastereoselective nitroaldol (Henry) reaction of different aldehydes with nitroethane in aqueous medium. Water was the solvent used for both the syntheses and catalytic studies.

Synthesis, structure and catalytic applications of amidoterephthalate copper complexes in the diastereoselective Henry reaction in aqueous medium

Terephthalic acid derivatives bearing amide side functional groups, viz. 2-propionamidoterephthalic acid (H2L1) and 2-acetamidoterephthalic acid (H2L2), have been structurally characterized using X-ray crystallography. While H2L1 is hydrogen bonded with DMF molecules forming a 1D hydrogen bonded network, H2L2 constructs a 2D hydrogen bonded network. They have been used to synthesize two new isostructural mononuclear copper complexes, [Cu(L1)(H2O)4] (1) and [Cu(L2)(H2O)4] (2), also characterized using X-ray crystallography. In these structures the hydrogen bonded assemblies of carboxylate and coordinated water molecules form a distorted cubane type of hydrogen bonded network. Complexes 1 and 2 act as heterogeneous catalysts for the diastereoselective nitroaldol (Henry) reaction in aqueous medium, 1 providing high yields (up to 77%) and good diastereoselectivities under ambient conditions. These catalysts can be recycled without significant loss of activity, and the catalytic process is efficient, simple, easy to work-up and operates under ‘green’ conditions.

Nanoporous lanthanide metal–organic frameworks as efficient heterogeneous catalysts for the Henry reaction

A series of self-assembled lanthanide coordination polymers formulated as [La(L1)2]n·1n(DMF)H·3n(DMF) (1), [Ce(L1)2]n·1n(DMF)H·2n(DMF) (2), [Sm(L1)2]n·1n(HCONH2)H·2n(HCONH2) (3), [La(L2)(HL2)(H2O)(DMF)2]n (4) and [Ce(L2)(HL2)(H2O)(DMF)2]n (5) [H2L1: 2-acetamidoterephthalic acid and H2L2: 2-benzamidoterephthalic acid] has been synthesized from the reactions of H2L1 or H2L2 with different lanthanide salts under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, X-ray single-crystal diffraction, powder X-ray diffraction, thermogravimetry and photoluminescence spectroscopy. X-ray diffraction analyses reveal that frameworks 1–3 have similar types of three-dimensional structures, composed of L12− ligands and trinuclear lanthanide nodes, in which two crystallographically independent lanthanide atoms are present. Frameworks 4 and 5 are isostructural, featuring a double chain-type one-dimensional coordination polymer which expands to 3D by means of H-bond interactions. These frameworks act as heterogeneous polymeric solid catalysts for the nitroaldol (Henry) reaction of different aldehydes with nitroalkanes, in water, and can be recycled without losing appreciable activity.

A cyclic tetranuclear cuboid type copper(II) complex doubly supported by cyclohexane-1,4-dicarboxylate: molecular and supramolecular structure and cyclohexane oxidation activity

Synthesis, characterization and catalytic study of the new bis(μ4-(ae)-cyclohexane-1,4-dicarboxylato-O,O′,O′′,O′′′)-tetracopper(II) complex [(CuL)2(μ4-O,O′,O′′,O′′′-CDC)]2·2H2O (1) (HL = 2-(2-pyridylmethyleneamino)benzenesulfonic acid and CDC = cyclohexane-1,4-dicarboxylate) are described. Complex 1 contains four copper(II) centres connected by four Schiff base ligands (L−) and doubly bridged by two cyclohexane-1,4-dicarboxylate moieties. The axial-equatorial conformation of the carboxylate groups of CDC stabilizes a tetracopper di-CDC ring in a cuboid type fashion. Compound 1 is applied as an efficient pre-catalyst for the oxidation of cyclohexane by aqueous H2O2 under mild conditions (50 °C) in CH3CN/H2O medium. Without any promoter, a total yield (based on substrate) of cyclohexanol and cyclohexanone up to 35% was achieved.

Zinc amidoisophthalate complexes and their catalytic application in the diastereoselective Henry reaction

Reactions of 5-propionamidoisophthalic acid (H2L1) and 5-benzamidoisophthalic acid (H2L2) with Zn(NO3)2·6H2O under different hydrothermal conditions lead to two pairs of Zn(II) compounds, viz. the mononuclear [Zn(L1)(H2O)3]·H2O (1) and [Zn(L1)(H2O)3]·3H2O (2), and the 1D polymers [Zn(L2)(H2O)2]n (3) and [{Zn(L2)(H2O)2}·2H2O]n (4). They crystallize in orthorhombic [Pbca (1) and P212121 (3)] or triclinic (P, 2 and 4) systems, and their formation depends on the particular reaction conditions. Compounds 1 and 2, as well as 3 and 4, are solvatomorphs, the latter presenting different 1D metal–organic polymeric chains. All of them act as heterogeneous catalysts for the diastereoselective nitroaldol (Henry) reaction of different aldehydes with nitroalkanes and can be recycled without losing activity.

Sulfonated Schiff base copper(II) complexes as efficient and selective catalysts in alcohol oxidation: syntheses and crystal structures

The reaction between 2-aminobenzenesulfonic acid and 2-hydroxy-3-methoxybenzaldehyde produces the acyclic Schiff base 2-[(2-hydroxy-3-methoxyphenyl)methylideneamino]benzenesulfonic acid (H2L·3H2O) (1). In situ reactions of this compound with Cu(II) salts and, eventually, in the presence of pyridine (py) or 2,2′-bipyridine (2,2′-bipy) lead to the formation of the mononuclear complexes [CuL(H2O)2] (2) and [CuL(2,2′-bipy)]·DMF·H2O (3) and the diphenoxo-bridged dicopper compounds [CuL(py)]2 (4) and [CuL(EtOH)]2·2H2O (5). In 2–5 the L2− ligand acts as a tridentate chelating species by means of one of the O-sulfonate atoms, the O-phenoxo and the N-atoms. The remaining coordination sites are then occupied by H2O (in 2), 2,2′-bipyridine (in 3), pyridine (in 4) or EtOH (in 5). Hydrogen bond interactions resulted in R22(14) and in R44(12) graph sets leading to dimeric species (in 2 and 3, respectively), 1D chain associations (in 2 and 5) or a 2D network (1). Complexes 2–5 are applied as selective catalysts for the homogeneous peroxidative (with tert-butylhydroperoxide, TBHP) oxidation of primary and secondary alcohols, under solvent- and additive-free conditions and under low power microwave (MW) irradiation. A quantitative yield of acetophenone was obtained by oxidation of 1-phenylethanol with compound 4 [TOFs up to 7.6 × 103 h−1] after 20 min of MW irradiation, whereas the oxidation of benzyl alcohol to benzaldehyde is less effective (TOF 992 h−1). The selectivity of 4 to oxidize the alcohol relative to the ene function is demonstrated when using cinnamyl alcohol as substrate.

1D hacksaw chain bipyridine–sulfonate Schiff base-dicopper(II) as a host for variable solvent guests

Syntheses, crystal structures and interconversion properties of the 1D coordination polymers [Cu2L2(bipy)]n·2nMe2SO (1), [Cu2L2(bipy)]n·3nNH2CHO·nH2O (2), [Cu2L2(bipy)]n·2nNH(Me)CHO (3), [Cu2L2(bipy)]n·2nN(Me)2CHO (4) and [Cu2L2(bipy)]n·2nMeOH (5) (bipy = 4,4′-bipyridine) derived from the acyclic Schiff base o-[(o-hydroxyphenyl)methylideneamino]benzenesulfonic acid (H2L) are described. Single-crystal X-ray diffraction analyses revealed their solvatomorph properties, featuring the formation of 1D polymeric chains with identical hacksaw patterns and adaptable host abilities, containing different guest solvent molecules. No amorphicity was detected upon desolvation of 1–5 and of the previously reported compound [Cu2L2(bipy)]n·nN(Me)2CHO (6), and these coordination polymers undergo reversible interconversion.

A sulfonated Schiff base dimethyltin(IV) coordination polymer: synthesis, characterization and application as a catalyst for ultrasound- or microwave-assisted Baeyer–Villiger oxidation under solvent-free conditions

The synthesis and crystal structure of the new dimethyltin(IV) compound [SnMe2(HL)(CH3OH)]n·(0.5nCH3OH) (1) derived from the Schiff base 2-[(2,3-dihydroxyphenyl)methylideneamino]benzenesulfonic acid (H3L) are described. Despite having six potentially donating centres (one imine nitrogen, two phenoxo and three sulfonate oxygen atoms), the monoprotonated dianionic ligand (HL2−) behaves as an O,O,O-tridentate chelator. Single crystal X-ray diffraction revealed that 1 is a 1D coordination polymer with every tin(IV) ion bound to two methyl groups, a methanol molecule, two Ophenoxo and one μ-Osulfonate atom from HL2−. The coordination polymer 1 was applied as a heterogeneous catalyst for the Baeyer–Villiger oxidation of ketones to esters or lactones, using aqueous hydrogen peroxide as oxidant, under ultrasound (US) or microwave (MW) irradiation and solvent- and additive-free conditions. Overall conversions up to 76/82, 98/93, 93/89, 91/94, 83/90, 68/62 and 81/87% under US/MW irradiations were obtained with 3,3-dimethyl-2-butanone, cyclopentanone, 2-methylcyclopentanone, cyclohexanone, 3-methylcyclohexanone, benzophenone and acetophenone, respectively. The catalyst can be recycled up to five cycles without losing appreciable activity.

Unfolding biological properties of a versatile dicopper(II) precursor and its two mononuclear copper(II) derivatives

Synthesis, inter-conversions and biological study of the dichloro bridged dicopper(II) compound [CuLCl]2 (1) and its two mononuclear derivatives [CuLCl(H2O)]·H2O (2) and [CuLCl(py)] (3) (HL=2-(2-pyridylmethyleneamino)benzenesulfonic acid) are described. The dimeric compound 1 collapses into monomers 2 and 3 in the presence of coordinating solvents, water and pyridine, respectively, and 1 is regenerated upon simple stirring of 2 or 3 in methanol. The reactions of 1 with neutral (present study) and charged (earlier studies) ligands result in monomeric and multimeric compounds, respectively, attesting that it is a versatile dicopper(II) precursor. The anticancer activity of these copper complexes (1-3) was screened against lung (A-549) and breast (MDA-MB-231) human cancer cell lines. The IC50 (half maximal inhibitory concentration) value for one (3) of the compounds suggests preferential cytotoxicity against breast cancer MDA-MB-231 cell line. Furthermore, the IC50 value obtained for complex 3 is found to be almost two-fold times cytotoxic than the standard drug cisplatin. In addition, the underlying possible mechanism of its apoptosis-inducing efficacy in MDA-MB-231 cells has been rationalized by using flow cytometry (FACS) and Hoechst 33342/propidium iodide (PI) fluorescence staining. The stimulation of apoptotic induction for complex 3 has further been affirmed by reactive oxygen species (ROS) generation and mitochondrial aggregations studies.

Synthesis, molecular and supramolecular structure of a new dinuclear aluminium(III) complex derived from 3-aminopyrazine- 2-carboxylic acid

Abstract Solvothermal reaction of aluminum(III) nitrate nonahydrate with 3-aminopyrazine-2-carboxylic acid (HL) gave rise to a bis(μ2-hydroxo)-tetrakis(3-aminopyrazine-2-carboxylato)-dialuminium(III) complex [Al(L)2(OH)]2 (1) (L = 3-aminopyrazine-2-carboxylate). Crystal structure analysis reveals that each hexacoordinated Al(III) centre adopts a distorted octahedral geometry occupied by two Ocarboxylate, two Npyrazine and two Ohydroxo atoms. The L– ligand binds the metal cation by means of one pyrazine N-atom and carboxylate O-atoms via chelating fashion. Two hydroxo groups bridge between two aluminum(III) centres, assisting to construct a dinuclear structure. In the crystal lattice of 1 two symmetry non-equivalent dinuclear complexes are present. A 3D supramolecular associate in the crystal lattice of 1 has been stabilized by a number of non-covalent H-bonding interactions. Topology of the hydrogen bonded network has been also analyzed.