Synthesis and characterization of insoluble cobalt(II), nickel(II), zinc(II) and palladium(II) Schiff base complexes: Heterogeneous catalysts for oxidation of sulfides with hydrogen peroxide

Abstract

The condensation reaction of 1,2-bis(2 0 -aminophenoxy)benzene with 2pyridinecarbaldehyde in a mole ratio of 1:2 gives a new Schiff base ligand (L). Four Schiff base complexes, CoL(NO 3 ) 2 (1), NiLCl 2 (2), ZnL(NO 3 ) 2 (3) and Pd 2 LCl 4 (4) have been prepared by direct reaction of the ligand (L) and appropriate metal salts. The Schiff base ligand (L) has been characterized by IR, 1 H NMR and 13 C NMR spectroscopy and elemental analysis. Also, all complexes have been characterized by IR and XRD spectroscopy techniques and elemental analysis. The synthesized complexes have very poor solubility in all polar and non-polar solvents such as: H 2 O, MeOH, EtOH, CH 3 CN, DMSO, DMF, CHCl 3 , CH 2 Cl 2 , THF, etc; therefore, they have been used as heterogeneous catalysts. Catalytic performance of the complexes was studied in oxidation of thioanisole using hydrogen peroxide (H 2 O 2 ) as the oxidant. Various factors including the reaction temperature, amount of oxidant and catalyst amount were optimized. The palladium Schiff base complex, Pd 2 LCl 4 (4), shows better catalytic activity than other complexes. Therefore, the Pd(II) Schiff base complex has been used as a catalyst for oxidation of different sulfides to their corresponding sulfones in acetonitrile with hydrogen peroxide as the oxidant. The palladium Schiff base complex, Pd 2 LCl 4 (4), has shown a very good recyclability, up to five times, without any appreciable decreases in catalytic activity and selectivity.

Synthesis, characterization, X-ray crystal structures and antibacterial activities of Schiff base ligands derived from allylamine and their vanadium(IV), cobalt(III), nickel(II), copper(II), zinc(II) and palladium(II) complexes

“…A comparison of the spectra of the free ligands, HL 1 [31] and HL 2 , and its Ni(II), Zn(II) and Pd(II) complexes, NiL 1 bonds [14].…”

“…The catalytic activity of Schiff base metal complexes has been analyzed critically in various reactions such as polymerization, oxidation, epoxidation, reduction of ketones, allylic alkylation and Michael addition reactions [4,[8][9][10][11][12][13][14][15][16][17].…”

Schiff base complexes and their versatile applications as catalysts in oxidation of organic compounds: part I

“…Menati et al have reported the synthesis of a new Schiff base ligand from the condensation reaction of 1,2‐bis(2′‐aminophenoxy)benzene with 2‐pyridinecarbaldehyde in a mole ratio of 1:2. Schiff base complexes were prepared by reaction of the ligand and metal ions.…”

Nickel(II) Schiff base complex supported on nano‐titanium dioxide: A novel straightforward route for preparation of supported Schiff base complexes applying 2,4‐toluenediisocyanate

“…Because of high cost, formation of by‐products and low amount of reactive and efficacious oxygen, most of the oxidants used are not adequate for large‐scale synthesis. Among them, aqueous hydrogen peroxide (H 2 O 2 ) is the most attractive one, as it is both environmentally safe and economical . Furthermore, being inexpensive, readily available, having high atom efficiency and generating water as the only by‐product are advantageous properties of hydrogen peroxide over other oxidants …”