Synthesis, Spectroscopic Investigation and Catalytic Studies of Nickel(ii) Aromatic Azomethine Complexes

Abstract

Coupling reaction between aryl halide and terminal alkyne in Sonogashira coupling reaction is important due to its extensive application in the resynthesis of natural products, production of drugs, dyes, and polymers. Efforts to increase rate of reaction has involved exploration of new catalysts. The current catalysts such as phosphine-based complexes are costly, air-sensitive and environmentally harmful. Nickel(II) Schiff base complexes were synthesized by reacting aromatic Schiff base ligands 2,2'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis(metha-nylylidene))diphenol (L1H), 2,2'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene))bis(4-fluorophenol) (L1F), and 2,2'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis-(methanylylidene))bis(4-methylphenol) (L1M) with nickel(II) acetate tetrahydrate to form NiL1H, NiL1F and NiL1M. The chemical structures were elucidated through physicochemical and spectral techniques namely elemental analysis, melting point, FTIR, 1H and 13C NMR, magnetic susceptibility and molar conductivity. All nickel(II) complexes were tested as catalysts in homogenous Sonogashira reaction between iodobenzene and phenylacetylene in DMSO for 12 hours at 140 oC. NiLF, a new nickel(II) complex, converted the highest percentage of iodobenzene (91%) while NiLH and NiLC converted 78% and 83% of iodobenzene, respectively.

2-methoxy-4-(((5-nitropyridin-2-yl)imino)methyl)phenol Schiff base ligand and its Cu(II) and Zn(II) complexes: synthesis, characterization and biological investigations

“…The complexation activity metal ions (Zn, Hg, or Cd) in the existence of multidentate Schiff base ligands has been systematically deliberated in the area of coordination chemistry over the last few decades [ 2 , 3 , 4 , 5 , 6 , 7 ]. Considering flexible functional behaviour, interesting structural motifs [ 8 , 9 , 10 , 11 ] and optoelectronics properties [ 12 , 13 , 14 ], the molecular metal ensembles formed from Schiff base ligands and metal ions have recently gained a lot of attention.…”

Schiff base complexes with different metals incorporating derivatives of 3,6‐di‐tert‐butylcarbazole

“…[1,2] The presence of donor hetero atoms makes these compounds effective as catalysts for oxidation, reduction, hydrolysis, and other transformations of inorganic and organic compounds. [3][4][5] It has been determined that azomethine ligands are able to form a stable mononuclear or polynuclear complexes with interesting structural architectures and, at the same time, both biological [6,7] and antibiotic [8,9] properties of Schiff bases increase when these are chelated with metal ions. Therefore, the detailed structural investigation of the new model complexes seems to be very important with the view of their potential applications.…”

A review of Titanium, Vanadium and Chromium transition metal Schiff base complexes with biological and catalytic activities

“…Schiff bases are formed when any primary amine reacts with an aldehyde or ketone under specific conditions. [1][2][3][4][5][6][7][8][9] Studies show that Schiff base ligands together with their complexes have many biological applications ranging from antimicrobial [10][11][12][13] and catalysis. 14 A number of homogeneous catalytic reactions involve Schiff base complexes which have a major role in such reactions as catalysts.…”