Abstract
Three neutral Cu(II)/ƞ4-NNNO Schiff base complexes (1-3) were prepared from the (E)-4-nitro-2-(((2-(piperazin-1-yl)ethyl)imino)methyl)phenol, tetradentate Schiff base (SB) ligand, and the corresponding copper(II) salts. The new SB and its complexes were fully characterized by CHN-EA, standard spectroscopic, thermal, and fluorescence analyses. The formation of the complexes was monitored by EDX, FT-IR, and UV-Vis. The chromotropism studies of the complexes reflected remarkable findings, in which bathochromic solvato- and thermochromism shifts were detected. The turn-off-on halochromism phenomena were observed in the acidic and basic medium. On the other hand, the fluorescence of the free SB ligand was turned off via complexation to the Cu(II) center. In the presence of H2O2 as green oxidant and under mild oxidation catalytic condition, the three complexes successfully catalyzed the formation benzaldehyde from benzyl alcohol.
Highlights
Schiff base (SB) group is a valuable subunit (R1R2C=NR3) present in a wide spectrum of compounds
We report the synthesis and full characterization of (E)-4-nitro2-(((2-(piperazin-1-yl)ethyl)imino)methyl)-phenol as a SBfunctionalized compound from condensation of 2-hydroxy5-nitrobenzaldehyde and 2-(1-piperazinyl)ethylamine
In an equimolar ratio with three copper(II) salts (CuCl2, CuBr2, and Cu(NO3)2 3H2O), separately, the ligand was coordinated in an NNNO-fashion to the metal center in a consecutive deprotonation/coordination process in the absence of base (Scheme1)
Summary
Schiff base (SB) group is a valuable subunit (R1R2C=NR3) present in a wide spectrum of compounds. These compounds are accessible from condensation of amines with aldehydes or ketones under conventional or microwave heating. The presence of salicyl moiety attached to SB derivatives could demonstrate exceptional photo- and thermochromism properties in different physical state. These attributes are typically generated from proton transfer from the o-hydroxyaryl moiety to the attached azomethine (imine) functional group [6,7,8]. Selective catalytic oxidation of benzyl alcohol to benzyl aldehyde was evaluated using the desired complexes in the presence of hydrogen peroxide as a green oxidant
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