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Synthesis, spectral characterization, electrochemistry and catalytic activities of Cu(II) complexes of bifunctional tridentate Schiff bases containing ONO donors
Author(s) -
Manimaran A.,
Prabhakaran R.,
Deepa T.,
Natarajan K.,
Jayabalakrishnan C.
Publication year - 2008
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/aoc.1400
Subject(s) - chemistry , electron paramagnetic resonance , salicylaldehyde , bifunctional , redox , imine , catalysis , cyclic voltammetry , schiff base , electrochemistry , copper , ligand (biochemistry) , crystallography , inorganic chemistry , medicinal chemistry , polymer chemistry , organic chemistry , biochemistry , physics , receptor , electrode , nuclear magnetic resonance
Paramagnetic copper(II) complexes of the type [Cu(PPh 3 )(L)] (where L = bifunctional tridentate Schiff bases) were synthesized from the reaction of anthranillic acid with salicylaldehyde (H 2 L 1 ), 2‐hydroxy‐1‐naphthaldehyde (H 2 L 2 ), o ‐hydroxyacetophenone (H 2 L 3 ) and o ‐vanillin (H 2 L 4 ) with monomeric metal precursor [CuCl 2 (PPh 3 ) 2 ]. The obtained complexes were characterized by elemental analysis, magnetic susceptility and spectroscopic methods (FT‐IR, UV–vis and EPR and cyclic voltammetry). EPR and redox potential studies have been carried out to elucidate the electronic structure, nature of metal–ligand bonding and electrochemical features. EPR spectra exhibit a four line pattern with nitrogen super‐hyperfine couplings originating from imine nitrogen atom. These planar complexes possess a significant amount of tetrahedral distortion leading to a pseudo‐square planar geometry, as is evidenced from EPR properties. Cyclic voltammograms of all the complexes display quasireversible oxidations, Cu(III)Cu(II), in the range 0.31–0.45 V and reduction peaks, Cu(II)Cu(I),in the range −0.29 to −0.36 V, involving a large geometrical change and irreversible. The observed redox potentials vary with respect to the size of the chelate ring of the Schiff base ligands. Further, the catalytic activity of all the complexes has been found to be high towards the oxidation of alcohols into aldehydes and ketones in the presence of N ‐methylmorpholine‐ N ‐oxide as co‐oxidant. The formation of high valent Cu IV O oxo species as a catalytic intermediate is proposed for the catalytic process. Copyright © 2008 John Wiley & Sons, Ltd.