International audienceThe synthesis, spectroscopic and structural characterization, electrochemical properties and theoretical studies of a series of eight robust neutral Nickel(II) and Copper(II) complexes (4-11) supported by unsymmetrically-substituted N2O2-tetradentate Schiff base ligands are reported. The M(salophen)-type compounds are substituted by either a pair of donor (anisyl, ferrocenyl, methoxy) or acceptor (fluoro, nitro) groups, forming D-pi-D and A-pi-A systems, respectively. The compounds were prepared in good yields by condensation of the free amino group of the desired ONN-tridentate half-unit with the appropriate substituted salicylaldehyde in the presence of hydrated Nickel(II) or Copper(II) acetate salts. They were characterized by elemental analysis, FT-IR, UV-vis, and for diamagnetic species by multinuclear NMR spectroscopy, mass spectrometry and cyclic voltammetry. The crystal structures of one Ni(II) (4) and four Cu(II) complexes (5, 7, 9 and 11) revealed a four-coordinate square-planar environment for the nickel and copper metal ions, with two nitrogen and two oxygen atoms as donors. In 4, 5, 7 and 9, the crystallization solvent interacts through hydrogen bonding with the phenolato oxygen atoms of the Schiff base pocket, while 11 packs as centrosymmetric dimers with an apical CuAO short contact interaction (2.63 angstrom). the cyclovoltammograms of the nickel complexes present an irreversible monoelectronic Ni(II)/Ni(I) reduction wave while those of their copper counterparts exhibit a reversible or quasi-reversible one-electron Cu(II)/Cu(I) redox process. The electronic structures of the eight complexes were analyzed by DFT and TD-DFT calculations

Abstract:Since their development in the 1930s, Schiff-base complexes have played an important role in the field of coordination chemistry. Here, we report the synthetic, spectral, structural, magnetic and electrochemical studies of two new pentacoordinated neutral chloro-iron(III) complexes (3,5) supported by dianionic [N 2 O 2 ] 2− tetradentate Schiff-base ligands unsymmetrically substituted by either a pair of acceptor (F and NO 2 ) or donor (ferrocenyl and OCH 3 ) groups. The electron-withdrawing Schiff-base proligand 2 and the complexes 3 and 5 were prepared in good yields (79-86%). Complex 3 was readily obtained upon reaction of 2 with anhydrous iron chloride under basic conditions, while the bimetallic derivative 5 was synthesized by condensation of the free amino group of the ferrocenyl-containing O,N,N-tridentate half-unit 4 with 5-methoxysalicylaldehyde in the presence of FeCl 3 . The three new compounds were characterized by elemental analysis, FT-IR, UV-Vis, mass spectrometry and in the case of 2 by multinuclear NMR spectroscopy. The crystal structures of 3 and 5 revealed that in the two five-coordinate monomers, the iron atom showed distorted square-pyramidal geometry, with the N and O atoms of the Schiff-base ligand occupying the basal sites and the chlorine atom at the apex of the pyramid. Magnetic measurements showed a high-spin configuration (S = 5/2) for the Fe(III) ion in 3 and 5. Reduction associated with the Fe(III)/Fe(II) redox couple occurred at −0.464 and −0.764 V vs. Ag/Ag + , and oxidation taking place at the Schiff-base ligand was observed at 1.300 and 0.942 V vs. Ag/Ag + for 3 and 5, respectively. A high-electronic delocalization of the Schiff-base ligand substituted by fluoro and nitro groups stabilizes the Fe(II) oxidation state and shifts the redox potential anodically.

Structural and NLO behavior of push–pull palladium(ii) complexes of metallocenyl-containing asymmetric Schiff base ligands.

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, et al.. Transfer hydrogenation of N-benzylideneaniline catalyzed by ruthenium complexes with pincer-type phosphorus nitrogen ligands using propan-2-ol as the hydrogen source. Catalysis Communications, Elsevier, 2017, 99, pp.150-153. <10.1016/j.catcom.2017.04.026>. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T AbstractRuthenium complexes containing phosphorus-nitrogen, pincer-type (NPN) ligands show high activities and selectivities in the transfer hydrogenation of Nbenzylideneaniline using propan-2-ol as the hydrogen source. Such is the case of complexes RuCl 2 PPh 3 (PPh(NHPy) 2 ) (1) and RuCl 2 PPh 3 (PPh(NHPyMe) 2 ) (2) which also show TOFs 5989 h -1 and 5928 h -1 , respectively. These remarkable results were obtained after only 10 minutes of reaction using a 1000/1 substrate/catalyst ratio. ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T IntroductionTransfer hydrogenation of ketones has several advantages over using molecular hydrogen in homogeneous catalysis. The former makes use of simple equipment, low catalyst loading, safe manipulation, and easy removal of volatile by-products. The good performance of [RuCl 2 (diphosphane)(diamine)] complexes in the asymmetric hydrogenation of ketones [1] has increased the great interest to study the reaction looking at the reactivity of Ru (II) complexes based on phosphorus and amino ligands [2,3].

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