Isolation of a novel intermediate during unsymmetrical to symmetrical rearrangement of a tetradentate Schiff base ligand in a manganese (III) complex: catalytic activity of the rearranged product towards alkene epoxidation

An attempt for the synthesis of a MnIII complex with unsymmetrical tetradentate Schiff base ligand uspen (1:1:1 condensate of salicylaldehyde, 2,4-pentanedione and 1,2-ethanediamine) resulted in the isolation of a novel complex, {[{Mn(salen)}{Mn(uspen)}(HCOO)]•ClO4}n (1) as an intermediate species that contains both the unsymmetrical and symmetrical tetradentate ligand uspen and salen (2:1 condensate of salicylaldehyde and 1,2-ethanediamine) respectively. The structure of the complex shows that half of the unsymmetrical Schiff base, uspen rearranged to its symmetrical analogue, salen. A phenoxo bridged dinuclear MnIII complex [Mn(salen)(sal)]2•2H2O (2) with only the symmetrical Schiff base was also obtained. Compound 1 that contains both unsymmetrical and symmetrical Schiff base ligands in one molecule is unprecedented and provides an insight into the unsymmetrical to symmetrical rearrangement of tetradentate Schiff base ligand. Complex 2 acts as an efficient catalyst in the alkene ((E)-stilbene, styrene) epoxidation reaction in presence of two terminal oxidants PhIO and NaOCl in solvents CH3CN and CH2Cl2 independently and it retains its reactivity with high efficiency for a long time

Synthesis, electron paramagnetic resonance and X-ray structure characterization of copper(II) ternary complexes of p-aminobenzoic and 3,4-dimethoxyhydrocinnamic acid with phenanthrolines

Dimers of the type [Cu(pAb)(phen)(H2O)]2(NO3)2• 2pAbH • 2H2O (1) and [Cu(DPP)(4,7-phen)(H2O)]2(NO3)2• 2H2O (2)(pAbH =p-aminobenzoic acid, DPPH = 3,4-dimethoxhydrocinnamic acid, phen = 1,10-phenanthroline and 4,7-phen = 4,7-dimethyl-1,10-phenanthroline) have been synthesized and characterized by means of EPR spectra in the solid and liquid states at room and low temperature, by magnetic measurements and by X-ray structure (1). Antiferromagnetic coupling of the unpaired electrons on each copper atom is evidenced by EPR spectra for both the compounds. They are, in fact, characteristic of dimers in which bridging nitrogen ligands are present. The Cu–Cu distance is 3.060 (1)Å and the dimer results through the bridging of two symmetry-related pAb molecules by bidentate carboxylic groups. The two phenanthroline molecules in the dimer are stacked with a minimum distance of 3.39 (1)Å

Square-planar copper(II) complexes with tetradentate amido-carboxylate ligands. Crystal structure of Na2[Cu(obap)]2.H2O. Strain and spectral assignments of complexes

Novel N–N–N–O-type of tetradentate ligands H3obap (H3obap = oxamido-N-aminopropyl-N0-benzoic acid) and H3maeb (H3maeb = malamido-N-aminoethyl-N0-benzoic acid) and the corresponding square-planar copper(II) complexes have been prepared and characterized. The obap3 and maeb3 ligands coordinate to the copper(II) ion via four ligating atoms (three deprotonated atoms: one carboxylate oxygen and two deprotonated amide nitrogens; one amine nitrogen) with in-plane square chelation. A four coordinate, square-planar geometry has been established crystallographically for the binuclear Na2[Cu(obap)]2 Æ 2H2O complex. Structural data correlating the square-planar geometry of the [Cu(obap)] unit and an extensive strain analysis are discussed in relation to the information obtained for similar complexes. The infrared and electronic absorption spectra of the complexes are discussed in comparison to the related complexes of known geometries. Antibacterial activity of ligands and copper(II) complexes towards common Gram-negative and Gram-positive bacteria are reported as well

Carbonyl compound dependent hydrolysis of mono-condensed Schiff bases: a trinuclear Schiff base complex and a mononuclear mixed-ligand ternary complex of copper(II)

Two Schiff bases, HL1 and HL2 have been prepared by the condensation of N-methyl-1,3-propanediamine (mpn) with salicylaldehyde and 1-benzoylacetone (Hbn) respectively. HL1 on reaction with Cu(ClO4)(2)center dot 6H(2)O in methanol produced a trinuclear Cu-II complex, [(CuL1)(3)(mu(3)-OH)](ClO4)(2)center dot H2O center dot 0.5CH(2)Cl(2) (1) but HL2 underwent hydrolysis under similar reaction conditions to result in a ternary Cu-II complex, [Cu(bn)(mpn)ClO4]. Both complexes have been characterised by single-crystal X-ray analyses, IR and UV-Vis spectroscopy and electrochemical studies. The partial cubane core [Cu3O4] of 1 consists of a central mu(3)-OH and three peripheral phenoxo bridges from the Schiff base. All three copper atoms of the trinuclear unit are five-coordinate with a distorted square-pyramidal geometry. The ternary complex 2 is mononuclear with the square-pyramidal Cu-II coordinated by a chelating bidentate diamine (mpn) and a benzoylacetonate (bn) moiety in the equatorial plane and one of the oxygen atoms of perchlorate in an axial position. The results show that the Schiff base (HL2) derived from 1-benzoylacetone is more prone to hydrolysis than that from salicylaldehyde (HL1). Magnetic measurements of 1 have been performed in the 1.8-300 K temperature range. The experimental data clearly indicate antiferromagnetism in the complex. The best-fit parameters for complex 1 are g = 2.18(1) and J = -15.4(2) cm(-1)