Symmetrical Schiff Base Research Articles

Novel Manganese(III) Complexes with the Schiff Base N,N′‐(1,2‐Phenylene)‐bis(3‐Hydroxysalicylidenimine)

Four novel manganese(III) complexes have been prepared using the tetradentate ONNO symmetrical Schiff base N,N′‐(1,2‐phenylene)‐bis(3‐hydroxysalicylidenimine) H4L and employing different manganese(II) and manganese(III) starting salts (chloride, acetate, acetylacetonate and perchlorate). These complexes were thoroughly characterised by elemental analysis, ES mass spectrometry, infrared and paramagnetic 1H NMR spectroscopies, magnetic susceptibility measurements and molar conductivities. Electrochemical studies by cyclic and normal pulse voltammetry were also performed. All complexes obtained are manganese(III) ones, in which the anions belonging to the starting salts have diverse coordinating tendencies; this fact seems to determine the nuclearity of the final complexes, with empirical formulae [Mn(H2L)(H2O)2]Cl(H2O)3 1, [Mn(H2L)(OAc)](H2O) 2, [Mn(H2L)(acac)](H2O)3 3, and [Mn(H2L)(H2O)(CH3OH)](ClO4) 4. The X‐ray crystal structure of H4L Schiff base has been determined.

Alumina-supported Mn(II), Co(II), Ni(II) and Cu(II) N, N-bis(salicylidene)-2,2-dimethylpropane-1,3-diamine complexes: Synthesis, characterization and catalytic oxidation of cyclohexene with tert-butylhydroperoxide and hydrogen peroxide

New square-planar manganese(II), copper(II), nickel(II) and cobalt(II) complexes of a tetradentate Schiff-base ligand “ N, N-bis(salicylidene)-2,2-dimethylpropane-1,3-diamine, H 2[salpnMe 2]” have been prepared and characterized by elemental analyses, IR, UV–Vis, conductometric and magnetic measurements. The results suggest that the symmetrical Schiff-base is a bivalent anion with tetradentate N 2O 2 donors derived from the phenolic oxygen and azomethine nitrogen. The formulae was found to be [M(salpnMe 2)] for the 1:1 non-electrolytic complexes. Alumina-supported metal complexes (ASMC; [M(salpnMe 2)/Al 2O 3]) catalyze the oxidation of cyclohexene with tert-buthylhydroperoxide (TBHP) and hydrogen peroxide. Oxidation of cyclohexene with TBHP gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-( tert-butylperoxy)-2-cyclohexene whereas, oxidation with H 2O 2 resulted in the formation of cyclohexene oxide and cyclohexene-1,2-diol. Manganese(II) complex supported on alumina “[Mn(salpnMe 2]–Al 2O 3” shows significantly higher catalytic activity than other catalysts.

Enol-keto tautomerism of aromatic photochromic Schiff base N,N′-bis(salicylidene)-p-phenylenediamine: Ground state equilibrium and excited state deactivation studied by solvatochromic measurements on ultrafast time scale

A photochromic symmetric Schiff base, N,N'-bis(salicylidene)-p-phenylenediamine, is proposed as a probe for the study of solvent dependent enol-keto tautomerism in the ground and excited states. The ground state equilibrium between the enol-keto tautomers is found to depend mainly not on polarity but on the proton donating ability of the solvent. Upon selective excitation of each of these tautomers, the same excited state of a keto tautomer is created: in enol, after the ultrafast excited state intramolecular proton transfer (ESIPT), reaction, and in keto tautomer, directly. Then some part (<30%) of excited molecules are transferred to the photochromic form in its ground state. The evidence of another ultrafast deactivation channel in the excited enol tautomer competing with ESIPT has been found. The solvent does not influence the ESIPT dynamics nor the efficiency of the creation of the photochrome.

Synthesis, characterization and biological activities of mononuclear and binuclear Fe(III) complexes with some symmetric and unsymmetric Schiff-base ligands

A series of mononuclear and binuclear Fe(III) complexes of some new symmetrical and unsymmetrical Schiff bases containing quinoline derivatives were synthesized and characterized by elemental and thermal analysis, conductance measurements and IR spectra. In mononuclear complexes, the unsymmetric Schiff bases are monobasic tetradentate towards the Fe(III) ion. However, in binuclear complexes, the symmetric Schiff-base ligands behave as monobasic bidentate towards each Fe(III) ion. The structure of the solid complexes are discussed and based on magnetic susceptibility measurements, electronic and ESR spectral studies. The biological activities of the ligands and their complexes are reported.

Epoxidation of Styrene Catalyzed by Zeolite-encapsulated Symmetrical and Unsymmetrical Co(II)Salen-type Schiff Base Complexes

用自由配体法将对称、不对称Co(II)Salen型席夫碱配合物封装于Y型沸石分子筛的超笼中,并采用FTIR、UV-Vis、热分析和催化技术研究了其空间结构和催化性能.结果表明,被封装于分子筛超笼中的Salen型席夫碱配合物,同样具有未封装配合物的物理化学性能,也没有影响分子筛的框架结构;在以O2作氧化剂,催化苯乙烯环氧化反应中表现了非常高的反应活性和稳定性;金属配合物的量子化学密度泛函计算结果揭示了配合物的催化性能与轨道能量密切相关.

Electrochemical Synthesis of MII Complexes with a Schiff Base containing an Amido Group. Crystal Structure of a Cobalt(II) Complex with a Reorganised Ligand

M(HL)(H2O)n complexes have been obtained by the electrochemical reaction of Fe, Co, Ni, Cu, Zn and Cd anodes with the potentially pentadentate and trianionic asymmetrical Schiff base 3-aza-N-{2-[1-aza-2-(5-nitro-2-hydroxylphenyl)-vinyl]phenyl}-4-(5-nitro-2-hydroxyphenyl)but-3-enamide (H3L), containing a hard amido donor atom. The complexes have been characterized by elemental analysis, mass spectrometry, IR and 1H NMR spectroscopies, magnetic measurements and molar conductivities. Co(HL)(H2O) (2) has been found to rearrange in DMF solution into a crystallographically solved octahedral complex, CoL1(H2O)2 (7) [where H2L1 is the symmetrical Schiff base ligand N,N′-(1,2-phenylene)-bis(5-nitro-3-hydroxysalicylidenimine)]. A hydrolysis mechanism is discussed to explain this rearrangement.

Oxidation of cyclohexene with tert-butylhydroperoxide and hydrogen peroxide catalysted by Cu(II), Ni(II), Co(II) and Mn(II) complexes of N, N′-bis-( α-methylsalicylidene)-2,2-dimethylpropane-1,3-diamine, supported on alumina

New square-planar manganese(II), copper(II), nickel(II) and cobalt(II) complexes of a tetradentate Schiff-base ligand “ N, N′-bis-( α-methylsalicylidene)-2,2-dimethylpropane-1,3-diamine”, H 2[Me 2salpnMe 2] have been prepared and characterized by elemental analyses, IR, UV–vis, conductometric and magnetic measurements. The results suggest that the symmetrical Schiff-base is a bivalent anion with tetradentate ONNO donors derived from the phenolic oxygen and azomethine nitrogen. The formulae was found to be [M(Me 2salpnMe 2)] for the 1:1 non-electrolytic complexes. Alumina-supported metal complexes (ASMC); [M(Me 2salpnMe 2]/Al 2O 3; catalyze the oxidation of cyclohexene with tert-buthylhydroperoxide (TBHP) and hydrogen peroxide. Oxidation of cyclohexene with TBHP gave 2-cyclohexene-1-one, 2-cyclohexene-2-ol and 1-( tert-butylperoxy)-2-cyclohexene whereas, oxidation with H 2O 2 resulted in the formation of cyclohexene oxide and cyclohexene-1,2-diol. Manganese(II) complex supported on alumina “[Mn(Me 2salpnMe 2]/Al 2O 3” shows significantly higher catalytic activity than other catalysts.

Synthetic Study of Symmetrical and Unsymmetrical Schiff Base Complexes of VO(IV) and Mn(III) Derived from 2,2′‐Diaminobiphenyl

The symmetrical and unsymmetrical Schiff base complexes of VO(IV) and Mn(III) derived from 2,2′‐diaminobiphenyl and derivatives of salicylaldehyde and 1‐hydroxy‐2‐naphthaldehyde have been synthesized and characterized by elemental analysis, NMR, infrared and electronic absorption spectroscopies, and conductivity measurements. The reaction of the ligands with oxovanadium(IV) was found to be kinetically unfavored, probably due to the small ionic radius of the metal ion, which is not in accordance with the cavity size of the ligands.

Synthesis and characterisation of four novel NxOy-Schiff-base macrocyclic ligands and their metal complexes

Macrocyclic Schiff-bases, L1 and L2, and bis-macrocyclic ligands, L3 and L4, have been prepared by [1 + 1] and [2 + 1] cyclocondensation of 1,7-bis(2′-formylphenyl)-1,4,7-trioxaheptane or 2,6-bis(2-formylphenoxymethyl)pyridine with 2,6-bis(o-aminophenoxymethyl)pyridine or 1,2,4,5-tetraaminebenzene · 4HCl, respectively. The related YIII, MII (M=Co, Ni, Zn, Cd or Pb) and LnIII nitrate or perchlorate complexes have been synthesised following a template procedure, demonstrating the effectiveness of these metal ions to promote the assembly of these four symmetric Schiff-base macrocycles. The complexes were characterised by elemental analyses, molar conductivity, mass spectrometry, i.r., u.v.–vis, and 1H-n.m.r spectroscopy.

Bimetallic complexes of a potentially pentadentate, acyclic, symmetrical compartmental Schiff base ligand that provides suitable topology for an exogenous bridge

The binucleating ligand LH3, 2,6-diformyl-p-cresol-bis(phenylthioacetyldrazone), a Schiff base condensation product of 2,6-diformyl-p-cresol and phenylthioacetyldrazide forms complexes of the [M2ClL] type with CoII, NiII and CuII ions, which were characterized by elemental analysis, magnetic susceptibility, electronic spectra, molar conductance, i.r., n.m.r., e.p.r., t.g. and FAB mass spectral measurements. Sub-normal magnetic moments indicate the operation of antiferromagnetic coupling between the metal centres. The ligand and its copper complex show a pronounced fungistatic activity.

Metal complexes with a chiral N4 symmetrical Schiff base. Crystal structures of the ligand and its Cu(ii) and Ni(ii) “mono-helicates”

The N4 Schiff base ligand N,N′-bis(2-tosylaminobenzylidene)-1,2-diaminocyclohexane (H2cyTs) and its divalent metal (Fe, Co, Ni, Cu, Zn and Cd) complexes have been prepared. Of these compounds only Zn(trans-cyTs)·3H2O can be considered as blue luminescent (λ = 435 nm, ϕ = 0, 12). Either demetallation or the absence of the tosyl groups, results in a loss of fluorescence. The X-ray crystal structures of a diastereoisomeric mixture of H2cyTs and its (1R,2R)-enantiomer, as well as those corresponding to Cu(trans-cyTs)·MeCN and Ni(trans-cyTs)·MeCN have been solved. The Cu(II) and Ni(II) ions assume tetrahedrally distorted square planar coordination geometries, involving the four donor N-atoms of the dianionic ligand. The spatial disposition of both tosyl groups prevents global consideration as an usual symmetric helicand.

METAL COMPLEXES OF NOVEL SYMMETRICAL SCHIFF BASE LIGANDS

Two novel symmetrical Schiff base ligands, H2L1 and H2L2, with tetradentate N2O2 and pentadentate N3O2 coordinating sites were prepared by the reaction of the aldehyde 2-methyl-7-formyl-8-hydroxy-quinoline with 1,3-diaminopropane or diethylenetriamine, respectively, in the molar ratio 2:1. Cu(II), Ni(II), Co(II), Mn(II), Fe(III) and VO(IV) complexes of both ligands were synthesized. The ligands and their metal complexes were characterized by elemental analyses, IR, UV-Vis, ESR, NMR and mass spectra and also by magnetic moment measurements. Both ligands behave as tetradentate ones when coordinating metal cations. The ligand H2L1 has a smaller cavity than the ligand H2L2, thus the former ligand yielded mononuclear products, through chelation of one ligand molecule to a metal cation, while the latter ligand yielded binuclear products, through the coordination of two metal cations to two ligand molecules. Each of the Fe(III) cations was coordinated to three halves of both ligand molecules yielding also a mononuclear product with ligand H2L1 and a binuclear product with ligand H2L2. Either mononuclear or binuclear complex molecules link together forming polymeric chains. The mononuclear and binuclear complex forms were well manifested in the ESR spectra of the vanadyl complexes. The polymeric structures of the metal complexes led to an enhanced decrease of their magnetic moments through antiferromagnetic exchange between neighbouring metal cations.

Intramolecular proton transfer reactions in internally hydrogen-bonded Schiff bases: ab initio and semiempirical study

The barrier heights of the ground state proton transfer reactions in a series of substituted salicylaldehyde anils and two symmetric Schiff bases, N, N′-bis(salicylidene)- p-phenylenediamine and N, N′-bis(2-hydroxy-1-naphthylmethylene)- p-phenylenediamine, were calculated using ab initio (4-31G and 6-31G ∗∗ basis sets) and semiempirical (AM1 and PM3) quantum-chemical methods. The minimum energy paths at the AM1 and 4-31G levels were followed for the salicylaldehyde anils. On the basis of the analysis of the intramolecular proton transfer reactions in the symmetric Schiff bases which may occur through a one- or two-step mechanism, it is suggested that the latter mechanism is more probable.

Carbenoid insertions into the siliconhydrogen bond catalyzed by chiral copper (I) schiff base complexes

An asymmetric insertion reaction of α-diazoesters derived from methyl arylacetates into the silicon-hydrogen bond of silanes was achieved using a copper (I) catalyst associated with a chiral, C 2 symmetric Schiff base. Addition of the diazoesters 1 (1 equiv) to the Cu·Lig complex (R,R)- 3 (0.1 equiv) in the presence of the silane reagent (1.5 equiv) at −40° C yielded the corresponding insertion products 2 or 4 in good yields with varying levels of selectivity (up to 84% ee).

Supramolecular and metallosupramolecular coordination compounds of nickel(II) with the half units of vicinal oxime–imine ligands; mixed ligand complexes of the metal ion

The [1+1] condensation of isonitrosoacetylacetone (Hisoacac) with o-phenylenediamine produces the diazepine (HLBD) (1), which reacts with Ni(OAc)2· 4H2O (1:1 molar ratio) to produce the mixed ligand complex (LBDN)Ni(OAc) (2); where LBDN is the anion of the half unit obtained by hydrolysis of one HLBD imine linkage. The reaction of (2) (1 mol) with mono-, bi- and trichloroethanoic acid (1mol) or picric acid (1mol) led to the exchange of the acetate in (2) with the anion of the added acid [(3)–(6), respectively]. The supramolecular structure of (2)–(6) is achieved through the dimerization of these complexes via intermolecular hydrogen bonding of the LBDN –NH2 group of one molecule and the monodentate acetate group of another molecule. The template reaction of o-phen with Hisoacac in the presence of Ni(OAc)2·4H2O (1:2:2 and 1:2:1 molar ratios, respectively) led to the formation of (LBDN)Ni(OAc)2Ni(isoacac) (7) and (isophen)Ni (8), respectively; H2isophen is a symmetrical Schiff base ligand formed by the (2:1) in situ condensation of Hisoacac with o-phen. The (1:1) condensation of Hisoacac with p-phen produced the half unit Hisopphen (9), whose 1:1 molar ratio reaction with Ni(OAc)2·4H2O led to the formation of (isopphen)Ni(OAc)·2H2O (10). The amino group of the isopphen ligand is available for further coordination with the nickel(II) ion to produce the metallosupramolecular complexes {[two molecules of complex (10)] [Ni(OAc)2]} and {[complex (10)] [Ni(OAc)2·H2O]} from the 2:1 and 1:1 molar ratio reactions, respectively, of (10) with Ni(OAc)2·4H2O. The 1:1 molar ratio reaction of (10) with Hisoacac led to replacement of OAc by isoacac. The suggested structures of the ligands and their coordination compounds are based on analytical, chemical, spectral data and magnetic moments.

Synthesis and characterisation of manganese(III) unsymmetrical Schiff-base complexes: a unique example of a cocrystallised manganese(III) unsymmetrical Schiff-base complex, and a symmetric Schiff-base complex arising from rearrangement of the former

Some manganese(III) complexes with unsymmetrical Schiff bases have been prepared and characterised. The ligands were prepared by condensation of 7-amino-4-methyl-5-azahept-3-en-2-one with salicylaldehyde, 2-hydroxyacetophenone or substituted salicylaldehydes (5-chloro, 5-methoxy, 3-ethoxy or 3,5-dibromo). On reaction with manganese(II) perchlorate in air, manganese(III) Schiff-base complexes are obtained. The crystal structures of two of these have been determined, one being cocrystallised with [{Mn(salen)(H2O)}2][ClO4]2 containing the symmetrical salen ligand [N,N′-ethane-1,2-diylbis-(salicylideneiminate)]. Unlike the dimeric structures previously found for similar complexes, the two structures are monomeric with octahedral MnN2O4 co-ordination spheres.

Nicke(II) complexes of half unit, symmetric and unsymmetric Schiff base ligands

The template reaction of isonitrosoacetylacetone (Hina) witho-phenylenediamine (o-phenen) in the presence of (MeCO2)2Ni·4H2O in EtOH yielded three types of nickel(II) complexes (depending on the molar ratio of the reactants) formulated as L1Ni(O2CMe)·2H2O (1), (L1)2Ni (2), and L2Ni·H2O (3). HL1 and H2L2 are the half unit and symmetric Schiff base ligands obtained from the (1∶1) and (2∶1) condensation of (Hina) with (o-phenen) respectively. The (1∶1) molar ratio reaction of (1) with either acetylacetone (Hacac) or (Hina) in CHCl3 led to the formation of mixed ligand complexes L1Ni(acac)·H2O (4) and L1Ni(ina)·H2O (5) whereas a similar reaction with salicylaldehyde (Hsal) produced L3Ni (6); H2L3 is the unsymmetric Schiff base formed by the (1∶1) condensation of the amino group in (1) with (Hsal). Analytical, spectral and magnetic moment evidence are compatible with the suggested structures of the metal complexes.

Non-symmetric Schiff base Co(II) complexes. Synthesis and catalytic activity in the oxidation of 2,6-Di-tert-butylphenol by molecular oxygen

We report the synthesis of a series of unsymmetrical tetradentate Schiff base ligands. In the reaction of o-phenylenediamines with aromatic aldehydes, use of chloroform as a solvent allows a kinetic control of the formation of mono-Schiff base. Further condensation of the half-unit with 5-formyl 1,3-dimethyl barbituric acid leads to the non- symmetric Schiff base. Cobalt(II) complexes of these ligands have been prepared and the influence of the structure of the ligands on half-wave Co(II)/Co(III) potential values and the catalytic activation of O 2 has been investigated.

Metal complexes of symmetric and non-symmetric tetradentate schiff bases derived from 1-(2mercaptophenyl)-ethanone

Preparation des bases de Schiff symetriques et non symetriques et des complexes de Ni(II), Cu(II), Co(II) et Zn(II)

Unsymmetrical ligand complexes of Cu II , Ni II , and Co II derived from salicylaldehyde and 1,3-propanediamine with either pyridine-2-carbaldehyde or pyrrole-2-carbaldehyde

The 1 : 1 : 1 condensates of salicylaldehyde, propanediamine, and either pyrrole-2-carbaldehyde (L1) or pyridine-2-carbaldehyde (L2) have been isolated and combined with selected first-row transition-metal ions. The copper(II) and nickel(II) complexes of L1 have been prepared and characterized, as has the pyridine adduct of the corresponding cobalt(II) derivative. The copper(II) and nickel(II) complexes of L2 have also been characterized. Spectral and chemical properties of these systems are compared with those of complexes involving analogous symmetrical Schiff-base ligands.